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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Low-power high-resolution superconducting flux-quantizing A/D converter for IR array readout

Sergey V. Rylov, R. P. Robertazzi

Published Jun 23, 1994• 1 citation
Publisher

Abstract

We have developed a new architecture for a superconducting high-resolution analog-to-digital converter (ADC) which is highly beneficial for IR array readout applications due to its high sensitivity, wide dynamic range and sub-mW power consumption. This ADC is based on the principles of magnetic flux quantization, direct differential coding and decimation filtering. The digital part of the ADC employs elements of the Rapid Single Flux Quantum logic family which are capable of clock frequencies in excess of 100 GHz. We discuss the limits of ADC performance and present an analysis of the power consumption in these ADCs. We also report experimental verification of several key components of this architecture in Niobium technology (operating at 4.2 K), particularly the implementation of a synchronizer unit (necessary for the generation of the differential digital code) as well as a dual-counter synchronous ADC.

DOI
10.1117/12.178490

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IEICE Transactions on Electronics•Feb 1, 2006•4 citations
We have developed a new architecture for a superconducting high-resolution analog-to-digital converter (ADC) which is highly beneficial for IR array readout applications due to its high sensitivity, wide dynamic range and sub-mW power consumption. This ADC is based on the principles of magnetic flux quantization, direct differential coding and decimation filtering. The digital part of the ADC employs elements of the Rapid Single Flux Quantum logic family which are capable of clock frequencies in excess of 100 GHz. We discuss the limits of ADC performance and present an analysis of the power consumption in these ADCs. We also report experimental verification of several key components of this architecture in Niobium technology (operating at 4.2 K), particularly the implementation of a synchronizer unit (necessary for the generation of the differential digital code) as well as a dual-counter synchronous ADC.
We have developed a flux-quantizing A/D converter (ADC) based on RSFQ elements, employing a novel front end capable of generating high-linearity multibit differential code within a wide dynamic range (up to 16 bits). The front end operates as a phase modulator/demodulator and uses fractional-flux-quantum least significant bit (LSB). It runs at multi-GHz speed, enabling ADCs with large oversampling ratio and effective resolution in excess of 20 bits (after decimation filtering). We have designed, fabricated and tested several versions of a complete ADC using this new architecture and demonstrated its operation with dynamic range of 14 bits. We have also confirmed continuous phase modulation of the flux quantizer with a carrier frequency of 10 GHz.>
Ultrafast switching speed, low power, natural quantization of magnetic flux, quantum accuracy, and low noise of cryogenic superconductor circuits enable fast and accurate data conversion between the analog and digital domains. Based on rapid single-flux quantum (RSFQ) logic, these integrated circuits are capable of achieving performance levels unattainable by any other technology. Two major classes of superconductor analog-to-digital converters (ADCs) are being developed - Nyquist sampling and oversampling converters. Complete systems with digital sampling at rates of /spl sim/20 GHz and above have been demonstrated using low-temperature superconductor device technology. Some ADC components have also been implemented using high-temperature superconductors. Superconductor ADCs have unique applications in true digital-RF communications, broadband instrumentation, and digital sensor readout. Their designs, test results, and future development trends are reviewed.
We have developed and verified experimentally a novel high-resolution superconducting ADC architecture based on phase modulation/demodulation principle and implemented in RSFQ logic. We have demonstrated an ADC chip providing full implementation of this architecture, including on-chip decimation filter and multiple-channel synchronizer. We have also developed a digital ADC evaluation system consisting of an interface electronics block converting the low-voltage ADC output to standard TTL form at multi-MHz sampling rate, and a computerized test station performing data acquisition, processing and display in real time. Using this system we have demonstrated that for low-frequency (kHz) signals our ADC chips possess linearity in excess of 16 bits with Spur-Free Dynamic Range over 108 dB, which is an important benchmark for any high-resolution ADC technology.
A new family of counter-type Josephson-junction A/D converters using ultrafast rapid single-flux quantum (RSFQ) logic/memory elements is proposed. The converters are built in two main blocks: a low-bit differential-code A/D converter running with subterahertz clock speed and a RSFQ-logic-based digital processing unit providing digital low-pass filtering and sample rate reduction. It is shown that such converters can be treated as digital SQUIDs possessing an extremely high slew rate (up to 10/sup 11/ phi /sub 0//s) combined with flux resolution close to that of analog DC SQUIDs (up to 10/sup -6/ phi /sub 0/Hz/sup -1/2/). Several ways of implementing both main blocks to make it possible to tradeoff these parameters against converter complexity are presented and discussed.
A wide variety of applications, ranging from radio-frequency (RF) receivers for broadband communications and signal detection, on earth and in space, would benefit from high-performance superconductor analog-to-digital converters (ADCs), based on magnetic flux quantization and fast switching Josephson junctions. Superconductor ADCs are capable of very high sample rates (100 GHz or more), very high linearity, and high sensitivity. Nyquist-rate ADCs use the high sample rate to digitize a wide instantaneous bandwidth (tens of GHz) and are useful for wideband spectrum monitoring as well as high-end scientific instrumentation. Delta and delta-sigma oversampling ADCs use the high linearity to achieve programmable trade-off between dynamic range and instantaneous bandwidth. These lowpass and bandpass ADCs have been used for direct digitization of narrower (tens to hundreds of MHz) RF bands in the 1-20 GHz range for a variety of communications, intelligence, electronic warfare, and radar applications. Another application area of these cryogenic ADCs is for outputs of cryogenic sensor arrays and terahertz mixers. Recent advances in various classes of ADCs for different applications are described.
We describe three types of software-defined-radio (SDR) receivers based on superconducting technologies. The superconducting analog bandpass filters are essential for all types of the receivers. Another key component is an analog-to-digital converters (ADCs), which are required to have high resolution with a broad band width. The complementary A ADC based on the single-flux-quantum circuit is a promising candidate for the SDR receivers because it has a practical nature together with above-mentioned requirements. The experimentally obtained signal-to-noise ratio (SNR) and sensitivity, which are closely related to the resolution, are 34 dB and 20 μA for a quarter of the full-scale input with a band width of about 20 MHz. If we use the optimum decimation filter, the ADC is expected to have the SNR of 82 dB and the sensitivity of 300 nA. These values meet the requirements of the easiest type of the SDR receiver. After new fabrication process has been introduced and the architecture of the ADC has been improved, all types of recievers could be realized based on suoerconductors.