Column Settling Speedup Proposal

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Patent application US20120091323 by Shoji Kawahito proposes to speed-up the column voltage sampling onto a big capacitor. The idea is to add small capacitor sampler 17 that samples the column first, then accelerates charging of the main sampling cap C1i. It's quite self-explanatory based on the schematics and the timing diagram below (Block 11 is a pixel driving column Vcol):

There are few other similar ideas, like pre-charging the large C1i capacitor through a unity-gain buffer and then completing the final charge stage directly from column. One can add a little bit high pass filtering in the buffer to compensate for low-pass nature of the pixel+column cap path.

On the other hand, in Kawahito's idea one can add a small time delay or a phase shift in the trans-impedance amplifier 25 on the figure above to achieve a kind of inductive impedance in the column load and get some speed up from it.

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