Development of SQIF-Based Output Broad Band Amplifier
ABSTRACT High-performance single flux quantum (SFQ) pulse amplifier (driver) based on superconducting quantum interference filter (SQIF) or near regular array of SQUIDs has been developed, fabricated, and tested. The driver part coupling method and circuit optimizations are discussed. The first test results of the driver prototype are reported. The experimental results confirm performance advantages of this driver design approach.
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ABSTRACT: Planar arrays of magnetoinductively coupled rf SQUIDs belong to the emergent class of superconducting metamaterials that encompass the Josephson effect. SQUID metamaterials acquire their electromagnetic properties from the resonant characteristics of their constitutive elements, i.e., the individual rf SQUIDs, which consist of a superconducting ring interrupted by a Josephson junction. We investigate the response of a two-dimensional SQUID metamaterial to frequency variation of an applied alternating magnetic field in the presence of disorder, arising from critical current fluctuations of the Josephson elements; in effect, the resonance frequencies of individual SQUIDs are distributed randomly around a mean value. Bistability is observed in the total current-frequency curves both in ordered and disordered SQUID metamaterials; moreover, bistability is favoured by disorder through the improvement of synchronization between SQUID oscillators. Relatively weak disorder widens significantly the bistability region by helping the system to self-organize itself and leads to nearly homogeneous states that change smoothly with varying frequency. Moreover, the total current of the metamaterial is enhanced compared with that of uncoupled SQUIDs, through the synergetic action of coupling and synchronization. Multistability of nearly homogeneous states allows the metamaterial to exhibit different magnetic responses corresponding to different values of the magnetic permeability. At low power of the incident field, high-current states exhibit extreme diamagnetic properties corresponding to negative magnetic permeability in a narrow frequency region.Superconductor Science and Technology 04/2013; 26(8). DOI:10.1088/0953-2048/26/8/084006 · 2.80 Impact Factor
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ABSTRACT: We are developing a direct digital synthesizer (DDS) based on a novel digital-to-analog converter (DAC) technology capable of directly generating wideband signals at RF with large signal-to-noise ratio (SNR) and spur-free dynamic range (SFDR). The key parts of this oversampling interpolating DAC are a digital interpolation filter (DIF), a digital sigma-delta modulator, a phase rotator, and an output amplifier array. We have developed first and second order DIF circuits to perform digital interpolation - accurate up-conversion of baseband data to RF (125 MS/s to 2 GS/s) followed by digital filtering using a Hogenauer cascaded integrator comb filter. The digital sigma-delta modulator performs sigma-delta encoding of the interpolated data and comprises circuits similar to the DIF circuits. The phase rotator provides the phase information for the output amplifier array to create an analog waveform from a digital time-varying signal. The phase rotator provides the reference phases as four quadrature outputs. Depending on the digital input the rotator is capable of shifting phase by either one or two clock periods in any direction. The output driver is a differential digital amplifier based on SQUID arrays. It also can be assembled using voltage multipliers or superconducting quantum interference filters (SQIFs). Design and experimental results of these DDS components are presented and discussed.IEEE Transactions on Applied Superconductivity 07/2007; DOI:10.1109/TASC.2007.898055 · 1.32 Impact Factor
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ABSTRACT: We have fabricated a series array of 280 superconducting quantum interference devices (SQUIDs) using YBa2Cu3O7−δ thin film ion damage Josephson junctions. The SQUID loop areas were tapered exponentially so that the response of the current-biased array to magnetic field is a single voltage spike at zero field. We fitted the current-voltage characteristics of the array to a model in which we summed the voltages across the SQUIDs assuming a resistively shunted junction model with a normal distribution of SQUID critical currents. At 75 K the standard deviation of these critical currents was 12%.Applied Physics Letters 11/2008; 93(18):182502-182502-3. DOI:10.1063/1.3013579 · 3.52 Impact Factor