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IEEE Transactions on Applied Superconductivity

Time-Division SQUID Multiplexing With Nanohenry Scale Input Mutual Inductance Using Transformers With Intracoil Damping

Malcolm Durkin, D. A. Bennett, William Bertrand Doriese, Johnathon D. Gard, Johannes Hubmayr, Richard A. Lew, Erin Maloney, C. D. Reintsema, Christopher Rooney, Robinjeet Singh, Daniel R. Schmidt, Joel N. Ullom, Leila R. Vale, Michael R. Vissers

Published Apr 6, 2026• 0 citations
Publisher

Abstract

Time division multiplexing (TDM) developed for the Athena X-ray integral field unit (X-IFU) has achieved readout performance that can be scaled to multiplexing factors of several hundred for TES bolometer missions. The lower slew rate requirements of bolometer and soft X-ray missions favor greater first stage SQUID amplifier input mutual inductance (Min) to reduce readout noise and compensate for aliasing as multiplexing factor is increased. We find that, asMinincreases, TDM performance becomes sensitive to the design of the TES bias circuit, with degraded noise performance and the emergence of resonant features. In TDM chips with nanohenry scaleMin, we demonstrate that this sensitivity can be eliminated by adding intra-coil damping resistors to the superconducting transformers, enabling the robust use of these higherMinmultiplexers.

DOI
10.1109/tasc.2026.3680761

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Time division multiplexing (TDM) developed for the Athena X-ray integral field unit (X-IFU) has achieved readout performance that can be scaled to multiplexing factors of several hundred for TES bolometer missions. The lower slew rate requirements of bolometer and soft X-ray missions favor greater first stage SQUID amplifier input mutual inductance (Min) to reduce readout noise and compensate for aliasing as multiplexing factor is increased. We find that, asMinincreases, TDM performance becomes sensitive to the design of the TES bias circuit, with degraded noise performance and the emergence of resonant features. In TDM chips with nanohenry scaleMin, we demonstrate that this sensitivity can be eliminated by adding intra-coil damping resistors to the superconducting transformers, enabling the robust use of these higherMinmultiplexers.
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Direct-current superconducting quantum interference devices (dc-SQUIDs) are one of the most sensitive magnetic detectors. These sensors are extensively used in the readout of superconducting transition edge sensors (TESs), which are used for the detection of weak signals. A cosmic microwave background (CMB) polarization telescope operating in 22-48 GHz is currently under developing. The TESs calorimeter of the telescope will be readout by a time-division multiplexer (TDM) SQUID readout system. We develop a two-stage dc-SQUID amplifier circuit, comprising an input-stage SQUID with 4 SQUID cells and a series SQUID array (SSA) with 100 SQUID cells. This configuration has been shown to achieve extremely high signal gain while effectively controlling system noise. We assess the system noise at 300300300 mKmKmK in an adiabatic demagnetisation refrigerator (ADR). The the measured magnetic flux noise of the two-stage SQUID circuit system is approximately 0.30.30.3 μΦ0/HzμΦ_{0}/\sqrt{Hz}μΦ0​/Hz​ at 101010 kHzkHzkHz. The current noise equivalent to the input coil of input SQUID is about 2.42.42.4 pA/HzpA/\sqrt{Hz}pA/Hz​. This result meets the low-noise readout requirements of the CMB TES and other applications with TES detectors.
Multiplexed superconducting quantum interference device (SQUID) readout systems are critical for measuring large arrays of superconducting transition-edge sensors (TES). We demonstrate a code-division SQUID multiplexing (CDM) architecture that is modulated by Walsh codes. Measurements and simulations of a prototype multiplexer show that this modulation scheme is not degraded by SQUID-noise aliasing, suppresses parasitic pickup, and has low levels of crosstalk. These properties enable this architecture to scale to large TES arrays. Furthermore, CDM modulation suppresses the 1/f knee in the noise to below 20 mHz, suggesting the use of this circuit for low-frequency-noise mitigation in more general SQUID applications.