Differential readout from pixels in CMOS sensor

Abstract

The present invention provides an improved pixel readout circuit that compensates for common mode noise during a read out operation. This is accomplished by using a differential readout of the signal and reset value from the desired pixel compared with the reset value from a reference pixel. In this manner common mode noise can be offset and therefore minimized. In one embodiment of the invention, the reference pixel is the nearest neighbor pixel in the same row. In another embodiment, the reference pixel is the nearest neighboring pixel in a different row.

1 - 79 . (canceled) 
     
     
         80 . A method of operating an imaging pixel array of an image sensor, said method comprising:
 sampling a reset and a charge accumulated signal from a desired pixel during a first time interval;   sampling a reset and a comparison signal from a reference pixel during said first time interval, wherein said reference pixel is a desired pixel at a different time interval; and   using said reset and comparison signals from said reference pixel to offset noise from said desired pixel.   
     
     
         81 . The method of  claim 80 , wherein said reset signal from said desired pixel is sampled simultaneously with said reset signal of said reference pixel. 
     
     
         82 . The method of  claim 81 , wherein said charge accumulated signal from said desired pixel is simultaneously sampled with said comparison signal of said reference pixel 
     
     
         83 . The method of  claim 80 , wherein said reference pixel is in a different column from said desired pixel. 
     
     
         84 . The method of  claim 80 , wherein said reference pixel is in the same row as said desired pixel. 
     
     
         85 . The method of  claim 80 , wherein said reference pixel is the nearest neighbor of said desired pixel. 
     
     
         86 . The method of  claim 80 , wherein said reference pixel is in a different row from said desired pixel. 
     
     
         87 . The method of  claim 80 , wherein said reference pixel is in the same column as said desired pixel. 
     
     
         88 . The method of  claim 80 , wherein said reference pixel is the nearest neighbor of said desired pixel. 
     
     
         89 . The method of  claim 84 , wherein said sampling further comprises:
 enabling a reset voltage to charge a respective Node A of said desired and reference pixel;   sampling said Node A of said desired pixel and storing as said reset signal of said desired pixel;   sampling said Node A of said reference pixel and storing as said reset signal of said reference pixel;   enabling a photodiode of said desired pixel to charge Node A of said desired pixel;   sampling said Node A of said desired pixel and storing as said charge accumulated signal of said desired pixel; and   sampling said Node A of said reference pixel and storing as said comparison signal of said reference pixel.   
     
     
         90 . The method of  claim 87 , wherein said sampling further comprises:
 enabling a reset voltage to charge a respective Node A of said desired and reference pixel;   sampling said Node A of said desired pixel and storing as said reset signal of said desired pixel;   sampling said Node A of said reference pixel and storing as said reset signal of said reference pixel;   enabling a photodiode of said desired pixel to charge Node A of said desired pixel;   sampling said Node A of said desired pixel and storing as said charge accumulated signal of said desired pixel; and   sampling said Node A of said reference pixel and storing as said comparison signal of said reference pixel.   
     
     
         91 . The method of  claim 89 , wherein said using further comprises:
 determining a differential signal using said reset signal and charge accumulated signal of said desired pixel and said reset signal and comparison signal of said reference pixel.   
     
     
         92 . The method of  claim 80 , wherein said using further comprises:
 determining a differential signal using said reset signal and charge accumulated signal of said desired pixel and said reset signal and comparison signal of said reference pixel.   
     
     
         93 . The method of  claim 80 , wherein said a desired circuit has a shared floating diffusion node and said reference circuit has a shared floating diffusion node. 
     
     
         94 . An image sensor, comprising:
 a desired pixel for generating a reset and charge accumulation signal during a first time interval;   a reference pixel for generating a reset signal and comparison signal during said first time interval, wherein said reference pixel is a desired pixel at a different time interval;   a circuit for sampling and holding said reset and charge accumulated signals generated by said desired pixel and said reset and comparison signals generated by said reference pixel; and   a combining circuit for generating an output based on combination of said reset and charge accumulated signals generated by said desired pixel and said reset and comparison signals generated by said reference pixel.   
     
     
         95 . The sensor of  claim 94 , wherein said desired pixel is in a same column of said reference pixel. 
     
     
         96 . The sensor of  claim 94 , wherein said desired pixel is the nearest neighbor of said reference pixel. 
     
     
         97 . The sensor of  claim 94 , wherein said desired pixel is in a same row of said reference pixel. 
     
     
         98 . The sensor of  claim 94 , wherein said desired pixel is the nearest neighbor of said reference pixel. 
     
     
         99 . The system of  claim 94 , wherein said desired pixel is in the row below said reference pixel.