For the first time, we synthesize single- and multiple-tone waveforms at gigahertz frequencies from arrays of Josephson junctions and demonstrate quantum-locked operation over a range of experimental input parameters. We first use a lumped-element circuit to synthesize 1~GHz and 2~GHz single-tone waveforms with \textendash71~dBm output power and in-band spurious-free dynamic range (SFDR) of \textendash66~dBc. We then introduce a narrow-band diplexer circuit and synthesize a 1~GHz sinusoid with higher power (\textendash49~dBm) and in-band SFDR of \textendash79~dBc. To demonstrate the spectrally-selective power- and phase- programmability of the diplexer circuit, we also synthesize multisine waveforms with total waveform power of \textendash52~dBm. The spectral purity of the reported waveforms is limited by the room- temperature electronics rather than by the quantized pulse-based synthesis technique. This paper provides direction for future circuit designs and uncovers the main factors that must be addressed to achieve higher power, higher spectral purity, and improved output power accuracy. The reported results represent progress towards a primary RF reference source that synthesizes programmable, quantum-referenced, low-distortion signals at gigahertz frequencies.
IEEE Transactions on Applied Superconductivity