As shown in FIG. 14D, the waveform generator circuitry 1464 also includes a voltage controlled oscillator (VCO) 1302, signal splitter 1304, programmable digital divider 1306 that is programmable by input provided via line 1305, and loop filter 1312. The DDS 1440 operates as a reference oscillator for the resulting phase locked loop. In some embodiments, the DDS 1440 may be a digital synthesizer that stores (e.g., in a memory part of DDS 1440) values for a digital waveform (e.g., a sinusoid, a chirp, or any other suitable waveform). The DDS 1440 may be configured to “play back” the stored values through a digital to analog converter (DAC). That is, the DDS 1440 may be configured to process the stored values using a DAC, which may be part of the DDS 1440 in some embodiments, and output the resulting analog values. The rate at which the DDS 1440 outputs the stored values for the digital waveform may determine its output frequency. In some embodiments, the DDS 1440 may be chirp-modulated above and below a center reference clock frequency, thereby causing the output of the VCO 1302 to chirp at its carrier frequency. The DDS 1310 may be chirp modulated in any of a variety of ways, examples of which are provided herein. The output of DDS 1310 is multiplied-up in the PLL thereby providing a chirp at the microwave frequency of interest at the RF Out line 1307.
