Unilateral power gain resonances and roll-off with frequency for the velocity-saturated MOSFET/MODFET wave equation

The bias, frequency, and gate length dependences of the intrinsic and extrinsic current gain and the unilateral power gain of the saturated MODFET are investigated using the velocity-saturated MOSFET/MODFET wave equation. Both short-channel and long-channel devices are considered. It is shown that when the ratio (V_GS-V_T)/(F_c L_g) becomes larger than one the ideal MOSFET/MODFET switches from the long- to the short-channel mode. The high-frequency analysis of the wave equation reveals the existence of unilateral power gain resonances in the intrinsic MODFET. Steady-state power gain is therefore conceptually possible in the intrinsic MODFET. The same frequency analysis for the extrinsic MODFET predicts, however, that realistic lossy parasitics will suppress these unilateral power gain resonances, and that under such conditions the resulting unilateral power gain of a FET in the short-channel mode will exhibit a switch from a 20- to 40-dB drop per decade at approximately the resonant frequency