This paper presents a modeling approach to simulate the impact of total ionizing dose (TID) degradation on low-power analog and mixed-signal circuits. The modeling approach has been performed on 180-nm n-type metal-oxide-semiconductor field-effect transistors (n-MOSFETs). The effects of the finger number, channel geometry, and biasing voltages have been tested during irradiation experiments. All Berkeley short-channel insulated gate field-effect transistor model (BSIM) parameters relevant to the transistor properties affected by TID have been modified in an algorithmic flow to correctly estimate the sub-threshold leakage current for a given dose level. The maximum error of the model developed is below 8 %. A case study considering a five-stage ring oscillator is simulated with the generated model to show that the power consumption of the circuit increases and the oscillation frequency decreases around by 14 %.