Using Modified Bessel Functions For Calculations of Drain Current Harmonics In a MOS Transistor Operating in Moderate Inversion

The paper describes evaluation of drain current harmonics in a MOS transistor operating in moderate inversion and strong saturation. The dependence of the drain current on the gate-source and drain-source voltages is described using a simplified 'reconciliation' model developed by Y. Tsividis. Then, in the proposed model the current components corresponding to the terms depending exponentially on normalized gate-source and/or drain-source modulating sinusoidal voltage are evaluated using modified Bessel functions. This approach allows one to omit the small-signal requirement for modulating signals, and calculate the first, second and third harmonics of the drain current caused by the gate-source or drain-source voltages and also find the intermodulation terms. The results are applied to the design of low-distortion low-voltage amplifiers. The recommendations are confirmed by simulations.