Two fundamental classes of gain nonlinearity exist for CMOS and CCD imagers: V/V nonlinearity and V/eâ nonlinearity. Ideally, V/V nonlinearity for a camera system is dominated by the pixel's source follower amplifier. Nonlinearity characteristics for the amplifier can typically be controlled to less than 1% over a sensor's dynamic range. V/eâ nonlinearity is related to sense node diode capacitance, which increases as charge collects (refer to Fig. 4.3). For CCDs, the sense capacitance change is usually negligible (typically < 0.2% nonlinearity). However, for CMOS detectors, V/eâ nonlinearity can be significant, exceeding 200% for some pixel architectures (e.g., refer to Sec. 7.3).
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