Pinned photodiode pixels including current mirror-based background light suppression, and imaging devices including the same
An imaging device includes a focal plane array of demodulation pixel cells. Each of the demodulation pixel cells includes a pinned photodiode, demodulation gates operable to demodulate optical signals sensed by the pinned photodiode and to transfer accumulated photo-charges to a respective one of a multitude of sense nodes, a readout circuit operable selectively to read out signals from the sense nodes, and a background light suppression circuit including cross-coupled current mirrors.
1. An imaging device comprising a focal plane array of demodulation pixel cells, each of the demodulation pixel cells comprising:
a pinned photodiode;
demodulation gates operable to demodulate optical signals sensed by the pinned photodiode and to transfer accumulated photo-charges to a respective one of a plurality of sense nodes;
a readout circuit operable selectively to read out signals from the sense nodes; and
a background light suppression circuit including a plurality of cross-coupled current mirrors.
2. The imaging device of claim 1 wherein the background light suppression circuit is operable to provide background light suppression based on direct common mode compensation in current domain.
3. The imaging device of claim 1 wherein the current mirrors are operable to compensate for common mode current resulting from background light.
4. The imaging device of claim 1 wherein the current mirrors include current mirror transistors, and wherein a power supply for a well of the current mirror transistors is separate from a main power supply.
5. The imaging device of claim 1 wherein each one of the demodulation pixel cells further included circuitry operable to apply time domain current mirror chopping.
6. The imaging device of claim 5 wherein the circuitry operable to apply time domain current mirror chopping includes a cross-coupled chopping current mirror circuit.
7. The imaging device of claim 5 wherein the cross-coupled chopping current mirror circuit is operable to apply time domain chopping to drains of transistors in the cross-coupled current mirrors.
8. The imaging device of claim 5 wherein the cross-coupled chopping current mirror circuit is operable to apply time domain chopping to gates of transistors in the cross-coupled current mirrors.
9. The imaging device of claim 5 wherein each one of the demodulation pixel cells further includes a charge exchange switch coupled to gates of transistors in the cross-coupled current mirrors.
10. The imaging device of claim 9 wherein the charge exchange switch is operable to be controlled by a clock signal different from clock signals that control switches of the circuitry operable to apply the time domain current mirror chopping.
11. The imaging device of claim 5 wherein the cross-coupled chopping current mirror circuit is operable to apply time domain chopping to drains and gates of transistors in the cross-coupled current mirrors.
12. The imaging device of claim 11 wherein the cross-coupled chopping current mirror circuit includes a plurality of switches each of which is operable to respond, respectively, either to first or second clock signals that are phase-inverted with respect to one another.
13. The imaging device of claim 12 wherein each one of the demodulation pixel cells further includes a charge exchange switch coupled to the gates of the transistors in the cross-coupled current mirrors.
14. The imaging device of claim 13 wherein the charge exchange switch is controlled by a third clock signal different from the first and second clock signals.
15. The imaging device of claim 1 wherein the readout circuit includes an output circuit coupled to the sense nodes and having a capacitance, each one of the demodulation pixel cells further being operable to alternate, from one integration period to the next, a phase of signals applied to the demodulation gates, and operable to change a polarity of connections for the capacitance.
16. The imaging device of claim 15 wherein each one of the demodulation pixel cells further includes a charge exchange switch coupled to the gates of transistors in the cross-coupled current mirrors.
17. The imaging device of claim 1 operable such that photocurrent generated as a result of background light is split substantially evenly between the current mirrors.
18. A demodulation pixel cell comprising:
a pinned photodiode;
demodulation gates operable to demodulate optical signals sensed by the pinned photodiode and to transfer accumulated photo-charges to a respective one of a plurality of sense nodes;
a readout circuit operable to read out signals from the sense nodes; and
a background light suppression circuit including a plurality of cross-coupled current mirrors.
19. The demodulation pixel cell of claim 18 wherein the current mirrors are operable to compensate for common mode current resulting from background light.
20. The demodulation pixel cell of claim 18 including circuitry operable to apply time domain current mirror chopping.