The SLAC Microresonator Radio Frequency (SMuRF) electronics is being deployed as the readout for the Cosmic Microwave Background (CMB) telescopes of the Simons Observatory (SO). A Radio Frequency System-on-Chip (RFSoC) based readout of microwave frequency resonator based cryogenic sensors is under development at SLAC as an upgrade path for SMuRF with simplified RF hardware, a more compact footprint, and lower total power consumption. The high-speed integrated data converters and digital data path in RFSoC enable direct RF sampling without analog up and down conversion for RF frequencies up to 6 GHz. A comprehensive optimization and characterization study has been performed for direct RF sampling for microwave SQUID multiplexers, which covers noise level, RF dynamic range, and linearity using a prototype implementation. The SMuRF firmware, including the implementation of closed-loop tone tracking, has been ported to the RFSoC platform and interfaced with the quadrature mixers for digital up and down conversion in the data converter data path to realize a full microwave SQUID multiplexer readout. In this paper, a selection of the performance characterization results of direct RF sampling for microwave SQUID multiplexer readout will be summarized and compared with science-driven requirements. Preliminary results demonstrating the read out of cryogenic sensors using the prototype system will also be presented here. We anticipate our new RFSoC-based SMuRF system will be an enabling readout for on-going and future experiments in astronomy and cosmology, which rely on large arrays of cryogenic sensors to achieve their science goals.
Low-energy threshold, high-resolution superconducting detector arrays with 103–105 pixels are increasingly necessary in ground- and space-based telescopes across the electromagnetic spectrum including mm-wave, far-infrared (Far-IR), near-infrared, X-ray, and gamma rays. Reading out such large numbers of sensors poses significant technical challenges, but recent cryogenic readout technology developments are enabling the simultaneous read out of significantly more channels with minimal performance impact. An especially promising set of cold readout technologies couple cryogenic sensors to superconducting resonators. These technologies rely on high-frequency RF electronics to interrogate and demodulate the sensors’ signals using digitally generated tones. Recently released Radio Frequency Systems-on-Chip (RFSoC) devices from Xilinx combine a FPGA with high-speed ADCs and DACs onto a single chip. These systems provide significant advantages for these applications, including lower cost, reduced size and weight, lower power consumption, and improved RF performance. While an RFSoC-based warm readout system would be attractive for a broad range of spacecraft applications, Xilinx has not announced plans for a space qualified version of its RFSoC devices and insufficient data is publicly available to evaluate the feasibility of using RFSoC devices in space. To evaluate the suitability of RFSoC devices for spacecraft applications, we have designed and built custom boards using all space-qualified components except for the RFSoC. In this contribution we present the design of our custom RFSoC board, measurements of critical aspects of board performance which relate to operation in the harsh space environment, and measurements of integrated RF performance targeting the readout of large superconducting sensor arrays and space-based radio spectrometry. In addition to a wide range of spacecraft applications including communications and radar, our RFSoC platform is a potentially critically enabling technology for missions prioritized by the recent 2020 Decadal Survey on Astronomy and Astrophysics including flagship Far-IR and X-ray missions, as well as Far-IR, X-ray, and Cosmic Microwave Background (CMB) probes.
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