Identification of degradation mechanisms in a bipolar linear voltage comparator through correlation of transistor and circuit response

Abstract

The input bias current (I/sub IB/) of the National LM111 voltage comparator exhibits a non-monotonic response to total dose irradiations at various dose rates. At low total doses, below 100 krad(SiO/sub 2/), increased I/sub IB/ is due primarily to gain degradation in the circuit's input transistors. At high total doses, above 100 krad(SiO/sub 2/), I/sub IB/ shows a downward trend that indicates the influence of compensating circuit mechanisms. Through correlation of transistor and circuit response, the transistors responsible for these compensating mechanisms are identified. Non-input transistors in the circuit's input stage lower the emitter-base operating point voltage of the input device. Lower emitter-base voltages reduce the base current supplied by the input transistors, causing a moderate "recovery" in the circuit response.