Buffer circuit

This invention relates to a buffer circuit of the kind incorporating a metal oxide-silicon field-effect transistor (MOSFET) for use in buffering circuits and sensors such as photosensitive elements and other transducers. A buffer circuit includes a MOSFET source follower (M) and a floating gate MOSFET (MFG) connected in series with the phototransistor (PT) to control current through it at an input circuit node (D). The source follower (M) buffers the phototransistor (PT), having a gate (G) connected to its emitter (PC). The floating gate (F) is programmable with charge to preset the phototransistor current under prearranged illumination conditions to counteract unwanted signal contributions (e.g. fixed pattern noise) or non-optimum circuit characteristics. The floating gate MOSFET (MFG) may alternatively be connected in series with the source follower output (D) to control current at an output circuit node. The circuit may be a member of a pixel circuit array and may include programming circuitry (M, M) to select it for programming and to isolate it to enable other array members to be programmed.