Ramp linearization for FMCW radar using digital down-conversion of a sampled VCO signal

摘要

The invention relates to an FMCW radar system and a method of operating an FMCW radar system to produce a linear frequency ramp. The FMCW radar system includes a VCO, a frequency divider coupled to the VCO output, followed by an A/D converter. A down-converter shifts the digitally converted signal to baseband samples, followed by a low-pass filter coupled to an output thereof. A VCO frequency estimator produces instantaneous VCO frequency estimates from phase differences determined from the filtered baseband samples. A D/A converter coupled to an output of the VCO frequency estimator produces an input signal for the VCO to produce therewith a linear VCO frequency ramp. A Δ-Σ modulator is coupled between the VCO frequency estimator and the input of the D/A converter to produce a dithered VCO control signal, thereby increasing the effective number of bits of the D/A converter.