Feedforward-Regulated Cascode OTA for Gigahertz Applications

A very high-frequency operational transconductance amplifier (OTA) with a new feedforward-regulated cascode topology is demonstrated in this paper. Experimental results show a bandwidth of 10 GHz and a large transconductance of 11 mS. A theoretical analysis of the OTA is provided which is in very good agreement with the measured results. We also carry out a Monte Carlo simulation to determine the effect of transistor mismatches and process variations on the transconductance and input/output parasitic capacitances of the OTA. The linearity and intermodulation distortion properties of the OTA, which are of particular interest in microwave applications, are experimentally determined using a purpose-built single-stage amplifier. For high-frequency demonstration purposes we built a larger circuit: an inductorless microwave oscillator. The fabricated oscillator operates at 2.89 GHz and has a significantly larger output voltage swing and better power efficiency than other inductorless oscillators reported in the literature in this frequency range. It also has a very good phase noise for this type of oscillators: ${-}116$ dBc/Hz at 1-MHz offset.