High-Voltage RF Waveform Generator

Quadrupole mass spectrometers steer ions by applying high-voltage RF to opposing rod pairs, which means driving multi-kilovolt sinusoids into capacitive loads across a wide frequency range. Commercial sources for that exist but are inflexible and expensive, and a custom mass spectrometer needs a custom drive. This software-defined generator delivers 3 kVpp sinusoids into 1 nF capacitive loads from DC to 10 MHz, built for the quadrupole ion guides of a charge detection mass spectrometer in the Williams lab at Berkeley. The signal chain runs in three stages: a host-controlled DDS arbitrary waveform synthesizer, a power amplifier, and a custom-wound 1:12 center-tapped step-up transformer that produces two 180-degree out-of-phase outputs to drive opposing rods of the quadrupole. The host interface speaks SPI over a custom serial driver that runs on both Windows and Linux. I owned the synthesis and amplifier PCB and validated the full chain in SPICE before bringup, paying particular attention to transformer parasitics and amplifier stability into the capacitive load. I also hand-wound the transformers and characterized them on the bench before integration. Team: Engineering Solutions @ Berkeley

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