Multiple sampling via a time-indexed method to achieve wide dynamic ranges

Abstract

An architecture for a digital pixel sensor is disclosed in which the dynamic range of the sensor is increased by taking samples of a subject to be recorded, where each sample is taken over an interval of a different duration than the other samples. In the preferred embodiment of the invention, an array of pixel elements is fabricated in an integrated circuit that also includes a memory space for storing selectively digital signals of the samples from the digital elements.

We claim:  
     
         1 . An image sensor comprising: 
 a two dimensional array of digital pixel elements producing frames of digital signals when the image sensor is operated to sense a scene, the frames representing sequentially increased exposures to the scene within a snapshot of the scene; and    a data memory space for storing a time index and a threshold value for each of the digital pixel elements, the data memory space further for storing at least one of the digital signals of one of the frames when the corresponding threshold detects that the one of the digital signals is not saturated.    
     
     
         2 . The image sensor of    claim 1   , wherein there are at least two of such frames in the snapshot.  
     
     
         3 . The image sensor of    claim 1   , wherein both the two dimensional array of the digital pixel elements and the data memory space are integrated in a same integrated circuit.  
     
     
         4 . The image sensor of    claim 1   , wherein each of the digital pixel elements includes a photodetector producing an analog signal when the image sensor is operated to sense a scene.  
     
     
         5 . The image sensor of    claim 4   , wherein each of the digital pixel elements is operatively connected to an analog-to-digital conversion circuit that digitizes the analog signal to one of the digital signals.  
     
     
         6 . An image sensor comprising: 
 a two dimensional array of digital pixel elements producing a 1 st , a 2 nd  . . . a N th  frame of digital signals when the image sensor is operated to sense a scene, the 1 st , 2 nd  . . . and N th  frames respectively representing an exposure at a 1 st  sample time, a 2 nd  sample time, . . . and a N th  sample time, wherein the 1 st  sample time, the 2 nd  sample time, . . . and the N th  sample time are within a snapshot of the scene;    a data memory space coupled to the two dimensional array of digital pixel elements;    a readout circuit to readout each of the 1 t , 2 nd  . . . N th  frames respectively to the data memory space; and    wherein the data memory space includes a threshold for each of the digital pixel elements, when one of the digital signals in one of the 1 st , 2 nd  . . . or N th  frames is acceptable with respect to the threshold, the one of the digital signals is read into in the data memory space in association with a time index to indicate which one of the 1 st , 2 nd  . . . or N th  frames.    
     
     
         7 . The image sensor of    claim 6   , wherein the threshold is updated when the one of the digital signals is read into in the data memory space.  
     
     
         8 . The image sensor of    claim 7   , wherein the time index is updated when one of the digital signals from another one of the 1 st , 2 nd  . . . or N th  frames is read into in the data memory space.  
     
     
         9 . The image sensor of    claim 6   , wherein each of the digital pixel elements includes a photodetector that is sensitive to light and produces an analog signal representing the light.  
     
     
         10 . The image sensor of    claim 9   , wherein the photodetector is electronically coupled to an analog-to-digital conversion circuit, and the analog signal from the photodetector is locally converted to one of the digital signals via the analog-to-digital conversion circuit.  
     
     
         11 . The image sensor of    claim 6   , wherein each of the 2 nd  . . . and N th  frames is accumulated in time from a corresponding preceding frame.  
     
     
         12 . The image sensor of    claim 6   , wherein the two dimensional array of digital pixel elements and the data memory space are integrated on a semiconductor core.  
     
     
         13 . The image sensor of    claim 12   , wherein the semiconductor core is based on complementary metal-oxide semiconductor (CMOS).  
     
     
         14 . The image sensor of    claim 6   , wherein N is an integer greater than 2.