Image sensors with reduced peak power
An image sensor may include a pixel array having pixels arranged in rows and columns, column readout circuitry, and control circuitry. Column readout circuitry may include corresponding readout circuits each coupled to a corresponding column path for a respective column of pixels. The readout circuits may each include signal processing circuits such as correlated double sampling circuitry and analog-to-digital converter circuitry. To reduce peak-to-average power ratio, during the signal processing operations for each pixel row, the control circuitry may control the signal processing circuits to perform time-domain multiplexing across the pixel columns to activate the signal processing circuits at varied times within the row time. If desired, the pattern of time-domain multiplexing may be varied across the signal processing operations for different pixel rows and/or for different image frames.
1. An image sensor comprising:
image sensor pixels arranged in columns and rows;
a plurality of readout circuits each coupled to a corresponding column of the image sensor pixels, the plurality of readout circuits being configured to perform readout operations during a row time; and
control circuitry configured to control the plurality of readout circuits to perform time-domain multiplexing for the readout operations across the plurality of readout circuits by activating the plurality of readout circuits during at least first and second offset time periods within the row time.
2. The image sensor defined in claim 1 , wherein the readout operations occur across the row time in a linear manner.
3. The image sensor defined in claim 1 , wherein the readout operations occur across the row time in a non-linear manner.
4. The image sensor defined in claim 1 , wherein the plurality of readout circuits each comprises analog-to-digital converter circuitry, and the readout operations comprise analog-to-digital conversion operations.
5. The image sensor defined in claim 4 , wherein each of the plurality of readout circuits is operable in a pipelined mode of operation, and the readout operations comprise sampling operations performed partly in parallel with or partly offset from the analog-to-digital conversion operations.
6. The image sensor defined in claim 1 further comprising:
a plurality of column paths, the plurality of readout circuits each being coupled to the corresponding column of the image sensor pixels via a respective column path in the plurality of column paths, wherein the row time includes settling time for pixel signals on the plurality of column paths.
7. The image sensor defined in claim 1 , wherein the plurality of readout circuits are configured to perform additional readout operations during an additional row time, and the control circuitry is configured to control the plurality of readout circuits to perform time-domain multiplexing for the additional readout operations across the plurality of readout circuits by activating the plurality of readout circuits in a different order than an order in which the plurality of readout circuit is activated to perform the time-domain multiplexing for the readout operations.
8. The image sensor defined in claim 1 , wherein the plurality of readout circuits are configured to perform additional readout operations during an additional row time associated with an image frame that is different from an image frame associated with the row time, and the control circuitry is configured to control the plurality of readout circuits to perform time-domain multiplexing for the additional readout operations across the plurality of readout circuits by activating the plurality of readout circuits in a different order than an order in which the plurality of readout circuit is activated to perform the time-domain multiplexing for the readout operations.
9. The image sensor defined in claim 1 , wherein the plurality of readout circuits each comprises correlated double sampling circuitry, and the readout operations comprise correlated double sampling operations.
10. The image sensor defined in claim 1 , wherein occurrences of the analog-to-digital conversion operations are distributed temporally across the row time in a uniform manner.
11. The image sensor defined in claim 1 , wherein the image sensor pixels are formed as a stitched image sensor array.
12. A method of operating an image sensor having image sensor pixels arranged in columns and rows, the method comprising:
receiving pixel signals from a row of the image sensor pixels at a plurality of readout circuits each coupled to a corresponding column of the image sensor pixels;
performing readout operations during a row time associated with the row of the image sensor pixels; and
performing time-domain multiplexing for the readout operations across the plurality of readout circuits by activating the plurality of readout circuits at different times across the row time.
13. The method defined in claim 12 , wherein performing the readout operations comprise performing analog-to-digital conversion operations during the row time.
14. The method defined in claim 12 further comprising:
performing additional readout operations during an additional row time associated with an additional row of the image sensor pixels; and
performing time-domain multiplexing for the additional readout operations across the plurality of readout circuits by activating the plurality of readout circuits in a different manner than a manner in which the plurality of readout circuits is activated for performing time-domain multiplexing for the readout operations.
15. The method defined in claim 12 further comprising:
performing additional readout operations during an additional row time associated with the row of the image sensor pixels; and
performing time-domain multiplexing for the additional readout operations across the plurality of readout circuits by activating the plurality of readout circuits in a different manner than a manner in which the plurality of readout circuits is activated for performing time-domain multiplexing for the readout operations.
16. The method defined in claim 12 , wherein the plurality of readout circuits is activated across the row time in a linear progression based on an order of the columns of the image sensor pixels.
17. The method defined in claim 12 , wherein the plurality of readout circuits is activated across the row time in a pseudo-random progression.
18. An image sensor comprising:
an image sensor array having first and second pixels arranged in first and second columns, respectively, and arranged in a same row;
first analog-to-digital converter circuitry coupled to the first pixel using a first column line and configured to begin a first analog-to-digital conversion operation during a row time associated with readout operations for the first and second pixels; and
second analog-to-digital converter circuitry coupled to the second pixel using a second column line and configured to begin a second analog-to-digital conversion operation during the row time, wherein the first analog-to-digital converter circuitry and the second analog-to-digital converter circuitry are switched to an active mode respectively at first and second different times across the row time to begin the first and second analog-to-digital conversion operations.
19. The image sensor defined in claim 18 , wherein the first and second analog-to-digital conversion operations occur during first and second nonoverlapping time periods across the row time.
20. The image sensor defined in claim 18 , further comprising:
data storage circuitry configured to store data indicative of a timing based on which the first analog-to-digital converter circuitry and the second analog-to-digital converter circuitry are switched to the active mode.