This paper uses the simplified charge-based EKV MOSFET model for studying the effects of total ionizing dose (TID) on analog parameters and figures-of-merit (FoMs) of 28nm bulk MOSFETs. These effects are demonstrated to be fully captured by the five key parameters of the simplified EKV model. The latter are extracted from the measured transfer characteristics at each TID. Despite the very few parameters, both the simplified large- and small-signal models present an excellent match with measurements at all levels of TID. The impacts of TID on essential parameters, including the drain leakage current, the threshold voltage, the slope factor, and the specific current, are then evaluated. Finally, TID effects on the transconductance Gm, the output conductance Gds, the intrinsic gain Gm/Gds and the transconductance efficiency Gm/ID are investigated.