Adaptive gain control using sample-and-hold circuit for analog CDS
An image processing circuit includes a first sample-and-hold circuit that samples a first data from a pixel, a second sample-and-hold circuit that samples a second data from the pixel, a voltage-to-current circuit that includes a resistor and a current source and receives the first and second data to output a difference data, an adaptive gain control determination circuit that determines whether a rate of change of a signal from the pixel exceeds a threshold based on an output of the second sample-and-hold circuit, and a current-mode ADC that converts the difference data from an analog form to a digital form.
1. An image processing circuit, comprising:
a first sample-and-hold circuit configured to sample a first data from a pixel;
a second sample-and-hold circuit configured to sample a second data from the pixel;
a voltage-to-current circuit including a resistor and a current source, and configured to receive the first data and the second data and output a difference data;
an adaptive gain control determination circuit configured to determine whether a rate of change of a signal from the pixel exceeds a first predetermined threshold based on an output of the second sample-and-hold circuit; and
a current-mode analog-to-digital converter configured to convert the difference data from an analog form to a digital form.
2. The image processing circuit according to claim 1 , wherein
in a case where the rate of change of the signal exceeds the first predetermined threshold, the adaptive gain control determination circuit is configured to determine that a first analog gain is to be applied, and
in a case where the rate of change of the signal does not exceed the first predetermined threshold, the adaptive gain control determination circuit is configured to determine that a second analog gain is to be applied.
3. The image processing circuit according to claim 2 , wherein the resistor is a variable resistor, and the adaptive gain control determination circuit is configured to set a resistance of the resistor to a first value in a case that the first analog gain is to be applied, and to a second value in a case where the second analog gain is to be applied.
4. The image processing circuit according to claim 2 , wherein the first analog gain is a gain of 1, and the second analog gain is a gain of G, where G>1.
5. The image processing circuit according to claim 4 , wherein the first predetermined threshold is a dynamic range of the pixel divided by G.
6. The image processing circuit according to claim 1 , wherein the second sample-and-hold circuit includes a switched capacitor comparator circuit and a threshold shifter circuit configured to shift a threshold of the switched capacitor comparator circuit.
7. The image processing circuit according to claim 1 , further comprising:
a black sun spot determination circuit configured to determine whether the rate of change of the signal from the pixel exceeds a second predetermined threshold based on the output of the second sample-and hold circuit at a timing different from a timing of the adaptive gain control determination circuit.
8. The image processing circuit according to claim 7 , wherein the second sample-and-hold circuit includes a switched capacitor comparator circuit, a first threshold shifter circuit configured to shift a threshold of the switched capacitor comparator circuit, and a second threshold shifter circuit configured to shift the threshold of the switched capacitor comparator circuit.
9. The image processing circuit according to claim 8 , wherein the first threshold shifter circuit and the second threshold shifter circuit are connected in series.
10. A method of processing an image, comprising:
sampling a first data from a pixel by a first sample-and-hold circuit;
sampling a second data from the pixel by a second sample-and-hold circuit;
receiving the first data and the second data by a voltage-to-current circuit including a resistor and a current source;
outputting a difference data by the voltage-to-current circuit;
determining whether a rate of change of a signal from the pixel exceeds a predetermined threshold by an adaptive gain control determination circuit based on an output of the second sample-and-hold circuit; and
converting the difference data from an analog form to a digital form by a current-mode analog-to-digital converter.
11. The method according to claim 10 , wherein the determining comprises:
determining that a first analog gain is to be applied in a case where the rate of change of the signal exceeds the first predetermined threshold, and
determining that a second analog gain is to be applied in a case where the rate of change of the signal does not exceed the first predetermined threshold.
12. The method according to claim 11 , wherein the resistor is a variable resistor, the method further comprising:
setting a resistance of the resistor to a first value by the adaptive gain control determination circuit, in a case that the first analog gain is to be applied, and
setting the resistance of the resistor to a second value by the adaptive gain control determination circuit, in a case where the second analog gain is to be applied.
13. The method according to claim 11 , wherein the first analog gain is a gain of 1, and the second analog gain is a gain of G, where G>1.
14. The method according to claim 13 , wherein the first predetermined threshold is a dynamic range of the pixel divided by G.
15. The method according to claim 10 , wherein the second sample-and-hold circuit includes a switched capacitor comparator circuit and a threshold shifter circuit configured to shift a threshold of the switched capacitor comparator circuit.
16. The method according to claim 10 , further comprising:
determining whether the rate of change of the signal from the pixel exceeds a second predetermined threshold by a black sun spot determination circuit based on the output of the second sample-and hold circuit at a timing different from a timing of the adaptive gain control determination circuit.
17. The method according to claim 16 , wherein the second sample-and-hold circuit includes a switched capacitor comparator circuit, a first threshold shifter circuit configured to shift a threshold of the switched capacitor comparator circuit, and a second threshold shifter circuit configured to shift the threshold of the switched capacitor comparator circuit.
18. The method according to claim 17 , wherein the first threshold shifter circuit and the second threshold shifter circuit are connected in series.
19. An imaging device, comprising:
a pixel including a photoelectric conversion device configured to convert an incident light into an analog signal; and
an image processing circuit, including:
a first sample-and-hold circuit configured to sample a first data from the pixel,
a second sample-and-hold circuit configured to sample a second data from the pixel,
a voltage-to-current circuit including a resistor and a current source, and configured to receive the first data and the second data and output a difference data,
an adaptive gain control determination circuit configured to determine whether a rate of change of the analog signal from the pixel exceeds a predetermined threshold based on an output of the second sample-and-hold circuit, and
a current-mode analog-to-digital converter configured to convert the difference data from an analog form to a digital form.
20. The imaging device according to claim 19 , wherein
in a case where the rate of change of the signal exceeds the first predetermined threshold, the adaptive gain control determination circuit is configured to determine that a first analog gain is to be applied, and
in a case where the rate of change of the signal does not exceed the first predetermined threshold, the adaptive gain control determination circuit is configured to determine that a second analog gain is to be applied.