[image sensor] correlated double sampling CDs

Creation time ：2022-06-16

The principle of correlated double sampling
Correlation double sampling （Correlated Double Sample, CDS） For image sensor .
Sample the two levels of the output signal respectively , That is, sampling the reset level once , The other is to sample the signal level ）.
If at the beginning of the integration of the photoelectric signal t1 And the end of the integral t2, Sample the output signal respectively （ In one signal output cycle , Generate two sampling pulses , Sample the two levels of the output signal respectively , That is, once is right “ Reset level ” sampling , Another time is right “ Signal level ” sampling ）., And the interval between two sampling times is much smaller than the time constant CRon（Ron Is the on resistance of the reset tube ）, In this way, the noise voltage of the two samples is almost the same , The time of two samples is also related If the two sampling values are subtracted , The interference of reset noise is basically eliminated , Get the actual effective amplitude of the signal level .

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Correlation double sampling （CDS）
This is a CCD A very important concept in , It is based on CCD Designed according to the characteristics of output signal and noise signal , It can eliminate the interference of reset noise , It also suppresses low-frequency noise , It can significantly improve the signal-to-noise ratio , Improve signal detection accuracy .
because CCD The output signal of each pixel contains both photosensitive signals , It also contains reset pulse voltage signal , If at the beginning and end of the integration of the photoelectric signal , Sample the output signal respectively （ In one signal output cycle , Generate two sampling pulses , Sample the two levels of the output signal respectively , That is, sampling the reset level once , The other is to sample the signal level ）, And grasp the time interval between two sampling , In this way, the noise voltage of the two samples is almost the same , Subtract the two sampling values , The interference of reset noise is basically eliminated , Get the actual effective amplitude of the signal level , The specific principle is shown in the figure below （ Every time AD Yes CCD Signal acquisition is in SHP and SHD Starting from the rising edge of ; The data output clock is placed on SHD The rising edge of and the next SHP Falling edge reading of ）：

http://blog.sina.com.cn/s/blog_7ae27eb10102vi01.html

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