A CMOS SOFT-SWITCHED TRANSCONDUCTOR AND ITS APPLICATION IN GAIN-CONTROL AND FILTERS

This paper presents a transconductor suitable for implementation in su bmicron CMOS technology. The transconductor is nearly insensitive for the second-order effects of the MOS transistors, which become more and more prevalent in today's submicron processes. The transconductor rel ies on a differential pair with variable degeneration resistance, whil e the degeneration resistors are ''soft-switched'' by means of MOS tra nsistors. The transconductance is continuously tunable. A transconduct or, using a device in which the degeneration resistors and ''soft swit ches'' are merged, is optimized for a maximum tuning range and can be used in variable gain stages like in an automatic gain control (AGC) c ircuit. Besides, a third-order 5.5 MHz low-pass filter has been realiz ed in a 0.5-mu m CMOS process using the ''soft-switched'' transconduct or. At a 3.3 V supply voltage the filter dissipates 12 mW and the dyna mic range equals 62 dB where the total harmonic distortion (THD) is -4 8 dB for an input voltage of 1 V-pp.