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, generat e both white noise and 1/f(alpha)-noise over several decades depending on b iasing current, operating temperature, and the characteristics of the proce ss used, limiting the detector dynamic range. Three readout circuits, based on a fully differential cascode operational transconductance amplifier, de signed and realized on a standard CMOS 0.7-mu m single polysilicon/double m etal process, are proposed for CMOS active-pixel imagers, The first is an u ncompensated switched-capacitor (SC) voltage amplifier; the second, an offs et-compensated SC amplifier; and the third, a commutable bandpass filter. A ll three amplifiers allow correlated double sampling and double delta sampl ing 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(alpha)- noise is used. The theoretical results are compared with experimental data.