CryoDE: A Digital Cryogenic Detector Emulator for Microwave SQUID Multiplexed Systems

Simultaneous readout of large-scale cryogenic detector arrays relies on multiplexing schemes such as frequency-division multiplexing (FDM) with microwave superconducting quantum interference device (SQUID) multiplexers and highly customized readout electronics. In traditional detector systems, where mixed-signal application-specific integrated circuit (ASIC)s are used in detector front ends and typically provide a digital interface, hardware-in-the-loop (HIL) testing can be readily implemented by reusing the existing digital logic of the front end for emulation purposes. Such straightforward emulation is not possible for FDM low-temperature detectors, where the sensor signal is encoded in a high-frequency microwave carrier via a two-stage modulation scheme depending on the cryogenic resonators and the SQUID response. To address this challenge, we present CryoDE, a digital cryogenic detector emulator for microwave SQUID multiplexed detector systems. CryoDE generates the encoded detector signals, including realistic pulse responses, enabling full HIL testing of the room temperature data acquisition (DAQ) system without requiring the cryogenic hardware. This resource-efficient detector twin integrates seamlessly into the field-programmable-gate-array (FPGA) firmware of existing DAQ systems and allows experiment-specific adjustment of detector signal parameters. We describe the internal architecture and capabilities of CryoDE within our custom HIL framework and demonstrate its use in evaluating the performance of real-time signal processing firmware optimized for different microwave SQUID multiplexed cryogenic detector experiments.