Image sensor architecture with power saving readout

Patent metadata

Field	Value
Publication number	US-9521349-B2
Application number	US-201514727869-A
Country	US
Kind code	B2
Filing date	Jun 2, 2015
Priority date	Jun 19, 2014
Publication date	Dec 13, 2016
Grant date	Dec 13, 2016

Abstract

Pixels within an image sensor pixel array are sampled by corresponding conditional read circuitry. A zero pixel value is outputted for each pixel associated with a sample less than a conversion threshold, and a saturated pixel value is outputted for each pixel associated with a sample greater than or equal to a saturation threshold. Samples greater than or equal to the conversion threshold and less than the saturation threshold are converted by an ADC, and a converted pixel value is output for each associated above threshold pixel. The ADC (along with any corresponding amplifiers) are powered on for a variable period depending on the number of pixels needing conversion during the conversion of such samples during a read period, and are powered off for the remainder of the read period.

First claim

What is claimed is:

1. An integrated-circuit image sensor comprising:
a pixel array comprising a plurality of pixels, each readable through at least one corresponding pixel readout circuit;
conditional read circuitry for a selected subgroup of the pixels and corresponding pixel readout circuits, to determine whether any of the subgroup of pixels are selected for readout, and perform a corresponding selection for parallel conditional full pixel sampling of the selected pixels in the subgroup for readout;
an Analog-to-Digital Converter (ADC); and
a controller configured to, for the selected subgroup of pixels:
operate the ADC during a power-on period, where the length of the power-on period varies in relation to the number of parallel conditional full pixel samplings performed by the conditional read circuitry, and
select samples corresponding to those pixels in the subgroup of pixels with conditional full pixel sampling for serial conversion by the ADC during the power-on period.

2. The integrated-circuit image sensor of claim 1 , wherein the conditional read circuitry comprises:
a plurality of comparators operable in a parallel readout operation, each comparator in a first parallel operation associated with at least one sample from a different selected pixel readout circuit, each comparator configured to:
access a sample from the selected readout circuit; and
determine whether a charge associated with a pixel corresponding to the accessed sample is less than a conversion threshold based on the accessed sample.

3. The integrated-circuit image sensor of claim 2 , wherein the controller is further configured to output a zero pixel value for the pixel in response to a determination by one of the comparators that the charge associated with the pixel is less than the conversion threshold.

4. The integrated-circuit image sensor of claim 2 , wherein each comparator is further configured to:
determine whether a charge associated with the pixel corresponding to the accessed sample is greater than or equal to a saturation threshold based on the accessed sample.

5. The integrated-circuit image sensor of claim 4 , wherein the controller is further configured to output a saturation pixel value for the pixel in response to a determination by one of the comparators that the charge associated with the pixel is greater than or equal to the saturation threshold.

6. The integrated-circuit image sensor of claim 4 , wherein the controller is further configured to, for each pixel based on the output of the corresponding comparator:
determine whether a charge associated with the pixel corresponding to the accessed sample is greater than or equal to the conversion threshold and less than the saturation threshold based on the accessed sample; and
select the pixel for readout if the charge associated with the pixel is greater than or equal to the conversion threshold and less than the saturation threshold.

7. The integrated-circuit image sensor of claim 1 , wherein the controller is further configured to, for the selected subgroup of pixels:
operate an amplifier during the power-on period, the amplifier configured to amplify the selected samples corresponding to the pixels in the subgroup of pixels before the samples are converted by the ADC.

8. A method comprising:
selecting a subset of pixels in a pixel array comprising a plurality of pixels for readout, each pixel in the subset readable through at least one corresponding pixel readout circuit;
performing a parallel conditional full pixel sampling for each of the selected subset of pixels;
operating an ADC during a variable power-on period of a readout period, where the length of the power-on period varies in relation to the number of parallel conditional full pixel samplings performed, and powering down the ADC in another portion of the readout period; and
converting, with the ADC, samples corresponding to those pixels in the set of pixels during the power-on period.

9. The method of claim 8 , further comprising:
accessing a sample from a selected readout circuit; and
determining whether a charge associated with a pixel corresponding to the accessed sample is less than a conversion threshold based on the access sample.

10. The method of claim 9 , further comprising:
outputting a zero pixel value for the pixel in response to a determination that the charge associated with the pixel is less than the conversion threshold.

11. The method of claim 9 , further comprising:
determining whether a charge associated with the pixel corresponding to the accessed sample is greater than or equal to a saturation threshold based on the accessed sample.

12. The method of claim 11 , further comprising:
outputting a saturation pixel value for the pixel in response to a determination that the charge associated with the pixel is greater than or equal to the saturation threshold.

13. The method of claim 11 , further comprising:
determining whether a charge associated with the pixel corresponding to the accessed sample is greater than or equal to the conversion threshold and less than the saturation threshold based on the accessed sample; and
selecting the pixel for readout if the charge associated with the pixel is greater than or equal to the conversion threshold and less than the saturation threshold.

14. The method of claim 8 , further comprising:
operating an amplifier during the power-on period, the amplifier configured to amplify samples corresponding to the pixels in the subset of pixels before the samples are converted by the ADC, and powering down the amplifier in another portion of the readout period.

15. An integrated-circuit image sensor comprising:
a pixel array comprising a plurality of pixels and corresponding readout circuitry configured to sample a subset of the plurality of pixels in parallel;
a plurality of classifiers each configured to classify a different one of the pixels in a sampled subset, wherein a pixel is classified as an above threshold pixel in response to a determination that a sample associated with the pixel is greater than or equal to a conversion threshold and less than a saturation threshold;
an Analog-to-Digital Converter (ADC); and
a controller configured to operate the ADC during a power-on period of a readout period, wherein the ADC converts samples associated with above threshold pixels in the sampled subset during the power-on period to produce converted pixel values, the length of the power-on period based on the number of above threshold pixels, the controller further configured to power down the ADC during at least one portion of the readout period when the ADC is not converting samples associated with above threshold pixels.

16. The integrated-circuit image sensor of claim 15 , wherein a pixel is classified as below threshold in response to a determination that a sample associated with the pixel is less than the conversion threshold, and wherein the controller is further configured to output a zero pixel value for each pixel classified as a below threshold pixel.

17. The integrated-circuit image sensor of claim 16 , wherein a pixel is classified as saturated in response to a determination that a sample associated with the pixel is greater than or equal to the saturation threshold, and wherein the controller is further configured to output a saturated pixel value for each pixel classified as a saturated pixel.

18. The integrated-circuit image sensor of claim 17 , wherein the power-on period begins at the beginning of readout of pixel values associated with the plura

Assignees

• Rambus Inc

Inventors

• Vogelsang Thomas
• Endsley Jay
• Guidash Michael

Classifications

• H04N25/709 Primary

  Circuitry for control of the power supply · CPC title

• H04N25/443 Primary

  by reading pixels from selected two-dimensional [2D] regions of the array, e.g. for windowing or digital zooming · CPC title

• H04N25/583

  with different integration times · CPC title

• H04N25/78

  Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters · CPC title

• H04N5/378 Primary

  Electricity · mapped topic