Sensing light and sensing the state of a memory cell

Abstract

A light-to-frequency converter includes a switch ( 130 ) connected in series with a reverse-biased photodiode ( 120 ). A node ( 150 ) in the current path through the switch and the photodiode is connected to the input of a Schmidt trigger ( 160 ), whose output controls the switch. New techniques are provided for motion compensation, partial readouts, dark current elimination, non-destructive testing, and sensing the state of a memory cell.

1 . An imager comprising:
 a plurality of pixels each of which comprises a photodetector and a digital storage device for incorporating data indicative of light detected by the photodetector;   shift control circuitry for controlling the digital storage devices to form one or more shift registers, at least one shift register having a plurality of cells each of which comprises one or more bits of a respective one of the digital storage devices.   
   
   
       2 . The imager of  claim 1  wherein each pixel's photodetector is part of the pixel's light-to-frequency converter, and each pixel's digital storage device comprises a counter for counting electrical pulses generated by the pixel's light-to-frequency converter. 
   
   
       3 . The imager of  claim 1  wherein said shift control circuitry is operable to form the one or more shift registers as circular shift registers. 
   
   
       4 . A method for obtaining a digital image of a scene with an imager comprising a plurality of pixels, each pixel comprising a light-to-frequency converter and a counter for counting pulses generated by the light-to-frequency converter, the counters forming one or more shift registers for shifting data out of the counters, the method comprising:
 (1) sensing light from the scene by the pixels;   (2) after operation (1), shifting data from the one or more shift registers and testing the data to determine if additional image acquisition of the scene is needed;   (3) if additional image acquisition of the scene is needed, then sensing light from the scene by the pixels.   
   
   
       5 . The method of  claim 4 , wherein in the operation (3) the sensing starts with the counters containing the data that was present in the counters at the end of the operation (1). 
   
   
       6 . The method of  claim 5  wherein each shift register is used as a circular shift register in the operation (2), the counters containing the same data at the end of the operation (2) as at the start of the operation (2). 
   
   
       7 . A control circuit for causing an imager to perform the method of  claim 4 . 
   
   
       8 . A method for obtaining image data with a light-to-frequency converter, the method comprising:
 the light-to-frequency converter generating first electrical pulses indicative of light sensed by the light-to-frequency converter;   a counter counting in a first direction (up or down) on the first pulses counting in a second direction (down or up) on second pulses provided to the counter.   
   
   
       9 . The method of  claim 8  wherein the second pulses are generated by a light-to-frequency converter that does not detect light. 
   
   
       10 . An imager comprising one or more pixels each of which includes a light-to-frequency converter and a counter having a first input connected to an output of the light-to-frequency converter to count in a first direction (up or down) on pulses from the light-to-frequency converter;
 wherein each said counter has a second input to count in a second direction (down or up) on pulses at the second input.   
   
   
       11 . The imager of  claim 10  wherein the second input is connected to a light-to-frequency converter shielded not to detect light. 
   
   
       12 . A method for obtaining a digital image of a scene with an imager comprising a plurality of pixels, each pixel comprising a light-to-frequency converter and a counter for counting pulses generated by the light-to-frequency converter, the method comprising:
 (1) loading at least one of the counters with data other than reset data; and   then   (2) acquiring a first image with the imager, with said at least one of the counters counting the pulses generated by the associated light-to-frequency converter starting with the data loaded in (1).   
   
   
       13 . The method of  claim 12  wherein the data in (1) corresponds to a second image. 
   
   
       14 . The method of  claim 12  wherein:
 the light-to-frequency converters are sensitive to light in a first range of wavelengths but not in a second range of wavelengths;   one of operations (1), (2) comprises acquiring an image of an object through a light converter which converts the second range of wavelengths to the first range of wavelengths; and   the other one of operations (1), (2) comprises acquiring an image of said object without light conversion from the second range to the first range.   
   
   
       15 . The method of  claim 12  wherein the first data corresponds to calibration data.