Code-division-multiplexed readout of large arrays of TES microcalorimeters
Kelsey M. Morgan, Bradley K. Alpert, Douglas A. Bennett, William B. Doriese, Joseph W. Fowler, Johnathon D. Gard, Gene C. Hilton, Kent D. Irwin, Young Il Joe, Galen C. O'Neil, Carl D. Reintsema, Edward V. Denison, Daniel R. Schmidt, Joel N. Ullom, Daniel S. Swetz
Code-division multiplexing (CDM) offers a path to reading out large arrays of transition edge sensor (TES) X-ray micro-calorimeters with excellent energy and timing resolution. We demonstrate the readout of X-ray TESs with a 32-channel flux-summed code-division multiplexing circuit based on superconducting quantum interference device (SQUID) amplifiers. The best detector has energy resolution of 2.28 +/- 0.12 eV FWHM at 5.9 keV and the array has mean energy resolution of 2.77 +/- 0.02 eV over 30 working sensors. The readout channels are sampled sequentially at a 160 ns row time, for an effective sampling rate of 5.12 $\mu$s per channel. The SQUID amplifiers that couple to the TESs have a measured flux noise of 0.17 $\mu$Phi0/rt(Hz) (non- multiplexed, referred to the first stage SQUID). The resulting multiplexed noise level and signal slew rate are sufficient to allow readout of more than 40 pixels per column, making CDM compatible with requirements outlined for future space missions. Additionally, because the modulated data from the 32 SQUID readout channels provides information on each X-ray event at the row rate, our CDM architecture allows determination of the arrival time of an X-ray event to within 275 ns FWHM with potential benefits in experiments that require detection of near-coincident events.