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Abstract-Ultra-low input bias current linear circuits are used in several applications requiring them to work under varying conditions of temperature, humidity, radiation etc. which influence their performance. This paper presents a first time study of gamma radiation effects on ultra low input bias current linear circuits under biased conditions for small signal dc applications. Under biased conditions, radiation-induced photo currents play a significant role. A noncatastrophic radiation leakage environment has been considered. The linear circuits selected are of different makes and have different input stages, such as those based on JFET and MOS structures. Variations of dc characteristic parameters, such as input offset voltage and input bias current have been studied. Extensive experimental results are presented, including the effects of annealing, on critical parameters. It is seen that these devices behave differently on exposure to gamma radiation, depending on the structure of their input stage. The MOSFET-based stages show a greater change in input offset voltage, whereas FET-based input stages exhibit a greater change in input bias currents. Chopper stabilised linear circuits exhibit lesser deviation in their offset voltages and bias currents due to an inherent chopping action at their input stage that automatically compensates for any variations in these parameters.

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