Maximizing multiplexing in 1–100 MHz frequency domain readout of transition edge sensor arrays via crosstalk suppression

The 1–100 MHz frequency band remains relatively unexplored for Frequency Division Multiplexing (FDM) readout of Transition Edge Sensor (TES) arrays, despite its potential to increase channel counts beyond the traditionally used 1–5 MHz range. This gap, however, is becoming increasingly addressable with advancements in the fabrication of high-resonance-frequency LC resonators and wide-band Superconducting Quantum Interference Devices (SQUIDs). It still partly stems from understudied crosstalk challenges in this higher-frequency regime, where mutual inductance, SQUID input inductance, and carrier leakage effects tend to be more pronounced, which may limit the feasibility of high-multiplexing systems. In this work, we aim to address this less explored area by modeling crosstalk between the 1–100 MHz range under a lumped-parameter framework, with a focus on static crosstalk ( \(ECT_{\text {static}}\) )—a metric that has received less attention in lower-frequency studies. To mitigate mutual inductance, we propose a chessboard pixel arrangement that maximizes frequency differences between adjacent channels. Leveraging the 1–100 MHz bandwidth with a 0.1 MHz channel spacing, this configuration can suppress crosstalk by up to 59.4 dB. Our simulations show that with this layout and through dynamic carrier frequency design, reducing mutual inductance to 3 nH enables 186 channels under a 1% \(ECT_{\text {static}}\) constraint when the SQUID input inductance is 1 nH; this count increases to 299 channels when the input inductance is reduced to 0.5 nH. Relaxing the threshold to 3.2% or 10% further expands the channel counts—for instance, reaching 612 or 2067 channels with 1 nH input inductance, respectively. This study preliminarily explores the crosstalk characteristics of 1–100 MHz FDM for TES arrays, offering a framework for low-crosstalk, high-channel-count readout systems and highlighting key trade-offs in this relatively unexplored frequency range.