US 4,831,257 A · Gate coupled input circuit

Abstract

What is disclosed is a preamplifier used with each pyroelectric detector in an infrared imaging array system. To bias the preamplifiers either a MOSFET transistor is utilized as a switch that is periodically operated to place charge on the gate of the MOSFET preamplifier transistor to maintain it at its bias level, or an NPN transistor is operated at a level to provide high impedance. When the bias switch is not operated, the associated detector detects and a reading is taken from each detector in the array. NPN transistor switches can be manufactured consistently and their conduction level can be adjusted to balance the gain of all preamplifiers in the detector array. The supply voltage to the preamplifiers in the array is monitored by a feedback circuit which compares a supply voltage to a reference voltage and adjusts the preamplifier bias voltage to compensate for changes in the supply voltage.

Claims12

Dependent claims

A circuit for use in a thermal imaging system comprising:

an infrared detector for detecting an infrared signal impinging thereon,
an amplifier having an input to which said detector is connected, and an output, said amplifier responding to said detector detecting an infrared signal to provide an amplified electrical signal representing said infrared signal at its output, and
a bias transistor associated with and connected to the input of said amplifier, said bias transistor being operated to act as a high impedance variable resistor and being used to bias both said detector and said amplifier, said bias transistor normally operating as to have an impedance in the range of 10.sup.12 to 10.sup.15 ohms.

Dependencies are inferred from the claim text.

Gate coupled input circuit

Life of this patent

Gate coupled input circuit

Life of this patent

Abstract

Claims12