Monday, July 02, 2012

Omnivision's Dual Conversion Gain and FD Boosting Application

Omnivision patent application US20120153123 presents dual conversion gain pixel with a possibility of FD voltage boost. A prior art dual conversion gain pixel just adds a cap on FD like this:


Omnivision proposes to connect the cap from outside of the array, like that:


The low CG setting can be made even lower by adding -G amp, like shown below:


Once we are at column amplifiers, one obvious improvement is to add a positive gain amp for the high CG setting, so that the effective FD capacitance would be reduced by a weak positive feedback. For some reason the application does not mention this option.

The added capacitor also allows to boost FD potential to (over)compensate the charge injection and control feedthrough when RST gate turns off (the first figure is prior art, the second one is improvement):

3 comments:

  1. Vladimir, it is not clear to me why it is needed this addition of complexity to the pixel. I guess a per pixel gain variation is more difficult to compensate than the column level one..

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  2. The low/high gain can be set globally, for the whole array, rather than per pixel. In low light mode high CG gives low noise. In strong light, low CG mode FD swing is reduced, so PD can have higher pinning voltage and, hence, larger full well.

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  3. Is it possible to be proven by silicon??

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