Frequency-division multiplexing (FDM) technologies are being developed for HUBS, which contains over 3000 transition-edge sensor (TES) microcalorimeters with an energy resolution of 2 eV (@0.6 keV). As a first step, an FDM system is designed and implemented for its pathfinder (DIXE), which employs a 10x10 TES microcalorimeter array, achieving an energy resolution of 6 eV or better over an energy range from 0.1 to 10 keV. The system has a multiplexing factor of 40 within the 1-5 MHz bandwidth. The warm electronics features a Kintex-7 FPGA and Magnicon Low-Noise Amplifier (LNA), coupled with baseband feedback software. Substantial progress has also been made on the cold electronics, with LC filters fabricated to achieve a 2 μm line width of the superconducting inductor and a dielectric constant of 11 for the capacitor. Superconducting Quantum Interference Devices (SQUIDs) have been fabricated, with the readout noise measured to be less than 6 pA/ √ Hz. This report presents the initial design both on the warm electronics and the superconducting circuit, offering an overview of the progress made. The findings support the conceptual viability of employing FDM for the multiplexed readout of TES microcalorimeters in the context of HUBS.
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