subsidiary and entire circuits of CMOS amplifiers with P channel transistor pair inputs have been investigated. It was shown that the main mechanisms of performance degrade of op-amps is unbalance of the current mirror caused by the non-symmetry output characteristics of the differential input transistors. So good match of the op-amps’ structure and the I-V characteristic of its transistors are the key issues to determine the tolerance of an op-amps to total dose radiation.