Development of RSFQ voltage drivers for arbitrary AC waveform synthesisers

We have realised RSFQ circuits for an integrated bit pattern generator to drive large Josephson junction arrays and synthesise arbitrary AC waveforms. We present test circuits to investigate the driving of junction arrays by sequences of voltage pulses. To elevate the level of voltage pulses, the circuits have been terminated by SQUID stack voltage drivers. Drivers of various bit lengths and different designs, in pure-serial and in combined parallel-and-serial SFQ pulse processing modes, were developed, fabricated and tested. Voltage amplification by factors four and eight were obtained. The circuits were realised in 4-µm Nb SIS trilayer technology with externally shunted Josephson junctions (critical current density: 1 kA/cm²).