| Summary: | A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s–1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ∼MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors. © 2012 American Institute of Physics. Received 18 December 2011; accepted 2 July 2012; published online 31 July 2012. We thank Andy Smith for useful discussions and design/fabrication of niobium inductors at Northrup Grumman, Kent Irwin and Gene Hilton for useful discussions and design/fabrication of the series array SQUIDs at NIST, and Hannes Hubmayr, Bryan Steinbach, Kam Arnold, and Graeme Smecher for useful discussions of bolometer responsivity and demodulator response. The National Science Foundation (NSF) funds APEXSZ through Grant Nos. AST-0138348 and AST-0709497 and the South Pole Telescope through Grant Nos. ANT-0638937 and ANT-0130612. Work at LBNL is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231. The McGill team ...
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