Low-noise cmos active pixel sensor for imaging arrays with high speed global or row reset

Abstract

An active-pixel low-noise imaging system for implementation in CMOS or in other semiconductor fabrication technologies uses three transistors and a single capacitance per pixel. The first transistor serves as a reset and a transimpedance amplifier to facilitate high impedance and suppress reset noise without requiring expensive on-chip or off-chip memory. The second transistor is an access MOSFET used to read the signal from each pixel and multiplex the signal outputs from an array of pixels. The third MOSFET resets the detector after the integrated signal has been read. Since the detector sense node is “pinned” by the feedback amplifier, reset noise is reduced to that generated by the much smaller feedback capacitance. In addition, by using a small but well-defined feedback capacitor, an amplifier with a narrow bandwidth can be used, provided its unity-gain frequency is sufficient. Since the pixel-base amplifier's output capacitance is far smaller than the bus capacitance, the total energy consumed during reset is very small and overall power consumption is kept at a level consistent with battery-powered operation.