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APPARATUS FOR CONTROLLING A SCREEN
POINTER THAT DISTINGUISHES BETWEEN
AMBIENT LIGHT AND LIGHT FROM ITS
CROSS REFERENCE TO RELATED
This application is a divisional application, which is based on and claims priority to U.S. patent application Ser. No. 10/341,710, filed on Jan. 14, 2003 now U.S. Pat. No. 7,295, 186, and which is incorporated herein by reference in its entirety.
THE FIELD OF THE INVENTION
This invention relates generally to devices for controlling a pointer (cursor) on a display screen, and relates more particularly to an apparatus for controlling a screen pointer that distinguishes between ambient light and light from its light source.
BACKGROUND OF THE INVENTION
The use of a hand operated pointing device for use with a computer and its display has become almost universal. One form of the various types of pointing devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Mechanical mice typically include a rubber-surfaced steel ball that rolls over the mouse pad as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to a computer, where software responds to the signals to change by a AX and a AY the displayed position of a pointer in accordance with movement of the mouse.
In addition to mechanical types of pointing devices, such as a conventional mechanical mouse, optical pointing devices have also been developed. In one form of an optical pointing device, rather than using a moving mechanical element like a ball, relative movement between an imaging surface, such as a finger or a desktop, and photo detectors within the optical pointing device, is optically sensed and converted into movement information. Battery operated optical mice are currently available based on Agilent's ADNS-2020 and ADNS-2030 optical image sensors. Other optical mice are available based on Agilent's ADNS-2001 and ADNS-2051, as well as other optical image sensors.
In a typical optical mouse, a light emitting diode (LED) illuminates the surface under the mouse. Under normal circumstances, the mouse body blocks ambient light from reaching the area of the navigation surface visible to the image sensor. However, when the mouse is lifted, ambient light can provide strong amplitude (but out of focus) images to the image sensor. It is desirable for the optical mouse sensor to report no motion in such situations, as the user is either finished with mouse usage (e.g., the mouse is set aside) or is attempting to reposition the screen pointer due to limited space on the navigation surface.
At present, optical mice use out-of-focus indications, low signal amplitude indications, or zero displacement answers from cross-correlation, in order to detect a mouse lifted condition and keep the screen pointer steady. For the out-of-focus technique, the pictures from the image array are typically passed through a high pass filter, and the output of the high pass filter provides an indication of whether the images are in
focus or not. If the images are not in focus, it is likely that the surface under the mouse is not at the correct, normal distance, and the mouse may have been lifted by the user. For the low signal amplitude technique, the total amount of signal output
5 by the image sensor, which could be comprised of both light bouncing off the surface from the LED and ambient light, is measured. When the amplitude of the signal out of the image sensor is low, an indication to stop moving the screen pointer is generated. If a sufficient amount of ambient light strikes the
10 image sensor when the mouse is lifted, a low signal amplitude signal will not be generated, and the screen pointer may continue moving. For the third technique (zero displacement answers from cross-correlation), images are captured and
15 correlated in the normal manner to determine how much motion has occurred. When the mouse is lifted, the captured images are typically blurry and appear to be essentially the same to the mouse, so the mouse typically, but not always, reports zero motion in this situation, causing the screen
20 pointer to stop moving.
These prior methods for detecting a mouse lifted condition are not always reliable. In some cases, the screen pointer moves in an unpredictable path, or jitters in place, when it should remain still, which results in an annoyance to the user
25 and an undesirable consumption of power. If the mouse lifted condition is not detected, the mouse may remain in a full power mode, rather than switching to a sleep mode. For a battery-operated mouse, if the mouse is left upside down or is left unused at the end of a desk for a long period of time, a
30 large amount of battery power can be consumed by not detecting this condition and freezing the screen pointer.
In addition, if there is a large amount of ambient light on the area under the mouse that is being imaged, this ambient light can interfere with navigation accuracy during normal use of
35 the mouse.
SUMMARY OF THE INVENTION
One form of the present invention provides an apparatus for 40 controlling the position of a screen pointer for an electronic device having a display screen. The apparatus includes a light source for illuminating an imaging surface with a plurality of light pulses, thereby generating reflected light pulses. A detection circuit is configured to sense light, distinguish 45 between the reflected pulses and ambient light, and generate a low signal indication if the magnitude of the reflected pulses falls below a threshold value. An optical motion sensor generates digital images based on the reflected pulses. The motion sensor is configured to generate movement data based 50 on the digital images. The movement data is indicative of relative motion between the imaging surface and the apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top view of an optical mouse according to one embodiment of the present invention.
FIG. 2 is a block diagram illustrating major components of the optical mouse shown in FIG. 1 according to one embodi60 ment of the present invention.
FIG. 3A is an electrical schematic/block diagram illustrating light sensing circuitry of the optical mouse shown in FIG. 1 with two capacitors per photo detector according to one embodiment of the present invention. 65 FIG. 3B is a timing diagram illustrating the timing of control signals for the light sensing circuitry shown in FIG. 3A.
FIG. 4A is an electrical schematic/block diagram illustrating light sensing circuitry of the optical mouse shown in FIG.
1 with one capacitor per photo detector according to another embodiment of the present invention.
FIG. 4B is a timing diagram illustrating the timing of 5 control signals for the light sensing circuitry shown in FIG. 4A.
DESCRIPTION OF THE PREFERRED
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention 15 may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present 20 invention is defined by the appended claims.
FIG. 1 is a top view of an optical mouse 10 according to one embodiment of the present invention. Mouse 10 includes plastic case 12, left mouse button (LB) 14A, right mouse button (RB) 14B, and optical motion sensor chip 16. Sensor 25 chip 16 is covered by plastic case 12, and is therefore shown with dashed lines in FIG. 1.
FIG. 2 is a block diagram illustrating major components of optical mouse 10 according to one embodiment of the present invention. Optical mouse 10 includes light source 2, lenses 4 30 and 8, and optical motion sensor 16. Optical motion sensor 16 includes photo detector array 148, electronic shutter 150, a plurality of sense capacitors 154A-154C (collectively referred to as sense capacitors 154), multiplexer 156, amplifier 157, analog to digital (A/D) converter 158, correlator 160, 35 photo detector 162, amplifier 164, multiplier 166, low pass filter (LPF) 168, comparator (COMP) 172, oscillator (OSC) 176, multiplier 178, light controller 180, shutter controller 184, and system controller 186.
In one embodiment, the operation of optical motion sensor 40 16 is primarily controlled by system controller 186, which is coupled to and controls multiplexer 156, A/D converter 158, correlator 160, shutter controller 184, and light controller 180. In operation, according to one embodiment, light source
2 emits light that is directed by lens 4 onto surface 6, which is 45 a desktop or other suitable imaging surface, and reflected images are generated. In one embodiment, light source 2 includes one ormore light emitting diodes (LED's). Reflected light from surface 6 is directed by lens 8 onto photo detector array 148 and photo detector 162. Photo detector 162 and 50 photo detectors in photo detector array 148 each provide a signal that varies in magnitude based upon the intensity of light incident on the photo detector. In one embodiment, photo detector 162 and the photo detectors in photo detector array 148 are photo diodes. 55
Electronic shutter 150 is controlled by a shutter signal 182 from shutter controller 184. When electronic shutter 150 is "open," charge accumulates on sense capacitors 154, creating voltages that are related to the intensity of light incident on the photo detectors in array 148. When electronic shutter 150 is 60 "closed," no further charge accumulates or is lost from sense capacitors 154. Multiplexer 156 connects each sense capacitor 154 in turn to amplifier 157 and A/D converter 158, to amplify and convert the voltage from each sense capacitor 154 to a digital value. Sense capacitors 154 are then dis- 65 charged through electronic shutter 150, so that the charging process can be repeated.
In one embodiment, light source 2 is controlled by shutter signal 182 from shutter controller 184. When shutter signal 182 goes high, the high signal causes light controller 180 to output a signal for turning on light source 2. The high shutter signal 182 also causes electronic shutter 150 to open, thereby allowing charge to accumulate on sense capacitors 154. When shutter signal 182 goes low, the low signal causes electronic shutter 150 to close, and causes light controller 180 to output a low signal to turn off light source 2. In one form of the invention, the signals output by light controller 180 are modulated by oscillator 176 and multiplier 178, thereby causing the light emitted by light source 2 to be modulated in the same manner. The modulation of light emitted by light source 2 is described in further detail below.
Based on the level of voltage from each sense capacitor 154, A/D converter 158 generates a digital value of a suitable resolution (e.g., one to eight bits) indicative of the level of voltage. The digital values represent a digital image or digital representation of the portion of the desktop or other imaging surface under optical mouse 10. The digital values are stored as frames within correlator 160.
In addition to providing digital images to correlator 160, A/D converter 158 also outputs digital image data to shutter controller 184 in one form of the invention. Shutter controller 184 helps to ensure that successive images have a similar exposure, and helps to prevent the digital values from becoming saturated to one value. Shutter controller 184 checks the values of digital image data and determines whether there are too many minimum values or too many maximum values. In one embodiment, if there are too many minimum values, controller 184 increases the charge accumulation time of electronic shutter 150, and if there are too many maximum values, controller 184 decreases the charge accumulation time of electronic shutter 150.
The overall size of photo detector array 148 is preferably large enough to receive an image having several features. Images of such spatial features produce translated patterns of pixel information as optical mouse 10 moves over a surface. The number of photo detectors in array 148 and the frame rate at which their contents are captured and digitized cooperate to influence how fast optical mouse 10 can be moved across a surface and still be tracked. Tracking is accomplished by correlator 160 by comparing a newly captured sample frame with a previously captured reference frame to ascertain the direction and amount of movement.
In one embodiment, the entire content of one of the frames is shifted by correlator 160 by a distance of one pixel successively in each of the eight directions allowed by a one pixel offset trial shift (one over, one over and one down, one down, one up, one up and one over, one over in the other direction, etc.). That adds up to eight trials. Also, since there might not have been any motion, a ninth trial "null shift" is also used. After each trial shift, those portions of the frames that overlap each other are subtracted by correlator 160 on a pixel by pixel basis, and the resulting differences are preferably squared and then summed to form a measure of similarity (correlation) within that region of overlap. In another embodiment, larger trial shifts (e.g., two over and one down) may be used. The trial shift with the least difference (greatest correlation) can be taken as an indication of the motion between the two frames. That is, it provides raw movement information that may be scaled and or accumulated to provide movement information (AX and AY) 161 of a convenient granularity and at a suitable rate of information exchange, which is output to a host device.
In one embodiment, sensor 16 is configured to distinguish between ambient light and light from light source 2, and
detect when optical mouse 10 is lifted away from surface 6 by sensing the level of light from light source 2 that is reflected from surface 6. When optical mouse 10 is lifted away from surface 6, the light from light source 2 no longer reaches photo detector 162 and the photo detectors in array 148 in the 5 same quantity that it did previously, if at all; the reflecting surface 6 is too far away or is simply not in view. However, when mouse 10 is lifted, ambient light from other light sources (e.g., fluorescent lights, a cathode ray tube (CRT), sunlight, etc.) may strike the photo detectors, and the outputs 10 of the photo detectors will vary based on the intensity of the ambient light.
In one embodiment, sensor 16 modulates the light from light source 2 at a frequency that is unlikely to occur in ambient light from other light sources that may be present 15 near the mouse 10, which allows sensor 16 to distinguish between light received from light source 2 and light received from ambient light sources. When the strength of the reflected modulated light from light source 2 falls below a predetermined threshold value, indicating that mouse 10 has likely 20 been lifted from surface 6, sensor 16 reports zero motion to the host device so that the screen pointer is held steady.
Ambient light that may cause interference with the operation of mouse 10 is typically at a low frequency, such as less than 200 Hertz (Hz). CRT's and fluorescent lights are typi- 25 cally the most problematic. CRT's typically flash at up to about 100 Hz, and fluorescent lights in the United States typically flash at 120 Hz. In one embodiment, light source 2 is modulated to provide light flashes or light pulses at a substantially higher frequency than such ambient light sources. 30
Light source 2 turns on when it receives a pulse from sensor 16. The amount of time that light source 2 remains on is determined by the width (duration) of the received pulse. In previous optical mice, when the mouse was being moved, 1500 images per second were typically captured, with the 35 light source being flashed once for each captured image (i.e., a flash rate of 1500 flashes per second), and with a typical flash duration between about ten and one hundred microseconds for each flash. In one embodiment of the present invention, rather than turning on the light source 2 with a single, 40 relatively wide pulse of the desired duration (e.g., one hundred microseconds) to capture an image, a high frequency digital modulation is used to modulate a wide pulse, and thereby generate many pulses having a smaller width that provide the same effective illumination as a single wide pulse. 45
In one embodiment, light controller 180 outputs a pulse to multiplier (modulator) 178 during each frame period that an image is to be captured. In one form of the invention, the pulses output by light controller 180 have a width of twice the desired duration of on time of light source 2 for a particular 50 image to be captured. In one embodiment, oscillator 176 generates a 100 KHz square wave, which is output to multiplier 178 and multiplier 166. In other embodiments, frequencies other than 100 KHz are used for the modulation waveform output by oscillator 176. Multiplier 178 multiplies the 55 pulse received from light controller 180 by the square wave received from oscillator 176, and outputs the resulting modulated signal to light source 2.
For example, if a one hundred microsecond duration of on time of light source 2 is desired for each image to be captured, 60 rather than driving light source 2 with a single pulse having a width of one hundred microseconds, in one form of the invention, light controller 180 outputs a pulse having a width of two hundred microseconds to multiplier 178. Multiplier 178 multiplies the received pulse by the 100 KHz square wave 65 received from oscillator 176, resulting in a modulated signal that drives light source 2. The modulated signal includes
twenty cycles of a 100 KHz square wave, with a total duration of two hundred microseconds and a cumulative on time of one hundred microseconds. The photo detector array 148 integrates the same amount of signal in each frame for the multiple narrower pulses as for a single wider pulse, and delivers identical images to those that would be delivered using a single wider pulse.
In one embodiment, a synchronous detection technique is used to detect the modulated light signal output by light source 2 and reflected by surface 6. In one form of the invention, a photo detector 162 separate from the photo detector array 148 is used to synchronously detect the modulated light from light source 2 in a continuous time manner. The electrical signal output by photo detectorl62 is amplified by amplifier 164. In one embodiment, amplifier 164 is AC coupled to photo detector 162, and clips for large signals in order to cover a large dynamic range. Multiplier (demodulator) 166 multiplies the amplified signal from amplifier 164 by the modulation waveform (e.g., 100 KHz square wave) output by oscillator 176.
In one form of the invention, multiplier 166 alternately multiplies by +1 then -1, so that the AC signals at the 100 KHz modulation frequency (i.e., the signals generated from light received from light source 2) output by amplifier 164 are synchronously rectified (i.e., demodulated down to a DC or low frequency signal), resulting in a demodulated signal that is passed through low pass filter 168 to comparator 172. For signals output by photo detector 162 that are at frequencies different than the modulation frequency (i.e., signals generated from light received from ambient light sources), these signals are typically DC or low frequency signals (e.g., 60 or 120 Hz) that are converted to high frequency signals when multiplied by the alternating +1 and -100 KHz square wave by multiplier 166. The high frequency signals output by multiplier 166 are blocked by low pass filter 168, so the output of low pass filter 168 will be near zero for such signals. Thus, photo detector 162 is essentially gated at the same frequency that the light source 2 is being flashed, so that ambient light is blocked, and the magnitude of light from light source 2 can be detected.
Comparator 172 includes a first input 170A coupled to the output of low pass filter 168, and a second input 170B coupled to a threshold voltage. Comparator 172 compares the signal received from low pass filter 168 with the threshold value, and thereby determines whether there is a sufficient amount of light from light source 2 reaching the photo detectors 148. If the signal received from low pass filter 168 falls below the threshold value, indicating that there is an insufficient amount of light from light source 2 reaching the photo detectors 148, and that mouse 10 has likely been lifted away from surface 6, comparator 172 outputs a low signal indication or "mouse lifted" signal 174 to correlator 160.
Components of the electrical signal generated by photo detector 162 based on ambient light are filtered out, and do affect the signal output to the comparator 172, even though the ambient light does affect the output of the photo detector array 148. In cases where photo detector array 148 generates poor (e.g., out of focus) images because of excessive ambient light, and very little light from light source 2 strikes the photo detector array 148, the separate path, including photo detector 162, amplifier 164, multiplier 166, low pass filter 168, and comparator 172, detects the problem, and comparator 172 outputs a mouse lifted signal 174 to correlator 160.
In one embodiment, when correlator 160 receives a mouse lifted signal 174, correlator 160 suppresses normal motion calculations from the captured images and stops reporting motion data 161 or reports zero motion, resulting in a freeze