Readout circuit for image sensors

Patent metadata

Field	Value
Publication number	US-9967499-B2
Application number	US-201414515263-A
Country	US
Kind code	B2
Filing date	Oct 15, 2014
Priority date	Oct 16, 2013
Publication date	May 8, 2018
Grant date	May 8, 2018

Abstract

The present description relates to a readout circuit for digitizing an analog input signal of an imaging device into a digital output. The readout circuit comprises a pixel signal input for providing an analog signal from at least one imaging pixel element, a variable gain amplifier for providing an amplified signal of the analog signal by a gain factor, and a first analog to digital conversion means for quantizing the analog signal into a first digital signal. The circuit further comprises a control means for setting the gain factor of the variable gain amplifier by taking into account the first digital signal, and a second analog to digital conversion means for quantizing the amplified signal into a second digital signal. The circuit also comprises a digital output for outputting a signal determined as function of at least the second digital signal.

First claim

What is claimed is:

1. A readout circuit of an imaging device, comprising:
a pixel signal input configured to receive an analog input signal from at least one imaging pixel element;
a variable gain amplifier configured to provide an amplified analog signal, the amplified analog signal being an amplification of the analog input signal by a gain factor;
a first analog to digital conversion means for quantizing the analog input signal into a first digital signal;
a control means for setting the gain factor of the variable gain amplifier by taking into account the first digital signal;
a second analog to digital conversion means for quantizing the amplified analog signal into a second digital signal; and
a digital output configured to output an output signal, the output signal being determined as function of at least the second digital signal, wherein the first analog to digital conversion means is configured to provide a coarse quantization of the analog input signal and the second analog to digital conversion means is configured to provide a finer quantization of the amplified analog signal than the first analog to digital conversion means.

2. The readout circuit according to claim 1 , wherein the first analog to digital conversion means for quantizing determines the variable gain amplifier gain setting.

3. The readout circuit according to claim 1 , wherein the input of the first analog to digital conversion means for quantizing, the input of the second analog to digital conversion means for quantizing and the output of the variable gain amplifier are electrically connected.

4. The readout circuit according to claim 1 , wherein the variable gain amplifier is adapted for subtracting an analog signal representative for the optical signal and a reset signal provided by the pixel signal input and for providing the amplified pixel signal, the amplified pixel signal being a correlated double sampling amplification of the subtraction of the signal representative for the optical signal and the reset signal by the gain factor.

5. The readout circuit according to claim 1 , wherein the digital output comprises a combination unit for outputting a combination signal of the first digital signal and the second digital signal.

6. The readout circuit according to claim 1 , further comprising:
at least one further variable gain amplifier electrically connected in a serial circuit to the output of the first variable gain amplifier, each of the at least one further variable gain amplifier providing a corresponding further amplified signal by amplifying the corresponding input of the at least one further variable gain amplifier by a corresponding further gain factor; and
at least one further analog to digital conversion means for quantizing the corresponding further amplified signal into a further digital signal,
wherein the control means for setting the gain factor comprises control means for setting the further gain factor of each of the at least one further variable gain amplifier by taking into account a corresponding digital signal which is provided by the second analog to digital conversion means for quantizing or the at least one further analog to digital conversion means for quantizing having its input connected to the output of the further variable gain amplifier.

7. An imaging device comprising a readout circuit according to claim 1 , and at least one imaging pixel element for supplying an analog input signal to a pixel signal input of the readout circuit.

8. The imaging device according to claim 7 , wherein the at least one imaging pixel element comprises a plurality of pixel elements forming a logical pixel column of a pixel array.

9. A method for digitizing an analog input signal of an imaging device into a digital output, the method comprising:
obtaining an analog input signal from at least one imaging pixel element;
coarse quantizing the analog input signal into a first digital signal;
setting a gain factor of a variable gain amplifier by taking into account the first digital signal;
amplifying the analog input signal by the gain factor to produce an amplified signal;
fine quantizing the amplified pixel signal into a second digital signal; and
outputting an output signal determined as function of at least the second digital signal.

10. The method according to claim 9 , wherein obtaining an analog input signal from at least one imaging pixel element comprises providing a difference signal as analog input signal, the difference signal being a difference between a reset signal received from the at least one imaging pixel element and an analog signal representative for the optical signal received from the at least one imaging pixel element.

11. The method according to claim 9 , wherein outputting the output signal comprises combining the first digital signal and the second digital signal.

12. The method according to claim 11 , wherein combining the first digital signal and the second digital signal comprises determining a weighted sum or product to obtain a quantized representation of the analog input signal.

13. The method according to claim 9 , further comprising setting the gain factor to a reference gain factor before quantizing the pixel signal input into a first digital signal by amplifying the analog input signal by the reference gain factor to produce a reference amplified signal and quantizing the reference amplified pixel signal into the first digital signal.

14. A readout circuit of an imaging device, comprising:
means for receiving an analog input signal from at least one imaging pixel element;
means for providing an amplified analog signal, the amplified analog signal being an amplification of the analog input signal by a gain factor;
a first analog to digital converter configured to quantize the analog input signal into a first digital signal;
a controller configured to set the gain factor of the variable gain amplifier by taking into account the first digital signal;
a second analog to digital converter configured to quantize the amplified analog signal into a second digital signal; and
a digital output configured to output an output signal, the output signal being determined as function of at least the second digital signal, wherein the first analog to digital converter is configured to provide a coarse quantization of the analog input signal and the second analog to digital converter is configured to provide a finer quantization of the amplified analog signal than the first analog to digital converter.

15. The readout circuit according to claim 14 , wherein the means for receiving an analog input signal comprises a pixel signal input.

16. The readout circuit according to claim 14 , wherein the means for providing an amplified analog signal comprises a variable gain amplifier.

17. The readout circuit according to claim 14 , wherein the first analog to digital converter determines the variable gain amplifier gain setting.

18. The readout circuit according to claim 14 , wherein the input of the first analog to digital converter, the input of the second analog to digital converter, and the output of the means for providing an amplified analog signal are electrically connected.

19. The readout circuit according to claim 16 , wherein the variable gain amplifier is configured to subtract an analog signal representative for the optical signal and a reset signal provided by the pixel signal input, and further configured to provide the amplified pixel signal, the amplified pixel signal being a correlated double sampling ampli

Assignees

• Imec Vzw

Inventors

• Borremans Jonathan

Classifications

• H04N23/76 Primary

  by influencing the image signals · CPC title

• H04N25/616

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

• H04N5/243

  Electricity · mapped topic

• H04N5/3575

  Electricity · mapped topic

• H04N5/378 Primary

  Electricity · mapped topic