Low-power Broadband Digitizer for Millimeter-Wave Sensor Array Readout

Multiplexing in frequency domain using a bank of high-Q micro-resonators is an emerging method of reading out large arrays of transition-edge sensors and kinetic-inductance detectors. Low-power digitization of the resultant wide multi-GHz frequency band (e.g., 2-8 GHz) using a broadband superconductor analog-to-digital converter (ADC) enables high fidelity digital readout with immunity from noise, interference and cross-talk. HYPRES, Inc. has recently demonstrated a series of broadband digital radio receivers, built around a fast superconductor ADC. This ADC has low noise, low power, high linear dynamic range, and high radiation resistance. HYPRES proposes to design a similar ADC which is optimized for readout of a frequency-multiplexed sensor array such as that in the MicroSpec far-infrared spectrometer now being developed by NASA GSFC for future space missions. The superconductor ADC can be closely integrated and matched with the cryogenic sensors, enabling both reduction in system power and scaling to large imaging arrays. During Phase I, HYPRES will adapt a phase modulation-demodulation ADC for broadband (8 GHz) input, layout and fabricate an IC combining ADC with digital readout circuitry, and measure ADC performance with RF tones and an RF comb to simulate the frequency-multiplexed output of a sensor array. We will also assess the digital readout system for noise and thermal budget, and design the array interface for Phase II implementation. During Phase II, HYPRES will work with GSFC to integrate the ADC with a system testbed for the MicroSpec spectrometer and demonstrate its performance.

Broadband low-noise ADCs have wide application to digital RF receivers for advanced communications and signal detection, in space and on earth. These include satellite communications (SATCOM), signals intelligence (SIGINT), medical imaging (such as magnetic resonance imaging), and ultrafast digitizers for advanced scientific instrumentation. Superconducting digitizers packaged on compact, efficient cryocooler systems may be practical for many challenging applications.

Future NASA space telescopes for the microwave and far-infrared regimes require large arrays of micro-bolometers and other ultra-sensitive sensors. Frequency-domain multiplexing with digital readouts can maintain low-noise and low crosstalk between pixels, while achieving low power, compact size, and radiation hardness compatible with satellite implementation. Superconducting ADCs based on rapid-single-flux-quantum (RSFQ) technology are ideal for such applications. Such ADCs can also be applied to digitize other cryogenic sensor outputs of interest to NASA, such as imaging arrays for x-ray astronomy, and the intermediate-frequency output of terahertz mixers. Similar ADCs may also be used for sensitive wideband microwave receivers for deep-space communications.

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