CN101521755A - Cmos image sensor reading circuit and reading method - Google Patents

Abstract

The invention relates to a CMOS image sensor reading circuit, which comprises an analog-to-digital converter, and also comprises a variable gain amplifier, a comparator and a gain adjusting device, wherein the variable gain amplifier is suitable for receiving and adjusting pixel exposing voltage of the image sensor, and outputting the voltage to the analog-to-digital converter; the comparator is suitable for judging the pixel exposing voltage; and the gain adjusting device is suitable for receiving a judgment result output by the comparator, and adjusting an amplification factor of the variable gain amplifier according to an exposing voltage section where the exposing voltage is positioned. The invention also relates to a method for reading digital signals from pixels by the CMOS image sensor, which comprises the following steps: adjusting the pixel exposing voltage by the variable gain amplifier; converting analog voltage signals output by the variable gain amplifier into digital signals for output; judging the pixel exposing voltage; and adjusting the amplification factor of the variable gain amplifier according to the exposing voltage section where the exposing voltage is positioned. Under the conditions of different light intensities, both the reading circuit and the method can obtain clear images to meet the requirement of human eye on image quality.

Description

Cmos image sensor reading circuit and reading method

Technical field

The present invention relates to technical field of image processing, relate in particular to complementary metal oxide semiconductors (CMOS) (CMOS) imageing sensor and read circuit and reading method.

Background technology

Cmos image sensor is the semiconductor device that optical imagery is converted to the signal of telecommunication.Basic transfer process is: the pixel in the cmos image sensor is exposed, and in certain time for exposure, the voltage on the pixel produces linear voltage with different light rays intensity, and reading circuit subsequently becomes digital signal output with this voltage transitions.

Generally, cmos image sensor adopts 10 analog to digital converters, so its numeral is output as 10 dateout scope.And the dynamic range that human eye can be seen is about 10 ⁶～10 ⁸Lumen.Though the people can not see the light of this gamut simultaneously, the most sensitive that human eye can be felt simultaneously is about 10,000:1.And human eye becomes logarithm to change to the susceptibility of light intensity, and is not the such linear variation of signal that the image pattern image-position sensor receives.Along with the increase of light intensity, human eye is insensitive more to the variation of brightness.

With reference to Fig. 1, be cmos image sensor reading circuit structure schematic diagram in the prior art, after 11 pairs of light of pixel exposed, its voltage was preserved by a sampling hold circuit 12 earlier, then by 13 outputs of a production line analog-digital converter.

The present inventor finds, the magnitude of voltage of the structure of this reading circuit on linear all the time output exposure back pixel under the different light intensities, therefore the output valve difference of high light and half-light is big, after the analog to digital converter conversion, the high light output valve can reach 1000, and the half-light output valve may have only tens, so half-light hypograph loss of detail is very big, can't satisfy the requirement of human eye to picture quality.

Summary of the invention

The problem to be solved in the present invention is, cmos image sensor reading circuit and reading method are provided, and can improve the quality of imageing sensor output image.

For addressing the above problem, the invention provides a kind of cmos image sensor reading circuit, comprise analog to digital converter; Also comprise:

Variable gain amplifier is suitable for receiving image sensor pixel exposure voltage and adjustment, and outputs to analog to digital converter;

Comparator is suitable for described pixel exposure voltage is judged;

Fader is suitable for receiving the judged result that described comparator is exported, according to the interval multiplication factor of adjusting variable gain amplifier of the residing exposure voltage of described exposure voltage.

Optionally, also comprise digital signal processor, be suitable for judged result, the digital signal of described analog to digital converter output is handled, form exposure value according to described comparator generation.

Optionally, described fader and described variable gain amplifier are integrated into programmable gain amplifier.

Optionally, described fader and described comparator are integrated into controller.

Optionally, described analog to digital converter is specially production line analog-digital converter.

Optionally, described production line analog-digital converter is specially 10 bit stream pipeline analog-to-digital converters.

Optionally, described comparator comprises first comparator, second comparator and the 3rd comparator, and each comparator is provided with different reference voltages.

The present invention also provides a kind of cmos image sensor, comprises pixel, also comprises the reading circuit of being introduced in above any technical scheme.

Optionally, also comprise digital signal processor in the above-mentioned cmos image sensor, be suitable for judged result, the digital signal of the output of the analog to digital converter in the described reading circuit is handled, and form exposure value according to comparator generation in the described reading circuit.

For solving the problems of the technologies described above, the present invention also provides the method for a kind of cmos image sensor from pixel reading number signal, and this method comprises:

Pixel exposure voltage is adjusted by variable gain amplifier;

Change the analog voltage signal of variable gain amplifier output into digital signal output;

Judge pixel exposure voltage;

According to the residing exposure voltage of described pixel exposure voltage interval, regulate the multiplication factor of variable gain amplifier.

Optionally, said method also comprises: according to the residing exposure voltage of exposure voltage interval, the digital signal of output is handled, formed exposure value.

Compared with prior art, technique scheme adopts comparator that pixel exposure voltage is judged, and according to the interval multiplication factor of regulating variable gain amplifier of described exposure voltage, can make imageing sensor like this under different light intensity, can allow analog to digital converter be operated in best input voltage range, therefore it is bigger to make image reading sensor go out the dynamic range of circuit dateout, and reduction noise, thereby make under different light intensity, all can obtain distinct image, satisfy the requirement of human eye picture quality.

Description of drawings

Fig. 1 is a cmos image sensor reading circuit structure schematic diagram in the prior art;

Fig. 2 is a cmos image sensor reading circuit structure schematic diagram in the embodiment of the invention one;

Fig. 3 is a cmos image sensor reading circuit structure schematic diagram in the embodiment of the invention two;

Fig. 4 is cmos image sensor reading circuit structure figure in the embodiment of the invention three;

Fig. 5 is cmos image sensor reading circuit structure figure in the embodiment of the invention four;

Fig. 6 is the method flow diagram that cmos image sensor is read picture element signal in the embodiment of the invention five.

Embodiment

It is linear all the time output to pixel exposure voltage that existing imageing sensor is read circuit, and human eye becomes the logarithm to change to the susceptibility of light intensity, and is not the equally linear variation of image pattern image-position sensor received signal.Along with the increase of light intensity, human eye is insensitive more to the variation of brightness.At 0.01 lumen between 100 lumens, the influence value that human eye changes brightness is one and increases progressively constant: human eye can feel that the brightness of 1 luminous intensity light, 0.02 lumen changes, the brightness of 10 luminous intensity light, 0.2 lumen changes, the 1 lumen brightness of 50 lumen light changes, and the 2 lumen brightness of 100 lumen light change.Brightness range outside this does not then increase progressively like this, follows more complicated rule.

For obtaining higher-quality image, the embodiment of the invention provides cmos image sensor reading circuit and reading method, promptly in conjunction with the accompanying drawings and embodiments the specific embodiment of the present invention is described in detail below.

With reference to Fig. 2, be the cmos image sensor reading circuit structure schematic diagram in the embodiment of the invention one.Described reading circuit is used for the pixel exposure voltage that comes from pixel 21 is handled, and comprising: variable gain amplifier 22, analog to digital converter 23, comparator 24 and fader 25, wherein:

Described variable gain amplifier 22 is suitable for receiving pixel exposure voltage and the adjustment that pixel 21 produces, and outputs to analog to digital converter 23;

Described comparator 24 is suitable for the pixel exposure voltage of pixel 21 outputs is judged;

Described fader 25 is suitable for receiving the judged result that comparator 24 is exported, according to the interval multiplication factor of adjusting variable gain amplifier 22 of the residing exposure voltage of described exposure voltage.

Its concrete course of work is as follows: variable gain amplifier 22 receives the pixel exposure voltage that pixel 21 exposure backs are exported, this voltage is amplified, and output to analog to digital converter 23, analog to digital converter 23 is converted into digital signal and output, among Fig. 2, Out is the digital signal after the output.In this process, the pixel exposure voltage that 24 pairs of pixels 21 of comparator are produced is judged, and be input to fader 25, fader 25 is according to the residing different exposure voltages of pixel exposure voltage interval, adjust the multiplication factor of variable gain amplifier 22, make the voltage signal that is input to analog to digital converter 23 be positioned at all the time within the identical reference voltage.

In concrete the application, analog to digital converter adopts production line analog-digital converter usually.

Since can adjust the multiplication factor of gain amplifier, therefore, even under the half-light condition, by increasing the multiplication factor of gain amplifier, also can make the bigger voltage signal of gain amplifier output, thereby can make the data area of analog to digital converter output bigger, and can reduce noise.

As seen, in the present embodiment, adopt comparator that pixel exposure voltage is judged, and, make the voltage of input analog-to-digital converter be positioned at identical reference voltage all the time according to the interval multiplication factor of regulating variable gain amplifier of exposure voltage of living in.Can make imageing sensor like this under different light intensity, can allow analog to digital converter be operated in best input voltage range, therefore it is bigger to make image reading sensor go out the dynamic range of dateout of circuit, and reduction noise, make under different light intensity conditions, all can obtain distinct image, satisfy the requirement of human eye picture quality.

In concrete the application, for ease of distinguishing the residing light intensity of the signal stage of analog to digital converter output, can the numeral that analog to digital converter is exported be further processed, below describe by another specific embodiment.

With reference to Fig. 3, be cmos image sensor reading circuit structure schematic diagram in the embodiment of the invention two, be with the difference of embodiment one, present embodiment also comprises a digital signal processor 31, be suitable for judged result according to comparator 24 outputs, digital signal to analog to digital converter 23 outputs is handled, and the output exposure value.

The signal that digital processing unit 31 can be exported according to comparator 24, know current range of light intensity, the digital signal that analog to digital converter 23 is exported is handled, export the residing light intensity stage of concrete digital signal and this digital signal, that is: be to be in the high light stage, still be in the half-light stage.

In concrete enforcement, the fader in the foregoing description can integrate with variable gain amplifier.The variable gain amplifier of integrated fader can be realized that programmable gain amplifier can be regulated the multiplication factor of input signal with digital signal by a programmable gain amplifier.

For those skilled in the art being understood better and realize the present invention, below describe by concrete an application.

With reference to Fig. 4, be cmos image sensor reading circuit structure figure in the embodiment of the invention three, wherein analog to digital converter is one 10 a production line analog-digital converter 23 ', after exposing, 21 pairs of images of pixel produce linear voltage, and be input to programmable gain amplifier 22 ', output to production line analog-digital converter 23 ' after programmable gain amplifier 22 ' amplifies, production line analog-digital converter 23 ' is converted into digital signal and outputs to digital signal processor 31.In this process, 24 pairs of pixel exposure voltages of comparator are judged, on the one hand, output to programmable gain amplifier 22 ', adjust self multiplication factor by programmable gain amplifier 22 ', on the other hand, output to digital signal processor 31 and handle.Digital signal processor 31 is handled the digital signal of production line analog-digital converter 23 ' output according to the judged result of comparator 24 outputs, the exposure value Out of output under the different light intensity condition.

In the present embodiment, comparator 24 specifically comprises three comparators, that is: comparator 241, comparator 242 and comparator 243, judge 4 voltage ranges with these three comparators, if input voltage is Vpix, 4 voltage ranges are respectively: Vpix〉1/2Vref, 1/2Vref〉Vpix〉1/4Vref, 1/4Vref〉Vpix〉1/8Vref, Vpix＜1/8Vref, if then according to 241～243 order, from left to right arrange, the digital signal of the output that comparator is possible is respectively 111,011,001,000.If the gain of variable gain amplifier is respectively 1 times, 2 times, 4 times and 8 times.Programmable gain amplifier 22 ' is respectively according to the set gain G ain of digital signal of comparator output:

$\mathrm{Gain}=\left\{\begin{array}{cc}1,& 111\\ 2,& 011\\ 4,& 001\\ 8,& 000\end{array}\right.;$

Then gain with the corresponding relation of the exposure voltage of input is:

$\mathrm{Gain}=\left\{\begin{array}{cc}1,& \mathrm{Vpix}>1/2\mathrm{<figure-callout\; id="2"\; label="Vref"\; filenames="A200810184061E00132.png"\; state="\{\{state\}\}">Vref</figure-callout>}\\ 2,& 1/2\mathrm{Vref}>\mathrm{Vpix}>1/4\mathrm{<figure-callout\; id="4"\; label="Vref"\; filenames="A200810184061E00132.png"\; state="\{\{state\}\}">Vref</figure-callout>}\\ 4,& 1/4\mathrm{Vref}>\mathrm{Vpix}>1/8\mathrm{<figure-callout\; id="8"\; label="Vref"\; filenames="A200810184061E00132.png"\; state="\{\{state\}\}">Vref</figure-callout>}\\ 8,& \mathrm{Vpix}<1/8\mathrm{Vref}\end{array}\right.;$

And digital signal processor can be distinguished the residing light intensity stage of concrete digital signal in the following way, for example, exposure voltage Vpix when pixel〉during 1/2Vref, mend 30 (mending the quantity that 0 quantity equals comparator) at the end of the data of production line analog-digital converter 23 ' output; When the exposure voltage Vpix of pixel is in 1/2Vref〉Vpix〉when 1/4Vref is interval, can mend 10 in the front of production line analog-digital converter 23 ' dateout, the end is mended 20; When the exposure voltage Vpix of pixel is in 1/4Vref〉Vpix〉when 1/8Vref is interval, can mend 20 in the front of production line analog-digital converter 23 ' dateout, the end is mended 10; When the exposure voltage Vpix of pixel＜1/8Vref, can mend 30 in the front of production line analog-digital converter 23 ' dateout.If 10 production line analog-digital converter 23 ' dateout is specially: a9 a8 a7 a6 a5 a4 a3 a2 a1 a0, then use the physical relationship of the dateout Out of function representation digital signal processor 31 and pixel exposure voltage Vpix and gain G ain as follows:

$\mathrm{Out}=\left\{\begin{array}{ccc}a9a8a7a6a5a4a3a2a1a0000,& \mathrm{Vpix}>1/2\mathrm{Vref}& \mathrm{Gain}=1\\ 0a9a8a7a6a5a4a3a2a1a000,& 1/2\mathrm{Vref}>\mathrm{Vpix}>1/4\mathrm{Vref}& \mathrm{Gain}=2\\ 00a9a8a7a6a5a4a3a2a1a00,& 1/4\mathrm{Vref}>\mathrm{Vpix}>1/8\mathrm{Vref}& \mathrm{Gain}=4\\ 000a9a8a7a6a5a4a3a2a1a0,& \mathrm{Vpix}<1/8\mathrm{Vref}& \mathrm{Gain}=8\end{array}\right.;$

Make imageing sensor under different light intensity, can both allow analog to digital converter be operated in the best input voltage range like this, therefore can reduce noise, the dynamic range of increase system dateout, can under the light intensity in different stages, can both obtain distinct image as human eye, therefore can improve picture quality, satisfy the needs of human eye picture quality.

Be understandable that, also can adopt other modes to distinguish the residing light intensity stage of resulting concrete data.And the corresponding relation of the gain of gain amplifier and comparator output signal and gain all is adjustable, can be provided with as required, illustrates no longer one by one.

In concrete enforcement, the fader among embodiment one and the embodiment two can also integrate with comparator, forms controller.

With reference to Fig. 5, be cmos image sensor reading circuit structure figure in the embodiment of the invention four.Be that with the difference of embodiment two integrated comparator and fader in the controller 51 are suitable for the multiplication factor according to the pixel exposure voltage-regulation variable gain amplifier of pixel 21 outputs.

The embodiment of the invention also provides the method for reading picture element signal from cmos image sensor, and with reference to Fig. 6, for read the method flow diagram of picture element signal in the embodiment of the invention from cmos image sensor, idiographic flow is as follows:

S601, obtain pixel exposure voltage from pixel;

S602, pixel exposure voltage is adjusted by variable gain amplifier;

S603, the analog voltage signal that variable gain amplifier is exported change digital signal and output into;

S604, judgement pixel exposure voltage;

S605, according to the residing exposure voltage of described pixel exposure voltage interval, regulate the multiplication factor of variable gain amplifier.

In the present embodiment, by exposure voltage is judged, and, make the voltage of input analog-to-digital converter be positioned at identical reference voltage all the time according to the interval multiplication factor of regulating variable gain amplifier of exposure voltage of living in.Can make imageing sensor like this under different light intensity, can allow analog to digital converter be operated in best input voltage range, therefore it is bigger to make image reading sensor go out the dynamic range of circuit dateout, and reduction noise, make under different light intensity conditions, all can obtain distinct image, satisfy the requirement of human eye picture quality.

In concrete enforcement, for ease of the digital signal of being exported under the identification different light intensity condition, can the digital signal of output be handled according to the residing exposure voltage of exposure voltage interval, form exposure value.

More than the cmos image sensor reading circuit among the present invention is described in detail by specific embodiment, be understandable that the cmos image sensor that comprises above-mentioned reading circuit is also in protection scope of the present invention.

Though the present invention with preferred embodiment openly as above; but it is not to be used for limiting the present invention; any those skilled in the art without departing from the spirit and scope of the present invention; can make possible change and modification, so protection scope of the present invention should be as the criterion with the scope that claim of the present invention was defined.

Claims (11)

1. a cmos image sensor reading circuit comprises analog to digital converter; It is characterized in that, also comprise:

Variable gain amplifier is suitable for receiving image sensor pixel exposure voltage and adjustment, and outputs to analog to digital converter;

Comparator is suitable for described pixel exposure voltage is judged;

Fader is suitable for receiving the judged result that described comparator is exported, according to the interval multiplication factor of adjusting variable gain amplifier of the residing exposure voltage of described exposure voltage.

2. cmos image sensor reading circuit according to claim 1, it is characterized in that, also comprise digital signal processor, be suitable for the judged result that generates according to described comparator, digital signal to described analog to digital converter output is handled, and forms exposure value.

3. cmos image sensor reading circuit according to claim 1 and 2 is characterized in that, described fader and described variable gain amplifier are integrated into programmable gain amplifier.

4. cmos image sensor reading circuit according to claim 1 and 2 is characterized in that, described fader and described comparator are integrated into controller.

5. cmos image sensor reading circuit according to claim 1 and 2 is characterized in that described analog to digital converter is specially production line analog-digital converter.

6. cmos image sensor reading circuit according to claim 5 is characterized in that, described production line analog-digital converter is specially 10 bit stream pipeline analog-to-digital converters.

7. cmos image sensor reading circuit according to claim 6 is characterized in that, described comparator comprises first comparator, second comparator and the 3rd comparator, and each comparator is provided with different reference voltages.

8. a cmos image processor comprises pixel; It is characterized in that, also comprise each described reading circuit of claim 1 to 7.

9. cmos image processor according to claim 8, it is characterized in that, also comprise digital signal processor, be suitable for the judged result that generates according to comparator in the described reading circuit, digital signal to the output of the analog to digital converter in the described reading circuit is handled, and forms exposure value.

10. a cmos image sensor is characterized in that from the method for pixel reading number signal, comprising:

Pixel exposure voltage is adjusted by variable gain amplifier;

Change the analog voltage signal of variable gain amplifier output into digital signal output;

Judge pixel exposure voltage;

According to the residing exposure voltage of described pixel exposure voltage interval, regulate the multiplication factor of variable gain amplifier.

11. cmos image sensor according to claim 10 is characterized in that from the method for pixel reading number signal, also comprises: according to the residing exposure voltage of exposure voltage interval, the digital signal of output is handled, formed exposure value.

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