Filtering pixels and uses thereof

Abstract

Embodiments of the technology disclosed herein provide filtering pixels for performing filtering of signals within the pixel domain. Filtering pixels described herein include a hybrid analog-digital filter within the pixel circuitry, reducing the need for computationally intensive and inefficient post-processing of images to filter out aspects of captured signals, and account for ineffectiveness of optical filters.

1 . A system, comprising:
 an array of filtering pixels, each filtering pixel comprising:   a photodiode;   a filter circuit;   a light source; and   an imaging system, comprising:   a lens; and   an aperture stop;   wherein the light source outputs a modulated light, and each filtering pixel of the array of filtering pixels is configured to detect a modulated light.   
     
     
         2 . The system of  claim 1 , wherein the array of filtering pixels comprises one or more derivative pixels, the filter circuit comprising a first differentiator configured to output a signal proportional to a change in intensity of light falling on the photodiode. 
     
     
         3 . The system of  claim 2 , the first differentiator comprising:
 a capacitor;   a resistor; and   a field-effect transistor.   
     
     
         4 . The system of  claim 2 , each derivative pixel further comprising a reset FET configured to enable setting a voltage of the photodiode equivalent to a drain voltage of the system. 
     
     
         5 . The system of  claim 2 , each derivative pixel further comprising a buffer electrically disposed between the photodiode and the derivative sensing circuit. 
     
     
         6 . The system of  claim 5 , wherein the buffer comprises:
 a buffer FET; and   a preliminary differentiator configured to output a signal proportional to an intensity of light falling on the photodiode.   
     
     
         7 . The system of  claim 5 , each derivative pixel further comprising a second differentiator configured to output a signal proportional to a change in the change in intensity of light falling on the photodiode, the second differentiator electrically disposed after the first differentiator. 
     
     
         8 . The system of  claim 1 , wherein the array of filtering pixels comprises one or more light source filtering pixels, the filter circuit comprising a sample-and-hold filter and a subtractor. 
     
     
         9 . The system of  claim 8 , the sample-and-hold filter comprising a sample FET and a capacitor, wherein the sample FET is configured to sample an output from the photodiode in accordance with the detected modulated light, and the capacitor stores the sample of the output from the photodiode. 
     
     
         10 . The system of  claim 8 , the filter circuit further comprising a current mirror. 
     
     
         11 . The system of  claim 10 , wherein the current mirror outputs a current proportional to a magnitude of a difference between a voltage of the sample of the output from the photodiode and a voltage of the output of the photodiode. 
     
     
         12 . The system of  claim 8 , wherein a high polarity of the filtering pixel is aligned with an ON state of the modulated light during a frame. 
     
     
         13 . The system of  claim 8 , wherein a high polarity of the filtering pixel is aligned with an ON state of the modulated light for a first half of a frame, and aligned with an OFF state of the modulated light for a second half of the frame. 
     
     
         14 . The system of  claim 8 , wherein the high polarity of the filtering pixel is modulated asynchronously with the modulated light of the light source. 
     
     
         15 . The system of  claim 8 , wherein the filter circuit comprises two sample-and-hold filters, wherein a first sample and hold filter stores a first sample of the output of the photodiode in a first capacitor and a second sample and hold filter stores a second sample of the output of the photodiode in a second capacitor. 
     
     
         16 . The system of  claim 15 , the filter circuit further comprises a current mirror. 
     
     
         17 . The system of  claim 16 , wherein the current mirror outputs a current proportional to the magnitude of a difference between a voltage of the first sample and a voltage of the second sample. 
     
     
         18 . The system of  claim 8 , wherein the filter circuit comprises a plurality of sample and hold filters. 
     
     
         19 . The system of  claim 2 , further comprising:
 a coherent detection component, comprising a laser diode and a prism configured as a band pass filter corresponding to a wavelength of light emitted by the laser diode.   
     
     
         20 . The system of  claim 19 , wherein the laser diode and the light source are the same. 
     
     
         21 . The system of  claim 1 , further comprising an integrator circuit at an output of the filter circuit. 
     
     
         22 . The system of  claim 21 , the integrator comprising a FET and a capacitor. 
     
     
         23 . The system of  claim 1 , wherein the filtering circuit is modulated synchronously with a modulation scheme applied to the light source. 
     
     
         24 . The system of  claim 1 , wherein the filtering circuit is modulated asynchronously with a modulation scheme applied to the light source. 
     
     
         25 . A method of programming a filtering pixel, comprising:
 determining a type of filtering to be performed on a signal outputted from a photodiode of the filtering pixel; and   setting one or more FETs to a particular state based on the determined type of filtering;   wherein the type of filtering includes one of: no filtering; derivative filtering; or sample and hold filtering.   
     
     
         26 . The method of  claim 25 , wherein the type of filtering further comprises: double derivative filtering; multiple derivative filtering; double sample and hold filtering; or multiple sample and hold filtering.