CA2330080A1 - Ambient light detection technique for an imaging array - Google Patents
Ambient light detection technique for an imaging array Download PDFInfo
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- CA2330080A1 CA2330080A1 CA002330080A CA2330080A CA2330080A1 CA 2330080 A1 CA2330080 A1 CA 2330080A1 CA 002330080 A CA002330080 A CA 002330080A CA 2330080 A CA2330080 A CA 2330080A CA 2330080 A1 CA2330080 A1 CA 2330080A1
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- photodiodes
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/70—Circuitry for compensating brightness variation in the scene
- H04N23/72—Combination of two or more compensation controls
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/70—Circuitry for compensating brightness variation in the scene
- H04N23/74—Circuitry for compensating brightness variation in the scene by influencing the scene brightness using illuminating means
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/70—Circuitry for compensating brightness variation in the scene
- H04N23/71—Circuitry for evaluating the brightness variation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/40—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled
- H04N25/46—Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled by combining or binning pixels
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/702—SSIS architectures characterised by non-identical, non-equidistant or non-planar pixel layout
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
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- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
- H04N25/77—Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
- H04N25/779—Circuitry for scanning or addressing the pixel array
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- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
- H04N25/78—Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
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- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
- H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
- H04N3/14—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices
- H04N3/15—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation
- H04N3/1506—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation with addressing of the image-sensor elements
- H04N3/1512—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation with addressing of the image-sensor elements for MOS image-sensors, e.g. MOS-CCD
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
- H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
- H04N3/14—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices
- H04N3/15—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation
- H04N3/155—Control of the image-sensor operation, e.g. image processing within the image-sensor
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- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
- H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
- H04N3/14—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices
- H04N3/15—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by means of electrically scanned solid-state devices for picture signal generation
- H04N3/155—Control of the image-sensor operation, e.g. image processing within the image-sensor
- H04N3/1562—Control of the image-sensor operation, e.g. image processing within the image-sensor for selective scanning, e.g. windowing, zooming
Abstract
This invention is directed to a method and apparatus for determining the level of ambient light impinging on a selected number of pixels in an imaging array where each pixel includes a photodiode. The ambient light may be determined by resetting the pixels in the array and by detecting current flow through the photodiodes in a selected number of the pixels as they are being reset. Alternately, the ambient light may be determined by resetting a selected number of the pixels in the array and by detecting current flow through the photodiodes in the selected number of the pixels as they are being reset. The photodiodes are reset by applying a reverse bias voltage across them and the current flow is detected measuring the current flow through a resistance in parallel to the selected photodiodes. The selected number of pixels may be divided into one or more groups each having at least one pixel, and the pixels in each group may be arranged in specific patterns within the array. The array may be laid out in rows and columns, and the groups may be located in predetermined rows or columns. When only a selected number of pixels are reset and these pixels are divided into groups, the groups may be sequentially reset to permit differentiation between the groups.
Description
Ambient Light Detection ~Cechnique for an Imaging ~r~-ay Field of the Invention The present invention rotates to the field of ima~~c scanninU clwices and il~
to particular to determining ambient light intensity for il~la~~c scaonin~
devices.
Background of the Invention In the imaging industry, scanners are expected to operate effectively under :.I
wide range of ambient li~ltt. A number of solutions have been developed wllmin t, ambient light is measured in order to control the scannin« system. The scnsin~~ of~
ambient li~~ht Inay be done by an ambient light detection circuit which is separate from the imaging array, or ambient light cm be detected through the use ofthc imaging array itself. The ambient light measurement is then used either to adjust the exposure tine for the imaging arrayilens, to set the gain ofthe il»a«c signal ur to 2o control the brightness offal li~~ht suurcc.
U. S. Patent 4, 970,379 which issued on November 13, 1990 to Danstrom discloses exposure,~illumination control for a bar code scanner consisting of a controllable light source and an optical sensor that is independent of the scanner ar~av.
2s The optical sensor converts the light re (lccting from the object to be scannccl into an electrical signal representative: ofthe ambient light. This si~~nal is couplccl tcv a comparator, which determines the illumination reduired by the scanner array, and then adjusts the poavcr to the controllable light source accordingly. A major drawback of this method is that during love li~uht conditions the light source will be driven by the:
s0 cOt1'Ipat'at01' t0 gelleratc: bl'1g11t ll1n111111a11On, W 111C11 COIISLInIeS a large an10Ul1t Ot L70~\'tl'.
In a hand held device this is extremely detrimental. as most hand held dcvicm have a sell=contained power supply.
Other systems use the imaging array itself to determine ambient light levels which is then used to control exposure time. l.i.S. Patent 4,471,??8 which issued on September 1 1, 1984 to Nishiiaw~a et al., describes an in~a~c sensor consistin« of ncn-a destructive readout-type in~a~;c cells, the sensor uses the away of image cells as both photo-detector cells for tile measurement of anobient li~~ht and as image capturing cells for imaging an object. The imaging array is exposed to the object and an ambient light measurement run is made through previo~.isly selected ima';ing cells.
The added value of the selected ima~~ing cells is cr~mhare~i to a reference value to detcrn~inc tlnc exposure Level rcduired. fhc selected ima;~iny cells arc then erased. and an ima'~c scan ofthc objet is pcriormcd with a controlled exposure time.
The shortcoming of this method is that it consists of too many steps. The multi-step process of using the array to measure ambient light and then iorcip~ the t > array to be reset before the image is scanned, slows the process down.
Additional l s~.
the extra step rcduircs an extra expenditure of power, which is a severe detrin~cnt io a hand-hclcl device.
Another method using the imaging array is U.S. Patent 4,338, 14, which 2o issued on .luly 6, 198? to l3ixbv, discloses a further method of coWrollin~~ evhosurc time by operating a mechanical shutter in response to radiant energy impin~~in'~ on the sensor array. 'f he semiconductor array substrate current is monitored ~iurin~~. tl~c csposure ofthc ima~~ing array to prc>ducc an intcgr:ncd si~~nal that is prolortioml to the exposure level of the array. The signal is compared to a threshold voltage and 2~ when it exceeds a threshc>Id value the shutter i~; closed.
There arc drawbacks to this method in that it rcduircs additional hroccssin'~
steps in order to create an apparatus to monitor tl~e substrate current.
Specifically, the apparatus recluircs the addition ol~u layer ul~cooductivc material bclocn tlm non-;t? conductive base-plate and the semi-conductive substrate. V'hilc this type u( process is typical in some CCD imagers, it would be a costly additional fabrication step in ;~
C MOS imager.
A further system In which exposure time is adjusted is described in l:.S.
Patent 5,9b6,70~ which issued on November l O, 1 O99 to Shibuya et al. A video camera is described having an image sensing device, an exposure adjustment apparatus which controls the gain of~the amplifier to adjust the scanned output signal and further controls a drive pulse generator to control the exposure lisle of"tllc sen~iny device. In one embodiment, the video camera controls exposure by capturing an ima~~e with t11~ ima~,~c scusin'~ device. an7lifvin'~ the output signal which is ~lrivcn externally as well as being fed back into the exposure adjustment apparatus wllcre ~hc l0 signal is compared to a reference. When the comparison indicates that the image is either overexposed, underexposed or without need of adjustment. control si«nals are sent to the drive pulse generator to adjust exposure lisle and to the amplifier lu ad,jllst the gain of the amplifier.
na This method has several disadvantages, its iterative style of exposure control is only advantageous for a video camera. Contrc>IlinU only exposure time and ~i~~nal gain is limiting in terms of the range of light intensity under which the device would remain useful. Mill cameras, bar-code readers and the like. would not lied such a method useful as it would reduire additional circuitry to filter oui the overexposed ;:md 3o underexposed images. Low-light Conditions would he difficult for the device tcl image as it has no control over an external light source.
While each of the measurement methods has its means, the measurement 111et110dS al'e 11111erelltly 111111ted by Cllllel" tllC aCldltl011 Of; Cxtl'a ClrCllltt'v, ltlCl'~LISIII'~
2~ COSt alld SILO; 1"abl'lCall011 SICpS. IIICI'eaSlilg COSt; t1111e, SlOwlll~~
tllC O~'el~~lll pCl'f01'111a1L1Ce of the ima~~in' circuit.
Therefore, there is a need Ior an ambient light detector that is integrated with a scanning device without adding costly additional circuitry and that provides reliable 3o ambient light detection without undue interference with the ima~~e capture pruc~ss.
Summary of the Invention This invention is directed to a method .md apparatus For detcrmininy~ the level of ambient li~~ht impin~in~~ on 411)ix~l having a photodiodc. The Illcthod comprises resetting the photodiode in the pixel and at the same tinge detecting the current flay-through the photodiode as an indication of the ambient light level. The photodiode is reset by aI)plying a reverse bias voltage across it and the current (low is detected by measuring the current flow through a resistance in parallel to the phutudiodc.
In accurdancc with another aspect, this invention is directed to a metllud amt apparatus Ior detel-Illinin,.: the level uFambient light impinging on a selected number of pixels in an imaging array where each pixel includes a photodiodc. The ambien:
light may be determined by resetting the pixels in tllc array' and by detectill~~ current flow through lhc phutodiodes in a selected number oFtlle pixels as they arc l5eip~
Is reset. Alternately, the anlbicnt light may be determined by resetting a selected number of the pixels in the array and by detecting current flow through the photodiodes in the selected number of the pixels as they are bein~~ reset.
The selected nun lt)er of pixels may be divided into one or more y~roul)s each 3o having at least one pixel, and the pixels in cacll ~~roup may be arran'~cd in specitic patterns within the array. TI» array may be laid out in Toms and columns, amt the groups may be located in predetermined rows or columns. ~'hcn only a selected number of pixels are reset and these pixels are divided into groups, the groups may be sequentially reset to permit differentiation betv,~een the groups.
,;
In accordance with another aspect uFtllis invention, an apparatus dclrn~ines anlblent 11'111 Un all 1I11U~'In~' ~ll'IaIV OF llghl SCIISItI~'c plXelS
~i'llCl'c caCll IIaS a photodiode and photodiodc rest switch adapted to apply a predetermined reset voltage across the photodiode and further Ilas one or more power rails each connected ~o to one or more of the pixels for supplying pow::r to them. The apparatus comprises current monitorin~~ circuitry that measures current slow in the 1)I~otodiodes uf~select~d pixels as the photodiodes arc being reset to provide an output siy~nal representative o1 the ambient li~~l~t.
With regard to a further aspect of this invention, tl~e current monitoring circuitry and the imaging array may be integrated on the same die.
The current monitoring circuitry may further inc lode one or more current monitors each connected to at least one ofthe power rails for monitorinu the current tlow in the photodiodes connected to the: bower rails and an analo~T-to-digital 1t) converter coupled to each of the current monitors to provide a di~~ital output signal representative of the ambient li'~IO. ~~h~ curreW monitor may be a current-to-volta;~c converter connected to a bower rail throu~~h a resistance. The current-to-voltage converter may include a o op-amp h,mip~ an itivurtin~~ input tcrmioal couplcc.i to the resistance, a non-tnvcrtmg input terminal adapted to be coupled to a reference voltage and an output terminal, tl~e output terminal being coupled to the invcrtin'J
input terminal throu~l~ a further resistance.
In accordance with an aspect of this invention, in an imay~in~; array wlmrc tl-tc pixels arc positioned in rows and columns, the power rails are my each be connected 20 to a different group of the pixels located in a row or a column. The power rails for the selected pixels may all be adapted to be connected to the same power supply directly.
Alternately, the power rails may each be adapted to be connected to a power supply throu~~h a diode or they nay each be adapted to be connected to a separate lo_wa cr supply.
With re~~ard to a l~urtl~er aspect ofthis invention, the apparatus may further include a control for the pixel reset switches that will reset individual groups of pixels sequentially to allow the current in the rrsct photodiodcs to be monitored individually and sequentially.
O
(n aCCOrdallCC With ailOt11C1' ~iSyCCt, this I11~'Clllloll l7lay bC
lntcgl'atcd illto a svstcm for comrollin'~ the output si;~nal durin~~ in7a're capture of',ll object bu mo in lager whore the ima~cr includes an imaging array of li~sht sensitive pixels each having a photocliode and photodio~le reset means adapted to apply a predetermined reset voltage across the hhotodiode, and olc or more power rails each connected to 0110 OI- ilore plxcls oll a dlc.
Other aspects and advanta~,cs o(~the invention. its well as tl~e strilcture and to operation o(~various embodiments oftl7e invention, will become apparent to tloose ordinarily skilled in the art upon review of the followinv~ description ofthe invention in conjunction with tl7c accon lpanying ~Irmvin';s.
Brief Description of the Dra~~ings Tl7e invention will be descriUed with reference to the ~iccomhanyin'~
~ir~iwil,~~s, wherein:
h'igure 1 schematically illustrates a voltage supply coupled to an array of light sensitive pixels as well as a pixel circuit that nl.ay be used in the present invention;
Figure 2a illustrates a block diagram of the present invention;
2o higure 2h illustrates a blc>ck di~i~~ram oCtho present invention havin_~ a sin;~,lc Ctll'I'cnl IllOnltol';
Figure 2c illustrates a block diagram of the present invention havin~~
multiple voltage supplies;
Figure 2d illustrates a block dia<~ram of the present invention having isolated _'S power rails;
Figure 3a illustrates a block dia~~ram ol~the ambient 1i~17t detector;
Figure 3b illustrates a circuit th~it may be used as a current monitor in the ambient light detector;
Figures Via, 4b, 4c and 4d illustrate various possible layouts for the ima~=in,.;
~e> array for the detection of~ambient light ill speeilic areas of an array.
Figure 5 illustrates a block ~li~i'~ram of an exposure control system with wh,cl~
the arobicnt light detector in accordance: with tl7e present invention may be used: and Figure 6 illustrates the Iacc of~an ima~~e scanner.
Detailed Description C:VIOS image sensors are comprised of an array of light sensitive pi~cls inteUrated on a die. In operation, ai~tcr the pix~:ls h~lvc been reset. thr si~~nul ';eneratcU
by each pixel is proportional to the amount of char~~e collected by the pixel durin~~ an exposure or integration period. Hiowemr, durin;~ thl; reset process for each pixel, a leakage current flows through the: reset transistor and the photodiodc in each pixel.
The current flowing through the reverse biased photodiode is proportional to the level Of p110LO17s 1177p117~1114~ Oll the phOlOdlOde al 117at tll77e. ~~171, IC~'Cl Of'an7bIe11L llt~lll pl'esC'.17t \v17C17 <l17 liTlage is belllg Capllll'CCI by' 1171; IlllFlge arl-ay Call gI'ttltlV lllfllil'l7cc IlIC
llllFlllly' Of'117e C~tl7llll'2Cl 1171~1'~C; 11115 Is parllClllal ly 1171p01'lalll \Vhell the Caplllrl:d Illlaf,C
is being used for image rl:cognition in instances such as bar-code reading.
The level of light present when an image is being captured may also influence the amount of amplification that the imu~~e signals reduirc a5 they ure l7ein'~ processed for in~a~~c 1 ~ r<tcognition.
With reference to tibure 1. an array 101 of light sensitive l7ixcls l02 which arc normally laid out in rows and columns, are powered by a stable voltage supply providing an output voltage V~,~. One type of active pixel 102 that may be used in 2o conjunction with the present invention i5 illustrated, however, the invention may be carried out in conjunction with 17117er types of active pixels. Some pixels may use photodiodcs sucl7 as p-n photodiodcs, p-i-n pllutodiodcs and Schottky photodiudcs.
The active pixel 102 illustrated consists of a reset transistor 108, a source-fullo\ver transistor 109, a p-n photOdiode 107, and a ro\v-selection transistor 110. In order to 2s reset each pixel 102, a positive voltage signal V,i is applied to the gate ofthc reset transistor 108 through reset line 106 turning the transistor 108 OV in order t~7 apply the voltage V,I,I across the photodiode 107.
The pixels 102 arc coupled to the voltage supply 103 through the arr~ly power ;o rail 104 and a row power rails IOS. As each pixel 102 is being reset_ a current \vill (low through the pixel 102 as a pixel leakage current I,~,,. The pixel leakage current I,~, flowin~~ through the reverse-biased p-n phutodiode 107 is proportional to the le\ cl of~photons In 7pinging on the photodiodc 107. In effect, the intensity of~li~~ht fittin~~
S
the photodiode 107 can be measured by monitoring the pixe-1 leal:a~~e current I,.,.. 'The total current Mowing through a row power rail 105 for all of the pixels 102 in that row during their rest is current Inn, and the total current Mowing through the power rail 104 for all of~the pixels 102 in the array 101 during their reset is current la,~. The, ambient light level impinging on the array 101 may be determined by mc~rsurin~, tlm current Mowing through a selected number of~loixels 102 while they arc being reset.
An embodiment of the present invention for monitoring the pixel lcal:age current is illustrated in >igure 2a wherein an ambient light detection circuit 220 is to connected to the ima~~in~~ array 201 in which tl~e pixels 202 are laid out in rows and columns. It is preferred to have the an nbicnt light detection circuit 220 inte«ratcd c>n the same die as the imaging array 2U1, however this is not essential for the proper operation ofthe present invention. Che voltage supply 203 provides power to the rmagmg array 201 through the main power rail 204 which is coupled to the row power is rails 205. Further, a number of selected indivic.iual row power rails 205 are each coupled to the ambient liy~ht detection circuit 220. The ambient li<~ht detection circuit 220 detects the individual currents flowing thruu~~h each of the selected row roils 2~D5.
and outputs a signal P«r , representative the currents tlowin~a. The output si;;nal P"r-,-is a function of the currems I,i,~ Mowing to the pixels 202 in each of the selceted row 2o rails 205 and therefore can be used as a representation ofthe leml of ambient light impinging on the pixels 202 in the array.
The ambient light detection circuit 220 shown is figure 3<~ illustrates one form that it may tale to monitor currents flowing in one or more groups of pixels 202 in 2~ array 201. A number of inputs 221 (or Individual connection to a selected number of row- rails 205, arc each connected to a current monitor 21 1 through a small resistance 212 of value R,t~r. Care must be taken to assure that the inputs 221 are isolated from one another such that the monitors 21 1 will only monitor the current in tl~e row arils 205 to which they are connected. -floe current monitor 21 1 detects the curreu flowin~~
;( throu~~h the small resistance 212, aocl outputs an analog si~~~nal relruscntativc of~thal current flow to an analog to digital converter 213. The analo<~ to digital converter 213 transforms the analog signal into a digital signal P cansistin'~ of a number ot-bits.
c) Analog to digital converters are well known to those skilled in the art, and hmcc shall not be described further I~erc. TI)c outlouts P I~z-om the various analog to di'~;tal converters 213 are led to a combines 222 which nay either combine all of tl~e I' signals into a single digital output signal P«~ I or wl~icl~ may sequence the P signals s into a string of digital outputs as signal Pr)r-r representing the currents in the row rails 205 that had been selected.
Figure 3b illustrates one form that the current manilas 211 may take. It consists basically of a current-to-voltage convurler 313. ~I'hc current Ilwl ilcwvin'g to through the small resistance 212 is equal to the total amount ol~currcnt I,t-~ flowing through the row power rail 205 Iess the total teal<age currents I,t,~ Mowing into the pixels 202 connected to that particular row rail 205. Tire voltage at the inverting input 315 to the op-amp 314 is approximately equivalent to the reference volta~m 1',z,..,:
applied to the non-inverting input 316 to tl~e op-amp 314. This is possible I~v what is commonly known as a mrtual '~rouncl betty een the inverting input 315 and non-inverting input 316 of the op-amp 314. Due to tl~e infinite impedance ofthc op-am.p 314 all of the current I,i~, is forced to flow through the large resistance 317 of value R,.. This leads to an output voltage Icvcl V«, , represented by the following.
equation:
?u y'mn = ~' m ~: Il~~n ~~ ~i ) This establishes an output voltage Icvel ~'~" -,- on output terminal 318 that is a function of the current I,f" Mowing through the small resistor 212, which is a function of the total leakage current I,t,> flowing through the pIxCIS 202 111 that particular row 20_>.
?~ which is a Junction ofthc amount ol~light impinging on the pixels 202 in thm particular row 205. In eflcct the output v~oliagu ~-'«,-,- is directly proportional to the intensity ol~an~bimt li~~ht impingip~ on the pixels 202 in the selected rov of the ima'~c sensor array 201. V«~;-,- on the output 318 is tUen applied to the analog to digital converter 213.
Alternate arrangements for monitorin;~ the pixel leal<a'~c currcnt(s) I,~,, of anywhere li~om one to all of the pixels 202 are also possible. For instance, as illustrated in t5~ure 2b, <z single current monitor 211 may be coupled to the array rail 204 so as to n~cusure the total leal:a~c current for all pixels 202 in the array 201 as they arc bcin~~ simultancouslv reset. R~t~errin«, to figure 1 for clctail, the upl>aratus in this embodimc;nl may be operated such that the reset transistors 108 for floe pixels 102 is controlled to reset sec)ucntially one or more pixels in selected rows or columns or groups of pixels 202 as illustrated in figure 2b. The resulting output signal V~" , \vill consist ofse~luential digital outputs representing ambient li~,ht from the cii(~fcrcnt parts to of the array which can be combined to provide an output signal rcpresentati~ c of~tlnc ambient li~~ht on the array.
It is usually preferred to measure tl~e ambient light on the array 201 while the imaging scanner is operating normally where the pixels 202 in the array 201 are reset is simultaneously clurin'~ the resetting process; in this manner, the scanning process is interfered with the least. Figure 2c is nn embodiment of the present inwenti~m where selected rows 205 of"pixels 202 to be monitored by the ambient light detection circuit 220 are individually connected to separate volta«e sources 203. As illustrated ro\v rails 205x, 205b, 205c and 205d are connected to voltage supplies 203x, 203b, 203c 2o and 203d respectively. 'I fee remaining ro\v rails 205 are connected to a furtl;er voltage supply 203. The ambient fight detection circuit 220 includes a current monitor 211 a, 21 1 b, 21 1 c and 211 d anti associated circuitry as describeli with respect to figure 3a for monitoring the current individl_lally on each of tllc row rails 205a, 205b, 205c and 2054 respectively. In this \vav, all of the pixels 202 in the entire array Za 201 can be reset simultaneously and at the sanne time the currents in row rails 205x, 205b, 205c and 2OSd can be monitored.
A f~llrther preferred embodiment is illustrated in tigure 2d where the ro\v roils 205x, 205b, 205c and 2054 are all connected to the same volla'~e supply 203 hove\=er ~c; through diodes 223x, 223b, 223c and 2234 respectively. The diodes 223x, 223b, 223c and 223d allow the row rails 205a, 205b, 205c and 205d to be monitored II1d1V1dUally while ''<lvOldlng illlel'let'ellce by Cll1'I'elltS In the 1'Cll~tlllllll'' r0\\' 1'allS 205.
As was described with regard to tigure 2a, all pixels 202 in an array 201 arc normally reset simultaneously, though this need not be the case to implement the present invention. When it is desired to monitor the ambient light in a certarn predetermined pattern on the imaging array 201, it is necessary to measure the leal:a<ae currents I,~r, tlowing through the pixels 202 that are contiguous with that pattern. In such a circumstance. only the pixels 202 wl~iclt arc: contiguous with that patmrn cao he reset at one point in time. allowing Ior the simple measurement of the Ical;a~~c current to all pixels 202 that are hcing reset.
In addition, though all pixels 202 are shown as being connected to the volta~~c supply 203 tllrOLlgl1 the row rail 205, other arrangements are possible.
Examples ol~
some such patterns are illustrated in figures 4v to 4d which each show pixels being laid out in an array 401 of 1 ~ row-s by 1 s columns.
1>
If it is desired to measure the ambient light level on the array 401 using only the center rows and columns for instance rows 7 to 9 and columns 7 to 9, then the voltage supply to these rows and columns must be isolated from the remainin~~
rows and columns in order to monitor the leakage currents while the pixels 402 are bein«
?o reset. Figure 4a, illustrates one such contiguratiun wherein the pixels 402 in colunon 7 are connected to a power rail 421, the pixels 402 in column 8 are connected to a power rail 422 and the pixels 402 in column 9 are connected to a power rail 423. In addition, the pixels 402 io row 7 that arc in columns l to 6 are connected to a rail 424.
tltc pixels 402 in row 8 that are in columns 1 to C arc connected to a rail 425, tlrc ?s pixels 402 in row- 9 that arc in columns I to O ~ra~e connected to a rail 426, the pixels 402 in row 7 that arc in columns 1t) to 1 > arc cunmcted to a rail 427, the pixels 4U2 in row 8 that arc in columns lU to 15 are connected to a rail 428, the pixels 402 in row 9 that are in columns 10 to 15 are connected to a rail 429. In addition, rails 424 and 427 may be connected together-, rails 425 and 428 may be connected together, and rails ;0 426 and 429 may be connected to'~clhcrSuch ~r coniiguratiun would allow ~;
current monitor to be cuonectcd to each oi~the rails 421 l0 426 in order to measure tl~c leakage currents in the pixels 402 in rows 7 to 9 and columns 7 to 9 which results in a measurement ot~the ambient light fallinV in a cross pattern on the array 401.
Similar results wcould be achieved if the pow er rails for tloc hircls 402 in row-s 7 to 9 carried across the entire array 401 while the power rails te>r the pixels 402 in columns 7 to 9 were interrupted for rows i to O, as illustrated in tigure 4b.
In addition, the configurations in figures 4a and 4b would allow ambient li'=ht measurements to be taken Cor the four corners of the array 401 il~tl~e Ieal:a~~c currents were measured on alternate power rails 431 to 450. hhe pixels 402 are connected to m these power rails in tlrc ti~llowin« manner: the pixels 402 in column 1 that ane in rows 1 to C are connected to a rail 43l and the pixels 402 that are in rows 10 to 1 ~ are connected to rail 441, the: pixels 402 in column 2 that are in row s 1 to 6 are connected to a rail 432 and the pixels 402 that are in rows 10 to 15 are connected to rail 442, the pixels 402 in column 3 that are in rows 1 to C arc connected to a rail 433 and tire 1 s pixels 402 that arc in rows 1 () to 1 ~ are connected to rail 443, the pixels 402 in column =~ drat arc in rwvs 1 to (> are connected to a rail -f34 <rnd the pixels 402 drat ,rrc in rows 10 to 15 are connected to rail 444, and the pixels 402 in column >
that arc io roes 1 to 6 arc connected to a rail 435 and the pixels 402 that arc in rows 1 () to 1 ~ arc connected to rail 445. Similarly, the pixels 402 111 Collllllll 1 1 that arc in rows 1 to C.
?o are connected to a rail 436 and the pixels 402 that are in rows 10 to l5 are connected to rail 446, the pixels 402 in columnl? that are in rows 1 to O arc connected to a rail 437 and the pixels 402 that arc in rows l0 to I ~ arc connected to rail 447, the pixels 402 in column 1 s that are in rows 1 to (3 arc connected to a rail 438 and the pixels 402 that arc in rows 10 to 1 ~ are connected to rail 448, the pixels 402 in column I 4 that 2~ are in rows 1 to li are connected to a rail 439 alrd the pixels 402 that are in rows 10 to 15 are connected to rail 449, and the pixels 402 in column 1 ~ that arc in rows 1 to O
are connected to a rail 440 and the pixels 402 drat are il rows 1 U to 1 ~ arc cunlrectc~a to rail 450. 13y nrunitc>rin~~ the leakage currents in power rails 331 to 350, the ~rmbicnt light level at the four corners of the array 401 nlav be determined.
;ci Figure 4c illustrates an array 401 having a conliguration wherein all of the pixels 402 in each column 1 to 15 are connectl;d to a different power rail 430. This configuration allows for the selection of particular columns, rather than roves as illustrated in figure 2a, to measure the ambient light on the array 401.
Figure 4d illustrates vet another conliL;uration wherein powrr rails 451 arc connected to the row 1 to 8 pixels 420 ill colurlms (~ to 10 and tile power rails 453 arc connected to the row 9 to I S pixels 420 in columns C to 10 the power rails 451 and to 453 extend across only half the ima~;in~~ array 401. Each of tile power rails 452 is connected to the column 1 to S pixels 420 for reach of the rows 1 to 1 j, while: each of the power rails 454 is connected to the column 1 l to 1 ~ pixels 420 for each of the rows 1 to 13 providing versatility in monitorin~~ the lcal:agc currl:nts.
is Figure 5 illustrates the use of the present invention in an exposure controlled images 500 as described in co-pending US Pitt°nl Application Serial '.vlo. 09-(o~),sOb filed on October 12, 2000 which is incorporated herein by reference. The inoa~;in'~
circuit 501 which is locaml on a water or die and which is rellrcsentcd by hrol:en lines, nol-lally includes an imaging array 502, wordlinc drivers 503 and worcllines 20 504, bitline readers 505 and bitlines 506, an integration timer 507, and a signal amplifier 509. 'l he bit(ine readers 505 are connected to the signal amplifier which amplif7es the bitline reader 505 signals to produce the image output data.
Further, light detector circuits 520 are also located on the die 501 adjacent to the imaging array 5U2.
w The imaging circuitry 501 on the die may further include an avera~iny~ circuit 510, a look-up table and signal driver 51 1 and an illumination source control 512.
The signal driver 511 includia output lines 513 to 515 respectively for signals to control the signal anlplilicr 508, the intey~ration tinier 507 and the illumination control 3O 512. The illumination control 512 is ~ui~Iptcd tea control an illumination source 513 Illav IIOt IIeCCSS81'lly be lOCatf:d 017 IhC Illlar~lll'~ 1.'ll'Cllltl'y 1110:
501.
Once the look-up table anti signal driver 511 detc;rnliws the proper values for tile tl111111111a11On SOUrCC C011tr01 Si~~ll~il, Ille 1111er,ra11011 tulle C011it'O1 SI;~I1L11, aild the ,~.lllll control signal, these signals arc fed to illumination source controller 512, tile s integration timer 507 anti the signal amplifier 508 respectively to adjust the briwhtness of~the light source 513, tile exposure time of tile imaging array 502 and the ~~ain of the amplifier 508. respectively.
The look-up table anti signal driv'cr 51 1 nlav consist of a nlicrocontrollcr ui device such as the Stron~~-Arm SA-1 1 10 and a read only memory provlramnlerl with data delining particular imaging needs in terms of~light intensity, integration time, and signal gain in response to a measured level oCambient light. ~(~he sort ofdata contained therein would dcpenc( on the type of~application the device was to be used for: for example a bar cone reader would try to relv mostly on alterations oC
the n Integration time as this would be the power conscious method of~anl(~ient li~~llt adj llstment.
The light source 513 may consist o(~any type of conventional light source that Call 17e COIlt1'Olled I11 111tC11SI2V. (~OVVi:~'CI', d paCtlClllal'ly adValltilgCOlls ell'I'elil'W 'IIIC ilt 1S
?o illustrated in l7gure 6, which schematically illustrates the Lace o(~a scanner 000. Tllc mla~png circuit 601 is located at the center of the scanner face 602. One or more (..ED
light sources 603 are positioned about the ima~;in~1 circuit 601 to provide further lighting if required. Ill operation, the one or more LED's 603 may each be controlled by a separate title in order to turn each I,ED 603 OFF or ON as desired. For example.
if an object or target is close to the scanner f<lce 602, only one or two L.ED's might hl' turned ON; with the t~lr~~ct a little further away, such as live or si.v inches, possibly three or four LED's 603 could he turned ON. :'\lli:rnalivclv, tile li~'ht source controller 512 could control the driving current to each LED 603, and increase or decrease the illumination from each LED 603 as required.
While the invention has been described according to what is presently considered to be the most ('practical alld (preferred embodiments. it must be undcrstooli that tile invention is not limited to the disclosed ernbodinlcnts. Those orc(inar;l~
skilled in the art will understand that various modifications and cduivalent structures and functions may be made without departing from the spirit and scope of tl~c invention as dclined in tloc claims. ~l~herelore, the invention as defined in the claims must he accorded the broadest possible interpretation so as to encompass all such n~odi(ications and cduivalcnt structures and flmetions.
to particular to determining ambient light intensity for il~la~~c scaonin~
devices.
Background of the Invention In the imaging industry, scanners are expected to operate effectively under :.I
wide range of ambient li~ltt. A number of solutions have been developed wllmin t, ambient light is measured in order to control the scannin« system. The scnsin~~ of~
ambient li~~ht Inay be done by an ambient light detection circuit which is separate from the imaging array, or ambient light cm be detected through the use ofthc imaging array itself. The ambient light measurement is then used either to adjust the exposure tine for the imaging arrayilens, to set the gain ofthe il»a«c signal ur to 2o control the brightness offal li~~ht suurcc.
U. S. Patent 4, 970,379 which issued on November 13, 1990 to Danstrom discloses exposure,~illumination control for a bar code scanner consisting of a controllable light source and an optical sensor that is independent of the scanner ar~av.
2s The optical sensor converts the light re (lccting from the object to be scannccl into an electrical signal representative: ofthe ambient light. This si~~nal is couplccl tcv a comparator, which determines the illumination reduired by the scanner array, and then adjusts the poavcr to the controllable light source accordingly. A major drawback of this method is that during love li~uht conditions the light source will be driven by the:
s0 cOt1'Ipat'at01' t0 gelleratc: bl'1g11t ll1n111111a11On, W 111C11 COIISLInIeS a large an10Ul1t Ot L70~\'tl'.
In a hand held device this is extremely detrimental. as most hand held dcvicm have a sell=contained power supply.
Other systems use the imaging array itself to determine ambient light levels which is then used to control exposure time. l.i.S. Patent 4,471,??8 which issued on September 1 1, 1984 to Nishiiaw~a et al., describes an in~a~c sensor consistin« of ncn-a destructive readout-type in~a~;c cells, the sensor uses the away of image cells as both photo-detector cells for tile measurement of anobient li~~ht and as image capturing cells for imaging an object. The imaging array is exposed to the object and an ambient light measurement run is made through previo~.isly selected ima';ing cells.
The added value of the selected ima~~ing cells is cr~mhare~i to a reference value to detcrn~inc tlnc exposure Level rcduired. fhc selected ima;~iny cells arc then erased. and an ima'~c scan ofthc objet is pcriormcd with a controlled exposure time.
The shortcoming of this method is that it consists of too many steps. The multi-step process of using the array to measure ambient light and then iorcip~ the t > array to be reset before the image is scanned, slows the process down.
Additional l s~.
the extra step rcduircs an extra expenditure of power, which is a severe detrin~cnt io a hand-hclcl device.
Another method using the imaging array is U.S. Patent 4,338, 14, which 2o issued on .luly 6, 198? to l3ixbv, discloses a further method of coWrollin~~ evhosurc time by operating a mechanical shutter in response to radiant energy impin~~in'~ on the sensor array. 'f he semiconductor array substrate current is monitored ~iurin~~. tl~c csposure ofthc ima~~ing array to prc>ducc an intcgr:ncd si~~nal that is prolortioml to the exposure level of the array. The signal is compared to a threshold voltage and 2~ when it exceeds a threshc>Id value the shutter i~; closed.
There arc drawbacks to this method in that it rcduircs additional hroccssin'~
steps in order to create an apparatus to monitor tl~e substrate current.
Specifically, the apparatus recluircs the addition ol~u layer ul~cooductivc material bclocn tlm non-;t? conductive base-plate and the semi-conductive substrate. V'hilc this type u( process is typical in some CCD imagers, it would be a costly additional fabrication step in ;~
C MOS imager.
A further system In which exposure time is adjusted is described in l:.S.
Patent 5,9b6,70~ which issued on November l O, 1 O99 to Shibuya et al. A video camera is described having an image sensing device, an exposure adjustment apparatus which controls the gain of~the amplifier to adjust the scanned output signal and further controls a drive pulse generator to control the exposure lisle of"tllc sen~iny device. In one embodiment, the video camera controls exposure by capturing an ima~~e with t11~ ima~,~c scusin'~ device. an7lifvin'~ the output signal which is ~lrivcn externally as well as being fed back into the exposure adjustment apparatus wllcre ~hc l0 signal is compared to a reference. When the comparison indicates that the image is either overexposed, underexposed or without need of adjustment. control si«nals are sent to the drive pulse generator to adjust exposure lisle and to the amplifier lu ad,jllst the gain of the amplifier.
na This method has several disadvantages, its iterative style of exposure control is only advantageous for a video camera. Contrc>IlinU only exposure time and ~i~~nal gain is limiting in terms of the range of light intensity under which the device would remain useful. Mill cameras, bar-code readers and the like. would not lied such a method useful as it would reduire additional circuitry to filter oui the overexposed ;:md 3o underexposed images. Low-light Conditions would he difficult for the device tcl image as it has no control over an external light source.
While each of the measurement methods has its means, the measurement 111et110dS al'e 11111erelltly 111111ted by Cllllel" tllC aCldltl011 Of; Cxtl'a ClrCllltt'v, ltlCl'~LISIII'~
2~ COSt alld SILO; 1"abl'lCall011 SICpS. IIICI'eaSlilg COSt; t1111e, SlOwlll~~
tllC O~'el~~lll pCl'f01'111a1L1Ce of the ima~~in' circuit.
Therefore, there is a need Ior an ambient light detector that is integrated with a scanning device without adding costly additional circuitry and that provides reliable 3o ambient light detection without undue interference with the ima~~e capture pruc~ss.
Summary of the Invention This invention is directed to a method .md apparatus For detcrmininy~ the level of ambient li~~ht impin~in~~ on 411)ix~l having a photodiodc. The Illcthod comprises resetting the photodiode in the pixel and at the same tinge detecting the current flay-through the photodiode as an indication of the ambient light level. The photodiode is reset by aI)plying a reverse bias voltage across it and the current (low is detected by measuring the current flow through a resistance in parallel to the phutudiodc.
In accurdancc with another aspect, this invention is directed to a metllud amt apparatus Ior detel-Illinin,.: the level uFambient light impinging on a selected number of pixels in an imaging array where each pixel includes a photodiodc. The ambien:
light may be determined by resetting the pixels in tllc array' and by detectill~~ current flow through lhc phutodiodes in a selected number oFtlle pixels as they arc l5eip~
Is reset. Alternately, the anlbicnt light may be determined by resetting a selected number of the pixels in the array and by detecting current flow through the photodiodes in the selected number of the pixels as they are bein~~ reset.
The selected nun lt)er of pixels may be divided into one or more y~roul)s each 3o having at least one pixel, and the pixels in cacll ~~roup may be arran'~cd in specitic patterns within the array. TI» array may be laid out in Toms and columns, amt the groups may be located in predetermined rows or columns. ~'hcn only a selected number of pixels are reset and these pixels are divided into groups, the groups may be sequentially reset to permit differentiation betv,~een the groups.
,;
In accordance with another aspect uFtllis invention, an apparatus dclrn~ines anlblent 11'111 Un all 1I11U~'In~' ~ll'IaIV OF llghl SCIISItI~'c plXelS
~i'llCl'c caCll IIaS a photodiode and photodiodc rest switch adapted to apply a predetermined reset voltage across the photodiode and further Ilas one or more power rails each connected ~o to one or more of the pixels for supplying pow::r to them. The apparatus comprises current monitorin~~ circuitry that measures current slow in the 1)I~otodiodes uf~select~d pixels as the photodiodes arc being reset to provide an output siy~nal representative o1 the ambient li~~l~t.
With regard to a further aspect of this invention, tl~e current monitoring circuitry and the imaging array may be integrated on the same die.
The current monitoring circuitry may further inc lode one or more current monitors each connected to at least one ofthe power rails for monitorinu the current tlow in the photodiodes connected to the: bower rails and an analo~T-to-digital 1t) converter coupled to each of the current monitors to provide a di~~ital output signal representative of the ambient li'~IO. ~~h~ curreW monitor may be a current-to-volta;~c converter connected to a bower rail throu~~h a resistance. The current-to-voltage converter may include a o op-amp h,mip~ an itivurtin~~ input tcrmioal couplcc.i to the resistance, a non-tnvcrtmg input terminal adapted to be coupled to a reference voltage and an output terminal, tl~e output terminal being coupled to the invcrtin'J
input terminal throu~l~ a further resistance.
In accordance with an aspect of this invention, in an imay~in~; array wlmrc tl-tc pixels arc positioned in rows and columns, the power rails are my each be connected 20 to a different group of the pixels located in a row or a column. The power rails for the selected pixels may all be adapted to be connected to the same power supply directly.
Alternately, the power rails may each be adapted to be connected to a power supply throu~~h a diode or they nay each be adapted to be connected to a separate lo_wa cr supply.
With re~~ard to a l~urtl~er aspect ofthis invention, the apparatus may further include a control for the pixel reset switches that will reset individual groups of pixels sequentially to allow the current in the rrsct photodiodcs to be monitored individually and sequentially.
O
(n aCCOrdallCC With ailOt11C1' ~iSyCCt, this I11~'Clllloll l7lay bC
lntcgl'atcd illto a svstcm for comrollin'~ the output si;~nal durin~~ in7a're capture of',ll object bu mo in lager whore the ima~cr includes an imaging array of li~sht sensitive pixels each having a photocliode and photodio~le reset means adapted to apply a predetermined reset voltage across the hhotodiode, and olc or more power rails each connected to 0110 OI- ilore plxcls oll a dlc.
Other aspects and advanta~,cs o(~the invention. its well as tl~e strilcture and to operation o(~various embodiments oftl7e invention, will become apparent to tloose ordinarily skilled in the art upon review of the followinv~ description ofthe invention in conjunction with tl7c accon lpanying ~Irmvin';s.
Brief Description of the Dra~~ings Tl7e invention will be descriUed with reference to the ~iccomhanyin'~
~ir~iwil,~~s, wherein:
h'igure 1 schematically illustrates a voltage supply coupled to an array of light sensitive pixels as well as a pixel circuit that nl.ay be used in the present invention;
Figure 2a illustrates a block diagram of the present invention;
2o higure 2h illustrates a blc>ck di~i~~ram oCtho present invention havin_~ a sin;~,lc Ctll'I'cnl IllOnltol';
Figure 2c illustrates a block diagram of the present invention havin~~
multiple voltage supplies;
Figure 2d illustrates a block dia<~ram of the present invention having isolated _'S power rails;
Figure 3a illustrates a block dia~~ram ol~the ambient 1i~17t detector;
Figure 3b illustrates a circuit th~it may be used as a current monitor in the ambient light detector;
Figures Via, 4b, 4c and 4d illustrate various possible layouts for the ima~=in,.;
~e> array for the detection of~ambient light ill speeilic areas of an array.
Figure 5 illustrates a block ~li~i'~ram of an exposure control system with wh,cl~
the arobicnt light detector in accordance: with tl7e present invention may be used: and Figure 6 illustrates the Iacc of~an ima~~e scanner.
Detailed Description C:VIOS image sensors are comprised of an array of light sensitive pi~cls inteUrated on a die. In operation, ai~tcr the pix~:ls h~lvc been reset. thr si~~nul ';eneratcU
by each pixel is proportional to the amount of char~~e collected by the pixel durin~~ an exposure or integration period. Hiowemr, durin;~ thl; reset process for each pixel, a leakage current flows through the: reset transistor and the photodiodc in each pixel.
The current flowing through the reverse biased photodiode is proportional to the level Of p110LO17s 1177p117~1114~ Oll the phOlOdlOde al 117at tll77e. ~~171, IC~'Cl Of'an7bIe11L llt~lll pl'esC'.17t \v17C17 <l17 liTlage is belllg Capllll'CCI by' 1171; IlllFlge arl-ay Call gI'ttltlV lllfllil'l7cc IlIC
llllFlllly' Of'117e C~tl7llll'2Cl 1171~1'~C; 11115 Is parllClllal ly 1171p01'lalll \Vhell the Caplllrl:d Illlaf,C
is being used for image rl:cognition in instances such as bar-code reading.
The level of light present when an image is being captured may also influence the amount of amplification that the imu~~e signals reduirc a5 they ure l7ein'~ processed for in~a~~c 1 ~ r<tcognition.
With reference to tibure 1. an array 101 of light sensitive l7ixcls l02 which arc normally laid out in rows and columns, are powered by a stable voltage supply providing an output voltage V~,~. One type of active pixel 102 that may be used in 2o conjunction with the present invention i5 illustrated, however, the invention may be carried out in conjunction with 17117er types of active pixels. Some pixels may use photodiodcs sucl7 as p-n photodiodcs, p-i-n pllutodiodcs and Schottky photodiudcs.
The active pixel 102 illustrated consists of a reset transistor 108, a source-fullo\ver transistor 109, a p-n photOdiode 107, and a ro\v-selection transistor 110. In order to 2s reset each pixel 102, a positive voltage signal V,i is applied to the gate ofthc reset transistor 108 through reset line 106 turning the transistor 108 OV in order t~7 apply the voltage V,I,I across the photodiode 107.
The pixels 102 arc coupled to the voltage supply 103 through the arr~ly power ;o rail 104 and a row power rails IOS. As each pixel 102 is being reset_ a current \vill (low through the pixel 102 as a pixel leakage current I,~,,. The pixel leakage current I,~, flowin~~ through the reverse-biased p-n phutodiode 107 is proportional to the le\ cl of~photons In 7pinging on the photodiodc 107. In effect, the intensity of~li~~ht fittin~~
S
the photodiode 107 can be measured by monitoring the pixe-1 leal:a~~e current I,.,.. 'The total current Mowing through a row power rail 105 for all of the pixels 102 in that row during their rest is current Inn, and the total current Mowing through the power rail 104 for all of~the pixels 102 in the array 101 during their reset is current la,~. The, ambient light level impinging on the array 101 may be determined by mc~rsurin~, tlm current Mowing through a selected number of~loixels 102 while they arc being reset.
An embodiment of the present invention for monitoring the pixel lcal:age current is illustrated in >igure 2a wherein an ambient light detection circuit 220 is to connected to the ima~~in~~ array 201 in which tl~e pixels 202 are laid out in rows and columns. It is preferred to have the an nbicnt light detection circuit 220 inte«ratcd c>n the same die as the imaging array 2U1, however this is not essential for the proper operation ofthe present invention. Che voltage supply 203 provides power to the rmagmg array 201 through the main power rail 204 which is coupled to the row power is rails 205. Further, a number of selected indivic.iual row power rails 205 are each coupled to the ambient liy~ht detection circuit 220. The ambient li<~ht detection circuit 220 detects the individual currents flowing thruu~~h each of the selected row roils 2~D5.
and outputs a signal P«r , representative the currents tlowin~a. The output si;;nal P"r-,-is a function of the currems I,i,~ Mowing to the pixels 202 in each of the selceted row 2o rails 205 and therefore can be used as a representation ofthe leml of ambient light impinging on the pixels 202 in the array.
The ambient light detection circuit 220 shown is figure 3<~ illustrates one form that it may tale to monitor currents flowing in one or more groups of pixels 202 in 2~ array 201. A number of inputs 221 (or Individual connection to a selected number of row- rails 205, arc each connected to a current monitor 21 1 through a small resistance 212 of value R,t~r. Care must be taken to assure that the inputs 221 are isolated from one another such that the monitors 21 1 will only monitor the current in tl~e row arils 205 to which they are connected. -floe current monitor 21 1 detects the curreu flowin~~
;( throu~~h the small resistance 212, aocl outputs an analog si~~~nal relruscntativc of~thal current flow to an analog to digital converter 213. The analo<~ to digital converter 213 transforms the analog signal into a digital signal P cansistin'~ of a number ot-bits.
c) Analog to digital converters are well known to those skilled in the art, and hmcc shall not be described further I~erc. TI)c outlouts P I~z-om the various analog to di'~;tal converters 213 are led to a combines 222 which nay either combine all of tl~e I' signals into a single digital output signal P«~ I or wl~icl~ may sequence the P signals s into a string of digital outputs as signal Pr)r-r representing the currents in the row rails 205 that had been selected.
Figure 3b illustrates one form that the current manilas 211 may take. It consists basically of a current-to-voltage convurler 313. ~I'hc current Ilwl ilcwvin'g to through the small resistance 212 is equal to the total amount ol~currcnt I,t-~ flowing through the row power rail 205 Iess the total teal<age currents I,t,~ Mowing into the pixels 202 connected to that particular row rail 205. Tire voltage at the inverting input 315 to the op-amp 314 is approximately equivalent to the reference volta~m 1',z,..,:
applied to the non-inverting input 316 to tl~e op-amp 314. This is possible I~v what is commonly known as a mrtual '~rouncl betty een the inverting input 315 and non-inverting input 316 of the op-amp 314. Due to tl~e infinite impedance ofthc op-am.p 314 all of the current I,i~, is forced to flow through the large resistance 317 of value R,.. This leads to an output voltage Icvcl V«, , represented by the following.
equation:
?u y'mn = ~' m ~: Il~~n ~~ ~i ) This establishes an output voltage Icvel ~'~" -,- on output terminal 318 that is a function of the current I,f" Mowing through the small resistor 212, which is a function of the total leakage current I,t,> flowing through the pIxCIS 202 111 that particular row 20_>.
?~ which is a Junction ofthc amount ol~light impinging on the pixels 202 in thm particular row 205. In eflcct the output v~oliagu ~-'«,-,- is directly proportional to the intensity ol~an~bimt li~~ht impingip~ on the pixels 202 in the selected rov of the ima'~c sensor array 201. V«~;-,- on the output 318 is tUen applied to the analog to digital converter 213.
Alternate arrangements for monitorin;~ the pixel leal<a'~c currcnt(s) I,~,, of anywhere li~om one to all of the pixels 202 are also possible. For instance, as illustrated in t5~ure 2b, <z single current monitor 211 may be coupled to the array rail 204 so as to n~cusure the total leal:a~c current for all pixels 202 in the array 201 as they arc bcin~~ simultancouslv reset. R~t~errin«, to figure 1 for clctail, the upl>aratus in this embodimc;nl may be operated such that the reset transistors 108 for floe pixels 102 is controlled to reset sec)ucntially one or more pixels in selected rows or columns or groups of pixels 202 as illustrated in figure 2b. The resulting output signal V~" , \vill consist ofse~luential digital outputs representing ambient li~,ht from the cii(~fcrcnt parts to of the array which can be combined to provide an output signal rcpresentati~ c of~tlnc ambient li~~ht on the array.
It is usually preferred to measure tl~e ambient light on the array 201 while the imaging scanner is operating normally where the pixels 202 in the array 201 are reset is simultaneously clurin'~ the resetting process; in this manner, the scanning process is interfered with the least. Figure 2c is nn embodiment of the present inwenti~m where selected rows 205 of"pixels 202 to be monitored by the ambient light detection circuit 220 are individually connected to separate volta«e sources 203. As illustrated ro\v rails 205x, 205b, 205c and 205d are connected to voltage supplies 203x, 203b, 203c 2o and 203d respectively. 'I fee remaining ro\v rails 205 are connected to a furtl;er voltage supply 203. The ambient fight detection circuit 220 includes a current monitor 211 a, 21 1 b, 21 1 c and 211 d anti associated circuitry as describeli with respect to figure 3a for monitoring the current individl_lally on each of tllc row rails 205a, 205b, 205c and 2054 respectively. In this \vav, all of the pixels 202 in the entire array Za 201 can be reset simultaneously and at the sanne time the currents in row rails 205x, 205b, 205c and 2OSd can be monitored.
A f~llrther preferred embodiment is illustrated in tigure 2d where the ro\v roils 205x, 205b, 205c and 2054 are all connected to the same volla'~e supply 203 hove\=er ~c; through diodes 223x, 223b, 223c and 2234 respectively. The diodes 223x, 223b, 223c and 223d allow the row rails 205a, 205b, 205c and 205d to be monitored II1d1V1dUally while ''<lvOldlng illlel'let'ellce by Cll1'I'elltS In the 1'Cll~tlllllll'' r0\\' 1'allS 205.
As was described with regard to tigure 2a, all pixels 202 in an array 201 arc normally reset simultaneously, though this need not be the case to implement the present invention. When it is desired to monitor the ambient light in a certarn predetermined pattern on the imaging array 201, it is necessary to measure the leal:a<ae currents I,~r, tlowing through the pixels 202 that are contiguous with that pattern. In such a circumstance. only the pixels 202 wl~iclt arc: contiguous with that patmrn cao he reset at one point in time. allowing Ior the simple measurement of the Ical;a~~c current to all pixels 202 that are hcing reset.
In addition, though all pixels 202 are shown as being connected to the volta~~c supply 203 tllrOLlgl1 the row rail 205, other arrangements are possible.
Examples ol~
some such patterns are illustrated in figures 4v to 4d which each show pixels being laid out in an array 401 of 1 ~ row-s by 1 s columns.
1>
If it is desired to measure the ambient light level on the array 401 using only the center rows and columns for instance rows 7 to 9 and columns 7 to 9, then the voltage supply to these rows and columns must be isolated from the remainin~~
rows and columns in order to monitor the leakage currents while the pixels 402 are bein«
?o reset. Figure 4a, illustrates one such contiguratiun wherein the pixels 402 in colunon 7 are connected to a power rail 421, the pixels 402 in column 8 are connected to a power rail 422 and the pixels 402 in column 9 are connected to a power rail 423. In addition, the pixels 402 io row 7 that arc in columns l to 6 are connected to a rail 424.
tltc pixels 402 in row 8 that are in columns 1 to C arc connected to a rail 425, tlrc ?s pixels 402 in row- 9 that arc in columns I to O ~ra~e connected to a rail 426, the pixels 402 in row 7 that arc in columns 1t) to 1 > arc cunmcted to a rail 427, the pixels 4U2 in row 8 that arc in columns lU to 15 are connected to a rail 428, the pixels 402 in row 9 that are in columns 10 to 15 are connected to a rail 429. In addition, rails 424 and 427 may be connected together-, rails 425 and 428 may be connected together, and rails ;0 426 and 429 may be connected to'~clhcrSuch ~r coniiguratiun would allow ~;
current monitor to be cuonectcd to each oi~the rails 421 l0 426 in order to measure tl~c leakage currents in the pixels 402 in rows 7 to 9 and columns 7 to 9 which results in a measurement ot~the ambient light fallinV in a cross pattern on the array 401.
Similar results wcould be achieved if the pow er rails for tloc hircls 402 in row-s 7 to 9 carried across the entire array 401 while the power rails te>r the pixels 402 in columns 7 to 9 were interrupted for rows i to O, as illustrated in tigure 4b.
In addition, the configurations in figures 4a and 4b would allow ambient li'=ht measurements to be taken Cor the four corners of the array 401 il~tl~e Ieal:a~~c currents were measured on alternate power rails 431 to 450. hhe pixels 402 are connected to m these power rails in tlrc ti~llowin« manner: the pixels 402 in column 1 that ane in rows 1 to C are connected to a rail 43l and the pixels 402 that are in rows 10 to 1 ~ are connected to rail 441, the: pixels 402 in column 2 that are in row s 1 to 6 are connected to a rail 432 and the pixels 402 that are in rows 10 to 15 are connected to rail 442, the pixels 402 in column 3 that are in rows 1 to C arc connected to a rail 433 and tire 1 s pixels 402 that arc in rows 1 () to 1 ~ are connected to rail 443, the pixels 402 in column =~ drat arc in rwvs 1 to (> are connected to a rail -f34 <rnd the pixels 402 drat ,rrc in rows 10 to 15 are connected to rail 444, and the pixels 402 in column >
that arc io roes 1 to 6 arc connected to a rail 435 and the pixels 402 that arc in rows 1 () to 1 ~ arc connected to rail 445. Similarly, the pixels 402 111 Collllllll 1 1 that arc in rows 1 to C.
?o are connected to a rail 436 and the pixels 402 that are in rows 10 to l5 are connected to rail 446, the pixels 402 in columnl? that are in rows 1 to O arc connected to a rail 437 and the pixels 402 that arc in rows l0 to I ~ arc connected to rail 447, the pixels 402 in column 1 s that are in rows 1 to (3 arc connected to a rail 438 and the pixels 402 that arc in rows 10 to 1 ~ are connected to rail 448, the pixels 402 in column I 4 that 2~ are in rows 1 to li are connected to a rail 439 alrd the pixels 402 that are in rows 10 to 15 are connected to rail 449, and the pixels 402 in column 1 ~ that arc in rows 1 to O
are connected to a rail 440 and the pixels 402 drat are il rows 1 U to 1 ~ arc cunlrectc~a to rail 450. 13y nrunitc>rin~~ the leakage currents in power rails 331 to 350, the ~rmbicnt light level at the four corners of the array 401 nlav be determined.
;ci Figure 4c illustrates an array 401 having a conliguration wherein all of the pixels 402 in each column 1 to 15 are connectl;d to a different power rail 430. This configuration allows for the selection of particular columns, rather than roves as illustrated in figure 2a, to measure the ambient light on the array 401.
Figure 4d illustrates vet another conliL;uration wherein powrr rails 451 arc connected to the row 1 to 8 pixels 420 ill colurlms (~ to 10 and tile power rails 453 arc connected to the row 9 to I S pixels 420 in columns C to 10 the power rails 451 and to 453 extend across only half the ima~;in~~ array 401. Each of tile power rails 452 is connected to the column 1 to S pixels 420 for reach of the rows 1 to 1 j, while: each of the power rails 454 is connected to the column 1 l to 1 ~ pixels 420 for each of the rows 1 to 13 providing versatility in monitorin~~ the lcal:agc currl:nts.
is Figure 5 illustrates the use of the present invention in an exposure controlled images 500 as described in co-pending US Pitt°nl Application Serial '.vlo. 09-(o~),sOb filed on October 12, 2000 which is incorporated herein by reference. The inoa~;in'~
circuit 501 which is locaml on a water or die and which is rellrcsentcd by hrol:en lines, nol-lally includes an imaging array 502, wordlinc drivers 503 and worcllines 20 504, bitline readers 505 and bitlines 506, an integration timer 507, and a signal amplifier 509. 'l he bit(ine readers 505 are connected to the signal amplifier which amplif7es the bitline reader 505 signals to produce the image output data.
Further, light detector circuits 520 are also located on the die 501 adjacent to the imaging array 5U2.
w The imaging circuitry 501 on the die may further include an avera~iny~ circuit 510, a look-up table and signal driver 51 1 and an illumination source control 512.
The signal driver 511 includia output lines 513 to 515 respectively for signals to control the signal anlplilicr 508, the intey~ration tinier 507 and the illumination control 3O 512. The illumination control 512 is ~ui~Iptcd tea control an illumination source 513 Illav IIOt IIeCCSS81'lly be lOCatf:d 017 IhC Illlar~lll'~ 1.'ll'Cllltl'y 1110:
501.
Once the look-up table anti signal driver 511 detc;rnliws the proper values for tile tl111111111a11On SOUrCC C011tr01 Si~~ll~il, Ille 1111er,ra11011 tulle C011it'O1 SI;~I1L11, aild the ,~.lllll control signal, these signals arc fed to illumination source controller 512, tile s integration timer 507 anti the signal amplifier 508 respectively to adjust the briwhtness of~the light source 513, tile exposure time of tile imaging array 502 and the ~~ain of the amplifier 508. respectively.
The look-up table anti signal driv'cr 51 1 nlav consist of a nlicrocontrollcr ui device such as the Stron~~-Arm SA-1 1 10 and a read only memory provlramnlerl with data delining particular imaging needs in terms of~light intensity, integration time, and signal gain in response to a measured level oCambient light. ~(~he sort ofdata contained therein would dcpenc( on the type of~application the device was to be used for: for example a bar cone reader would try to relv mostly on alterations oC
the n Integration time as this would be the power conscious method of~anl(~ient li~~llt adj llstment.
The light source 513 may consist o(~any type of conventional light source that Call 17e COIlt1'Olled I11 111tC11SI2V. (~OVVi:~'CI', d paCtlClllal'ly adValltilgCOlls ell'I'elil'W 'IIIC ilt 1S
?o illustrated in l7gure 6, which schematically illustrates the Lace o(~a scanner 000. Tllc mla~png circuit 601 is located at the center of the scanner face 602. One or more (..ED
light sources 603 are positioned about the ima~;in~1 circuit 601 to provide further lighting if required. Ill operation, the one or more LED's 603 may each be controlled by a separate title in order to turn each I,ED 603 OFF or ON as desired. For example.
if an object or target is close to the scanner f<lce 602, only one or two L.ED's might hl' turned ON; with the t~lr~~ct a little further away, such as live or si.v inches, possibly three or four LED's 603 could he turned ON. :'\lli:rnalivclv, tile li~'ht source controller 512 could control the driving current to each LED 603, and increase or decrease the illumination from each LED 603 as required.
While the invention has been described according to what is presently considered to be the most ('practical alld (preferred embodiments. it must be undcrstooli that tile invention is not limited to the disclosed ernbodinlcnts. Those orc(inar;l~
skilled in the art will understand that various modifications and cduivalent structures and functions may be made without departing from the spirit and scope of tl~c invention as dclined in tloc claims. ~l~herelore, the invention as defined in the claims must he accorded the broadest possible interpretation so as to encompass all such n~odi(ications and cduivalcnt structures and flmetions.
Claims (54)
1. A method of determining the level of ambient light impinging on a pixel having a photodiode comprising:
a. resetting the pixel; and b. detecting the current flow through the photodiode during the resetting step to determine the ambient light level.
a. resetting the pixel; and b. detecting the current flow through the photodiode during the resetting step to determine the ambient light level.
2. A method of determining the level of ambient light impinging on a pixel having a photodiode as claimed in claim 1 wherein the resetting step (a) includes a.1. applying a reverse bias voltage across the photodiode.
3. A method of determining the level of ambient light impinging on a pixel having a photodiode as claimed in claim 2 wherein the detecting step (b) includes:
b.1. detecting the current flow through a resistance in parallel to the photodiode.
b.1. detecting the current flow through a resistance in parallel to the photodiode.
4. A method of determining the level of ambient light impinging on a pixel having a photodiode as claimed in claim 3 wherein the detecting step (b) further includes:
b.2. converting the detected current flow signal to a voltage signal;
and b.3. converting the voltage signal to a digital signal.
b.2. converting the detected current flow signal to a voltage signal;
and b.3. converting the voltage signal to a digital signal.
5. A method of determining the level of ambient light on an imaging array of pixels having photodiodes comprising:
a. resetting the pixels in the array; and b. detecting the current flow through the photodiodes in a selected number of pixels during the resetting step to determine the ambient light level.
a. resetting the pixels in the array; and b. detecting the current flow through the photodiodes in a selected number of pixels during the resetting step to determine the ambient light level.
6. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 5 wherein the resetting step (a.) includes:
a.1. applying a reverse bias voltage across the photodiodes.
a.1. applying a reverse bias voltage across the photodiodes.
7. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 5 wherein the selected number of pixels are divided in one or more groups of pixels.
8. A method of detecting the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 7 wherein the pixels in the imaging array are positioned in rows and columns.
9. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 8 wherein the pixels in each group are located in a predetermined row.
10. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 8 wherein the pixels in each group are located in predetermined column.
11. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 8 wherein the pixels in each group are located in a specific pattern in the array.
12. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 7 wherein detecting step (b.) includes:
b.1. detecting the current flow through a resistance in parallel to the photodiodes in each group of pixels.
b.1. detecting the current flow through a resistance in parallel to the photodiodes in each group of pixels.
13. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 11 wherein detecting step (b.) further includes:
b.2. converting each detected current flow signal to a voltage signal:
and b.3. converting each of the voltage signals to a digital signal.
b.2. converting each detected current flow signal to a voltage signal:
and b.3. converting each of the voltage signals to a digital signal.
14. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 12 wherein detecting step (b.) further includes:
b.4. combining the digital signals to provide a digital signal representative of the ambient light level.
b.4. combining the digital signals to provide a digital signal representative of the ambient light level.
15. A method of determining the level of ambient light on an imaging array of pixels having photodiodes comprising:
a. resetting a selected number of pixels in the array; and b. detecting the current flow through the photodiodes in the selected number of pixels during the resetting step to determine the ambient light level.
a. resetting a selected number of pixels in the array; and b. detecting the current flow through the photodiodes in the selected number of pixels during the resetting step to determine the ambient light level.
16. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 15 wherein the resetting step (a.) includes:
a.1. applying a reverse bias voltage across the photodiodes.
a.1. applying a reverse bias voltage across the photodiodes.
17. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 15 wherein the selected number of pixels are divided in one or more groups of pixels.
18. A method of determining the level of ambient light impinging on an array of active pixels having photodiodes as claimed in claim 15 wherein groups of pixels are reset sequentially.
19. In an imaging array of light sensitive pixels each having a photodiode and photodiode reset means adapted to apply a predetermined reset voltage across the photodiode and one or more power rails each connected to a group of one or more of the pixels for supplying power to the pixels, apparatus for determining ambient light comprising:
- current monitoring means for measuring current flow in the photodiodes of selected pixels as the photodiodes are being reset for determining the ambient light.
- current monitoring means for measuring current flow in the photodiodes of selected pixels as the photodiodes are being reset for determining the ambient light.
20. Apparatus for measuring ambient light as claimed in claim 19 wherein the current monitoring means includes one or more current monitors each connected to at least one of the power rails for monitoring the current flow in the photodiodes connected to the power rail.
21. Apparatus for measuring ambient light as claimed in claim 20 comprising analog-to-digital converter means coupled to each of the current monitors to provide a digital signal representative of the ambient light
22. Apparatus for measuring ambient light as claimed in claim 21 comprising resistor means couple between the current monitor and the power rail.
23. Apparatus for measuring ambient light as claimed in claim 22 wherein the current monitor comprises a current-to-voltage converter.
24. Apparatus for measuring ambient light as claimed in claim 23 wherein the current-to-voltage converter comprises an op-amp having an inverting input terminal coupled to the resistor means. a non-inverting input terminal adapted to he coupled to a reference voltage and an output terminal, the output terminal being coupled to the inverting input terminal through a further resistor means.
25. Apparatus for measuring ambient light as claimed in claim 19 wherein the imaging array and the current monitoring means are integrated on the same die.
26. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in inner rows and columns.
27. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in outer rows and columns.
28. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and a wherein the selected pixels are located in one or more columns.
29. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the selected pixels are located in one or more rows.
30. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the power rail is connected to the selected pixels arranged is a specific pattern in the array.
31. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the power rails are connected to rows of pixels.
32. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in the imaging array are positioned in rows and columns and wherein the power rails are connected to columns of pixels.
33. Apparatus for measuring ambient light as claimed in claim 19 wherein each pixel includes a photodiode and a reset switch.
34. Apparatus for measuring ambient light as claimed in claim 33 which further includes means for controlling the reset switches to reset individual groups of pixels sequentially.
35. Apparatus for measuring ambient light as claimed in claim 19 wherein all pixels are coupled to the same power supply.
36. Apparatus for measuring ambient light as claimed in claim 19 wherein the pixels in each group are adapted to be connected to the power supply through a separate power rail.
37. Apparatus for measuring ambient light as claimed in claim 36 wherein each separate rail is adapted to be connected to a separate power supply.
38. Apparatus for measuring ambient light as claimed in claim 36 wherein each separate rail is adapted to be connected to the power supply through a diode.
39. A system for controlling the output signal during image capture of an object by an images having an imaging array of light sensitive pixels each having a photodiode and photodiode reset means adapted to apply a predetermined reset voltage across the photodiode and one or more power rails each connected to one or more pixels on a die comprising:
- ambient light detection means located on the die adjacent to the imaging array for sensing the ambient light on the object;
- means for generating an electrical signal representative of the ambient light;
- means for sampling the representative electrical signal; and - means for controlling the output signal as a function of the sampled representative signal.
- ambient light detection means located on the die adjacent to the imaging array for sensing the ambient light on the object;
- means for generating an electrical signal representative of the ambient light;
- means for sampling the representative electrical signal; and - means for controlling the output signal as a function of the sampled representative signal.
40. A system for controlling the output signal during image capture of all object by an imager having an imaging array on a die as claimed in claim 39 wherein the ambient light detection means comprises current monitoring means for measuring current flow in the photodiodes of selected pixels as the photodiodes are being reset for determining the ambient light.
41. A system for controlling the output signal during image capture of an object by an images having an imaging array on a die as claimed in claim 40 wherein the current monitoring means includes one or more current monitors each connected to at least one power rail for monitoring the current flow in the photodiodes connected to the power rail.
42. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 41 wherein the electrical signal generating means includes analog-to-digital converter means coupled to each of the current monitors to provide a digital signal representative of the ambient light.
43. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 42 comprising resistor means couple between the current monitor and the power rail.
44. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 43wherein the current monitor comprises a current-to-voltage converter.
45. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 44 wherein the current-to-voltage converter comprises an op-amp having an inverting input terminal coupled to the resistor means, a non-inverting input terminal adapted to be coupled to a reference voltage an an output terminal, the output terminal being coupled to the inverting input terminal through a further resistor means.
46. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 40 wherein the means for controlling the output signal as a function of the sampled representative signal comprises a look-up table having a variety of control signal levels as a function of light intensity and a signal driver to control the output signal.
47. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 46 comprising integrator timer means coupled to the signal driver to control the exposure time of the imaging array to the object illumination.
48. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 46 comprising illumination source control means coupled to the signal driver to control the illumination intensity.
49. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 46 comprising amplifier gain control means coupled to the signal driver to control the amplification of the output signal.
50. A system for controlling the output signal during image capture of an object by an images having an imaging array on a die as claimed in claim 47 comprising illumination source control means coupled to the signal driver to control the illumination intensity.
51. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 50 comprising amplifier gain control means coupled to the signal driver to control the amplification of the output signal.
52. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 40 comprising a light source for illuminating the object to be imaged.
53. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 52 in which the light source comprises one or more LED's positioned about the scanning array.
54. A system for controlling the output signal during image capture of an object by an imager having an imaging array on a die as claimed in claim 52 in which the light source comprises at least one LED positioned at one or more corners of the scanning array.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US17749600P | 2000-01-21 | 2000-01-21 | |
| US60/177,496 | 2000-01-21 | ||
| US09/718,137 | 2000-11-21 | ||
| US09/718,137 US6469289B1 (en) | 2000-01-21 | 2000-11-21 | Ambient light detection technique for an imaging array |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2330080A1 true CA2330080A1 (en) | 2001-07-21 |
Family
ID=26873371
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002330080A Abandoned CA2330080A1 (en) | 2000-01-21 | 2001-01-03 | Ambient light detection technique for an imaging array |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US6469289B1 (en) |
| EP (1) | EP1162831A1 (en) |
| JP (1) | JP4585694B2 (en) |
| CA (1) | CA2330080A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6631842B1 (en) | 2000-06-07 | 2003-10-14 | Metrologic Instruments, Inc. | Method of and system for producing images of objects using planar laser illumination beams and image detection arrays |
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-
2000
- 2000-11-21 US US09/718,137 patent/US6469289B1/en not_active Expired - Lifetime
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2001
- 2001-01-03 CA CA002330080A patent/CA2330080A1/en not_active Abandoned
- 2001-01-10 EP EP01300207A patent/EP1162831A1/en not_active Withdrawn
- 2001-01-22 JP JP2001012631A patent/JP4585694B2/en not_active Expired - Fee Related
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| US6469289B1 (en) | 2002-10-22 |
| EP1162831A1 (en) | 2001-12-12 |
| JP2002033881A (en) | 2002-01-31 |
| JP4585694B2 (en) | 2010-11-24 |
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