Method and system to enhance differential dynamic range and signal/noise in CMOS range finding systems using differential sensors
AssigneeCanesta, Inc.
InventorsCyrus Bamji, Khaled Salama
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Abstract
Dynamic range of a differential pixel is enhanced by injecting, synchronously or asynchronously, a fixed compensating offset (ΔV) into a differential signal capacitor whenever magnitude of the differential signal across the capacitor exceeds a predetermined value. The number (N) of ΔV offsets made is counted. Effective differential signal capacitor voltage V(t)=Vo+N·ΔV, where Vo is capacitor voltage. Differential pixel signal/noise ratio is increased by dynamically maximizing operational amplifier gain AG for each differential pixel.
Claims20
A method to increase effective differential dynamic range of a differential pixel responsive to optical energy, a detection response of said differential pixel having a common mode component and a differential component, the method including:
- (a) adding a fixed magnitude compensating offset selected from +ΔV and −ΔV to a differential signal V(t) detected by said differential pixel, to avoid a saturation magnitude differential signal level;
- and
- (b) counting number N of times said compensating offset has been added to avoid said saturation magnitude;
- wherein effective magnitude of said differential signal V(t) is proportional to V(t)±N ΔV.
For use with a differential pixel responsive to optical energy, a detection response of said differential pixel having a common mode component and a differential component, differential dynamic range enhancing circuitry to enhance effective dynamic range of said differential pixel, said differential dynamic range enhancing circuitry comprising:
- means for adding a fixed magnitude compensating offset selected from +ΔV and −ΔV to a differential signal V(t) detected by said differential pixel, to avoid a saturation magnitude differential signal level;
- and
- means for counting number N of times said compensating offset has been added to avoid said saturation magnitude;
- wherein effective magnitude of said differential signal V(t) is proportional to V(t)+N ΔV.
A method to reduce effective noise in the pixel signal readout path of an array of differential pixels, the method including:
- (a) individually varying signal gain for each pixel to determine a maximum allowable gain;
- (b) for each said pixel, recording said pixel's maximum allowable gain determined at step (a) and also recording a signal value for said pixel at said maximum allowable gain;
- and
- (c) operating said pixel at said maximum allowable gain;
- wherein effect of noise in components downstream of said pixel is reduced and signal/noise ratio is enhanced.
For use with a differential pixel responsive to optical energy, said differential pixel having a detection response with a common mode component and a differential component, signal/noise enhancement circuitry to reduce effective noise in the pixel signal readout path of an array of differential pixels, the signal/noise enhancement circuitry including:
- means for individually varying signal gain for each pixel to determine a maximum allowable gain;
- for each said pixel, means for recording said pixel's maximum allowable gain determined at step (a) and also recording a signal value for said pixel at said maximum allowable gain;
- and
- operating said pixel at said maximum allowable gain;
- wherein effect of noise in components downstream of said pixel is reduced and signal/noise ratio is enhanced.
A CMOS-implementable range finding system that emits amplitude modulated optical energy towards a target object and includes an array of differential pixels including pixel photodetectors to differentially detect at least a fraction of said optical energy reflected by said target object even in the presence of ambient optical energy, said differential pixel photodetectors having a detection response with a common mode component, the range finding system including:
- means for substantially rejecting said common mode component such that saturation of said differential pixel photodetectors therefrom is reduced;
- means for retaining differentially detected reflected said optical energy;
- and at least one of:
- (i) means for increasing effective differential dynamic range of said differential pixels;
- and
- (ii) means for enhancing signal/noise through a detection signal path of said system.
Dependencies are inferred from the claim text.