Pixel sensor having multiple photodiodes and shared comparator

1. An apparatus comprising:

a first photodiode to generate a first charge in response to incident light;

a second photodiode to generate a second charge in response to the incident light;

a quantizer;

a first memory bank and a second memory bank; and

a controller configured to:

control the quantizer to perform a first quantization operation and a second quantization operation of the first charge to generate, respectively, a first digital output and a second digital output, the first quantization and the second quantization operations being associated with different intensity ranges;

store one of the first digital output or the second digital output in the first memory bank;

control the quantizer to perform a third quantization operation of the second charge to generate a third digital output, the third quantization operation being associated with a different intensity range from at least one of the first quantization operation or the second quantization operation; and

store the third digital output in the second memory bank.

2. The apparatus of claim 1 , wherein the quantizer comprises a comparator; and

wherein the comparator comprises a different type of transistor devices from the first and second photodiodes and from the first and second memory banks.

3. The apparatus of claim 1 , wherein the first photodiode and the second photodiode are formed on a first semiconductor substrate;

wherein the quantizer, the first memory bank, and the second memory bank are formed on a second semiconductor substrate; and

wherein the first semiconductor substrate and the second semiconductor substrate form a stack.

4. The apparatus of claim 1 , further comprising:

a charge sensing unit comprising a capacitor and a buffer, the buffer being coupled with the quantizer;

a first transfer switch coupled between the first photodiode and the capacitor; and

a second transfer switch coupled between the second photodiode and the capacitor;

wherein the controller is configured to:

control the first transfer switch, while disabling the second transfer switch, to transfer first overflow charge of the first charge from the first photodiode to the capacitor to generate a first voltage;

control the quantizer to measure, based on the first voltage, a time of saturation of the capacitor by the first overflow charge as the first digital output;

control the quantizer to measure, based on the first voltage, a quantity of the first overflow charge transferred by the first photodiode as the second digital output;

control the second transfer switch, while disabling the first transfer switch, to transfer second residual charge of the second charge from the second photodiode to the capacitor to generate a second voltage; and

control the quantizer to measure, based on the second voltage, a quantity of the second residual charge transferred by the second photodiode as the third digital output.

5. The apparatus of claim 4 , wherein the quantizer is configured to:

measure the time of saturation based on comparing the first voltage against a static threshold to generate a first decision;

measure the quantity of the first overflow charge transferred by the first photodiode based on comparing the first voltage against a first voltage ramp to generate a second decision; and

measure the quantity of the second residual charge transferred by the second photodiode based on comparing the second voltage against a second voltage ramp to generate a third decision;

and wherein the controller is configured to:

forward the first decision and the second decision to the first memory bank to control a first time when the first memory bank stores a count value from a counter as the first digital output or the second digital output; and

forward the third decision to the second memory bank to control a second time when the second memory bank stores a count value from the counter as the third digital output.

6. The apparatus of claim 4 , wherein the controller is configured to:

control the first transfer switch to transfer first residual charge of the first charge to the capacitor to generate a third voltage;

control the quantizer to measure, based on the third voltage, a quantity of the first residual charge transferred by the first photodiode as a fourth digital output; and

store one of the first, second, or fourth digital outputs in the first memory bank.

7. The apparatus of claim 6 , wherein the capacitor comprise a primary capacitor and an auxiliary capacitor;

wherein the first overflow charge is stored in a parallel combination of the primary capacitor and the auxiliary capacitor; and

wherein the first residual charge and the second residual charge are stored in the primary capacitor but not in the auxiliary capacitor.

8. The apparatus of claim 1 , further comprising:

a first charge sensing unit comprising a first capacitor and a first buffer, the first buffer being coupled with the quantizer;

a second charge sensing unit comprising a second capacitor and a second buffer, the second buffer being coupled with the quantizer;

a first transfer switch coupled between the first photodiode and the first capacitor; and

a second transfer switch coupled between the second photodiode and the second capacitor;

wherein the controller is configured to:

control the first transfer switch to transfer first overflow charge of the first charge from the first photodiode to the first capacitor to generate a first voltage;

control the second transfer switch to transfer second overflow charge of the second charge from the second photodiode, after the second photodiode saturates, to the second capacitor to generate a second voltage;

control the quantizer to measure, based on the first voltage, a time of saturation of the first capacitor by the first overflow charge as the first digital output;

control the quantizer to measure, based on the first voltage, a quantity of the first overflow charge transferred by the first photodiode as the second digital output; and

control the quantizer to measure, based on the second voltage, a quantity of the second overflow charge transferred by the second photodiode as the third digital output.

9. The apparatus of claim 8 , wherein the quantizer is configured to:

measure the time of saturation based on comparing the first voltage against a static threshold to generate a first decision;

measure the quantity of the first overflow charge transferred by the first photodiode based on comparing the first voltage against a first voltage ramp to generate a second decision; and

measure the quantity of the second overflow charge transferred by the second photodiode based on comparing the second voltage against a second voltage ramp to generate a third decision;

and wherein the controller is configured to:

forward the first decision and the second decision to the first memory bank to control a first time when the first memory bank stores a count value from a counter as the first digital output or the second digital output; and

forward the third decision to the second memory bank to control a second time when the second memory bank stores a count value from the counter as the third digital output.

10. The apparatus of claim 8 , wherein the controller is configured to:

control the first transfer switch to transfer first residual charge of the first charge to the first capacitor to generate a third voltage;

control the quantizer to measure, based on the third voltage, a quantity of the first residual charge transferred by the first photodiode as a fourth digital output;

control the second transfer switch to transfer second residual charge of the second charge to the second capacitor to generate a fourth voltage;

control the quantizer to measure, based on the fourth voltage, a quantity of the second residual charge transferred by the second photodiode as a fifth digital output;

store one of the first, second, or fourth digital outputs in the first memory bank; and

store one of the third or fifth digital outputs in the second memory bank.

11. The apparatus of claim 1 , further comprising:

a first group of photodiodes including the first photodiode and a third photodiode, the third photodiode configured to generate a third charge; and

a second group of photodiodes including the second photodiode and a fourth photodiode, the fourth photodiode configured to generate a fourth charge;

wherein the controller is configured to:

control the quantizer to quantize the third charge to generate a fourth digital output;

control the quantizer to quantize the fourth charge to generate a fifth digital output;

at a first time:

store one of the first digital output or the second digital output in the first memory bank, and

store the third digital output in the second memory bank;

and at a second time:

store the fourth digital output in the first memory bank, and

store the fifth digital output in the second memory bank.

12. The apparatus of claim 11 , wherein the first photodiode and the second photodiode are configured to detect visible light components of incident light and to generate, respectively, the first charge and the second charge within a first exposure period; and

wherein the third photodiode and the fourth photodiode are configured to detect an infra-red light component of the incident light and to generate, respectively, the third charge and the fourth charge within a second exposure period.

13. The apparatus of claim 11 , wherein the first group of photodiodes includes the first photodiode, the third photodiode, a fifth photodiode, and a sixth photodiode, the fifth photodiode configured to generate a fifth charge and the sixth photodiode configured to generate a sixth charge;

wherein the apparatus further includes a third memory bank and a fourth memory bank; and

wherein the controller is configured to:

control the quantizer to quantize the fifth charge to generate a sixth digital output;

control the quantizer to quantize the sixth charge to generate a seventh digital output;

store one of the first digital output or the second digital output in the first memory bank;

store the sixth digital output in the third memory bank; and

store the seventh digital output in the fourth memory bank.

14. The apparatus of claim 11 , wherein the first group of photodiodes and the second group of photodiodes are part of different pixel cells.

15. The apparatus of claim 1 , further comprising a third memory bank;

wherein the controller is configured to:

quantize, at a first time, the first charge to generate the second digital output;

quantize, at a second time, the first charge to generate a fourth digital output;

store the second digital output in the first memory bank; and

store the fourth digital output in the third memory bank.

16. The apparatus of claim 1 , further comprising a third photodiode to generate a third charge in response to incident light,

wherein the controller is configured to control the quantizer to perform the first quantization operation and the second quantization operation of a combination of the first charge and the third charge to generate, respectively, a first digital output and a second digital output, the first quantization and the second quantization operations being associated with different intensity ranges.

17. The apparatus of claim 16 , wherein the first photodiode and the third photodiode are configured to detect same component of the incident light.

18. A method comprising:

enabling a first photodiode to generate a first charge in response to incident light;

enabling a second photodiode to generate a second charge in response to the incident light;

controlling a quantizer to perform a first quantization operation and a second quantization operation of the first charge to generate, respectively, a first digital output and a second digital output, the first quantization and the second quantization operations being associated with different intensity ranges;

storing one of the first digital output or the second digital output in a first memory bank;

controlling the quantizer to perform a third quantization operation of the second charge to generate a third digital output, the third quantization operation being associated with a different intensity range from at least one of the first quantization operation or the second quantization operation; and

storing the third digital output in a second memory bank.

19. The method of claim 18 , further comprising:

transferring first overflow charge of the first charge from the first photodiode, after the first photodiode saturates, to a capacitor to generate a first voltage;

controlling the quantizer to measure, based on the first voltage, a time of saturation of the capacitor by the first overflow charge as the first digital output;

controlling the quantizer to measure, based on the first voltage, a quantity of the first overflow charge transferred by the first photodiode as the second digital output;

transferring second residual charge of the second charge from the second photodiode to the capacitor to generate a second voltage; and

controlling the quantizer to measure, based on the second voltage, a quantity of the second residual charge transferred by the second photodiode as the third digital output.

20. The method of claim 18 , wherein the first photodiode and the second photodiode generate, respectively, the first charge and the second charge in response to different components of the incident light.