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

The input bias current (I-IB) Of the National LM111 voltage comparator exhi bits a non-monotonic response to total dose irradiations at various dose ra tes. At low total doses, below 100 krad(SiO2), increased I-IB is clue prima rily to gain degradation in the circuit's input transistors. At high total doses, above 100 krad(SiO2), I-IB shows a downward trend that indicates the influence of compensating circuit mechanisms. Through correlation of trans istor and circuit response, the transistors responsible for these compensat ing mechanisms are identified. Mon-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 t ransistors, causing a moderate "recovery" in the circuit response.