Software-Defined Radio Readout System for the ECHo Experiment

Abstract

Metallic magnetic calorimeters (MMCs) are cryogenic detectors that offer an excellent energy resolution, a signal rise time of <100 ns, a high dynamic range and almost optimal linearity. MMCs are of high interest for many experiments. One of them, the ECHo experiment, requires the utilization of large MMC detector arrays. The readout of such MMC arrays is a challenging task, which can be tackled using softwaredefined radios (SDRs). Though SDR is a well-known approach in communications engineering, a dedicated implementation for frequency division multiplexed readout of MMCs is new and one of the technological key elements of the ECHo project. ECHo will be the first experiment to use microwave SQUID multiplexed MMC detectors and therefore pioneering the hardware, firmware and software development in this domain. This paper presents the detailed concepts and current status of the development.

SDR-Based Readout Electronics for the ECHo Experiment

“…The signal processing chain includes both analog RF mixing and digital signal processing within a field-programmable gate array (FPGA). The electronics of ECHo divides the spectrum into five sub-bands that cover after anti-aliasing filters a bandwidth of 800 MHz each [9]. Five I&Q mixers are used, in which the in-phase and quadrature components are generated by AD9144 digital-toanalog converters and recorded by AD9680 analog-to-digital converters.…”

“…The last step is event detection for each pixel and the transmission of the event data to the backend server. The processor on the board is mostly used for calibration and configuration purposes as well as forwarding data to the backend server [9].…”

“…The channelization of the resonator signals is one of the critical components of the ECHo SDR system. In comparison with existing readout systems for MKID 3 [7,8] and TES 4 [12] ECHo's channelization takes advantage of new design space parameters-a next-generation FPGA and ADCs [9]. This allows on the one hand operating the filters with higher clock frequencies up to 500 MHz and on the other hand, ADCs with internal signal processing.…”

Flux ramp modulation based hybrid microwave SQUID multiplexer

“…For basic device characterization, we used a vector network analyzer in combination with an arbitrary waveform generator injecting a static flux or flux ramp signal into the modulation line. For multiplexing demonstration, we used our custom SDR based readout electronics 21,22 to continuously stream the output signal of the multiplexer. Demodulation of the modulated signal was then performed offline.…”

Flux ramp modulation based MHz frequency-division dc-SQUID multiplexer

“…We dc-biased the multiplexer using the low-noise bias current source of a commercial high-speed dc-SQUID electronics 12 and amplified the voltage drop across the array by means of a capacitively coupled, low-cost amplifier cascade 13 . For synthesizing the modulation signal, digitizing the output voltage of the multiplexer as well as real-time channelization and phase determination, we employed a prototype SDR electronics we had previously developed for operating a microwave SQUID multiplexer 14,15 UltraScale+ FPGA board 16 as well as ADC 17 and DAC 18 evaluation boards. The latter are connected to the FPGA board via FMC connectors and are synchronized via an external 10 MHz reference.…”