Image sensor utilizing a low fpn high gain capacitive transimpedance amplifier

Abstract

An imaging element and an imaging array constructed from such elements. The preferred imaging element is constructed from a photodiode having a parasitic capacitance C ; and an amplifier for measuring the charge stored on the parasitic capacitor. The amplifier includes an opamp having a signal input, reference input and output; the first terminal of the parasitic capacitor is connected to the signal input. The imaging element includes a reset switch for shorting the signal input and the output of the opamp, and capacitive network. The capacitive network connects the signal input and the output of the opamp, and provides a capacitance of C between the signal input and the output of the opamp wherein C <C . The capacitive network is constructed from a plurality of component capacitors. Preferably each component capacitor has a capacitance greater than or equal to C . An imaging array according to the invention includes a plurality of imaging elements, a signal bus, a reset bus, and a reset circuit. Each imaging element also includes a coupling switch for connecting the output of the opamp to the signal bus and a reset coupling switch for connecting the photodiode to the reset bus via a low-pass filter. The reset circuit includes a second opamp having a signal input, a reference input connected to a second reference potential, and an output connected to the reset bus; and a reset coupling switch for connecting the signal input of the second opamp to the signal bus.