Spaceflight KID Readout Electronics for PRIMA

TL;DR

PRIMA's KID readout electronics address the challenge of space-based, multiplexed KID readouts, enabling $N_{tones}=1008$ detectors over 2.5 GHz with ~30 W per chain on L2. The solution uses SpaceCube Mini v3.0 KU060 FPGA-based digital back-end, a 1024-point synthesis PFB with 32 NCOs, and RF switching to support FIRESS and PRIMAger bands. Phase A prototypes demonstrated 100-tone operation with white NSD around $-105$ dBc/Hz and 1/f noise around $-95$ dBc/Hz at 1 Hz, with extrapolated performance for 1008 tones guiding optimization. The hardware and firmware design, together with on-board glitch mitigation planning (PCA-based deglitching), lays a feasible path toward deployment with PRIMA KID arrays in flight-tested cryogenic environments.

Abstract

We present the design and testing of a prototype multiplexing kinetic inductance detector (KID) readout electronics for the PRobe far-Infrared Mission for Astrophysics (PRIMA) space mission. PRIMA is a Probe-class astrophysics mission concept that will answer fundamental questions about the formation of planetary systems, the co-evolution of stars and supermassive black holes in galaxies, and the rise of heavy elements and dust over cosmic time. The readout electronics for PRIMA must be compatible with operation at Earth-Sun L2 and capable of multiplexing more than 1000 detectors over 2.5 GHz bandwidth while consuming around 30 W per readout chain. The electronics must also be capable of switching between the two instruments, which have different readout bands: the hyperspectral imager (PRIMAger, 2.6-4.9 GHz) and the spectrometer (FIRESS, 0.4-2.4 GHz). The PRIMA readout electronics use high-heritage SpaceCube digital electronics with a build-to-print SpaceCube Mini v3.0 board using a radiation-tolerant Kintex KU060 field programmable gate array (FPGA) and a custom high-speed digitizer board, along with RF electronics that provide filtering and power conditioning. We present the driving requirements for the system, as well as the hardware, firmware, software, and system-level design that meets those requirements.

Figures (4)

• Figure 1: Block diagram of the PRIMA KID readout chain. The 8 chains are switched between FIRESS and PRIMAger with filtering to allow readout of FIRESS in the first Nyquist zone and PRIMAger in the second Nyquist zone of the ADC and DAC when sampling at 5 Gsps. A high-heritage SpaceCube Mini v3.0 FPGA board houses a Xilinx Kintex Ultrascale KU060 FPGA and has high-speed interfaces with the ADC/DAC digitizer board over a backplane. The FPGA and digitizer boards can each read out 2 detector chains as illustrated. The radio-frequency (RF) electronics provide switching between the two instruments, filtering, and adjustment of overall gain for system noise optimization. Digitized detector timestreams are sent over SpaceWire to the spacecraft control and data handling (C&DH) computer via an input-output (I/O) card.
• Figure 2: Photographs of the PRIMA prototype electronics. (Left panel:) Combined rack-mount readout electronics with radio-frequency (RF) electronics on top and digital electronics on the bottom. (Middle panel:) Digital electronics prototype with lid opened with ADC, DAC, and FPGA evaluation modules (EVMs) labeled, along with the FPGA Mezzanine Card (FMC) combiner board that connects them together. The enclosure also contains a reference clock, Raspberry Pi for control, USB hub, and power supplies. (Right panel:) The RF electronics box with lid opened and the Quantic X-Microwave prototype circuit labeled. The RF enclosure houses a Raspberry Pi for control and power supplies.
• Figure 3: Frequency comb generated by the phase A prototype digital and RF electronics for the FIRESS band (0.4 to 2.4 GHz) measured in three different configurations. The first of which shown in light blue is measured directly from the DAC port on the digital electronics front panel and shows the first, second, and start of the third Nyquist images. Shown in red is the same comb after it has passed through the RF electronics prototypes transmit chain while in "FIRESS science" mode. The third configuration in dark blue was measured at the input to the ADC. This represents an RF electronics loopback configuration with a 20 dB attenuator between the TX and RX ports as a stand in for cryostat loss.
• Figure 4: Noise spectral density (NSD) of 100 sets of time-ordered data (TOD) taken with the PRIMA prototype readout, corresponding to tones spread across the FIRESS 0.4-2.4 GHz band. The blue curve is the NSD of the raw data, while the black curve shows the noise after removal of 3 common modes using a principal component analysis. The bold curve in each case is the median in each frequency bin of the set of faint 100 per-tone NSDs shown. This demonstrates a white noise level of $-105$ dBc/Hz and $1/f$ noise of approximately $-95$ dBc/Hz at a frequency of 1 Hz.