Signal resolution of RSFQ comparators

Filippov, T.V.; Polyakov, Yu. A.; Семенов, В.К.; Likharev, K. K.

doi:10.1109/77.403031

Cited by 67 publications

(45 citation statements)

References 6 publications

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“…Detailed theoretical analyses of the gray zone for the balanced comparator have been done, 4,11 and the theoretical model demonstrates good agreement with experiment. 5,6 At relatively low SFQ pulse repetition rate, the dependence of switching probability ͑p͒ of one of the two junctions on signal current I x is described by an error function and the probability density dp / dI x is represented by a Gaussian distribution. The gray zone of the comparator ⌬I x is usually defined as [4][5][6]11 ⌬I x ϵ ͯ dp dI x ͯ p=1/2 −1 .…”

Section: High-resolution Superconducting Single-flux Quantum Comparatmentioning

confidence: 99%

“…In the regime where thermal fluctuations dominate over quantum effects strong dependence on temperature of the comparator uncertainty zone ͑gray zone͒ 2,5,6 can be utilized for measurements of the electronic temperature in SFQ circuits. Moreover, the width of the gray zone directly characterizes current ͑or magnetic flux͒ sensitivity and noise properties of SFQ circuits.…”

Section: High-resolution Superconducting Single-flux Quantum Comparatmentioning

confidence: 99%

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High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures

Savin¹,

Pekola²,

Holmqvist³

et al. 2006

Applied Physics Letters

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Section: High-resolution Superconducting Single-flux Quantum Comparatmentioning

confidence: 99%

Section: High-resolution Superconducting Single-flux Quantum Comparatmentioning

confidence: 99%

High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures

Savin¹,

Pekola²,

Holmqvist³

et al. 2006

Applied Physics Letters

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“…Thus, the comparison of theory and experiments was not completely conclusive. The goal of this work has been to develop a general method of calculation of ∆I x for an arbitrary waveform φ e (t) and to compare the results with experimental data [2,5]. The potential energy of the balanced comparator (Fig.…”

mentioning

confidence: 99%

“…This means that the state choice problem in the original, nonlinear system is reduced to that of a damped time-dependent harmonic oscillator with frequency ω(t) defined as ω 2 (t) = µ(t)ω 2 p , where µ is switched rapidly from a positive initial value µ i (in experiments [2,5], close to 1) to a negative final value µ f = −µ i . The probability of switching to a final state with φ f < φ i may be found as…”

mentioning

confidence: 99%

Quantum Fluctuations in Josephson Junction Comparators

2002

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We have developed a method for calculation of quantum fluctuation effects, in particular of the uncertainty zone developing at the potential curvature sign inversion, for a damped harmonic oscillator with arbitrary time dependence of frequency and for arbitrary temperature, within the Caldeira-Leggett model. The method has been applied to the calculation of the gray zone width ∆Ix of Josephson-junction balanced comparators driven by a specially designed low-impedance RSFQ circuit. The calculated temperature dependence of ∆Ix in the range 1.5 to 4.2K is in a virtually perfect agreement with experimental data for Nb-trilayer comparators with critical current densities of 1.0 and 5.5 kA/cm 2 , without any fitting parameters.The current attention to quantum information processing (see, e.g., the recent monograph [1]) has renewed interest in fast "single-shot" quantum measurements, especially in potentially scalable solid-state systems. Among such systems, superconductor "balanced comparator", based on two similar Josephson junctions (Fig. 1a), stands apart as a very simple, scalable system for which quantum-limited sensitivity has already been demonstrated experimentally [2].The device is essentially a SQUID (see, e.g., [3]) in which two similar junctions are biased in series by a source of Josephson phase difference φ e (t), and in parallel by the current I x to be measured. Let the system with |φ e | < π settle in an equilibrium state φ = φ i , and then apply a rapid phase change ∆φ e = 2π. (This can be readily done using the so-called RSFQ circuitry -see, e.g., the recent review [4].) As a result, the system becomes statically unstable and the Josephson phase φ has to switch to one of adjacent stable states, depending on the sign of I x . (For junctions with substantial damping, the choice is limited by two states closest to the initial value of φ: φ f = φ i ± π).This process may be readily understood using the "magnetic language": the driver circuit providing the pulse ∆φ e = 2π in fact injects a single flux quantum into a superconducting loop formed by its output stage and the comparator (Fig. 1a). Since the loop is lowinductive (non-quantizing), the flux quantum has to drop out across one of the comparator junctions, depending on the sign of I x . This transient process produces a large (discrete) output signal, the so-called SFQ pulse V (t) with V (t)dt = Φ 0 = h/2e across the corresponding junction. Such a pulse may be readily picked up and registered by relatively crude devices [4], so that the accuracy of the

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“…Ref. [12]). Properties of the quantizer with noise may be readily analyzed using the following finite-difference 'master' equation that SI x 12pA.…”

Section: Introductionmentioning

confidence: 95%

Design of SFQ-counting analog-to-digital converter

Lin

Семенов

Likharev

1995

IEEE Trans. Appl. Supercond.

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We describe the design of an oversampling single-flux-counting analog-to-digital converter with the estimated bandwidth of a few tens MHz, based on Rapid Single-Flux-Quantum (RSFQ) devices. It consists of an input analog circuit, highspeed quantizer with an original analog/digital negative feedback loop, decimation (comb) Alter, and supporting subsysems including clock distribution circuits, quantization signal conditioner, and output drivers. We have applied a new approach, the 'symmetrizing' negative feedback, to free the quantizer from the intrinsic hysteresis without dynamic range sacriAce. The 16-bit version of the system comprises about 1,500 Josephson junctions and consumes 1.2 mW of dc power, when implemented using Nb-trilayer technology with 1 -kA/cm2, 3.5 -pm Josephson junctions.All subsystems of the converter have been successfully tested and testing of the system as a whole is in progress.

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Signal resolution of RSFQ comparators

Cited by 67 publications

References 6 publications

High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures

High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures

Quantum Fluctuations in Josephson Junction Comparators

Design of SFQ-counting analog-to-digital converter

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