A comparative study of gamma radiation effects on a logarithmic amplifier based multiplier circuit using common and Precision Devices

Abstract

Logarithmic circuits facilitate the compression of a wide range of current signals and are, therefore, highly suitable in nuclear instrumentation. Functioning of these circuits, however, can be seriously affected if the characteristic properties of operational amplifiers (Op Amps) (which make up these circuits) such as input offset voltage and input bias current get altered in the harsh nuclear environment. Reliability considerations demand that performance of such circuits be predicted under such conditions. This paper reports a comparative study of the performance of logarithmic amplifier circuits, comprising of different types of Op Amps, when exposed to gamma radiation. Study is done using a multiplier circuit where log and antilog circuits are used. A useful approach has been adopted wherein the multiplier circuit is modelled using the commonly used Op Amp model which allows simulation of the effect of gamma radiation damage using the experimentally obtained bias current and offset voltage values, without the need for dedicated software. The type of input stage of the Op Amp (FET, Bipolar etc.) significantly affects the performance of these circuits under radiated conditions. Therefore, a wide range of commonly used devices (HA17741, LM324 etc. having bipolar stages) and precision devices (OP15, OPA128JM and LMC6001AIN having JFET stages) are considered. Simulation and experimental results are included.