Photodetector circuit

摘要

A photodetector circuit (100) fabricated in BiCMOS exhibits improved temperature stability. A bipolar phototransistor (200) generates a photocurrent (Ibi) in response to illumination. This photocurrent (Ibi) is passed through a diode connected load MOSFET (114) operating subthreshold which gives a logarithmic voltage output. This ensures a large dynamic range of the photon detection system. The phototransistor (200) has gain ( b ) which amplifies an initial current response and ensures that current Ibi) through the load MOSFET (114) is significantly higher than MOSFET leakage current. This improves performance at high temperatures when the leakage current is large, whilst maintaining photodetector sensitivity to low illumination levels. The photodetector circuit (100) is particularly suitable for incorporation in a detector array (315) for use in a digital camera.