Nonlinearity compensation circuit for voltage-controlled oscillator operating in linear frequency sweep mode

Abstract

A circuit that can compensate for nonlinearity in frequency modulation of a voltage-controlled oscillator (VCO) is proposed. The circuit uses a fixed-length delay line and an analog phase-locked loop (PLL). It sweeps the frequency of VCO output linearly in time and easily adjusts the rate of frequency sweep. For a VCO operating in a frequency range of 5.3 similar to 5.4 GHz, the nonlinearity in frequency modulation was measured by observing the beat frequency f(B)(t) between the VCO and delayed VCO outputs. The deviations of f(B) (t) of similar to 28% from its average values (2, 5, and 10 KHz) were reduced to <2% after compensation, indicating that the linearity in frequency modulation was improved significantly independent of the rate of frequency sweep.