Improved Performance of TES Bolometers using Digital Feedback

Abstract

Voltage biased, frequency multiplexed TES bolometers have become a widespread tool in mm-wave astrophysics. However, parasitic impedance and dynamic range issues can limit stability, performance, and multiplexing factors. Here, we present novel methods of overcoming these challenges, achieved through digital feedback, implemented on a Field-Programmable Gate Array (FPGA). In the first method, known as Digital Active Nulling (DAN), the current sensor (e.g. SQUID) is nulled in a separate digital feedback loop for each bolometer frequency. This nulling removes the dynamic range limitation on the current sensor, increases its linearity, and reduces its effective input impedance. Additionally, DAN removes constraints on wiring lengths and maximum multiplexing frequency. DAN has been fully implemented and tested. Integration for current experiments, including the South Pole Telescope, will be discussed. We also present a digital mechanism for strongly increasing stability in the presence of large series impedances, known as Digitally Enhanced Voltage Bias (DEVB).

References in corpus (3)

• Digital Frequency Domain Multiplexer for mm-Wavelength Telescopes
• The new generation CMB B-mode polarization experiment: POLARBEAR
• Biasing and Demodulation Firmware for Kilopixel TES Bolometer Arrays

Cited by in corpus (3)

• Measurements of E-Mode Polarization and Temperature-E-Mode Correlation in the Cosmic Microwave Background from 100 Square Degrees of SPTpol Data
• Development and characterization of the readout system for POLARBEAR-2
• Multiplexed readout demonstration of a TES-based detector array in a resistance locked loop