Method and system for implementing correlated multi-sampling with improved analog-to-digital converter linearity

Patent metadata

Field	Value
Publication number	US-9491390-B2
Application number	US-201414555062-A
Country	US
Kind code	B2
Filing date	Nov 26, 2014
Priority date	Nov 26, 2014
Publication date	Nov 8, 2016
Grant date	Nov 8, 2016

Abstract

A method of implementing Correlated Multi-Sampling (CMS) in an image sensor with improved analog-to-digital converter (ADC) linearity starts with an ADC circuitry included in a readout circuitry that generates a plurality of uncorrelated random numbers used as a plurality of ADC pedestals for sampling image data. A Successive Approximation Register (SAR) included in the ADC circuitry stores a different one of the ADC pedestals before each sampling of the image data. The ADC circuitry samples an image data from a row a plurality of times against plurality of ADC pedestals to obtain a plurality of sampled input data. The ADC circuitry converts each of the plurality of sampled input data from analog to digital, which includes performing a binary search using the SAR. Other embodiments are also described.

First claim

The invention claimed is:

1. A method of implementing Correlated Multi-Sampling (CMS) in an image sensor with improved analog-to-digital converter (ADC) linearity, comprising:
acquiring by a readout circuitry an image data from a first row in a color pixel array;
generating by an ADC circuitry included in the readout circuitry a plurality of uncorrelated random numbers used as a plurality of ADC pedestals for the first row, the ADC pedestals including a first ADC pedestal and a second ADC pedestal;
storing by a Successive Approximation Register (SAR) included in the ADC circuitry the first ADC pedestal;
sampling by the ADC circuitry the image data from the first row against the first ADC pedestal stored in the SAR to obtain a first sampled input data; and
converting by the ADC circuitry the first sampled input data from analog to digital to obtain a first ADC output value;
once the first ADC output value is obtained,
storing by the SAR the second ADC pedestal,
sampling by the ADC circuitry the image data from the first row against the second ADC pedestal stored in the SAR to obtain a second sampled input data, and
converting by the ADC circuitry the second sampled input data from analog to digital to obtain a second ADC output value.

2. The method of claim 1 , wherein the uncorrelated random numbers are uniformly distributed between 64 and 79.

3. The method of claim 1 , wherein acquiring by the readout circuitry the image data from the first row further comprises:
selecting and amplifying by a scanning circuitry included in the readout circuitry the image data from the first row; and
transmitting the image data from the first row to the ADC circuitry.

4. The method of claim 1 , wherein sampling by the ADC circuitry the image data from the first row to obtain the first and second sampled input data further comprises:
sampling the image data on a digital-to-analog (DAC) circuitry included in the ADC circuitry to obtain the first and the second sampled input data, respectively.

5. The method of claim 4 , wherein converting by the ADC circuitry the first and the second sampled input data from analog to digital to obtain, respectively, the first and the second ADC output value further comprises:
performing a binary search using the DAC circuitry and the SAR.

6. The method of claim 5 , wherein converting by the ADC circuitry the first and the second sampled input data from analog to digital to obtain, respectively, the first and the second ADC output values further comprises:
determining by a comparator included in the ADC circuitry to set or reset a plurality of bits stored in the SAR in succession from most significant bit (MSB) to least significant bit (LSB),
setting or resetting by the SAR each of the plurality of bits stored in the SAR based on the determination by the comparator to obtain the first and the second ADC output values, respectively, and
outputting from the SAR the first and the second ADC output values respectively to a function logic.

7. The method of claim 6 , wherein converting by the ADC circuitry the first and the second sampled input data from analog to digital to obtain, respectively, the first and the second ADC output values further comprises:
resetting an inverting input of the comparator to a predetermined value during the sampling of the image data on the DAC circuitry to obtain the first and the second sampled input data, respectively.

8. The method of claim 7 , wherein converting by the ADC circuitry the first and the second sampled input data from analog to digital to obtain, respectively, the first and the second ADC output values further comprises:
receiving and storing by a latch the comparator output values, and
selecting by a selector circuitry values outputted from the latch to be transmitted to the SAR.

9. The method of claim 8 , further comprising:
receiving by the readout circuitry control signals from the logic circuitry, wherein the control signals control at least one of: the latch, the selector circuitry, a switch to receive the image data, a switch to reset the comparator, and a switch to reset the DAC circuitry.

10. The method of claim 9 , further comprising:
generating by the readout circuitry a non-linearity error for each of the ADC output values respectively corresponding to the first and the second sampled input data and generating an average of the non-linearity errors; and
generating by the readout circuitry a final ADC output based on the first ADC output value and the second ADC output value.

11. A method of implementing Correlated Multi-Sampling (CMS) in an image sensor with improved analog-to-digital converter (ADC) linearity, the method comprising:
generating by the ADC circuitry a plurality of uncorrelated random numbers used as a plurality of ADC pedestals for sampling from the first row;
storing by a Successive Approximation Register (SAR) included in the ADC circuitry a different one of the ADC pedestals before each sampling of the image data;
sampling by an ADC circuitry included in a readout circuitry an image data from a first row a plurality of times against the plurality of ADC pedestals stored in the SAR to obtain a plurality of sampled input data; and
converting by the ADC circuitry each of the plurality of sampled input data from analog to digital, wherein converting by the ADC circuitry includes performing a binary search using the SAR.

12. The method of claim 11 , wherein the uncorrelated random numbers are uniformly distributed between 64 and 79.

13. The method of claim 11 , wherein sampling by the ADC circuitry further comprises:
sampling the image data on a digital-to-analog (DAC) circuitry included in the ADC circuitry to obtain the plurality of sampled input data.

14. The method of claim 13 , wherein converting by the ADC circuitry includes:
performing the binary search using the DAC circuitry.

15. The method of claim 14 , wherein converting by the ADC circuitry includes:
determining by a comparator included in the ADC circuitry to set or reset a plurality of bits stored in the SAR in succession from most significant bit (MSB) to least significant bit (LSB),
setting or resetting by the SAR each of the plurality of bits stored in the SAR based on the determination by the comparator to obtain ADC output values, and
outputting from the SAR the ADC output values to a function logic.

16. The method of claim 15 , wherein converting by the ADC circuitry includes:
resetting an inverting input of the comparator to a predetermined value during the sampling of the image data on the DAC circuitry to obtain the plurality of sampled input data.

17. The method of claim 16 , further comprising:
determining by the readout circuitry a non-linearity error for each of the ADC output values and generating an average of the non-linearity errors.

18. An imaging system comprising:
a color pixel array for acquiring image data, the pixel array including a plurality of rows and columns;
a readout circuitry coupled to the color pixel array to acquire an image data from a first row in the color pixel array, wherein the readout circuitry includes an analog-to-digital conversion (ADC) circuitry to:
generate a plurality of uncorrelated random numbers used as a plurality of ADC pedestals for sampling from the first row;
store in a Successive Approximation Register (SAR) included in the ADC circuitry a different one of the ADC pedestals before each sampling of the image data;
sample the image data from the first row a plurality of times against the plurality

Assignees

• Omnivision Tech Inc

Inventors

• Johansson Robert

Classifications

• H03M1/0634 Primary

  by averaging out the errors, e.g. using sliding scale · CPC title

• H04N25/616

  involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling · CPC title

• H04N25/78 Primary

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

• H04N5/378 Primary

  Electricity · mapped topic

• H04N5/3575

  Electricity · mapped topic