Extremely high speed, real-time background filter for radiation detectors

Abstract

A five stage background filter circuit 10 is disclosed which is capable of responding to background radiation changes at speeds which are from one to two orders of magnitude faster than conventional prior filters. The invention utilizes a cross scan multiplexing technique in combination with filter circuitry depicted in schematic overview in FIG. 1. Circuit 10 includes a differential amplifier 12, a sample and hold device 14, a responsivity corrector 16, a recursive filter 18, and a background subtractor 20. Output signals 11 from a focal plane array of detectors (shown in FIG. 3) are passed through impedance matching input resistors 12a,b to an amplifier. A sample and hold circuit 14a cyclically selects and stores a signal received from first stage 12. The detector outputs are then normalized by responsivity corrector stage 16 which employs a digital-to-analog converter 16a and random access memory 16c. A threshold band comparison and time-out logic circuit 21 within background subtractor stage 20 controls the operation of recursive filter stage 18 in order to suppress signals due to sensed radiation bursts and to eliminate the unwanted, dynamically varying background radiation portion of the signal present at node 17b. A processed output signal present at node 20i is then passed to a target detection processor (not shown).