Experimental digital SQUID with integrated feedback circuit

Fath, U.; Hundhausen, R.; Fregin, T.; Gerigk, P.; Eschner, W.; Schindler, Alexis; Uhlmann, Friedrich

doi:10.1109/77.621806

Cited by 12 publications

(6 citation statements)

References 8 publications

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“…Digital SQUIDs are devices in which the sensor itself or, in multistage configurations, at least one of the following cryogenic stages is operated in a digital mode. There are various digital SQUID concepts reported in the literature: concepts involving room-temperature feedback electronics [32,59], latching Josephson logic [60][61][62][63][64][65][66][67], rapid single-fluxquantum (RSFQ) logic [68,69] or DROSs [57,58].…”

Section: Digital Squidsmentioning

confidence: 99%

“…To close the digital feedback loop, the flux in the counter loop is magnetically coupled to the comparator SQUID. The minimum flux change LSB 0 in the comparator SQUID (corresponding to 1 0 in the counter loop) determines slew rate and quantization noise [58,65]. The comparator output pulses are transmitted to room temperature and counted to obtain the digital sensor output.…”

Section: Digital Squidsmentioning

confidence: 99%

“…The comparator output pulses are transmitted to room temperature and counted to obtain the digital sensor output. A low bit error rate is required to avoid drift and low-frequency excess noise [65].…”

Section: Digital Squidsmentioning

confidence: 99%

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High-T_cand low-T_cdc SQUID electronics

Drung

2003

Supercond. Sci. Technol.

125

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Superconducting quantum interference devices (SQUIDs) are commonly operated in a flux-locked loop (FLL). The SQUID electronics amplifies the small SQUID signal to an acceptable level without adding noise, and it linearizes the transfer function of the SQUID in order to provide sufficient dynamic range. In this paper, the fundamentals of SQUID readout are reviewed including a discussion of preamplifier noise. The basic FLL concepts, direct readout and flux modulation readout, are discussed both with dc bias and bias reversal. Alternative readout concepts such as additional positive feedback (APF), two-stage SQUIDs, SQUID series arrays, relaxation oscillation SQUIDs and digital SQUIDs are briefly described. The FLL dynamics are discussed on the basis of a simple model with finite loop delay. It is shown that with optimized SQUID electronics a system bandwidth of ≈18 MHz and a corresponding slew rate of ≈8 Φ0 µs−1 are possible. A novel FLL scheme involving a Smith predictor is presented which allows one to increase the FLL bandwidth to about 100 MHz. The theoretical predictions are experimentally checked using a high-speed SQUID electronics prototype with a small-signal bandwidth of 300 MHz. Methods for increasing the dynamic range of SQUID systems are described: flux-quanta counting and dynamic field compensation (DFC). With DFC, the residual magnetic field at the SQUID can be kept close to zero even if the device is moved in the Earth's field. Therefore, the noise level of a high-Tc magnetometer measured inside a magnetically shielded room (60 fT Hz−1/2 with a 1/f corner at 2 Hz) remained unchanged after moving the device in the magnetic field outside the room (60 µT dc plus 0.8 µT peak-to-peak power line interference).

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Section: Digital Squidsmentioning

confidence: 99%

Section: Digital Squidsmentioning

confidence: 99%

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High-T_cand low-T_cdc SQUID electronics

Drung

2003

Supercond. Sci. Technol.

125

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“…In 1980's, a digital SQUID based on the superconductive latching logic circuits have been designed and fabricated [9,10]. The digital SQUID carries out the digital feedback using a delta modulator.…”

Section: Introductionmentioning

confidence: 99%

Asynchronous Digital SQUID Magnetometer With an On-Chip Magnetic Feedback for Improvement of Magnetic Resolution

Tsuga

Yamanashi

Yoshikawa

2013

IEEE Trans. Appl. Supercond.

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An asynchronous digital SQUID with complementary output, which needs no periodic high-frequency readout clock input, has been investigated. The magnetic flux resolution of the asynchronous digital SQUID has been improved using an on-chip magnetic feedback. A wide dynamic range asynchronous digital SQUID magnetometer system with improved magnetic resolution has been devised using alternating readout of two digital SQUIDs placed in parallel. The slew rate and the dynamic range of the asynchronous digital SQUID magnetometer were estimated to be 4 × 10 10  0 /s and the quite large, respectively. We have designed the asynchronous digital SQUID magnetometer system using 2.5 kA/cm 2 Nb process. We have experimentally confirmed the magnetic flux resolution of less than flux quantum ( 0) and the good linearity of the magnetic response of the asynchronous digital SQUID magnetometer system up to 3000  0 .

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“…For the measurement of small magnetic fields, digital SQUID devices can be seen as a very promising competitor to conventional analogue SQUIDs. There are a lot of publications presenting digital SQUIDs, for example [1,2]. But a first full digital approach was presented in [3] by utilizing nonhysteretic Josephson junctions in a rapid single flux quantum (RSFQ) [4] electronics.…”

Section: Introductionmentioning

confidence: 99%

New approach for a highly sensitive magnetometer utilizing a multi-stage digital SQUID

Reich¹,

Ortlepp²,

Uhlmann³

2006

Supercond. Sci. Technol.

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Highly sensitive measurement of magnetic fields can be made by analogue SQUIDs with analogue-to-digital conversion in a semiconductor environment. An alternative way is the use of digital SQUIDs consisting of superconducting digital Josephson electronics. Previously we presented a full digital SQUID device based on the bidirectional single flux quantum (SFQ) technique, which featured a very high dynamic range due to intrinsic flux compensation, a high slew rate and low complexity of the superconducting digital electronics. Analogue external feedback circuitry is replaced by the internal digital feedback. The intrinsic digital processing of measured flux makes external analogue-to-digital conversion dispensable. The remaining semiconducting electronics is reduced to a high-speed up–down counter. The whole system will be clocked by a bidirectional bias signal. The achieved tristate operation ensures a serial data output stream in the range of gigabits per second. The proper function of such a single-stage digital SQUID was recently proved by experiments. This concept of flux counting suffers intrinsically from its resolution of one flux quantum, which is not sufficient for the measurement of small magnetic fields. In this paper we present investigations on novel circuit topologies utilizing digital SQUID devices to overcome the restrictions in flux resolution without losing the dynamics advantages of a full digital SQUID device.

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Experimental digital SQUID with integrated feedback circuit

Cited by 12 publications

References 8 publications

High-T_cand low-T_cdc SQUID electronics

High-T_cand low-T_cdc SQUID electronics

Asynchronous Digital SQUID Magnetometer With an On-Chip Magnetic Feedback for Improvement of Magnetic Resolution

New approach for a highly sensitive magnetometer utilizing a multi-stage digital SQUID

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Experimental digital SQUID with integrated feedback circuit

Cited by 12 publications

References 8 publications

High-Tcand low-Tcdc SQUID electronics

High-Tcand low-Tcdc SQUID electronics

Asynchronous Digital SQUID Magnetometer With an On-Chip Magnetic Feedback for Improvement of Magnetic Resolution

New approach for a highly sensitive magnetometer utilizing a multi-stage digital SQUID

Contact Info

Product

Resources

About

High-T_cand low-T_cdc SQUID electronics

High-T_cand low-T_cdc SQUID electronics