SDR-Based Readout Electronics for the ECHo Experiment
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SDR‑Based Readout Electronics for the ECHo Experiment N. Karcher1 · D. Richter2 · F. Ahrens2 · R. Gartmann1 · M. Wegner2 · O. Krömer1 · S. Kempf2 · C. Enss2 · M. Weber1 · O. Sander1 Received: 5 August 2019 / Accepted: 31 March 2020 © The Author(s) 2020
Abstract Due to their excellent energy resolution, the intrinsically fast signal rise time, the huge energy dynamic range, and the almost ideally linear detector response, metallic magnetic calorimeters (MMC)s are very well suited for a variety of applications in physics. In particular, the ECHo experiment aims to utilize large-scale MMC-based detector arrays to investigate the mass of the electron neutrino. Reading out such arrays is a challenging task which can be tackled using microwave SQUID multiplexing. Here, the detector signals are transduced into frequency shifts of superconducting microwave resonators, which can be deduced using a high-end softwaredefined radio (SDR) system. The ECHo SDR system is a custom-made modular electronics, which provides 400 channels equally distributed in a 4 to 8 GHz frequency band. The system consists of a superheterodyne RF frequency converter with two successive mixers, a modular conversion, and an FPGA board. For channelization, a novel heterogeneous approach, utilizing the integrated digital down conversion (DDC) of the ADC, a polyphase channelizer, and another DDC for demodulation, is proposed. This approach has excellent channelization properties while being resource-efficient at the same time. After signal demodulation, on-FPGA flux-ramp demodulation processes the signals before streaming it to the data processing and storage backend. Keywords Metallic magnetic calorimeters · Software-defined radio · Frequencydivision multiplexing · Microwave SQUID multiplexer · Data acquisition · Polyphase channelizer
* N. Karcher [email protected] 1
Institute for Data Processing and Electronics, Karlsruhe Institute of Technology, Karlsruhe, Germany
2
Kirchhoff‑Institute for Physics, Heidelberg University, Heidelberg, Germany
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Vol.:(0123456789)
Journal of Low Temperature Physics
1 Introduction Metallic magnetic calorimeters (MMC) offer excellent sensor properties for various applications. The energy resolution and dynamic range, fast signal rise time, and the almost ideally linear detector response are the main benefits compared to other calorimeter types [1]. One of the first experiments employing large-scale MMC detector arrays with thousands of pixels is the Electron Capture in 163Ho experiment (ECHo) [2]. ECHo is designed to reach sub-eV∕c2 sensitivity on the electron neutrino mass by calorimetrically measuring the electron capture (EC) spectrum of the nuclide 163Ho with MMCs. The present stage of the experiment, ECHo-100k, aims at an event rate of over 105 Bq over all sensors. Assuming 10 Bq per sensor, the experiment will require an amount of 104 sensors. As a consequence, the use of a conventional dcSQUID1-based parallel readout [1] requiring up to ten leads per detector channel is impossible, due to constrain
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