Performance of 32-channel time-division SQUID multiplexer for cryogenic detector arrays

Multiplexed readout is a requirement for the successful deployment of large-scale cryogenic detector arrays in applications ranging from x-ray microanalysis to sub-millimeter astronomy. We report on the development of a time-division SQUID multiplexer (SQUID MUX) to read out one column of a 32×32 transition-edge sensor (TES) array. The new SQUID MUX has three stages. Individual TES pixels inductively couple to first-stage SQUID´s, which are summed and coupled to a second-stage SQUID via a superconducting transformer. The first- and second-stage SQUID´s are integrated on the same chip and are operated at the working temperature of the detectors of about 100 mK. The second stage SQUID is read out by a SQUID series array at 4K. Compared to former designs, the new SQUID MUX features a balanced input configuration to reduce crosstalk between read-out channels. In this paper we discuss the SQUID MUX design and analyze the noise and bandwidth performance of the SQUID multiplexer. Multiplexing of test input signals utilizing digital feedback electronics is demonstrated.