A high-temperature superconducting delta-sigma modulator based on a multilayer technology with bicrystal Josephson junctions

We have designed, fabricated and successfully tested a first-order delta-si gma modulator using a high-temperature superconducting multilayer technolog y with bicrystal Josephson junctions. The circuit has been fabricated on a SrTiO3 bicrystal substrate. The YBa2Cu3O7/SrTiO3/YBa2Cu3O7 trilayer was fab ricated by laser deposition. The bottom layer served as a superconducting g roundplane. The Josephson junctions were formed at the bicrystal line in th e upper layer. The integrator resistance has been made from a Pd/Au thin fi lm. The circuit consists of a dc-SFQ converter, a Josephson transmission li ne, a comparator, an L/R integrator and an output stage. The correct operat ion of the modulator has been tested using de measurements. The linearity o f the modulator was studied by measuring the harmonic distortions of a 19.5 kHz sine wave input signal. From the recorded spectrum, a minimum resoluti on of at least 5 bits can be estimated. This accuracy was limited by the no ise of the preamplifier. The correct operation of the current feedback loop was demonstrated by cutting the feedback inductance.