Reset noise reduction for pixel readout with pseudo correlated double sampling

• US 9,973,716 B2
• Filed: 04/02/2014
• Issued: 05/15/2018
• Est. Priority Date: 08/02/2013
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Wang, Yibing M., Wang, Hongyu, Kim, Tae-Chan
• Primary Examiner(s): Haskins, Twyler
• Assistant Examiner(s): Trehan, Akshay
• Application Number:
  US14/242,919
• Publication Number:
  US 20150036035A1
• Time in Patent Office: 1,504 Days
• Field of Search: 348308
• CPC Class Codes: H04N 25/616 involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling
• CPC Class Codes: H04N 25/65 applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS

Abstract

Provided are an imaging device implementing pseudo correlated double sampling (CDS), and an imaging method and a control method of the image device. The imaging device includes: a pixel array comprising a pixel configured to generate a current in response to incident light; a readout circuit configured to read out a plurality of output signals of the pixel, the plurality of output signals corresponding to a plurality of consecutive integration periods of the pixel within an aggregating period; and an aggregator configured to aggregate the plurality of output signals read out by the readout circuit to obtain a final aggregated output corresponding to illuminance for the aggregating period, wherein the readout circuit is configured to read out the plurality of output signals by, for each output signal, sampling a signal voltage of the pixel and sampling a subsequent reset voltage of the pixel and obtaining a difference therebetween.

Claims

1. An imaging device implementing pseudo correlated double sampling (CDS) for pixel readouts, the imaging device comprising:

a pixel array comprising a pixel configured to generate a current in response to incident light;

a readout circuit configured to read out a plurality of output signals of the pixel, the plurality of output signals corresponding to a plurality of consecutive integration periods of the pixel within an aggregating period; and

an aggregator configured to aggregate the plurality of output signals read out by the readout circuit to obtain a final aggregated output corresponding to illuminance for the aggregating period,

wherein the readout circuit is configured to read out the plurality of output signals by, for each output signal, sampling a signal voltage of the pixel and sampling a reset voltage, subsequent to the signal voltage, of the pixel and obtaining a difference between the sampled signal voltage and the sampled reset voltage, and

wherein a thermal noise component of the final aggregated output includes only a thermal noise component of a first output signal of the plurality of output signals and a thermal noise component of a last output signal of the plurality of output signals.

2. The imaging device according to claim 1, wherein the pixel is a 1T pixel, a 2T pixel, a 3T pixel, a 5T pixel, or any pixel that uses a pseudo-CDS readout.

3. The imaging device according to claim 1, wherein a signal-to-noise ratio for the final aggregated output corresponds to:

SNR_{k_full}=k·

Vlight/√

{square root over (2σ

_kTC²+kσ

_rd²)},

where k corresponds to a number of the plurality of consecutive integration periods, Vlight corresponds to illuminance voltages for the plurality of consecutive integration periods, σ

kTC corresponds to standard deviation of kTC noise, and σ

rd corresponds to standard deviation of read noise.

4. The imaging device according to claim 1, wherein thermal noise components corresponding to consecutive output signals are correlated in the final aggregated output.

5. The imaging device according to claim 1, wherein the final aggregated output Vfinal corresponds to:

Vfinal=k*Vlight+Nktc(k+1)−

Nktc(0)+Nrd(1)+Nrd(2)+ . . . +Nrd(k),

where k corresponds to a number of the plurality of consecutive integration periods within the aggregating period, k*Vlight corresponds to a sum of illuminance voltages for the plurality of consecutive integration periods, Nktc(k+1) corresponds to the thermal noise component of the last output signal of the plurality of output signals, Nktc(0) corresponds to the thermal noise component of the first output signal of the plurality of output signals, and Nrd( ) corresponds to a readout noise.

6. The imaging device according to claim 1, wherein the plurality of consecutive integration periods vary in length.

7. The imaging device according to claim 1, wherein the plurality of consecutive integration periods are of equal length.

8. The imaging device according to claim 1, wherein the aggregating period corresponds to an image frame.

9. The imaging device according to claim 1, wherein the aggregating period is less than a period of an image frame.

10. The imaging device according to claim 1, wherein the aggregating period corresponds to a plurality of consecutive image frames.

11. The imaging device according to claim 1, wherein the pixel array is a complementary metal-oxide-semiconductor (CMOS) image sensor pixel array.

12. An image sensing method of an imaging device implementing pseudo-CDS for pixel readouts, the method comprising:

reading out a plurality of output signals of a pixel of the imaging device, the plurality of output signals corresponding to a plurality of consecutive integration periods of the pixel within an aggregating period; and

aggregating the plurality of output signals read out by the readout circuit to obtain a final aggregated output corresponding to illuminance for the aggregating period,

wherein the reading out comprises, for each output signal, sampling a signal voltage of the pixel and sampling a reset voltage, subsequent to the signal voltage, of the pixel and obtaining a difference between the sampled signal voltage and the sampled reset voltage, and

wherein a thermal noise component of the final aggregated output includes only a thermal noise component of a first output signal of the plurality of output signals and a thermal noise component of a last output signal of the plurality of output signals.

13. The method according to claim 12, wherein the aggregating comprises, for an integration period of the plurality of consecutive integration period, reading a stored aggregating period readout sum from a memory, adding a digitized value of an output signal for the integration period to the read aggregating period readout sum, and writing the aggregating period readout sum to which the digitized value is added to the memory.

14. The method according to claim 12, wherein a signal-to-noise ratio for the final aggregated output corresponds to:

SNR_{k_full}=k·

Vlight/√

{square root over (2σ

_kTC²+kσ

_rd²)},

where k corresponds to a number of the plurality of consecutive integration periods, Vlight corresponds to illuminance voltages for the plurality of consecutive integration periods, σ

kTC corresponds to standard deviation of kTC noise, and σ

rd corresponds to standard deviation of read noise.

15. The method according to claim 12, wherein thermal noise components corresponding to consecutive output signals are correlated in the final aggregated output.

16. The method according to claim 12, wherein the final aggregated output Vfinal corresponds to:

Vfinal=k*Vlight+Nktc(k+1)−

Nktc(0)+Nrd(1)+Nrd(2)+ . . . +Nrd(k),

where k corresponds to a number of the plurality of consecutive integration periods within the aggregating period, k*Vlight corresponds to a sum of illuminance voltages for the plurality of consecutive integration periods, Nktc(k+1) corresponds to the thermal noise component of the last output signal of the plurality of output signals, Nktc(0) corresponds to the thermal noise component of the first output signal of the plurality of output signals, and Nrd( ) corresponds to a readout noise.

17. A control method of an imaging device implementing pseudo-CDS for pixel readouts, the method comprising:

controlling a readout circuit of the imaging device to read out a plurality of output signals of a pixel of the imaging device, the plurality of output signals corresponding to a plurality of consecutive integration periods of the pixel within an aggregating period; and

obtaining a final aggregated output in which thermal noise components corresponding to consecutive output signals, of the plurality of output signals, are correlated and thereby reduced, the final aggregated output corresponding to illuminance for the aggregating period of the pixel,

wherein a thermal noise component of the final aggregated output includes only a thermal noise component of a first output signal of the plurality of output signals and a thermal noise component of a last output signal of the plurality of output signals.

18. The method according to claim 17, wherein a signal-to-noise ratio for the final aggregated output corresponds to:

SNR_{k_full}=k·

Vlight/√

{square root over (2σ

_kTC²+kσ

_rd²)},

where k corresponds to a number of the plurality of consecutive integration periods, Vlight corresponds to illuminance voltages for the plurality of consecutive integration periods, σ

kTC corresponds to standard deviation of kTC noise, and σ

rd corresponds to standard deviation of read noise.

19. The method according to claim 17, wherein the final aggregated output Vfinal corresponds to:

Vfinal=k*Vlight+Nktc(k+1)−

Nktc(0)+Nrd(1)+Nrd(2)+ . . . +Nrd(k),

where k corresponds to a number of the plurality of consecutive integration periods within the aggregating period, k*Vlight corresponds to a sum of illuminance voltages for the plurality of consecutive integration periods, Nktc(k+1) corresponds to the thermal noise component of the last output signal of the plurality of output signals, Nktc(0) corresponds to the thermal noise component of the first output signal of the plurality of output signals, and Nrd( ) corresponds to a readout noise.

20. A non-transitory computer readable recording medium having recorded thereon a program executable by a computer for performing the method of claim 17.