Digital Frequency Domain Multiplexer for mm-Wavelength Telescopes

TL;DR

This paper introduces an FPGA-based digital signal processing system designed for multiplexed bolometric detectors in mm-wavelength telescopes, enabling precise measurement of cosmic microwave background signals for cosmology research.

Contribution

It presents a novel digital readout system with real-time DSP algorithms and multi-frequency comb synthesis for biasing and reading out detectors in cosmology experiments.

Findings

Successfully synthesizes 8 to 32 carriers for detector biasing

Achieves stable digitization and demodulation of sky signals

Demonstrates effective filtering for low-frequency sky signals

Abstract

An FPGA based digital signal processing (DSP) system for biasing and reading out multiplexed bolometric detectors for mm-wavelength telescopes is presented. This readout system is being deployed for balloon-borne and ground based cosmology experiments with the primary goal of measuring the signature of inflation with the Cosmic Microwave Background Radiation. The system consists of analog superconducting electronics running at 250mK and 4K, coupled to digital room temperature backend electronics described here. The digital electronics perform the real time functionality with DSP algorithms implemented in firmware. A soft embedded processor provides all of the slow housekeeping control and communications. Each board in the system synthesizes multi-frequency combs of 8 to 32 carriers in the MHz band to bias the detectors. After the carriers have been modulated with the sky-signal by the detectors, the same boards digitize the comb directly. The carriers are mixed down to base-band and low pass filtered. The signal bandwidth of 0.050 Hz - 100 Hz places extreme requirements on stability and requires powerful filtering techniques to recover the sky-signal from the MHz carriers.