Generation, design and tuning of OTA-C high-frequency sinusoidal oscillators

Abstract

A systematic approach to derive practical CMOS sinusoidal oscillators is presented. A general topology is given to implement sinusoidal oscillators by using operational transconductance amplifier capacitor (OTA-C) techniques. To illustrate the proposed approach five different structures are presented from this general topology and analysed, taking into account the CMOS OTAs dominant non-idealities. Building blocks are presented for amplitude control, both by automatic gain control (AGC) schemes and by limitation schemes. Experimental results from 3 μm and 2 μm CMOS (MOSIS) prototypes showing oscillation frequencies up to 69 MHz are included. The amplitudes can be adjusted between 1 V peak-to-peak and 100 mV peak-to-peak. Total harmonic distortions (THD) from 2.8% down to 0.2% have been experimentally measured in the laboratory. A frequency tuning loop for these structures is introduced that provides a precise, temperature and parasitic independent frequency-to-voltage relationship. Experimental results for the tuning loop are presented.