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IEEE Electron Device Letters

A superconducting 6-bit analog-to-digital converter with operation to 2 × 109samples/second

C.A. Hamilton, Frances L. Lloyd

Published May 1, 1980• 26 citations
Publisher

Abstract

The design and performance of a 6-bit superconducting A/D converter are described. The converter is based on double junction interferometers used as current comparators. The unique periodic response of these comparators makes possible a fully parallel N-bit converter requiring only N comparators. Conversion rates up to 2 × 109samples per second have been demonstrated.

DOI
10.1109/edl.1980.25242

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The design and performance of a 6-bit superconducting A/D converter are described. The converter is based on double junction interferometers used as current comparators. The unique periodic response of these comparators makes possible a fully parallel N-bit converter requiring only N comparators. Conversion rates up to 2 × 109samples per second have been demonstrated.
This paper presents the progress we have made on our design, fabrication, and testing of a fully parallel superconducting analog-to-digital converter (ADC) with multi-GHz clock frequencies and input bandwidth. To our best knowledge, this converter is the first flash-type analog-to-digital converter ever reported in Josephson technology that fully integrates a quantizer and a thermometer-to-binary encoder to achieve binary outputs. In this design, the quantizer consists of 2(superscript N-1 comparators, each of which is realized using a hysteretic one- junction sampling SQUID driving a two-junction readout SQUID. A new logic family has been designed based on the same comparator building block and has been used to implement the thermometer-to- binary encoder. Taking advantage of the fact that the encoder's input is thermometer-coded, we have designed three-input and four-input quasi-XOR gates with only three NAND gates and therefore reduced significantly the total gate count. Functionalities of all the sub-circuits have been verified experimentally at clock frequencies up to 3 GHz, which is limited by our currently available testing equipment.
This work addresses new signal processing circuits using the special features of superconductivity. A novel flash-type analog-to-digital converter based on a comparator invented in the preceding contract period was demonstrated. The comparator was shown to be useful as a logic gate and an encoder was designed with it. A high-resolution delta-sigma analog-to-digital converter was devised with superconductive components in spite of the lack of an analog integrator in this technology. Positive theoretical results are being followed up experimentally. A simple flux-shuttle single-flux-quantum shift register was devised and several different readout schemes were studied. A six- bit-long version was successfully tested at 1 GHz. A decoder that takes in a five-bit word to select one of 32 output lines was completed. The design involved very tight limitations on current and power. The decoder was combined with a serial-to-parallel converter and operated at 2 GHz. A study of the appropriate architectures for various types of superconductive or Josephson digital technology was developed: an inductance-extraction program.
Contents: Superconducting Analog-to-Digital Converter Work at MITRE; Development of a Rapidly Tunable Microwave Source; Design and Evaluation of a Josephson Array Oscillator; Obtaining High-Accuracy Measurements from Low-Accuracy Measurements; Superconducting Microwave Transmission Lines; High Performance, Superconducting Analog-to-Digital Converter; Edge Sharpening with Josephson Junction; Design Evaluation of a Subranging Superconducting Analog-to-Digital Converter; Feasibility Study of a Superconducting Sigma-Delta Analog-to- Digital Converter, and VHDL Simulation Study of Superconducting Sigma Delta Modulators.