TUNING-RANGE EXTENSION CIRCUIT FOR SYSTEMS UTILIZING MOSFETS AS TUNABLE RESISTORS

摘要

A tuning range extension circuit for systems utilizing MOSFETs as tunable resistors is provided. The circuit utilizes an extra MOSFET in parallel to each existing MOSFET, in combination with a switching system. The switching system receives a tuning voltage, a supply voltage and reference voltages indicative of the operating limits of a filter. The switching system maintains the MOSFET of the system in a defined on or off mode by comparing the tuning voltage value to the reference voltage values, and switching the gates of the additional MOSFET between the tuning and supply voltages.