A floating voltage-controlled linear resistor and its application to active RC filters

A new floating voltage-controlled linear resistor that employs four identical small-dimension MOS transistors is presented. The proposed circuit utilizes only a single external voltage to control the active resistor through its full range. Simulation results using SPICE 3 show that the total harmonic distortion (THD) is less than -74 dB for signals up to 3.5 V peak-to-peak applied across the proposed floating resistor. Using MOS transistors with W/L of 2/4 mu m and 2/7 mu m, it has been possible to achieve resistances in the ranges 3-12.5 k Omega and 4.9-20 k Omega, respectively. The application of the proposed floating resistor to various active RC filters is discussed.