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 5.3-5.4 GHz, the nonlinearity in frequency modulation was measured by observing the beat frequency f/sub B/(t) between the VCO and delayed VCO outputs. The deviations of f/sub B/ (t) of /spl sim/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.
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Kang et al. (2000) studied this question.