100 mV PEAK OUTPUT DEMONSTRATED FOR THE JOSEPHSON WAVEFORM SYNTHESIZER.

For the first time NIST has been able to synthesize waveforms with peak output voltages exceeding 100 mV using the Josephson waveform synthesizer. This two-times increase in voltage was possible by summing the output voltage of two 4100-junction series arrays. Achieving large output voltages has been difficult with the Josephson synthesizer because the arrays are biased with broadband dc to 18 GHz input waveforms that are not easily divided and summed from different circuits. Fortunately, the recently developed ac coupling technique that divides the low ([less than] 10 MHz) and high frequency input signals allows researchers to drive multiple arrays in parallel at high frequency and to bias the arrays in series at low frequency. Combining the low frequency output waveforms of N arrays in series results in an N-fold increase in output voltage compared to a single array. This is the first time that the output voltage of two arrays has been combined for ac waveforms. Researchers have demonstrated waveforms with 121 mV peak voltage by driving two arrays with a 7.5 GHz sine wave and a 5 Gbit/s digital code input signals. The harmonic distortion for a synthesized 5 kHz sine wave was more than 100 dB below the fundamental. This is the lowest distortion measured for any Josephson synthesizer circuit and it demonstrates that both arrays have good operating margins.