Ultra-high dynamic range two photodiode pixel architecture

1. An ultra-high dynamic range two-photodiode pixel consisting of a first photodiode and a second photodiode said pixel further comprising:

wherein said first photodiode is a high-response photodiode having a higher quantum efficiency than said second photodiode;

a first transfer gate in electrical contact with said first photodiode;

wherein said second photodiode is a low-response photodiode having a lower quantum efficiency than said first photodiode, and is in electrical contact with said first transfer gate;

a second transfer gate in electrical contact with said second photodiode;

a floating diffusion in electrical contact with said second transfer gate;

a means of resetting said floating diffusion; and

a source-follower in electrical contact with said floating diffusion.

2. The device of claim 1 , wherein said high-response photodiode collects photocharge and said high-response photodiode has a higher quantum efficiency than said low-response photodiode.

3. The device of claim 1 , wherein said first transfer gate enables a charge to be transferred off said high-response photodiode, completely emptying it onto said low-response photodiode.

4. The device of claim 1 , wherein said second transfer gate enables a charge to be transferred off said low-response photodiode, completely emptying it onto said floating diffusion.

5. The device of claim 1 , wherein said floating diffusion collects a transferred charge creating a change of voltage.

6. The device of claim 1 , wherein said source-follower is modulated by a voltage on said floating diffusion to control a voltage on an output signal line.

7. The device of claim 1 , wherein a photocharge is integrated onto both said high-response photodiode and onto said low-response photodiode.

8. The device of claim 1 , wherein said low-response photodiode is an isolated diode without contacts to interconnect layers, thereby including lower dark defects.

9. The device of claim 1 , further comprising a third transfer gate in electrical contact with said high-response photodiode.

10. A method for reading out an ultra-high dynamic range two-photodiode pixel comprising the steps of:

integrating one frame;

integrating a high-response photocharge onto a high-response photodiode;

integrating a low-response photocharge onto a low-response photodiode;

resetting a floating diffusion;

resetting a column amplifier to create a reference voltage;

capturing said reference voltage with a switch S 1 ;

transferring a low-response charge from said low-response photodiode to said floating diffusion;

capturing a low-response signal voltage V 2 with a switch S 2 ;

transferring a high-response charge from said high-response photodiode through said low-response photodiode to said floating diffusion;

adding a charge to said low-response charge already present;

capturing a high-response signal voltage V 3 with a switch S 3 ;

said switch S 3 going low;

enabling a comparator by setting a comparator input Comp_en high;

in said comparator, if said voltage V 2 is higher than a threshold voltage V T , then sel is high and sel complement is low, and then a combined reset V outm , said sel, and output V outp , which is substantially equal to said voltage V 2 , are read out; and

in said comparator, if said voltage V 2 is lower than said threshold voltage V T , then said sel is low and said sel complement is high, and then said combined reset V outm , said sel, and said output V outp , which is substantially equal to said voltage V 3 , are read out.

11. The method of claim 10 wherein said sel comparator output and said sel complement comparator output are non-overlap signals, thereby avoiding charge sharing between capacitors C 2 and C 3 , wherein said capacitor C 2 corresponds to said sel comparator output, said voltage V 2 , and said switch S 2 , and said capacitor C 3 corresponds to said sel complement comparator output, said voltage V 3 , and said switch S 3 .

12. The method of claim 10 wherein said threshold voltage V T is adjusted to get an optimized dynamic range.

13. The method of claim 10 wherein a signal for a low end of an optical response is a difference of said high-response signal voltage V 3 and said combined reset V outm .

14. The method of claim 10 wherein a signal for a high end of an optical response is a difference of said low-response signal voltage V 2 and said combined reset V outm .

15. The method of claim 10 wherein a signal for a low end of an optical response and a signal for a high end of an optical response have significantly different responses because said high-response photodiode has a higher quantum efficiency than said low-response photodiode.

16. The method of claim 10 , wherein a line readout requires only three readouts of:

said combined reset V outm , said low-response readout V 2 , and said high-response readout V 3 .

17. The method of claim 10 , wherein a first transfer gate enables said high-response charge to be transferred off said high-response photodiode, completely emptying it onto said low-response photodiode.

18. The method of claim 10 , wherein a second transfer gate enables said low-response charge to be transferred off said low-response photodiode completely emptying it onto said floating diffusion.

19. The method of claim 10 , wherein both low-response readout and high-response readout have a same polarity.

20. An ultra-high dynamic range two-photodiode pixel imaging system comprising:

a high-response photodiode;

a first transfer gate in electrical contact with said high-response photodiode;

a low-response photodiode in electrical contact with said first transfer gate;

a second transfer gate in electrical contact with said low-response photodiode;

a floating diffusion in electrical contact with said second transfer gate;

a means of resetting said floating diffusion;

a source-follower in electrical contact with said floating diffusion;

integrating a high-response photocharge onto said high-response photodiode;

integrating a low-response photocharge onto said low-response photodiode, wherein amounts of said high response charge and said low response charge integrated onto said high-response and said low-response photodiodes are different;

resetting said floating diffusion;

resetting a column amplifier to create a reference voltage;

capturing said reference voltage with a switch S 1 ;

transferring a low-response charge from said low-response photodiode to said floating diffusion;

capturing a low-response signal voltage V 2 with a switch S 2 ;

transferring a high-response charge from said high-response photodiode through said low-response photodiode to said floating diffusion;

adding a charge to said low-response charge already present;

capturing a high-response signal voltage V 3 with a switch S 3 ;

said switch S 3 going low;

enabling a comparator by setting a comparator input Comp_en high;

in said comparator, if said voltage V 2 is higher than a threshold voltage V T , then sel is high and sel complement is low, and then a combined reset V outm , said sel, and output V outp , which is substantially equal to said voltage V 2 , are read out; and

in said comparator, if said voltage V 2 is lower than said threshold voltage V T , then said sel is low and said sel complement is high, and then said combined reset V outm , said sel, and said output V outp , which is substantially equal to said voltage V 3 , are read out.

21. The device of claim 1 , wherein the high-response photodiode and the low-response photodiode are proximate each other and at substantially the same depth.

22. The device of claim 1 , wherein the high-response photodiode and the low-response photodiode are different sizes.

23. The device of claim 1 , wherein the high-response photodiode and the low-response photodiode extend a dynamic range but do not perform color separation.