The waveform generator circuitry 1320 is configured to generate RF chirps using an auxiliary input such as a step or an impulse to perturb the phase locked loop in a so-called “feedback loop perturbation” approach. As shown in FIG. 13B, waveform generator circuitry 1320 includes a voltage controlled oscillator (VCO) 1322, signal splitter 1324, programmable digital divider 1326 that is programmable by input provided via line 1325, frequency multiplier (sometimes termed “phase comparator”) 1328, summation block 1330, and loop filter 1332. Additionally, waveform generator circuitry includes a fixed frequency reference oscillator 1336 (e.g., a quartz crystal) and a step/impulse generator 1334. The summation block 1330 is within the PLL so that a step and/or impulse generated by step/impulse generator 1334 may be fed directly into the loop thereby perturbing the loop to sweep up to a desired frequency then correct-back-down to its programmed frequency. This perturbation in the feedback loop would cause an up-then-down chirp, relying on a second order transfer function of the loop filter 1332 so that the output provided on line 1327 is a linear chirp. This feedback loop perturbation technique may be less precise than the PLL techniques described with reference to FIGS. 13A and 13C, but may be cheaper to implement.
