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

Progress towards a double flux-locked-loop scheme for SQuID readout of TES detector arrays

G. Torrioli, Simona Lombardo, C. Macculi, L. Piro, L. Colasanti

Published Jul 24, 2014• 0 citations
Publisher

Abstract

Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.

DOI
10.1117/12.2056317

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Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.
User-friendly ultra-high-speed readout electronics for dc superconducting quantum interference devices (SQUIDs) are presented. To maximize the system bandwidth, the SQUID is directly read out without flux modulation. A composite preamplifier is used consisting of a slow dc amplifier in parallel with a fast ac amplifier. In this way, excellent dc precision and a high amplifier bandwidth of 50 MHz are achieved, simultaneously. A virtual 50 Ω amplifier input resistance with negligible excess noise is realized by active shunting, i.e., by applying feedback from preamplifier output to input via a high resistance. The white voltage and current noise levels are 0.33 nV Hz −1 and 2.6 pA Hz −1/2 , respectively. The electronics is fully computer controlled via a microcontroller integrated into the flux-locked loop (FLL) board. Easy-to-use software makes the various electronic settings accessible. A wide bias voltage range of 1.3 mV enables the readout of series SQUID arrays. Furthermore, additional current sources allow the operation of two-stage SQUIDs or transition edge sensors. The electronics was tested using various SQUIDs with input inductances between 30 nH and 1.5 µH. Typically, the maximum FLL bandwidth was 20 MHz, which is close to the theoretical limit given by transmission line delay within the FLL. Slew rates of up to 4.6 Φ 0 µs −1 were achieved with series SQUID arrays. Current noise levels as low as 0.47 pA Hz −1/2 and coupled energy sensitivities between 90 h and 500 h were measured at 4.2 K, where h is the Planck constant. The noise did not degrade when the system bandwidth was increased to the maximum value of about 20 MHz. With a two-stage set-up, intrinsic white energy sensitivities of 30 h and 2.3 h were measured at 4.2 and 0.3 K, respectively.
A novel double dc superconducting quantum interference device (SQUID) is proposed. It consists of two SQUIDs with different geometries in cascade configuration. The structure makes the device particularly suitable for flux-locked-loop operation without need of a room-temperature heterodyne modulation circuitry and a matching network between the SQUID and the preamplifier, thus simplifying the readout electronic system. The noise performance is calculated as a function of the electrical parameters of the device. The noise contribution of the room-temperature preamplifier can be made negligible using <m1;&2p>appropriate SQUID parameters while the slew rate of the system can approach 106Φ0/s.
We have designed and tested a superconducting quantum interference device (SQUID) readout circuit, which can be operated at liquid helium temperatures. Although room-temperature SQUID electronics perform well, it is sometimes desirable to keep the wires between SQUID, readout electronics, and feedback coil as short as possible to minimize phase shifts and time delays. Cooling the readout circuit to low temperatures can also decrease its thermal noise. Our readout circuit uses conventional ac-flux modulation, which significantly reduces low frequency excess noise and drift in the preamplifier. In this case, simple complementary metal–oxide–semiconductor circuits with low power dissipation can be used as amplifier, phase-sensitive detector and integrator. The power dissipation of the complete readout is less than 15mW at 5V supply voltage.
We have designed and demonstrated a superconducting quantum interference device (SQUID) array linearized with cryogenic feedback. To achieve the necessary loop gain, a 300-element series array SQUID is constructed from three monolithic 100-element series arrays. A feedback resistor completes the loop from the SQUID output to the input coil. The short feedback path of this linearized SQUID array (LISA) allows for a substantially larger flux-locked loop bandwidth as compared to a SQUID flux-locked loop that includes a room temperature amplifier. The bandwidth, linearity, noise performance, and 3 Phi(0) dynamic range of the LISA are sufficient for its use in our target application: the multiplexed readout of transition-edge sensor bolometers.
We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge. Frequency-domain multiplexing can greatly simplify the instrumentation of large arrays by reducing the number of SQUID's (superconducting quantum interference devices) and wires to the low temperature stages. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. Each sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single SQUID. The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.
We have designed and demonstrated a Superconducting Quantum Interference Device (SQUID) array linearized with cryogenic feedback. To achieve the necessary loop gain a 300 element series array SQUID is constructed from three monolithic 100-element series arrays. A feedback resistor completes the loop from the SQUID output to the input coil. The short feedback path of this Linearized SQUID Array (LISA) allows for a substantially larger flux-locked loop bandwidth as compared to a SQUID flux-locked loop that includes a room temperature amplifier. The bandwidth, linearity, noise performance, and dynamic range of the LISA are sufficient for its use in our target application: the multiplexed readout of transition-edge sensor bolometers.