Simulation and Measurement of Fully-differential CMOS OTAs

Simulation and testing methods for fully-differential operational transconductance amplifier (OTA) circuits are described. Difficulties of measuring OTA performance caused by the generally large bandwidth of OTAs and the need for measuring current signals are illustrated. A fully-differential OTA fabricated through the MOSIS 2μ-CMOS technology is the demonstration circuit for simulations and tests. This OTA has a simulated 3 dB frequency of 1 GHz with a load of 100 Ω. The simulation softwares are SPICE, Version 3f4, and ADS from Tektronix, Version 5a8. The measurement equipment includes a 500 MHz gain-phase and spectrum analyzer, a 200 MHz oscilloscope, a 100 MHz synthesized arbitrary function generator, and high-precision power supplies. The approaches shown in this paper can be used to provide design guidelines for OTAs, and practical directions for the design of continuous-time filters.

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