Abstract: Disclosed are a plurality of different circuits employing a field effect transistor (FET), that preferably is a pseudomorphic high-electron-mobility transistor (PHEMT) that may be fabricated on a large-size monolithic chip, wherein the PHEMT is operated as a variable resistance in response to a first operating signal voltage applied to its gate and a second operating signal voltage having at least a first of two opposite polarities applied to its drain-source path, at least one of first and second operating signal voltages includes a multigigahertz frequency signal component having a certain phase; and the respective amplitudes of the first and second operating signal voltages are sufficiently low that the maximum power dissipation by the circuit is in the order of microwatts or less.