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 non-hysteretic 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 array, using intrinsic shunting of the Josephson junctions, and a SIS 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.