An electronic circuit

A signal generator circuit generates an asymmetric triangular-modulated FM-CW swept frequency signal. The circuit provides a desirable reduction in frequency overshoot (30, fig.2) at the end of the sweep fly-back, while maintaining the linearity of the sweep (10, fig.2). The circuit includes a phase lock loop (PLL) section comprising a frequency synthesizer IC 100, and a VCO 110 driven by an error signal 180 from the synthesiser IC via a loop filter 190. The invention reduces the frequency overshoot present in prior art by adding a triangular voltage waveform VRG to the output of the loop filter 190. A generator 210 produces the voltage VRG in the form of an asymmetric triangular waveform signal substantially matched to the shape of the frequency sweep programmed into the PLL. A combiner 200 receives the signal output from the loop filter 200 and the signal VRG from the waveform generator 210. The circuit monitors (fig.4) the output of the PLL loop filter for a non-DC component that would indicate that the sweep differs from the ideal programmed into the PLL frequency synthesizer integrated circuit.