Developments in Time-Division Multiplexing of X-ray Transition-Edge Sensors

Abstract

Time-division multiplexing (TDM) is a mature scheme for the readout of arrays of transition-edge sensors (TESs). TDM is based on superconducting-quantum-interference-device (SQUID) current amplifiers. Multiple spectrometers based on gamma-ray and X-ray microcalorimeters have been operated with TDM readout, each at the scale of 200 sensors per spectrometer, as have several astronomical cameras with thousands of sub-mm or microwave bolometers. Here we present the details of two different versions of our TDM system designed to read out X-ray TESs. The first has been field-deployed in two 160-sensor (8 columns $\times$ 20 rows) spectrometers and four 240-sensor (8 columns $\times$ 30 rows) spectrometers. It has a three-SQUID-stage architecture, switches rows every 320 ns, and has total readout noise of 0.41 $\mu \Phi _{\mathrm {0}} / \surd$Hz. The second, which is presently under development, has a two-SQUID-stage architecture, switches rows every 160 ns, and has total readout noise of 0.19 $\mu \Phi _{\mathrm {0}} / \surd$Hz. Both quoted noise values are non-multiplexed and referred to the first-stage SQUID. In a demonstration of this new architecture, a multiplexed 1-column $\times$ 32-row array of NIST TESs achieved average energy resolution of $2.55\pm 0.01$ eV at 6 keV.