A Microwave OTA Using a Feedforward-Regulated Cascode Topology

A CMOS operational transconductance amplifier (OTA) with a novel feedforward-regulated cascode topology is proposed and experimentally demonstrated in this paper. It enables high-speed operation of the proposed OTA up to 8 GHz. For demonstration purposes, a microwave variable resistor and a variable active inductor using this OTA were fabricated using 0.18 mum CMOS process. Experimental results show that this OTA has a relatively high transconductance of about 10.5 mA/V at frequencies up to 8 GHz, with a tuning ratio of 1:5.3. The fabricated active inductor can achieve over 4.7 nH inductance at GHz frequencies and an inductance tuning ratio of 1:3.6 for microwave applications. The OTA basic cell integrated circuit measures 145times67 mum², excluding bonding pads.