Differential pixel circuit and method of computer vision applications

1. A pixel cell, comprising:

four photodiodes; and

four storage diodes;

wherein each storage diode is disposed between a first adjacent photodiode and a second adjacent photodiode, and each storage diode is configured to receive photo charges from either or both of the first adjacent photodiode and the second adjacent photodiode;

wherein each photodiode is disposed between a first adjacent storage diode and a second adjacent storage diode, and each photodiode is configured to transfer photo charges to either or both of the first adjacent storage diode and the second adjacent storage diode; and

wherein the four photodiodes are arranged in a 2 by 2 array, with each storage diode disposed between two adjacent photodiodes.

2. The pixel cell of claim 1 , further comprising a transfer gate between each pair of adjacent photodiode and storage diode.

3. The pixel cell of claim 1 , further comprising a charge control gate overlying each storage diode.

4. The pixel cell of claim 1 , further comprising four floating diffusion regions, each floating diffusion regions disposed adjacent to a corresponding storage diode.

5. The pixel cell of claim 4 , further comprising a transfer gate between each pair of adjacent storage diode and floating diffusion region.

6. The pixel cell of claim 1 , further comprising a global shutter control gate associated with each photodiode for draining the charges in the photodiode.

7. An image sensor device, comprising a plurality of pixel cells of claim 1 arranged in a pixel array.

8. A method for operating a pixel cell, the method comprising:

exposing a pixel cell to a light during an exposure time window, the pixel cell including four photodiodes and four storage diodes;

wherein each storage diode is disposed between two adjacent photodiodes in the pixel cell, and each storage diode is configured to receive photo charges from either or both of the two adjacent photodiodes;

wherein each photodiode is disposed between two adjacent storage diodes in the pixel cell, and each photodiode is configured to transfer photo charges to either or both of the two adjacent storage diodes; and

wherein each pair of adjacent photodiodes has a storage diode disposed therebetween.

9. The method of claim 8 , further comprising:

during a first time period,

transferring collected photo charges from a first pair of photodiodes to a first storage diode disposed between the first pair of photodiodes; and

transferring collected photo charges from a second pair of photodiodes to a second storage diode disposed between the second pair of photodiodes;

during a second time period,

transferring collected photo charges from a third pair of photodiodes to a third storage diode disposed between the third pair of photodiodes; and

transferring collected photo charges from a fourth pair of photodiodes to a fourth storage diode disposed between the fourth pair of photodiodes; and

producing a differential signal by:

providing a sum of the photo charges from the first storage diode and the second storage diode to a first input of a differential amplifier; and

providing a sum of the photo charges from the third storage diode and the fourth storage diode to a second input of the differential amplifier.

10. The method of claim 9 , further comprising:

transferring photo charges from the first storage diode and the second storage diode to a first floating diffusion region;

transferring photo charges from the first storage diode and the second storage diode to a second floating diffusion region;

transferring photo charges from the first floating diffusion region to a first sample-and-hold capacitor;

transferring photo charges from the second floating diffusion region to a second sample-and-hold capacitor; and

transferring signals from the first and second sample-and-hold capacitors to the differential amplifier.

11. The method of claim 9 , wherein;

the first pair of photodiodes and the second pair of photodiodes have no photodiode in common; and

the third pair of photodiodes and the fourth pair of photodiodes have no photodiode in common.

12. The method of claim 8 , further comprising:

transferring collected photo charges in a first pair of adjacent photodiodes to a first storage diode;

transferring collected photo charges in a second pair of adjacent photodiodes to a second storage diode; and

sensing photo charges in the first storage diode and the second storage diode to provide two sensed signals for binning.

13. The method of claim 8 , further comprising:

transferring collected photo charges in each photodiode to a respective adjacent storage diode; and

sensing photo charges in each storage diode to provide sensed signals for four sub-pixels.

14. The method of claim 8 , wherein the four photodiodes are arranged in a 2 by 2 array, with each storage diode disposed between two adjacent photodiodes.

15. A pixel cell for differential light sensing, comprising:

a plurality of photodiodes;

a corresponding plurality of storage diodes; and

a corresponding plurality of floating diffusion regions, each floating diffusion region disposed adjacent to a corresponding storage diode;

wherein each storage diode is disposed between a first adjacent photodiode and a second adjacent photodiode, and each storage diode is configured to receive photo charges from either or both of the first adjacent photodiode and the second adjacent photodiode; and

wherein each photodiode is disposed between a first adjacent storage diode and a second adjacent storage diode, and each photodiode is configured to transfer photo charges to either or both of the first adjacent storage diode and the second adjacent storage diode.

16. An image sensing device, comprising:

a plurality of pixel cells arranged in a pixel array, wherein each pixel cell includes four photodiodes, four storage diodes, and four floating diffusion regions, wherein:

each storage diode is disposed between a first adjacent photodiode and a second adjacent photodiode, and each storage diode is configured to receive photo charges from either or both of the first adjacent photodiode and the second adjacent photodiode;

each photodiode is disposed between a first adjacent storage diode and a second adjacent storage diode, and each photodiode is configured to transfer photo charges to either or both of the first adjacent storage diode and the second adjacent storage diode; and

each floating diffusion region is disposed adjacent to a corresponding storage diode;

a first summing device for receiving photo charges from a second floating diffusion region and a fourth floating diffusion region;

a second summing device for receiving photo charges from a first floating diffusion region and a third floating diffusion region;

a differential amplifier coupled to the first and second summing devices; and

a control circuit for controlling charge transfer in the image sensing device.

17. The image sensing device of claim 16 , wherein the control circuit is configured for:

exposing a pixel cell to a light during an exposure time window;

during a first time period,

transferring collected photo charges from a first pair of photodiodes to a first storage diode disposed between the first pair of photodiodes; and

transferring collected photo charges from a second pair of photodiodes to a second storage diode disposed between the second pair of photodiodes;

during a second time period,

transferring collected photo charges from a third pair of photodiodes to a third storage diode disposed between the third pair of photodiodes; and

transferring collected photo charges from a fourth pair of photodiodes to a fourth storage diode disposed between the fourth pair of photodiodes; and

producing a differential signal by:

providing a sum of the photo charges from the second storage diode and the fourth storage diode to a first input of the differential amplifier; and

providing a sum of the photo charges from the first storage diode and the third storage diode to a second input of the differential amplifier.

18. The image sensing device of claim 16 , wherein the control circuit is configured for:

exposing a pixel cell to a light during an exposure time window;

transferring collected photo charges in a first pair of adjacent photodiodes to a first storage diode;

transferring collected photo charges in a second pair of adjacent photodiode to a second storage diode; and

sensing photo charges in the first storage diode and the second storage diode to provide two sensed signals for binning.

19. The image sensing device of claim 16 , wherein the control circuit is configured for:

exposing a pixel cell to a light during an exposure time window;

transferring collected photo charges in each photodiode to a corresponding adjacent storage diode; and

sensing photo charges in each storage diode to provide sensed signals for four sub-pixels.