This paper reports on the design of a Schmitt trigger for the generation of high-speed switching signals with pulse-width modulation capability. The circuit is implemented using HBT transistors in a 130nm SiGe BiCMOS process, and shows broadband operation from 200 MHz up to 18 GHz. It has a single-ended output voltage swing of 400 mV, and rise/fall times of 10 ps and 13 ps at 10 GHz. The output-waveform duty cycle is tuned by varying the circuit’s threshold levels for the switching transitions, resulting in a continuous tuning range between 13% and 85% at 1 GHz. A push-pull Totem-Pole output buffer is designed to enable measurements with 50 Ω measurement equipment. The trigger circuit has 24.6 mW power consumption, in addition to 20.8 mW for the output buffer at the 50% duty cycle setting. The circuit implementation is very compact, requiring only 0.02 mm2 of active area. To the best knowledge of the authors, this is by far the fastest reported Schmitt trigger to date.