On the Design of Voltage-Controlled Sinusoidal Oscillators Using OTA's

A unified systematic approach to the design of voltage-controlled oscillators using only operational transconductance amplifiers (OTA's) and capacitors is discussed in this paper. Two classical oscillator models, i.e., quadrature and bandpass-based, are employed to generate several oscillator structures. They are very appropriate for silicon monolithic implementations. The resulting oscillation frequencies are proportional to the transconductance of the OTA and this makes the reported structures well-suited for building voltage controlled oscillators (VCO's). Amplitude stabilization circuits using both automatic gain control (AGC) mechanisms and limitation schemes are presented which are compatible with the transconductance amplifier capacitor oscillator (TACO). Experimental results from bipolar breadboard and CMOS IC prototypes are included showing good potential of OTA-based oscillators for high frequency VCO operation.