Abstract The Microwave SQUID Multiplexer (
μMUX) is a critical readout technology for large-scale Superconducting Transition-Edge Sensor (TES) array. It is considered as a promising readout system for both bolometer and calorimeter applications of large-scale TES array. It has been employed in several Cosmic Microwave Background (CMB) experiments, in which the TESes are used as bolometers. However, in the field of calorimeter applications of TESes, such as X-ray detection, the
μMUX system has not been widely used. The main reason is the slew rate of calorimeter pulse signal is much faster than that of bolometer, which will increase the difficulties of data processing in
μMUX electronics. In a typical microwave SQUID Multiplexed readout scheme, the sampling rate is determined by the frequency of the flux-ramp modulation. For CMB experiment, the frequency of the flux-ramp is usually set to about
O(10~kHz). However, for X-ray detection, it is necessary to improve the frequency of flux-ramp to about 1~MHz. It is a challenge to implement the high speed data processing with current
μMUX electronics.%The
μMux readout algorithm is a crucial component.Currently, the implementation of the
μMux readout algorithm is complex, and the sampling rate for each TES is low, only reaching kHz.We propose a recursive algorithm to reconstruct the fast TES signals with high sampling rate in case of no hardware changes. This algorithm is simple enough to implement in real time data collection. %In this paper, we describe and demonstrate this technique with a reasonable simulation model of
μMUX. The simulation results shows that the recovered sampling rate can break through the frequency limitation of the flux ramp, reaching up to analog-to-digital converter (ADC) sampling rate. The non-linearity is lower to 0.25\% in full dynamic range.
In order to read out current signals from large-scale arrays of transition edge sensors (TES), microwave SQUID multiplexers (MW-MUX) have been developed by several groups. Reduction of crosstalk induced in the multiplexer is important in order to maintain the energy resolution or the noise equivalent power of detector arrays. In the present study, crosstalk between channels in MW-MUX with five different designs is experimentally evaluated. The resonance frequency separation is ten times as large as the resonator bandwidth. Without flux-ramp modulation, crosstalk between two adjacent channels neighboring in position decreases to ≈1 × 10-3with increasing resonance frequency separation to ≈100 MHz. Crosstalk between SQUID channels neighboring in resonance frequency also decreases to 4 × 10-3with increasing the distance to 2.5 mm. We show that nonlinear error can occur due to the crosstalk with flux-ramp modulation. Flux readings from a well-designed multiplexer exhibit crosstalk of less than 1 mΦ0peak-to-peak and nonlinear errors of less than 2 mΦ0peak-to-peak, which is sufficient for the readout of the gamma-ray TES arrays being developed. These results can provide guidelines for suppressing both the crosstalk and the nonlinear error to less than the criterion of TES spectrometers with typical energy-resolving ability.