HIGH-FREQUENCY LINEAR MULTIPLE-OUTPUT CMOS TRANSCONDUCTANCE AMPLIFIER FOR CURRENT-MODE FILTERS

Abstract

A high-frequency highly linear tunable CMOS multiple-output operational transconductance amplifier (MO-OTA) for fully balanced current-mode OTA and capacitor (OTA-C) filters is presented. The MO-OTA is based on the cross-coupled pairs at the input and provides two pairs of differential outputs. A simple common-mode feedback (CMFB) circuit to stabilize the DC output levels of the MO-OTA is also proposed and two such CMFB circuits are used by the MO-OTA. The proposed MO-OTA is suitable for relatively low voltage (2.5 V) applications as its circuit has only two MOS transistors between the supply and ground rails. Simulated in a TSMC 0.25 μm CMOS process using PSpice, the MO-OTA has at least ± 0.3 V linear differential input signal swing with a single 2.5 V power supply and operates up to 1 GHz frequency. The MO-OTA has a THD less than -46 dB for a differential input voltage of 0.9 Vp-p at 10 MHz, dynamic range (DR) at THD = -46 dB is over 50 dB, and power consumption (with the common-mode feedback circuit) is below 8 mW for the whole tuning range. A fully balanced multiple loop feedback current-mode OTA-C filter example using the proposed MO-OTA is presented. This example also shows that the current-mode follow-the-leader-feedback (FLF) structure can achieve good performances for OTA-C filter design.