FIELD EFFECT TRANSISTOR DETECTOR AMPLIFIER CELL AND CIRCUIT PROVIDING A DIGITAL OUTPUT AND/OR INDEPENDENT OF BACKGROUND

摘要

A light sensitive element, typically a photo-transistor, diode or the like, is suitably coupled to a load element, typically an FET device suitably biased as a linear load. An output circuit including a high input impedance element, typically an FET inverter, is coupled between the linear load and the diode. Little or no current flows in the input circuit in the absence of light applied to the light sensitive element. When light is applied current flows through the light sensitive element and modulates current flow through the inverter. The output circuit has high sensitivity to low level light signals by reason of the linear load and the absence of "Johnson" or thermal noise. A suitable connection between the light sensitive element and the load element sets the output circuit in a threshold state for immediate response to light signals. Connecting the inverter output to suitable circuitry, i.e., amplifiers, differential amplifiers, level shifters and the like, provides an analog or digital output sensitive to extremely low light levels.