Ultra-Low-Voltage Operation of CMOS Analog Circuits: Amplifiers, Oscillators, and Rectifiers

This letter presents MOS analog circuits that can operate with very low supply voltages. Operation of the MOS transistor in the triode region is emphasized owing to the limited voltages available. Special attention has been given to the properties of the zero-VT transistor due to its high drive capability at low voltages. Simulation and measurement results for a Colpitts oscillator prototype set up around a zero-VT MOSFET demonstrated that the oscillator operates with supply voltages lower than the thermal voltage kT/q. Finally, ultra-low-voltage rectifiers using diodes or diode-connected MOSFETs operating in weak inversion are analyzed.