Analysis of nonlinearities in a voltage-controlled oscillator

Abstract

A voltage-controlled oscillator is investigated to determine the source of nonlinearities in the frequency-to-voltage characteristic. A computer model for the voltage-controlled oscillator is developed which emphasizes’ the nonlinear behavior of the current gain in its transistors. Additionally, a comprehensive model of the current mirror circuit is derived. The current mirror circuit plays an important role in determining the output frequency of the VCO. Included in the current mirror model are the effects of the unequal transistor power dissipation on the VCO performance. An inexpensive and practical solution is proposed that allows the voltage-controlled oscillator to operate in a more linear fashion. The experimental measurements of the implementation of the proposed solution on a sample voltage-controlled oscillator yield favorable results. Additionally, a computer simulation incorporating the proposed solution compares favorably with the experimental data.