Non-stationary noise responses of some fully differential on-chip readout circuits suitable for CMOS image sensors

CMOS active-pixel image sensors, as well as charge-coupled devices, generate both white noise and 1/f/sup /spl alpha//-noise over several decades depending on biasing current, operating temperature, and the characteristics of the process used, limiting the detector dynamic range. Three readout circuits, based on a fully differential cascode operational transconductance amplifier, designed and realized on a standard CMOS 0.7-/spl mu/m single polysilicon/double metal process, are proposed for CMOS active-pixel imagers. The first is an uncompensated switched capacitor (SC) voltage amplifier; the second, an offset compensated SC amplifier; and the third, a commutable bandpass filter. All three amplifiers allow correlated double sampling and double delta sampling for pixel and column fixed pattern noise suppression, respectively. The amplifiers offer up to 10-Mpixels/s readout rates. A detailed theoretical analysis of the amplifiers response to white noise and low-frequency excess noise is given, considering nonstationary nature of the output signals. An original method based on diffusive Markovian representation of 1/f/sup /spl alpha//-noise is used. The theoretical results are compared with experimental data.