Investigation of binary Josephson arrays for arbitrary waveform synthesis

Arrays of Josephson junctions have been used successfully for many years as the primary standard of voltage. A recent development has been the fabrication of arrays, based on nonhysteretic Josephson junctions, which allows the voltage output to be changed almost instantaneously. When these arrays are divided into binary segments a ´digital-to-analogue converter´ with quantum accuracy is created. The properties of two types of array, a SINIS (superconductor-insulator-normal conductor-insulator-superconductor) array, using intrinsic shunting of the Josephson junctions, and a SIS (superconductor-insulator-superconductor) array with external, on-chip shunting have been investigated. The accuracy of the generated voltages and AC properties of the arrays when driven with a purpose-built, programmable current bias source are discussed. It is anticipated that a Josephson standard having waveforms with calculable RMS values of AC voltage will soon be available.