[Background]: Encoders are susceptible to total dose effects

leading to performance degradation and posing a threat to the safety of nuclear industry and aerospace systems. [Purpose]: This study aims to investigate the total ionizing dose (TID) radiation effects on a custom-designed BCD (Bipolar-CMOS-DMOS) process photoelectric encoder control circuit employing enclosed layout devices. [Methods]: This research involved an overall circuit of the encoder and its various modules within the circuit to elucidate the radiation damage mechanisms of the encoder. By testing the output voltage and current of the overall circuit and modular circuits under varying doses as a function of input

the influence patterns of total-dose irradiation on the output parameters of different circuit sections were compared. From this comparison

sensitive areas within the circuits were identified. Simulations were conducted to determine the impact of changes in the threshold voltage and capacitance of devices on the output. [Results]: The results reveal varying degrees of degradation in the output characteristics of different encoder circuit modules during irradiation

with the comparator module being the most sensitive to radiation. The overall output remains largely unaffected when the total dose reaches 5 Mrad(Si). [Conclusions]: It is determined that the gate-to-drain capacitance of the devices significantly contributes to radiation damage in the comparator module

while the degradation of the inverter module is attributed to threshold voltage shift. The stability of the overall circuit output is due to the compressive effect of the inverter module on the output distortion of the previous stage.