High Performance Integrated Circuits Laboratory

Stevens Institute of Technology

The Limbsounder Experiment is a two band CMOS spectrometer developed for high altitude balloon flights in the upper stratosphere (the edge of space). The instrument detects and maps water vapor as well as several other pollutants. The instrument features a 500-600 GHz spectrometer band focused on NO2, O3, and other pollutant spectral lines, with the front-end receiver provided by the JPL sub-millimeter wave group. The LO is implemented using a CMOS W-band frequency synthesizer for the base LO generation, as well as our 3 GHz bandwidth CMOS spectrometer processor. The second band is a 180 GHz receiver implemented entirely in 28nm CMOS except for a single InP pre-amplifier stage to improve system noise temperature. The 180 GHz receiver is focused on the H2O line at 183.31 GHz. Base-band spectrometer processing was again provided by our 3 GHz processor chip. Our instrument participated in the 2018 NASA high-altitude balloon campaign operated by the Columbia Scientific Balloon Facility (CSBF) in Ft. Sumners, New Mexico.

Dielectric fibers at millimeter-wave frequencies offer excellent propagation properties. Our lab is developing millimeter-wave CMOS transmitters and receivers to enable an energy-efficient and broadband interconnect solutions for mid-range distance (meters) applications.

While the RF components for THz remote sensing systems have improved tremendously in the last 5 years with the appearance of InP hemt amplifiers (up to 800 GHz) and new silicon micro-machined integration, digital wide-band spectral processing has remained limited to FPGA solutions which consume far too much power (>30W) for most planetary missions and even some spaceborne astrophysics platforms (where large receiver arrays with 100s of pixels are being planned). To address this planetary science and astrophysics need, we have recently developed CMOS-SoC wideband spectral processors which provide much higher processing capability than existing FPGA solutions, with much less power consumption. The latest in this series of SoC chips employs a wideband 6 GS/s ADC mated with an 4096 point FFT processor and integrated SRAM accumulator to capture the time-domain output signals from THz receivers and compute the power spectral density. As these spectrometer processors are intended for use on planetary missions where extreme radiation and temperature effects exist, several intelligent and adaptive calibration algorithms are embedded within the processor to adjust a wide range of parameters related to the interleaved ADC including timing skew, radiation annealing effects on the comparators, and the dependence of the ADC channel mismatch effects on both extreme temperatures and high total ionized doses.

The Ku-Band radar system is a project with JPL that began in 2016 under JPL Earth Science funding with the purpose of sensing snow-packs in the Sierra Nevada and other mountain ranges to estimate the snow depth, snow coverage, melted liquid water content and snow density. These radar measurements are important as they provide a path for remotely estimating the snow water equivalence or “SWE” which describes the amount of water available during the melting season, a quantity critical for water resource planning during drought conditions. The radar we developed is an FMCW Ku-Band (15 GHz) 65nm CMOS SoC with 2 GHz bandwidth that contains all the required FMCW radar functional blocks including radar waveform generation with a (DDFS/DAC based chirper) all the RF components (Tx, Rx, LO) and base-band receiver digital electronics. The radar was packaged in a JPL instrument package with telemetry, and weatherproofed antennas for deployment in the field with network connectivity. We currently have one system operating at the CUES site at Mammoth mountain resort in cooperation with Prof Dozier at UCSB, and have a second system deployed with Prof. HP Marshall at Boise state.

Back-scatter wireless data links are a potential candidate for Internet-of-things (IoT) connectivity as their power consumption is extremely low for modest data-rates of 10s of Mb/s. Similar to RFID technology, these links work by reflecting or “back-scattering” a carrier from a base-station and modulating the reflection to carry data. This was our first and simplest demonstration which was a very straight forward OOK line of sight system capable of operating up to 330 Mb/s at several meters. As a follow up to the above work, we have developed a back-scatter link system, and have demonstrated both pulse-shaping, and pre-distortion in a reflective link. Pulse shaping the reflection allows the system to co-exist with other WiFi networks as the signal energy can be confined within the frequency boundaries of a defined network channel. Pre-distortion allows the link to compensate for distortion introduced by both the transmitter and receiver circuitry as well as frequency dependence of the antenna and indoor free-space channel. The demonstrated system supports QPSK & QAM signaling, over a distance of several meters and consumes only 2.6 mW of power at the IoT device. The third generation of reflective link uses a combination of an offset-carrier and digital pre-distortion as well as the pulse-shaping techniques from the previous work to allow fully 802.11.b compatible signalling while avoiding all the issues related to a directly reflected carrier. The demonstrated backscattering system supports QPSK signaling up to 12.5MB/s, over a distance of several meters and consumes only 1.2 mW of power.