CA1220829A - Ambient light ad electromagnetic noise reduction circuit - Google Patents
Ambient light ad electromagnetic noise reduction circuitInfo
- Publication number
- CA1220829A CA1220829A CA000458555A CA458555A CA1220829A CA 1220829 A CA1220829 A CA 1220829A CA 000458555 A CA000458555 A CA 000458555A CA 458555 A CA458555 A CA 458555A CA 1220829 A CA1220829 A CA 1220829A
- Authority
- CA
- Canada
- Prior art keywords
- circuit
- level
- photodetector
- output
- state
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
- G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
- G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
- G06F3/042—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by opto-electronic means
- G06F3/0421—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by opto-electronic means by interrupting or reflecting a light beam, e.g. optical touch-screen
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
Abstract
ABSTRACT OF THE DISCLOSURE
A circuit for reducing noise and increasing the reliability of touch panels involves the use of a supplemental noise or electromagnetic interference pickup lead (63) which extends generally coextensively with the parallel connected outputs from a series of successively coupled photodetectors (42) and high pass filters (49, 58, and 60 and 64, 65 and 66) for substantially reducing the noise signals created by variations in the level of ambient light, When the photodetectors output (46) is connected to one of the inputs (-) of a differential operational amplifier (56), and the com-pensating pickup lead (63) is connected to the opposite polarity other input (+), the noise is substantially can-celled out, and a cleaned-up photodetector pulse is provided. A pulse forming circuit (74, 75 and 77) squares up the photodetector output signal pulse; and a hysteresis type storage or buffer circuit (76 and 78) is employed to indicate the presence or absence of photodetector output signals, from successive photodetectors, thereby indica-ting whether or not the light beams are interrupted either fully or partially.
A circuit for reducing noise and increasing the reliability of touch panels involves the use of a supplemental noise or electromagnetic interference pickup lead (63) which extends generally coextensively with the parallel connected outputs from a series of successively coupled photodetectors (42) and high pass filters (49, 58, and 60 and 64, 65 and 66) for substantially reducing the noise signals created by variations in the level of ambient light, When the photodetectors output (46) is connected to one of the inputs (-) of a differential operational amplifier (56), and the com-pensating pickup lead (63) is connected to the opposite polarity other input (+), the noise is substantially can-celled out, and a cleaned-up photodetector pulse is provided. A pulse forming circuit (74, 75 and 77) squares up the photodetector output signal pulse; and a hysteresis type storage or buffer circuit (76 and 78) is employed to indicate the presence or absence of photodetector output signals, from successive photodetectors, thereby indica-ting whether or not the light beams are interrupted either fully or partially.
Description
~MBIENT LIGHT A~D ELECTROMAGNETIC
N9ISE ~EDUC~ION CIRCUIT
1 R~CK~ROU~D OF THE INVENTION
1 Field of the Invention Thi~ inventi~n relates generally to de~ection circuits that c~n be used wi~h optical ouch panels and more par~icularly e~ a circuit ~hich eompçnsates for ~he noise ~ignal~ created by ~bient light v~ri~tions and by ~l*ctromagnetic in~erference.
N9ISE ~EDUC~ION CIRCUIT
1 R~CK~ROU~D OF THE INVENTION
1 Field of the Invention Thi~ inventi~n relates generally to de~ection circuits that c~n be used wi~h optical ouch panels and more par~icularly e~ a circuit ~hich eompçnsates for ~he noise ~ignal~ created by ~bient light v~ri~tions and by ~l*ctromagnetic in~erference.
2~ De cription ~f the Prior ~rt Prior ~rran~ements which have be~n proposed ~or touch panel~ are di~closed in ~.S. Patent ~o~
3j764,813, granted October 9, 1973~ U.~. Patent No.
3j764,813, granted October 9, 1973~ U.~. Patent No.
3,775,560, ~ranted Nove~ber 2~, 1973, and U.S. Patent No. 4,19~,623, granted April 15, 1980. In ~ystems of the type di~clo~ed in the above pa~ent~, the interrup-tion of clo5ely ~paced beams ~f light is ~mployedto locate the coordinat~s o~ ~ point ~hich is being pointed to on the invisible ~pto-matrix; and ~emi-conductor switching circuits are often employ~d to ~equentially turn on ~uccessive pair~ of opposing photosouree ~nd photodet~ctor~, to thereby ~can scross the f~ce o the di~play, both horizont~lly ~nd YeEtic~llyc ~ common output circuit is connece~d from all of the photodet~ctors samplin~ switches which ~re ~equenti~lly energi7ed to sense whether or not there 25 i5 anythin~, ~uch ~s ~ fin~er, blocking vne or more of the light beams. The photodetector output circuit ~4 `~
1 normally extends ~ub~t~ntially alvng ~wo e~dyes ~f a ~ircuit board 9 ~nd th~refore, can be ~ubject to ol@ctr~agnetic interfereneeO fr~m volt~ge~, currents ~nd radi~tion ~ypic~lly withan the proximity of the t~uch panel hou6ing. In ~ddition, t~e photodetectors ~re ~fected by vari~tion6 in the smbient lighting c~ndition~ where ~he unit is loc~ted, and these may Dlso adversely affec~ the operation of ~h~e unit.
Heretofore~ one approach disclosed in ~.S~ Patent ~o. ~,243,879, granted on January 6, l9Bl, used a digit~l ~ample ~nd hold ~echnique to mi~iga~e the effects of vari~ions in the level of ambi~nt light by sampling ambient light level as s@en by ~he photo~
transi~tor just before the photode~ec~or is ~nergized.
~hile ~ome prot~ction was provided ~or ~ariation in ambient lig~t it does not compensate for ~lec~romagnetic interference.
Accordingly/ it is ~ principal obje~t of th~
present invention to provide an improved pho~odetection circuit ~hich is ~ore reliable ~nd more re~dily compensat~s }or both electromagneti~ interference and ambient light variations th~n those which have been employ~d heretof ore .
SUMMARY OF THE INVENTION
In aGcordance with Dne important ~spect of ~he invention~ the photodetector output circuit is coupled to one input of a dif~erential amplifier circuit, ~nd a noi~e sign~l compensation circuit extending ~ub~tantially cvexten~vely with the photodetector output circuit i5 connected t~ the opposite polarity input ~o ~he differen-tial amplifier. Accordingly, the desired photodetect~r output ~ign~ls are transmitted through the diferential amplifier, while the noi~e signals which are picked up substantially equ~lly both by the photodetector QUtpUt o 3~ 2~
circuit and the compensati,ng circuit, cancel one another out to substantially eliminate the nolse signal component on the output signal of the di~ferential amplifier.
In accordance with another aspect of the invention, the inpu*,-~rom the photodetector circuit is fed through a high pass filter circuit to suhstantially eliminate the relatively low frequency effects Gf the more slowly changing variations in ambient lighting, while transmitting the relatively higher frequency pulses produced by the gating of light impulses from selected successive photodetectors. By eliminating the need to compensate for variations in ambient 1ight each time a photodetector output is sampled, it is possible to operate the system at a much higher scan rate.
Consequently larger detector arrays can be built and faster response time can be attained.
In accordance with still another aspect of the invention, the differential amplifier may be provided with a diode in the feedback circuit so that the desired photodetected signal pulses of one polarity are amplifie~ at high gain levels; whereas pulses of the , opposite polarity are not amplified, in accordance with the feedback characteristics of the diode.
Other aspects of the invention are as follows:
An interference reduction circuit comprising:
means for providing at least one pair of light emitting devices and photodetectors each disposed along a light beam path extending therebetween;
a photodetector output circuit;
switching means for successively coupling the output of said at least one photodetector to said photodetector output circuit;
an electromagnetic noise compensation pickup circuit extending generally coextensively with and electrically balanced with said photodetector output circuit; and circuit means including combining means for differentially combining the outputs from said -3a- ~ 8~
photodetector output circuit and said electromagnetic noise compensation pickup circuit to substantially eliminate the electromagnetic noise component presen~ on the output signal of said photodetector output c.ircuit.
A light beam responsive circuit with interference reduction circuitry comprising: -means for providing a plurality of pairs of photoemitters and photodetectors each pair being disposed in spaced apart relationship on a beam path and about the periphery of a face plate;
a photodetector output circuit;
switching means for successively coupling the outputs from a plwrality of said photodetectors to said photodetector output circuit;
compensation pickup circuit disposed substantially coextensively with said and electrically balanced with said photodetector output circuit; and means coupled to differentially combine signals from said photodetector output circuit and said compensation circuit to substantially eliminate electromagnetic noise which is presen~ on said photodetector output circuit.
_ A still further aspect of the invention involves the use of hysteresis type output circuitry for the photodetected pulse sensing circuits, which only changes state when a change is encountered when going from a beam transmission to a beam interruption, or vice-versa, as s~ccessive pairs of light emitters and photodetectors are scanned across the face of the touch panel faceplate.
One advantage resides in the reference sample hysteresis circuit wherein the data sampled from the position of the finger or other object which interrupts the beam is smoothed in spite of slight irregular movement (such as tremors~ of the finger, or slight ~zzo~æ~
1 ~riation in t~e ~i~nal level due to changes in ambient light, ~r ~lectr~agnetic noise. Consequentlyd ~ore ~t~ble data i~ obt~ined ~n ~he po5ition of the finger, Other advantages of ~he invention includes ~ignificant r~duction in ~ensi~iYity to ambient lighting noi~e and inrreased reli~bility ~s a res~ of noise co~pensation by ~ 6u~stantial eli~in~tioll of the noise component from the photodetect~r output ~ignal. As a result, relatively inexpen~ive light emitting diodes 1~ ~nd phototransistors may be employed ~o ~ignificantly reduc~ ~e oveE~ll co~S of the touch p~nel.
Another ~dvantage is that the higher attainable ~ignal to noise ratio permits the use of ~maller photo-emitter and photodetector devices 6ince at i~ not ~5 nec~s~ary to ~verp~wer the ~mbien~ light level because ~he devices are capable of operating at ~ level below the intensity of the ~mbient light.
Other objects, features"~nd ~dvantages of ~he invention will become ~pparent from a consideration of ~ ~ following detailed description and from the accom-panying dra~ings.
BRIEF DESCRIPTION ~F THE DRAWINGS
FIG~ 1 represents ~ t~uch panel unit of the type to w~ich the present inv~ntion r21~tes;
FIG. 2 is a circuit diagram of a preferred embodiment illustrating the principles sf the present ~nvention;
FIG. 3 is idealized plot of ~ photodet~ctor 3~ current pulse during ga~ing and t~e receipt of ~ beam of i~lumination;
s PIG. ql ~hows ~ typical noi6e siç nal c~ponent ~ich ~ight be ~u perimposed upon a ph~todletect~r c~utput pul~e in ~ touch panel unit of the type æh~wn ~rl FIG. l;
FIG. S ~hows Dln idealized amplif ied ~n~ ited S pulse deri~ed from the photode~cector ou~put pulse of ~I(;. 3;
FIG. 6 a~ ~ representa~ion ~f ~n ~ctual output pulse P~fi ~mplified and limi~ed, ~ h ~he low level s:)f residual noise ~ollowing ~c>mpensati;~n in accordance 10 ~ith the present invention;
FIG. 7 is ~ ~c~ematic dr~wing of a ~ec~nd ~mbodiment at ~he hysteresis pc~rtion of ~he circuit;
FIG. 8 i~ a schematic of a ~econd embodiment of the detec'cion portion of the circuit of FIG~ 2.
iDETAILED DESCRPTION O~ INYENTION
Referrin ~Qore particularly ~o the dr~wings, FIG. 1 i~ ~n overall view of ~ touch panel uni'L 12 which h~s a facepl~te 140 In addition, ~ series of 20 photoemitters ~uch as light emitting diod~s are located, for ex~mple, ~t one ~ide 18 of the ~aceplate to direct beams of infrared light across the acepla~e 14 to photodetectors ~uch as phototransi~tors located at the opposite edge 20 of the f~cepl~te 14, Similarly, ~n additional ~et of li~ht e~itting diodes ~ay be provided to direct illumin~ti~n from the lower edge ~ of the faceplat~ upwardly to pho~otransi6tor~ loca~ed at the upper edge 24 of the f~ceplate. Preferably the p~irs ~f li~ht emitting diodes and phototransistors are 3~ en~rgized ~quentially to scan across the facepl~te both in the horizontal direction and in the vereical direction ~uch th~t they interSect to form a grid pattern. The li~ht from each light emi~t~ng diode is direc~ed acro6s ~he ~aceplate to impinge on t~e opposin~
phototransistor~
1 locatin~ the c~rdin~tes of ~here a fin~er 26 may be poin~in~, or example, either ~o ~ ~witch point ~r a p~rtion of ~ di~play~ 0~ course, ~he int~rruption Df one or ~ore ~f ~he beams in ~ach ~irection, 3~rves ~o locate the position of the finger 26~
set ~f four ~ircuit boards 32, 3~, 36 and 3B may ~erve to ~ount ~he ligh~ emitting diod~s and ~he photo-tranci~tors, ~l~ng with their as~ci~ted electr~nic circuitry~ In practice, the ~pposing pairs of light emittin~ diodes and phototransi~ors ~re ~witched on ~nd off concurrently, with ~gu~ntial energizati~n of ~he successive pairs of p~t~tran~istors an~ ligh~
emitting diodes ~erving ~o ~can across the f~ce ~f the ~cepl~te in both t~e horiz~ntal and ver~ic~l directions.
In practice, t~e output from the phototransistors may be connect~d in par~llel to de~ection and processing circuit~, with the par~icular phototr~nsis~or from which ~ pul~e i~ being received being iden~ified by the timing of t~e ~witching circuitry which ~equentially turns o~ the paired light ~mitting diodes and pho~o-transi~ ors.
Ref~rence ~ill now be made to the circuit diagram of FIG. 2 which includes a circuit illu~trating ~he prin iples of th~ present inYention. Mor¢ speci~ically, 25 in FIG. 2p ~ phvtotransi~tor 42 is shown connected by ~witch 44 to ~ phototran~i~tor output lead 46. A
piurality o~ additional ~witches 48 are ~l~o shown, ~nd ~re representative ~f a ~eries ~f parallel semiconductor ~witches which ~equentially gate ~ serie~ of parallel 3~ phototran~istors to their conducting 6ta~e5~ ~imul-taneously ~ith the energi~tion of the opposite paired light emi~ing diode 40 which directs lig~t onto the pho~otransistors 42. The ~equential energi~ati~n of the switch 44 and the many switches indicated ~t 48, 35 ~nd their precise timing, identifies or ~he system which photc>transistor i~ generating (or not generating ) ~n ~utput p~lse 52 o~ ~IG. 3. The curren~ ~s~t~ciated ~it,h thi~ pulse 52 flc~ws through the loald r~ tor 49 whi~h has one ~nd cc~nnected to ~ r~ference voltage-VO
5 rhis c~uses ~he ~olt~ge l~vel a'L ~l~e en~ c)f the load re~ r 4g ~o ri~e ~rc~ducing the ~utput pulse 52.
FIG. 3 ~hows an idealized positive s~oing output ~ul~e ~uch ~s 2Digh~c be recovered ~rom the phototran-~istor ~2 ~h~n the beam is not interrupted. However, 10 as mentioned above, bec3use ~he pho~otransistor output lead ~6 es6tends ~ consider~ble distance æcross the printed circui'c bo~rà, ~or example printed circuit boards 34 ~nd 36 of FIG. 1, ~ s3reat deal of electro-~agne~ie noi~e i~ pieked up and ~dded to he pho~o-lS transistor output ~i~nal~ This i& indicated for examplein FIG. 4 t)f the drawirl~s ldhere ~he phototransistor sis3nal 52 ~ay be rela~ively ~;mall, in ~he order s:
t~n to fifteen millivolts, while ~he noise ~ignals 54 alay be 6ubstantially greater ~nd may for example be even 100 ~o lSO millivolts.
In ~rder to ~ubstantially cancel out th0se unde~ired noise ~ignals, a differenti~l operational amplif ier 56 is u~ed wi'ch the ~ignal from the photo-transistor output le~d 46 fed through ~ high pass 25 filter circuit, which include~ lvad resistor 49, series capacitor SB ~nd resistor 60, to the negative (-) input terminal o~ the amplifier 56; and a compensating ~ignal ~quivalen~ to the noi~e signal components picked up on the nc~i~e compensating piekup lead 62 i~ coupled to t~ e 3~ iti~e (~ input, tsrminal of oper~tional amplif ier 56 through a high pass 5~ilt~r circuit which incltJdes load resistor 65 and series connected eapacitor 64 ~nd res istor 66 .
~2~2~
. 8 The compensation pick-up lead 62 indicated ~chemati ally ~t 62 in FIG. 1 i~ ~ long electric~l ccnductor ~xtending for ~u~s~anti~lly ~e full l~ngth ~f ~he circuit board~ 34 ~nd 36, co~men~urat~ ln ~xten~
S with the phototransistor ou~put circuit ~l6, a~ lndicated ~t the lef~ in FIG. 2. The l~ad 62 c~n ~)e in the fvrm of a wire, ~ prin~ed circuit, plDting, p:L~nar ~tch, etc. Th~ ~nd o~ th~ lead 62 has a lo~d tenmination cir~uit 63 equivalent to a photo~r~nsistor 42 and a ~witch 48 coupled ~o it. Thi~ eguiv~len~ load circuit 63 can be in the form of a capaci~vr and ~ diode ~onnected in parallel wit~ one anot~er. Accordingly, ~he noise 6ignals picked up on lead 62 results in current flow through load resi~tor 65 which will be sub~tan~i~lly ~he ~a~e as the electromagnetic noise 6ign21~ on photo-transistor ~ueput lead 46. ~s a result of ~he two ~quiv~lent ~nd bal~nced input circuit branches to the operational amplifiers 56, the~e two 6ets of noise ~ignals will 6ubstantially cancel one another out, while leaving only the desired characteristios of the phototransi~tor outpu~ signal 52 to be ~mplified and ~haped by ~he ~im~ it ~rrives at test point TP-2 as ~hown in FIGS. 5 ~nd 6.
It iS ~150 noted ~h~t the high pass filter including ~eries capacitor 58, ~nd resistor 60 and the load resi6tor~ connected in ~hunt to the capacitor di~criminates against the relatively slowly changing level~ of ~mbien~ light which will be received by the photodiodes ~nd which mis~ht otherwise v~ry ~he c)utput ~ign~l r~m the operational amplifier 56. ~or example, in ~ne embodiment the high pass filter wvuld pass 4 of the ~ignal a~ 400 cps ;cycles per second), ~0~ at 2000 cps, ~n~ 90~ ~t 6000 cp~. The circuit formed by capacitor 64,re5i5~0r 66, ~nd load resi~t~r 65 ~n the COmpenSa~iQn pickup lead branch is equivalent t~ the high p~ss ~ilter.
~.
~ttentiLon is il!ll60 directed to ~he diode 72 in the ~edback loop of the operati~nal ~mplifier 56. When the ~ignal received by ~he diferenti~1 ~nplifier 1-) ~nput ~erminal is neg~tive rela~iYe ~o ~ r~ference level, the diode i~ for~ard biased, the feedback r~eE;i6t~1T~Ce is ~ery low, ~and the gsin a~t ~31e op~r~tional amplifier 56 i~ v~ry low whereupc~n the ne~ative input ~;ignal i~ not ~mpllfied. ~owever when ~he input ~o ~he (-~ input termirlal of opera~ional amplifer 56 is po~itive, ~he 9LO diode 72 is b~ck biased r~ ing ghe feedback resistance ~nd the gain of the ~pera~ional amplifier 56 whereupon the lnput ~ignal is amplified.
~ first ~esl: poin~, desi5~nated TP-l in FIG. 2, is the point at which noi~y ~i~nals ~uch as ~hose ~hown in FIG. ~ may be ob~erved. Similarly ~he represen~a~ive ~ignal of PIG. 5 ~ ltest point ~P-~ ~a~ clamped by di~des 75 and 77 (~hich do not conduct negative pulse ~ignal~ or 6i~n~1~ of more than ~0.7 vol~ ~uch as might be cau6ed by ~witching ~r~n~ients ~nd noise) and was ~mplified by operatic~nal ~mplif~er~ 56 ~nd 74. The actual ~ignal with ~ome ~lig~t re~iàual uncompen~a~ed noi~e, i~ shown in FIG. 6. The diode 75 ~1513 ÇerVe5 ~0 provide ~ pat~ of cc~ndwtion when tlle ~eedb~ck diode 72 i~ ~or~rd biased. The resistor 79 conrlec~ed to cl~mping diode 77 C~ersres to tenninate ~he input to ~he ~) terminal of operation 2Implifier 56 ~nd ~o a~id the circuit in comming l~p to operation when the power is turned c~n~ Incidentally both olE the ~per~tional ampli-f iers 56 and 74 ~s ~hown in FIG. 2 may, for example, b~ of the types known a TL072 or LS353 oper~tional amplifier~, ~nd which ~re ~vail~ble rosll a n~nber of manufac~lrer~. Inciden~ially~ the compar~atc~r6 8~ and 82 ~o be di6cu~sed below may ~ ior example, b~ v~ ~ype LM393. ~he t~ h ~nd low vQ1tages for the ~;ystem may, by way of example but not limitation, be either the cc~mmonly a~ilable plu~ ~nd minus five volt~ ~r plus and llninus twelve ~lt~ owever i~ ha6 b~e2n determined th~t ~he his~her the voltDQes; ~ithin li~it~" the mt~re effs~ctive the circuit becomes.
'rhe comparatc)r 80 ~nd ~2 each have one input ~er~inal ~ connec~ed ~:o rec:eive the amplified ou~put pul~e iErc~m operatic~nal ~mplifier 74 and ~he o~her input ter~inal ~) coupled ~o receive reference signals VREF-l ~nd VR~F-2 r~spectively. Shus an output pulse fr~m cosnparator B0 i~ fed ~o the 9 inpu~ terminal of ~lip~flop 76 after i~ pro~e~sed and limi~ed by the clamping diode 81 and pull up re6i~tor 830 Incidently, the flip-flops 76 ~nd 78 ~y,ft)r example, be of the type LS74. Similarly the output c~f comparatc~r B2 is fed to the D input terminal of flip-flop 78 ~f~er i~ is processed and limit~d by cl~mping diode 85 ~nd pullup re~istor 87.
In oper~tic~n the hy~teresi6 portion of ~he eircuit of FIG. 2 which includes flip-flops 76 ~nd 78 evaluates the pul~e level on the output line~ r~m comp~rators 80 and 82 during 0ate pul~e or clock pul~e LED ~nd stores it ~s data d~pending upon 1che level~ of the signals.
For example if the level~ o the 6ignal on the~e two c~utput lines ~re bc~ch higher in smplitude than the ro f ere nce vol tage ~ VRE~ nd VREF- 2 ( non i n ~er rup ted bea~ uch a~ ~g ti~ne tl ~n FIG. 6 or both lower in ampli~ude th~n the referenced e~o~tage~ VREF~ 1 ~nd VREF-2 1~ interrupted beam~ 6~ch a~ at time t3 th~t 6tate of ~he data i~ ~tored in the flip-flopQ 76 and 78 and used ~6 the ol~put data Q an~ Q on c~utput lines 9 2 and 9 41~
If h~wever the ~tate of two sign~l~ from eomparatc)r~ 80 ~nd 82 ~re not both low or both lligh relatiYe tc3 the reference voltage~ VREF-l ~nd VREF-2, 3~
~uch ~ ~t ti~e $2 (21fi ~ ht occur if a beAm ~ only g?arti~lly interrupted~, ~he 6tate~ of ~he ~lip-10ps typically ~tor~d by an external da~ rec~v~r ~ ot ~hown) ~ro~n the preceding sc~n c~r ~eam would ~ypic~lly be used.
~imilElrly a ~ty~tere6is circuit can be i~plemented wich ~ gle J~ flip-fl~p 98 suc:h ~s J~n LS 109 in the ~anner illu6tr~ted ~n ~IG. 7. ~n th:i~ em~odiment, ~f the input~ to the 3 input and t~e K inpu~c to ~Lhe flip-flop 98 ~re both lo~, the output Q i~ low. If ~ however the ~ignal to the J and K inputs are ~o~h high the output Q ~s high. Bowever lf ~he ~iign~ f ~he J
input i~ low and the &ignal to the ~ input ~.5 high t~)e ~utput ~;ignal Q remains in it~ ~;tored sta~ce from the preceding bea~ oreover i the ~ignal of ~he J
inpu~c is high and the input ~ignal ~o the ~ input is low the 1ip--flop c~nnot toggle and the c>utput ~;2 will resnain in the ~me ~tate ~t w~s in from the preceding beam .
Consequently, if the finger ~h~uld m~ve only ~;lightly, ~uch a5 mis~ht occllr a~ a re~ult of 1~ slight finger tremor~ ~nd re6ult in pul~es ~uch a5 the eimes t2, t3~ tn+l ~nd tn+2 shown in FIG~ 6, the ~t~te of the circuit Qf FIGo 2 will indic~te or, ~n the case of FIG. 7, ~ill remain stable in re ponse to ~lch ~light irregular novement~. At the ~ame time he circuit will be able tt~ rapidly de~ect the desireà f inger movements.
Of course such transient conditions could ~l~o be caused by p~rtial ~clipsing of th~ be~m by ~ finger, low level uncompensated ~lectr~magnetic r~oi~e signal~, and 61ight v~ria~ ns ~n ~he level of ambient light.
~2~
In addition while the pho~od~tector circ-lit of I~IG. 2 ~ho~s one type Df circul~c it i possible to u~0 another type illu~.trat~d ~i n ~IG. l3 13uch 3~ d re~sis~ors 100 and 102 coup~ed t:~etwe~en the coll~ctor c~f
1 normally extends ~ub~t~ntially alvng ~wo e~dyes ~f a ~ircuit board 9 ~nd th~refore, can be ~ubject to ol@ctr~agnetic interfereneeO fr~m volt~ge~, currents ~nd radi~tion ~ypic~lly withan the proximity of the t~uch panel hou6ing. In ~ddition, t~e photodetectors ~re ~fected by vari~tion6 in the smbient lighting c~ndition~ where ~he unit is loc~ted, and these may Dlso adversely affec~ the operation of ~h~e unit.
Heretofore~ one approach disclosed in ~.S~ Patent ~o. ~,243,879, granted on January 6, l9Bl, used a digit~l ~ample ~nd hold ~echnique to mi~iga~e the effects of vari~ions in the level of ambi~nt light by sampling ambient light level as s@en by ~he photo~
transi~tor just before the photode~ec~or is ~nergized.
~hile ~ome prot~ction was provided ~or ~ariation in ambient lig~t it does not compensate for ~lec~romagnetic interference.
Accordingly/ it is ~ principal obje~t of th~
present invention to provide an improved pho~odetection circuit ~hich is ~ore reliable ~nd more re~dily compensat~s }or both electromagneti~ interference and ambient light variations th~n those which have been employ~d heretof ore .
SUMMARY OF THE INVENTION
In aGcordance with Dne important ~spect of ~he invention~ the photodetector output circuit is coupled to one input of a dif~erential amplifier circuit, ~nd a noi~e sign~l compensation circuit extending ~ub~tantially cvexten~vely with the photodetector output circuit i5 connected t~ the opposite polarity input ~o ~he differen-tial amplifier. Accordingly, the desired photodetect~r output ~ign~ls are transmitted through the diferential amplifier, while the noi~e signals which are picked up substantially equ~lly both by the photodetector QUtpUt o 3~ 2~
circuit and the compensati,ng circuit, cancel one another out to substantially eliminate the nolse signal component on the output signal of the di~ferential amplifier.
In accordance with another aspect of the invention, the inpu*,-~rom the photodetector circuit is fed through a high pass filter circuit to suhstantially eliminate the relatively low frequency effects Gf the more slowly changing variations in ambient lighting, while transmitting the relatively higher frequency pulses produced by the gating of light impulses from selected successive photodetectors. By eliminating the need to compensate for variations in ambient 1ight each time a photodetector output is sampled, it is possible to operate the system at a much higher scan rate.
Consequently larger detector arrays can be built and faster response time can be attained.
In accordance with still another aspect of the invention, the differential amplifier may be provided with a diode in the feedback circuit so that the desired photodetected signal pulses of one polarity are amplifie~ at high gain levels; whereas pulses of the , opposite polarity are not amplified, in accordance with the feedback characteristics of the diode.
Other aspects of the invention are as follows:
An interference reduction circuit comprising:
means for providing at least one pair of light emitting devices and photodetectors each disposed along a light beam path extending therebetween;
a photodetector output circuit;
switching means for successively coupling the output of said at least one photodetector to said photodetector output circuit;
an electromagnetic noise compensation pickup circuit extending generally coextensively with and electrically balanced with said photodetector output circuit; and circuit means including combining means for differentially combining the outputs from said -3a- ~ 8~
photodetector output circuit and said electromagnetic noise compensation pickup circuit to substantially eliminate the electromagnetic noise component presen~ on the output signal of said photodetector output c.ircuit.
A light beam responsive circuit with interference reduction circuitry comprising: -means for providing a plurality of pairs of photoemitters and photodetectors each pair being disposed in spaced apart relationship on a beam path and about the periphery of a face plate;
a photodetector output circuit;
switching means for successively coupling the outputs from a plwrality of said photodetectors to said photodetector output circuit;
compensation pickup circuit disposed substantially coextensively with said and electrically balanced with said photodetector output circuit; and means coupled to differentially combine signals from said photodetector output circuit and said compensation circuit to substantially eliminate electromagnetic noise which is presen~ on said photodetector output circuit.
_ A still further aspect of the invention involves the use of hysteresis type output circuitry for the photodetected pulse sensing circuits, which only changes state when a change is encountered when going from a beam transmission to a beam interruption, or vice-versa, as s~ccessive pairs of light emitters and photodetectors are scanned across the face of the touch panel faceplate.
One advantage resides in the reference sample hysteresis circuit wherein the data sampled from the position of the finger or other object which interrupts the beam is smoothed in spite of slight irregular movement (such as tremors~ of the finger, or slight ~zzo~æ~
1 ~riation in t~e ~i~nal level due to changes in ambient light, ~r ~lectr~agnetic noise. Consequentlyd ~ore ~t~ble data i~ obt~ined ~n ~he po5ition of the finger, Other advantages of ~he invention includes ~ignificant r~duction in ~ensi~iYity to ambient lighting noi~e and inrreased reli~bility ~s a res~ of noise co~pensation by ~ 6u~stantial eli~in~tioll of the noise component from the photodetect~r output ~ignal. As a result, relatively inexpen~ive light emitting diodes 1~ ~nd phototransistors may be employed ~o ~ignificantly reduc~ ~e oveE~ll co~S of the touch p~nel.
Another ~dvantage is that the higher attainable ~ignal to noise ratio permits the use of ~maller photo-emitter and photodetector devices 6ince at i~ not ~5 nec~s~ary to ~verp~wer the ~mbien~ light level because ~he devices are capable of operating at ~ level below the intensity of the ~mbient light.
Other objects, features"~nd ~dvantages of ~he invention will become ~pparent from a consideration of ~ ~ following detailed description and from the accom-panying dra~ings.
BRIEF DESCRIPTION ~F THE DRAWINGS
FIG~ 1 represents ~ t~uch panel unit of the type to w~ich the present inv~ntion r21~tes;
FIG. 2 is a circuit diagram of a preferred embodiment illustrating the principles sf the present ~nvention;
FIG. 3 is idealized plot of ~ photodet~ctor 3~ current pulse during ga~ing and t~e receipt of ~ beam of i~lumination;
s PIG. ql ~hows ~ typical noi6e siç nal c~ponent ~ich ~ight be ~u perimposed upon a ph~todletect~r c~utput pul~e in ~ touch panel unit of the type æh~wn ~rl FIG. l;
FIG. S ~hows Dln idealized amplif ied ~n~ ited S pulse deri~ed from the photode~cector ou~put pulse of ~I(;. 3;
FIG. 6 a~ ~ representa~ion ~f ~n ~ctual output pulse P~fi ~mplified and limi~ed, ~ h ~he low level s:)f residual noise ~ollowing ~c>mpensati;~n in accordance 10 ~ith the present invention;
FIG. 7 is ~ ~c~ematic dr~wing of a ~ec~nd ~mbodiment at ~he hysteresis pc~rtion of ~he circuit;
FIG. 8 i~ a schematic of a ~econd embodiment of the detec'cion portion of the circuit of FIG~ 2.
iDETAILED DESCRPTION O~ INYENTION
Referrin ~Qore particularly ~o the dr~wings, FIG. 1 i~ ~n overall view of ~ touch panel uni'L 12 which h~s a facepl~te 140 In addition, ~ series of 20 photoemitters ~uch as light emitting diod~s are located, for ex~mple, ~t one ~ide 18 of the ~aceplate to direct beams of infrared light across the acepla~e 14 to photodetectors ~uch as phototransi~tors located at the opposite edge 20 of the f~cepl~te 14, Similarly, ~n additional ~et of li~ht e~itting diodes ~ay be provided to direct illumin~ti~n from the lower edge ~ of the faceplat~ upwardly to pho~otransi6tor~ loca~ed at the upper edge 24 of the f~ceplate. Preferably the p~irs ~f li~ht emitting diodes and phototransistors are 3~ en~rgized ~quentially to scan across the facepl~te both in the horizontal direction and in the vereical direction ~uch th~t they interSect to form a grid pattern. The li~ht from each light emi~t~ng diode is direc~ed acro6s ~he ~aceplate to impinge on t~e opposin~
phototransistor~
1 locatin~ the c~rdin~tes of ~here a fin~er 26 may be poin~in~, or example, either ~o ~ ~witch point ~r a p~rtion of ~ di~play~ 0~ course, ~he int~rruption Df one or ~ore ~f ~he beams in ~ach ~irection, 3~rves ~o locate the position of the finger 26~
set ~f four ~ircuit boards 32, 3~, 36 and 3B may ~erve to ~ount ~he ligh~ emitting diod~s and ~he photo-tranci~tors, ~l~ng with their as~ci~ted electr~nic circuitry~ In practice, the ~pposing pairs of light emittin~ diodes and phototransi~ors ~re ~witched on ~nd off concurrently, with ~gu~ntial energizati~n of ~he successive pairs of p~t~tran~istors an~ ligh~
emitting diodes ~erving ~o ~can across the f~ce ~f the ~cepl~te in both t~e horiz~ntal and ver~ic~l directions.
In practice, t~e output from the phototransistors may be connect~d in par~llel to de~ection and processing circuit~, with the par~icular phototr~nsis~or from which ~ pul~e i~ being received being iden~ified by the timing of t~e ~witching circuitry which ~equentially turns o~ the paired light ~mitting diodes and pho~o-transi~ ors.
Ref~rence ~ill now be made to the circuit diagram of FIG. 2 which includes a circuit illu~trating ~he prin iples of th~ present inYention. Mor¢ speci~ically, 25 in FIG. 2p ~ phvtotransi~tor 42 is shown connected by ~witch 44 to ~ phototran~i~tor output lead 46. A
piurality o~ additional ~witches 48 are ~l~o shown, ~nd ~re representative ~f a ~eries ~f parallel semiconductor ~witches which ~equentially gate ~ serie~ of parallel 3~ phototran~istors to their conducting 6ta~e5~ ~imul-taneously ~ith the energi~tion of the opposite paired light emi~ing diode 40 which directs lig~t onto the pho~otransistors 42. The ~equential energi~ati~n of the switch 44 and the many switches indicated ~t 48, 35 ~nd their precise timing, identifies or ~he system which photc>transistor i~ generating (or not generating ) ~n ~utput p~lse 52 o~ ~IG. 3. The curren~ ~s~t~ciated ~it,h thi~ pulse 52 flc~ws through the loald r~ tor 49 whi~h has one ~nd cc~nnected to ~ r~ference voltage-VO
5 rhis c~uses ~he ~olt~ge l~vel a'L ~l~e en~ c)f the load re~ r 4g ~o ri~e ~rc~ducing the ~utput pulse 52.
FIG. 3 ~hows an idealized positive s~oing output ~ul~e ~uch ~s 2Digh~c be recovered ~rom the phototran-~istor ~2 ~h~n the beam is not interrupted. However, 10 as mentioned above, bec3use ~he pho~otransistor output lead ~6 es6tends ~ consider~ble distance æcross the printed circui'c bo~rà, ~or example printed circuit boards 34 ~nd 36 of FIG. 1, ~ s3reat deal of electro-~agne~ie noi~e i~ pieked up and ~dded to he pho~o-lS transistor output ~i~nal~ This i& indicated for examplein FIG. 4 t)f the drawirl~s ldhere ~he phototransistor sis3nal 52 ~ay be rela~ively ~;mall, in ~he order s:
t~n to fifteen millivolts, while ~he noise ~ignals 54 alay be 6ubstantially greater ~nd may for example be even 100 ~o lSO millivolts.
In ~rder to ~ubstantially cancel out th0se unde~ired noise ~ignals, a differenti~l operational amplif ier 56 is u~ed wi'ch the ~ignal from the photo-transistor output le~d 46 fed through ~ high pass 25 filter circuit, which include~ lvad resistor 49, series capacitor SB ~nd resistor 60, to the negative (-) input terminal o~ the amplifier 56; and a compensating ~ignal ~quivalen~ to the noi~e signal components picked up on the nc~i~e compensating piekup lead 62 i~ coupled to t~ e 3~ iti~e (~ input, tsrminal of oper~tional amplif ier 56 through a high pass 5~ilt~r circuit which incltJdes load resistor 65 and series connected eapacitor 64 ~nd res istor 66 .
~2~2~
. 8 The compensation pick-up lead 62 indicated ~chemati ally ~t 62 in FIG. 1 i~ ~ long electric~l ccnductor ~xtending for ~u~s~anti~lly ~e full l~ngth ~f ~he circuit board~ 34 ~nd 36, co~men~urat~ ln ~xten~
S with the phototransistor ou~put circuit ~l6, a~ lndicated ~t the lef~ in FIG. 2. The l~ad 62 c~n ~)e in the fvrm of a wire, ~ prin~ed circuit, plDting, p:L~nar ~tch, etc. Th~ ~nd o~ th~ lead 62 has a lo~d tenmination cir~uit 63 equivalent to a photo~r~nsistor 42 and a ~witch 48 coupled ~o it. Thi~ eguiv~len~ load circuit 63 can be in the form of a capaci~vr and ~ diode ~onnected in parallel wit~ one anot~er. Accordingly, ~he noise 6ignals picked up on lead 62 results in current flow through load resi~tor 65 which will be sub~tan~i~lly ~he ~a~e as the electromagnetic noise 6ign21~ on photo-transistor ~ueput lead 46. ~s a result of ~he two ~quiv~lent ~nd bal~nced input circuit branches to the operational amplifiers 56, the~e two 6ets of noise ~ignals will 6ubstantially cancel one another out, while leaving only the desired characteristios of the phototransi~tor outpu~ signal 52 to be ~mplified and ~haped by ~he ~im~ it ~rrives at test point TP-2 as ~hown in FIGS. 5 ~nd 6.
It iS ~150 noted ~h~t the high pass filter including ~eries capacitor 58, ~nd resistor 60 and the load resi6tor~ connected in ~hunt to the capacitor di~criminates against the relatively slowly changing level~ of ~mbien~ light which will be received by the photodiodes ~nd which mis~ht otherwise v~ry ~he c)utput ~ign~l r~m the operational amplifier 56. ~or example, in ~ne embodiment the high pass filter wvuld pass 4 of the ~ignal a~ 400 cps ;cycles per second), ~0~ at 2000 cps, ~n~ 90~ ~t 6000 cp~. The circuit formed by capacitor 64,re5i5~0r 66, ~nd load resi~t~r 65 ~n the COmpenSa~iQn pickup lead branch is equivalent t~ the high p~ss ~ilter.
~.
~ttentiLon is il!ll60 directed to ~he diode 72 in the ~edback loop of the operati~nal ~mplifier 56. When the ~ignal received by ~he diferenti~1 ~nplifier 1-) ~nput ~erminal is neg~tive rela~iYe ~o ~ r~ference level, the diode i~ for~ard biased, the feedback r~eE;i6t~1T~Ce is ~ery low, ~and the gsin a~t ~31e op~r~tional amplifier 56 i~ v~ry low whereupc~n the ne~ative input ~;ignal i~ not ~mpllfied. ~owever when ~he input ~o ~he (-~ input termirlal of opera~ional amplifer 56 is po~itive, ~he 9LO diode 72 is b~ck biased r~ ing ghe feedback resistance ~nd the gain of the ~pera~ional amplifier 56 whereupon the lnput ~ignal is amplified.
~ first ~esl: poin~, desi5~nated TP-l in FIG. 2, is the point at which noi~y ~i~nals ~uch as ~hose ~hown in FIG. ~ may be ob~erved. Similarly ~he represen~a~ive ~ignal of PIG. 5 ~ ltest point ~P-~ ~a~ clamped by di~des 75 and 77 (~hich do not conduct negative pulse ~ignal~ or 6i~n~1~ of more than ~0.7 vol~ ~uch as might be cau6ed by ~witching ~r~n~ients ~nd noise) and was ~mplified by operatic~nal ~mplif~er~ 56 ~nd 74. The actual ~ignal with ~ome ~lig~t re~iàual uncompen~a~ed noi~e, i~ shown in FIG. 6. The diode 75 ~1513 ÇerVe5 ~0 provide ~ pat~ of cc~ndwtion when tlle ~eedb~ck diode 72 i~ ~or~rd biased. The resistor 79 conrlec~ed to cl~mping diode 77 C~ersres to tenninate ~he input to ~he ~) terminal of operation 2Implifier 56 ~nd ~o a~id the circuit in comming l~p to operation when the power is turned c~n~ Incidentally both olE the ~per~tional ampli-f iers 56 and 74 ~s ~hown in FIG. 2 may, for example, b~ of the types known a TL072 or LS353 oper~tional amplifier~, ~nd which ~re ~vail~ble rosll a n~nber of manufac~lrer~. Inciden~ially~ the compar~atc~r6 8~ and 82 ~o be di6cu~sed below may ~ ior example, b~ v~ ~ype LM393. ~he t~ h ~nd low vQ1tages for the ~;ystem may, by way of example but not limitation, be either the cc~mmonly a~ilable plu~ ~nd minus five volt~ ~r plus and llninus twelve ~lt~ owever i~ ha6 b~e2n determined th~t ~he his~her the voltDQes; ~ithin li~it~" the mt~re effs~ctive the circuit becomes.
'rhe comparatc)r 80 ~nd ~2 each have one input ~er~inal ~ connec~ed ~:o rec:eive the amplified ou~put pul~e iErc~m operatic~nal ~mplifier 74 and ~he o~her input ter~inal ~) coupled ~o receive reference signals VREF-l ~nd VR~F-2 r~spectively. Shus an output pulse fr~m cosnparator B0 i~ fed ~o the 9 inpu~ terminal of ~lip~flop 76 after i~ pro~e~sed and limi~ed by the clamping diode 81 and pull up re6i~tor 830 Incidently, the flip-flops 76 ~nd 78 ~y,ft)r example, be of the type LS74. Similarly the output c~f comparatc~r B2 is fed to the D input terminal of flip-flop 78 ~f~er i~ is processed and limit~d by cl~mping diode 85 ~nd pullup re~istor 87.
In oper~tic~n the hy~teresi6 portion of ~he eircuit of FIG. 2 which includes flip-flops 76 ~nd 78 evaluates the pul~e level on the output line~ r~m comp~rators 80 and 82 during 0ate pul~e or clock pul~e LED ~nd stores it ~s data d~pending upon 1che level~ of the signals.
For example if the level~ o the 6ignal on the~e two c~utput lines ~re bc~ch higher in smplitude than the ro f ere nce vol tage ~ VRE~ nd VREF- 2 ( non i n ~er rup ted bea~ uch a~ ~g ti~ne tl ~n FIG. 6 or both lower in ampli~ude th~n the referenced e~o~tage~ VREF~ 1 ~nd VREF-2 1~ interrupted beam~ 6~ch a~ at time t3 th~t 6tate of ~he data i~ ~tored in the flip-flopQ 76 and 78 and used ~6 the ol~put data Q an~ Q on c~utput lines 9 2 and 9 41~
If h~wever the ~tate of two sign~l~ from eomparatc)r~ 80 ~nd 82 ~re not both low or both lligh relatiYe tc3 the reference voltage~ VREF-l ~nd VREF-2, 3~
~uch ~ ~t ti~e $2 (21fi ~ ht occur if a beAm ~ only g?arti~lly interrupted~, ~he 6tate~ of ~he ~lip-10ps typically ~tor~d by an external da~ rec~v~r ~ ot ~hown) ~ro~n the preceding sc~n c~r ~eam would ~ypic~lly be used.
~imilElrly a ~ty~tere6is circuit can be i~plemented wich ~ gle J~ flip-fl~p 98 suc:h ~s J~n LS 109 in the ~anner illu6tr~ted ~n ~IG. 7. ~n th:i~ em~odiment, ~f the input~ to the 3 input and t~e K inpu~c to ~Lhe flip-flop 98 ~re both lo~, the output Q i~ low. If ~ however the ~ignal to the J and K inputs are ~o~h high the output Q ~s high. Bowever lf ~he ~iign~ f ~he J
input i~ low and the &ignal to the ~ input ~.5 high t~)e ~utput ~;ignal Q remains in it~ ~;tored sta~ce from the preceding bea~ oreover i the ~ignal of ~he J
inpu~c is high and the input ~ignal ~o the ~ input is low the 1ip--flop c~nnot toggle and the c>utput ~;2 will resnain in the ~me ~tate ~t w~s in from the preceding beam .
Consequently, if the finger ~h~uld m~ve only ~;lightly, ~uch a5 mis~ht occllr a~ a re~ult of 1~ slight finger tremor~ ~nd re6ult in pul~es ~uch a5 the eimes t2, t3~ tn+l ~nd tn+2 shown in FIG~ 6, the ~t~te of the circuit Qf FIGo 2 will indic~te or, ~n the case of FIG. 7, ~ill remain stable in re ponse to ~lch ~light irregular novement~. At the ~ame time he circuit will be able tt~ rapidly de~ect the desireà f inger movements.
Of course such transient conditions could ~l~o be caused by p~rtial ~clipsing of th~ be~m by ~ finger, low level uncompensated ~lectr~magnetic r~oi~e signal~, and 61ight v~ria~ ns ~n ~he level of ambient light.
~2~
In addition while the pho~od~tector circ-lit of I~IG. 2 ~ho~s one type Df circul~c it i possible to u~0 another type illu~.trat~d ~i n ~IG. l3 13uch 3~ d re~sis~ors 100 and 102 coup~ed t:~etwe~en the coll~ctor c~f
4~ch phototr~nsi~tor ~2 and in c;:)mmon to the l~d 62.
The ~mi~cters of photo~r2lnsi~tor6 ~2 are ~witched to ~rc>und to ~el~c~ the d~sired beam. These load resistors 100 ~nd 102 wc>uld be tapped with ~ reference voltage ~V: ~uch as 5 vol~, with ~he l~st load resistor tapped l:O ground. The collectors of each of the photo-tr~nci~tors ~l2 are ganged ~o the lead ~6 ~o that a negative 5;oing pul~e i~ produced in respc~nse to ~n unblocked beam when ~che ~witc~es ~B ~re ~equentially clos~d O
~hile the circuit of FIG. 2 has been descri~d as gener~ting and proces~ing po~itive ~ing phototransitor output pul~es 52 it ~ possible to handle negative going output pul~es 52 that w~uld be prc>duced by the ~:iFCUit ~f ~I~o B by rever ing the pol~rity ~f clamping diodes 75 ~nd 77 ~nd feedb~ck diode 72.
In ~ummary, in th~ ~ppended dr~wing~ ~nd the f~regoing det~iled description, one preferred embodiment of the inv~ntion has been d~scribed. It i8 to be under~tood that minor variations in t~e implement~tion ~f the ~nvention are cont~mplDt~d~ Por ~x~mple, alternative forms of ou~put circuitry, and circuits for the differential combining of the ~ign~l and compens~ting noise voltage ~ign~ls, ~ay ~e utili~ed, ~nd ~he ~nvention is ~pplicabl~ to ~ther ~ystems incl~dins par~llel output photosensitive ~lemen~s.
Acc~rdingly, tne present invention is not limit~d ~o th~t preci~ely ~s ~hown in the dra~ing~ and de~crib~d hereinabove.
The ~mi~cters of photo~r2lnsi~tor6 ~2 are ~witched to ~rc>und to ~el~c~ the d~sired beam. These load resistors 100 ~nd 102 wc>uld be tapped with ~ reference voltage ~V: ~uch as 5 vol~, with ~he l~st load resistor tapped l:O ground. The collectors of each of the photo-tr~nci~tors ~l2 are ganged ~o the lead ~6 ~o that a negative 5;oing pul~e i~ produced in respc~nse to ~n unblocked beam when ~che ~witc~es ~B ~re ~equentially clos~d O
~hile the circuit of FIG. 2 has been descri~d as gener~ting and proces~ing po~itive ~ing phototransitor output pul~es 52 it ~ possible to handle negative going output pul~es 52 that w~uld be prc>duced by the ~:iFCUit ~f ~I~o B by rever ing the pol~rity ~f clamping diodes 75 ~nd 77 ~nd feedb~ck diode 72.
In ~ummary, in th~ ~ppended dr~wing~ ~nd the f~regoing det~iled description, one preferred embodiment of the inv~ntion has been d~scribed. It i8 to be under~tood that minor variations in t~e implement~tion ~f the ~nvention are cont~mplDt~d~ Por ~x~mple, alternative forms of ou~put circuitry, and circuits for the differential combining of the ~ign~l and compens~ting noise voltage ~ign~ls, ~ay ~e utili~ed, ~nd ~he ~nvention is ~pplicabl~ to ~ther ~ystems incl~dins par~llel output photosensitive ~lemen~s.
Acc~rdingly, tne present invention is not limit~d ~o th~t preci~ely ~s ~hown in the dra~ing~ and de~crib~d hereinabove.
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An interference reduction circuit comprising:
means for providing at least one pair of light emitting devices and photodetectors each disposed along a light beam path extending therebetween;
a photodetector output circuit;
switching means for successively coupling the output of said at least one photodetector to said photodetector output circuit;
an electromagnetic noise compensation pickup circuit extending generally coextensively with and electrically balanced with said photodetector output circuit; and circuit means including combining means for differentially combining the outputs from said photodetector output circuit and said electromagnetic noise compensation pickup circuit to substantially eliminate the electromagnetic noise component present on the output signal of said photodetector output circuit.
means for providing at least one pair of light emitting devices and photodetectors each disposed along a light beam path extending therebetween;
a photodetector output circuit;
switching means for successively coupling the output of said at least one photodetector to said photodetector output circuit;
an electromagnetic noise compensation pickup circuit extending generally coextensively with and electrically balanced with said photodetector output circuit; and circuit means including combining means for differentially combining the outputs from said photodetector output circuit and said electromagnetic noise compensation pickup circuit to substantially eliminate the electromagnetic noise component present on the output signal of said photodetector output circuit.
2. A circuit as defined in claim 1 in which said circuit means comprises pulse forming circuitry and means responsive to the output from said combining means for forming a pulse signal corresponding to such output signal.
3. A circuit as defined in claim 2 in which said circuit means further comprising hysteresis type circuitry, and means for selectively changing the state of said hysteresis type circuitry only when there is a change in the state of successive output signals of a photodetector, from about a full light beam reception state to a state in which the successive light beam reception is about fully interrupted, and vice-versa.
4. A circuit as defined in claim 1 further comprising a high pass filter circuit means disposed to conduct signals from said photodetector output circuit and said electromagnetic noise compensation pickup circuit to said combining means, whereby the effects of variations in signal level which have a rate of change higher than the normally expected rate of change in the level of ambient light is so conducted.
5. A circuit as defined in claim 1 wherein said combining means is an operational amplifier having diode feedback means disposed between the output and input thereof for increasing the amplification of photodetector output pulses which are of a predetermined polarity and for significantly reducing the amplification of pulses of the opposite polarity.
6. A circuit as defined in claim 1 wherein said electromagnetic noise compensation pickup circuit is an electrically equivalent circuit to said photodetector output circuit.
7. A circuit as defined in claim 2 wherein said electromagnetic noise compensation pickup circuit is a loaded lead line which is electrically equivalent to said photodetector output circuit.
3. A circuit as defined in claim 3 wherein said circuit means includes comparator means for comparing the level of the output signal from said combining-means and actuating said hysteresis type circuitry to change states in response to each output signal only when the level of such output signal changes from greater than a first reference level to less than a second reference level and vice-versa.
9. A circuit as defined in claim 3 wherein said hysteresis type circuitry includes at least one flip-flop disposed to receive and store a signal corresponding to the change in the level output signal from said combining means and to remain in its previous stored state when the light beam reception state is between about full light beam reception and interruption.
10. A circuit as defined in claim 3 wherein said hysteresis type circuitry includes two flip-flops disposed to receive and store a pair of signals corresponding to the change in the level of the output signal from said combining means to store first condition signals if the light is about fully interrupted, second condition signals if the light beam is about fully received, and third condition signals if the light beam condition is therebetween.
11. A circuit as defined in claim 1 further comprising hysteresis type digital storage circuitry, and means for selectively changing the state of said hysteresis type circuitry only when there is a change in the level of the output signals of said photodetectors between successive couplings thereof from close to a full light beam reception state to a state where the next successive light beam reception is close to fully interrupted, and vice-versa.
12. A circuit as defined in claim 2 further comprising high pass filter circuit including a capacitor and resistor coupled in series and a shunting load resistor all disposed along a circuit path between said photodetector output circuit and said combining means, whereby the conduction of signals corresponding to changes in the level of ambient light at the rates of change which ambient light is expected to change is effectively eliminated.
13. A system as defined in claim 8 wherein said circuit means includes clamping diode means coupled to inputs of said hysteresis type circuitry for setting the first reference level and the second reference level.
14. A system as defined in claim 10 wherein said light emitting devices are infrared light emitting diodes.
15. A system as defined in claim 11 wherein circuit means includes comparator means for controlling the state of said hysteresis type digital storage circuitry in response to output signals from said pulse forming circuitry such that the hysteresis circuit indicates a first reception state if, on successive couplings, the level of the input signal thereto remains greater than the levels of two reference signals operatively applied thereto, remains the same if the level of such output signal moves between the two reference level signals, and indicates a second beam reception state if the level of such output signal moves from greater than the first reference level to less than the level of the two reference signals and vice-versa.
16. A system as defined in claim 11 wherein said hysteresis type storage circuitry includes at least one flip-flop disposed to receive and store a signal state corresponding to the last change in the level of the output signal from said combining means.
17. A system as defined in claim 11 wherein said hysteresis type storage circuitry includes two flip-flops disposed to receive and store a signal state corresponding to the last change in the level of the output signal from said combining means.
18. A light beam responsive circuit with interference reduction circuitry comprising:
means for providing a plurality of pairs of photoemitters and photodetectors each pair being disposed in spaced apart relationship on a beam path and about the periphery of a face plate;
a photodetector output circuit;
switching means for successively coupling the outputs from a plurality of said photodetectors to said photodetector output circuit;
compensation pickup circuit disposed substantially coextensively with said and electrically balanced with said photodetector output circuit; and means coupled to differentially combine signals from said photodetector output circuit and said compensation circuit to substantially eliminate electromagnetic noise which is present on said photodetector output circuit.
means for providing a plurality of pairs of photoemitters and photodetectors each pair being disposed in spaced apart relationship on a beam path and about the periphery of a face plate;
a photodetector output circuit;
switching means for successively coupling the outputs from a plurality of said photodetectors to said photodetector output circuit;
compensation pickup circuit disposed substantially coextensively with said and electrically balanced with said photodetector output circuit; and means coupled to differentially combine signals from said photodetector output circuit and said compensation circuit to substantially eliminate electromagnetic noise which is present on said photodetector output circuit.
19. A circuit as defined in claim 18 further comprising hysteresis type digital storage circuitry, and means for selectively changing the state of said hysteresis type circuitry only when there is a change in the state of photodetectors on successive couplings, from at least about a full light beam reception by a photodetector state to situations where the successive light beam reception state by such photodetector is at least about fully interrupted, and vice-versa and said hysteresis type circuitry remains in its stored state resulting from the previous coupling when the light beam reception is between these two conditions.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US512,821 | 1983-07-11 | ||
| US06/512,821 US4591710A (en) | 1983-07-11 | 1983-07-11 | Ambient light and electromagnetic noise reduction circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1220829A true CA1220829A (en) | 1987-04-21 |
Family
ID=24040720
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000458555A Expired CA1220829A (en) | 1983-07-11 | 1984-07-10 | Ambient light ad electromagnetic noise reduction circuit |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US4591710A (en) |
| EP (1) | EP0149668B1 (en) |
| JP (1) | JPS60501825A (en) |
| KR (1) | KR890004769B1 (en) |
| AU (1) | AU572536B2 (en) |
| CA (1) | CA1220829A (en) |
| DE (1) | DE3467944D1 (en) |
| ES (1) | ES8603666A1 (en) |
| IL (1) | IL72296A (en) |
| IT (1) | IT1179391B (en) |
| WO (1) | WO1985000682A1 (en) |
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| US4712003A (en) * | 1983-07-27 | 1987-12-08 | Itsuki Ban | Blind person guide device |
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| US4943806A (en) * | 1984-06-18 | 1990-07-24 | Carroll Touch Inc. | Touch input device having digital ambient light sampling |
| US4695827A (en) * | 1984-11-20 | 1987-09-22 | Hughes Aircraft Company | Electromagnetic energy interference seal for light beam touch panels |
| JPH0337062Y2 (en) * | 1985-05-17 | 1991-08-06 | ||
| US4878107A (en) * | 1985-10-29 | 1989-10-31 | Hopper William R | Touch sensitive indicating light |
| US4799044A (en) * | 1986-02-18 | 1989-01-17 | Amp Incorporated | Phototransistor apparatus with current injection ambient compensation |
| US4684801A (en) * | 1986-02-28 | 1987-08-04 | Carroll Touch Inc. | Signal preconditioning for touch entry device |
| US4893120A (en) * | 1986-11-26 | 1990-01-09 | Digital Electronics Corporation | Touch panel using modulated light |
| US4845479A (en) * | 1986-12-22 | 1989-07-04 | Xerox Corporation | High reliability PWB interconnection for touch input systems |
| US4818859A (en) * | 1987-06-01 | 1989-04-04 | Carroll Touch Inc. | Low profile opto-device assembly with specific optoelectronic lead mount |
| US4855590A (en) * | 1987-06-25 | 1989-08-08 | Amp Incorporated | Infrared touch input device having ambient compensation |
| US5164714A (en) * | 1988-06-20 | 1992-11-17 | Amp Incorporated | Modulated touch entry system and method with synchronous detection |
| US4988983A (en) * | 1988-09-02 | 1991-01-29 | Carroll Touch, Incorporated | Touch entry system with ambient compensation and programmable amplification |
| US5113068A (en) * | 1990-12-28 | 1992-05-12 | Square D Company | Photoelectrical sensor with multistaged, filtered amplifier circuit |
| US5577848A (en) * | 1992-08-24 | 1996-11-26 | Bowen; James H. | Light controlled touch pad for cursor and selection control on a computer display |
| US5378069A (en) * | 1992-08-24 | 1995-01-03 | Product Engineering & Mfg., Inc. | Environmentally safe touch typing keyboard |
| US5605406A (en) * | 1992-08-24 | 1997-02-25 | Bowen; James H. | Computer input devices with light activated switches and light emitter protection |
| US5508521A (en) * | 1994-12-05 | 1996-04-16 | Cardiovascular Diagnostics Inc. | Method and apparatus for detecting liquid presence on a reflecting surface using modulated light |
| US6256157B1 (en) | 1998-05-15 | 2001-07-03 | International Business Machines Corporation | Method and apparatus for removing noise spikes |
| WO2005029394A2 (en) * | 2003-09-22 | 2005-03-31 | Koninklijke Philips Electronics N.V. | Light guide touch screen |
| JP2007525761A (en) | 2004-02-27 | 2007-09-06 | エヌ−トリグ リミテッド | Noise reduction in digitizer systems |
| JP4550712B2 (en) * | 2005-10-17 | 2010-09-22 | ルネサスエレクトロニクス株式会社 | Light receiving circuit |
| US9092092B2 (en) | 2008-08-07 | 2015-07-28 | Rapt Ip Limited | Detecting multitouch events in an optical touch-sensitive device using touch event templates |
| JP5378519B2 (en) * | 2008-08-07 | 2013-12-25 | ドラム，オウエン | Method and apparatus for detecting multi-touch events in optical touch sensitive devices |
| JP5345007B2 (en) * | 2009-06-29 | 2013-11-20 | 株式会社ワコム | Position detecting device, position detecting circuit and position detecting method |
| US9052778B2 (en) * | 2009-12-16 | 2015-06-09 | Beijing Irtouch Systems Co., Ltd | Infrared touch screen |
| US8836672B2 (en) | 2011-02-09 | 2014-09-16 | Dornerworks, Ltd. | System and method for improving machine vision in the presence of ambient light |
| TWI497376B (en) | 2011-07-22 | 2015-08-21 | Rapt Ip Ltd | Optical coupler assembly for use in an optical touch sensitive device |
| US9524060B2 (en) | 2012-07-13 | 2016-12-20 | Rapt Ip Limited | Low power operation of an optical touch-sensitive device for detecting multitouch events |
| US10095361B2 (en) | 2015-03-18 | 2018-10-09 | Microsoft Technology Licensing, Llc | Stylus detection with capacitive based digitizer sensor |
| US10296146B2 (en) | 2015-12-22 | 2019-05-21 | Microsoft Technology Licensing, Llc | System and method for detecting grip of a touch enabled device |
| US10423268B2 (en) | 2015-12-22 | 2019-09-24 | Microsoft Technology Licensing, Llc | System and method for detecting grounding state of a touch enabled computing device |
| US9823774B2 (en) | 2016-02-23 | 2017-11-21 | Microsoft Technology Licensing, Llc | Noise reduction in a digitizer system |
| US10678348B2 (en) | 2018-03-12 | 2020-06-09 | Microsoft Technology Licensing, Llc | Touch detection on an ungrounded pen enabled device |
| US10616349B2 (en) | 2018-05-01 | 2020-04-07 | Microsoft Technology Licensing, Llc | Hybrid sensor centric recommendation engine |
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| CN114594494B (en) * | 2022-01-13 | 2022-10-21 | 杭州宏景智驾科技有限公司 | Laser radar system and ambient light denoising method thereof |
| CN117079975A (en) * | 2023-07-28 | 2023-11-17 | 厦门亿芯源半导体科技有限公司 | High-speed TIA (wireless local area network) 5G WIFI electromagnetic interference resisting method |
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| US3576452A (en) * | 1968-05-28 | 1971-04-27 | Motorola Inc | Photodiode preamplifier circuit for a card reader system |
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| US4198623A (en) * | 1978-11-13 | 1980-04-15 | Sanders Associates, Inc. | Touch entry interactive cathode ray tube arrangement |
| US4335316A (en) * | 1980-04-09 | 1982-06-15 | Baldwin-Korthe Web Controls, Inc. | Web break detector with adjustable scanning head |
-
1983
- 1983-07-11 US US06/512,821 patent/US4591710A/en not_active Expired - Lifetime
-
1984
- 1984-06-29 AU AU31527/84A patent/AU572536B2/en not_active Ceased
- 1984-06-29 EP EP84902860A patent/EP0149668B1/en not_active Expired
- 1984-06-29 JP JP59502680A patent/JPS60501825A/en active Granted
- 1984-06-29 WO PCT/US1984/001035 patent/WO1985000682A1/en active IP Right Grant
- 1984-06-29 DE DE8484902860T patent/DE3467944D1/en not_active Expired
- 1984-07-04 IL IL72296A patent/IL72296A/en not_active IP Right Cessation
- 1984-07-09 IT IT48530/84A patent/IT1179391B/en active
- 1984-07-10 ES ES534167A patent/ES8603666A1/en not_active Expired
- 1984-07-10 CA CA000458555A patent/CA1220829A/en not_active Expired
- 1984-07-11 KR KR1019840004042A patent/KR890004769B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| ES534167A0 (en) | 1985-12-16 |
| IT8448530A0 (en) | 1984-07-09 |
| WO1985000682A1 (en) | 1985-02-14 |
| IL72296A0 (en) | 1984-11-30 |
| AU572536B2 (en) | 1988-05-12 |
| KR890004769B1 (en) | 1989-11-25 |
| JPS60501825A (en) | 1985-10-24 |
| KR850001590A (en) | 1985-03-30 |
| ES8603666A1 (en) | 1985-12-16 |
| EP0149668A1 (en) | 1985-07-31 |
| AU3152784A (en) | 1985-03-04 |
| IT1179391B (en) | 1987-09-16 |
| JPS633333B2 (en) | 1988-01-22 |
| IL72296A (en) | 1987-10-20 |
| EP0149668B1 (en) | 1987-12-02 |
| US4591710A (en) | 1986-05-27 |
| DE3467944D1 (en) | 1988-01-14 |
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