Design, Realization, and Evaluation of a Riemann Pump in GaN Technology

The realization of a novel Riemann Pump for radio frequency digital-to-analog converters (RF DACs) in combination with a power amplifier is presented, which improves the signal-to-noise ratio of conventional converter concepts. The presented concept results in an arbitrary waveform generator that at the same time is capable to provide several watts of output power at RF-frequencies to 50 Ω. Furthermore, the gallium nitride (GaN) high-electron-mobility transistor technology provides high-switching frequencies to ensure an oversampling ratio of 5 for a wide baseband bandwidth. The Riemann Pump, which is controlled with a digital bit-stream, is based on the current-steering topology and provides the possibility to synthesize arbitrary waveforms. A 2-b RF DAC was designed with multiple GaN monolithic microwave-integrated circuits and proves the feasibility to generate arbitrary waveforms. Measurement results yield triangular signals with a baseband frequency of 100 MHz for an input-control data rate of 200 Mb/s.