Analog-to-digital converter calibration systems and methods

1. A method comprising:

for each time instance of a plurality of time instances:

generating a first ramp signal started at the time instance relative to a respective start of a first counter signal;

generating a respective first comparator output signal based on the first ramp signal and a first threshold signal, wherein the respective first comparator output signal is associated with a first state or a second state;

capturing a respective first value of the first ramp signal in response to a transition of the respective first comparator output signal from the first state to the second state; and

determining a respective second counter value of a second counter signal based on the respective first value; and

determining a scaling factor based on the second counter values and the plurality of time instances, wherein each of the first values is associated with the same first counter value of the first counter signal.

2. The method of claim 1 , further comprising for each time instance of the plurality of time instances:

generating a respective second ramp signal based on the respective first value; and

generating a respective second comparator output signal based on the respective second ramp signal and a second threshold signal, wherein the respective second comparator output signal is associated with a third state or a fourth state,

wherein, for each time instance of the plurality of time instances, the determining the respective second counter value comprises capturing the respective second counter value in response to a transition of the respective second comparator output signal from the third state to the fourth state.

3. The method of claim 1 , further comprising determining a best fitting curve based on the second counter values and the plurality of time instances, wherein the scaling factor is based on the best fitting curve.

4. The method of claim 1 , wherein the first counter signal is associated with a first clock, and wherein the second counter signal is associated with a second clock having a faster clock speed than the first clock.

5. The method of claim 4 , wherein the scaling factor is further based on the first clock and the second clock.

6. The method of claim 5 , wherein the scaling factor is based on a ratio of a clock speed of the first clock to a clock speed of the second clock.

7. The method of claim 1 , wherein for at least one time instance of the plurality of time instances:

the first comparator output signal transitions from the first state to the second state between a start of a first clock cycle and a start of a second clock cycle temporally adjacent to the first clock cycle,

the respective first value is indicative of a value of the first ramp signal at the start of the second clock cycle, and

the first counter value is associated with the second clock cycle.

8. The method of claim 1 , further comprising:

receiving a detector signal; and

determining a digital representation of the detector signal based on the scaling factor.

9. The method of claim 8 , wherein the digital representation comprises a coarse count value associated with the first counter signal and a fine count value associated with the second counter signal, the method further comprising:

applying the scaling factor to the coarse count value to obtain a scaled coarse count value; and

generating a total count value associated with the detector signal based on a sum of the scaled coarse count value and the fine count value.

10. The method of claim 8 , further comprising:

generating a third ramp signal and a third counter signal synchronous with the third ramp signal;

generating a second comparator output signal based on the third ramp signal and the first threshold signal;

capturing a third count value of the third count signal in response to a transition of the second comparator output signal;

generating a fourth ramp signal and a fourth counter signal synchronous with the fourth ramp signal;

generating a third comparator output signal based on the fourth ramp signal and a second threshold signal;

capturing a fourth count value of the fourth counter signal in response to a transition of the third comparator output signal; and

applying the scaling factor to one of the third count value or the fourth count value, wherein the digital representation is based on the third count value, the fourth count value, and the scaling factor.

11. A system comprising:

an analog-to-digital converter (ADC) configured to:

for each time instance of a plurality of time instances:

generate a first ramp signal started at the time instance relative to a respective start of a first counter signal;

generate a respective first comparator output signal based on the first ramp signal and a first threshold signal, wherein the respective first comparator output signal is associated with a first state or a second state;

capture a respective first value of the first ramp signal in response to a transition of the respective first comparator output signal from the first state to the second state; and

determine a respective second counter value of a second counter signal based on the respective first value; and

a logic device configured to determine a scaling factor based on the second counter values and the plurality of time instances, wherein each of the first values is associated with the same first counter value of the first counter signal.

12. The system of claim 11 , wherein:

the ADC is further configured to:

generate a respective second ramp signal based on the respective first value; and

generate a respective second comparator output signal based on the respective second ramp signal and a second threshold signal, wherein the respective second comparator output signal is associated with a third state or a fourth state; and

for each time instance of the plurality of time instances, the ADC is configured to determine the respective second counter value by capturing the respective second counter value in response to a transition of the respective second comparator output signal from the third state to the fourth state.

13. The system of claim 11 , wherein the logic device is further configured to determine a best fitting curve based on the second counter values and the plurality of time instances, and wherein the scaling factor is based on the best fitting curve.

14. The system of claim 11 , further comprising a clock generator circuit configured to generate a first clock and a second clock, wherein the second clock has a faster clock speed than the first clock, wherein the first counter signal is associated with the first clock, and wherein the second counter signal is associated with the second clock.

15. The system of claim 14 , wherein the scaling factor is further based on the first clock and the second clock.

16. The system of claim 11 , wherein for at least one time instance of the plurality of time instances:

the first comparator output signal transitions from the first state to the second state between a start of a first clock cycle and a start of a second clock cycle temporally adjacent to the first clock cycle,

the respective first value is indicative of a value of the first ramp signal at the start of the second clock cycle, and

the first counter value is associated with the second clock cycle.

17. The system of claim 16 , wherein a third counter value is associated with the first clock cycle, and wherein the first counter value and the third counter value are consecutive integers.

18. The system of claim 11 , further comprising an image sensor device configured to receive electromagnetic radiation and generate a detector signal based on the electromagnetic radiation, wherein the logic device is further configured to determine a digital representation of the detector signal based on the scaling factor.

19. The system of claim 18 , wherein the digital representation comprises a coarse count value associated with the first counter signal and a fine count value associated with the second counter signal, and wherein the logic device is further configured to:

apply the scaling factor to the coarse count value to obtain a scaled coarse count value; and

generate a total count value associated with the detector signal based on a sum of the scaled coarse count value and the fine count value.

20. The system of claim 18 , wherein the scaling factor is associated with a column of detectors of the image sensor device.