The readout of transition-edge sensor (TES) bolometers with a large multiplexing factor is key for the next generation Cosmic Microwave Background (CMB) experiment, Polarbear-2, having 7,588 TES bolometers. To enable the large arrays, we have been developing a readout system with a multiplexing factor of 40 in the frequency domain. Extending that architecture to 40 bolometers requires an increase in the bandwidth of the SQUID electronics above 4 MHz. This paper focuses on cryogenic readout and shows how it affects cross talk and the responsivity of the TES bolometers. A series resistance, such as equivalent series resistance (ESR) of capacitors for LC filters, leads to non-linear response of the bolometers. A wiring inductance modulates a voltage across the bolometers and causes cross talk. They should be controlled well to reduce systematic errors in CMB observations. We have been developing a cryogenic readout with a low series impedance and have tuned bolometers in the middle of their transition at a high frequency (> 3 MHz).
@article{arxiv.1512.07663,
title = {Development of readout electronics for POLARBEAR-2 Cosmic Microwave Background experiment},
author = {K. Hattori and Y. Akiba and K. Arnold and D. Barron and A. N. Bender and A. Cukierman and T. de Haan and M. Dobbs and T. Elleflot and M. Hasegawa and M. Hazumi and W. Holzapfel and Y. Hori and B. Keating and A. Kusaka and A. Lee and J. Montgomery and K. Rotermund and I. Shirley and A. Suzuki and N. Whitehorn},
journal= {arXiv preprint arXiv:1512.07663},
year = {2016}
}