Integrating photosensor and imaging system having wide dynamic range

Abstract

An integrating photosensor includes an NPN phototransistor having its collector connected to a source of positive voltage, a P-channel MOS transistor having its gate connected to row-select line, its source connected to the emitter of the phototransistor, and its drain connected to a column sense line. The NPN phototransistor has an intrinsic base-collector capacitance. An integrating sense amplifier according to the present invention includes an amplifying element having an inverting input and a non-inverting input. The non-inverting input is connected to a source of reference voltage the inverting input is connected to a sense line. A P-channel balance transistor is connected between the inverting input and the output of the amplifying element and a capacitor is also connected between the inverting input and output of the amplifying element. An exponential feedback element is connected between the output and the inverting input of the amplifying element. A plurality of integrating photosensors is disposed in an array of rows and columns, with a given row select line connected to the gates of P-channel MOS transistors associated with that given row and a given column sense line connected to the drains of the P-channel MOS transistors associated with that given column.