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about PGA of CMOS image sensor

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lhlbluesky

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if the gain range of PGA (used in cmos image sensor) is 1~9，then for the sensor of small(for example,300,000) pixel array, is it that smaller gain range should be used,such as 1~2, and for the sensor of large(for example,10,000,000)pixel array, is it that larger gain range should be used,such as 7~9?

am i right?pls give me some advice.thanks all.
 

What do you mean by PGA, and the gain range?

I have a PhD in CMOS image sensor design and I design them for a living, but I'm not sure what you're asking.

What type of CMOS sensor? Is it just the sensor you're reffering to, or is it a sensor integrated into a camera?
 

it is a sensor(general) integrated into a camera.and PGA is programmable gain amplifier.gain range refers to magnification range.
 

The sensor is a chip with a an array of pixels, nothing more (well, address decoders and output amps etc.). A camera is a sensor with addressing, clocking, processing etc.
The mognification is an optical phenomena and has nothing to do with amplification.

Digital zoom is basically picture cropping.

Where is this PGA amp in the citcuit? is it after the analogue output of the sensor (within the camera)?
If it is, I assume it is just a sort of contrast control (or gain), if biased correctly a white balance.
 

pixel out---PGA---ADC----digital processing
 

lhlbluesky said:
pixel out---PGA---ADC----digital processing
Click to expand...

So it's after the analogue output of the sensor, then refer to my previous post.
 

lhlbluesky,haw-haw,you should have posted this problem in our weekly subject discussion.In our
CIS Chip,Digital Programmble Gain Amplifier is used as a color adjust.After the Bayer Pixel convert the photocurrent into the drop of the storage node, the R and B pixel's output are readouted by the upper bus of the CIS,while the G pixel's are done by the lower bus. Because color balancing often be a main function of our chip,the DPGA will act as a analogue multiplier which can change the signal without the DSP processing. The original design come from the CCD analog-front-end circuit.as for the different gain range(1-3,2-6,3-9),that's just aimed at different illumination condition,not the size of pixel array.
 

zhaoshibin said:
you should have posted this problem in our weekly subject discussion.
Click to expand...

Sorry, is there such thing as weekly subject discussion? Where is it?

Thanks
 

The PGA gain has nothing to do with the sensor array size.
When you change the ISO sensitivity of your digital camera, you are basically tweaking your PGA gain. In low light conditions the sensor outputs are low and to get the full ADC resolution the signal is amplified by the PGA.
 

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