Search

A low-power integer-N frequency synthesizer for flexible on-chip clock generation has been designed in 65 nm CMOS technology. The circuit can be programmed to generate two independent low-jitter clocks between 30 MHz and 3 GHz that are locked a 10-50 MHz reference input. The design uses a phase-locked loop (PLL) with a dual-tuned LC voltage-controlled oscillator (VCO), programmable feedback divider, and dual output dividers. The total power consumption from 1.2 V and 0.8 V supplies is 4.0 mW. Experimental results confirm the functionality of the proposed synthesizer over a wide range of output frequencies., Comment: Under review for publication in JINST

Extreme edge-AI systems, such as those in readout ASICs for radiation detection, must operate under stringent hardware constraints such as micron-level dimensions, sub-milliwatt power, and nanosecond-scale speed while providing clear accuracy advantages over traditional architectures. Finding ideal solutions means identifying optimal AI and ASIC design choices from a design space that has explosively expanded during the merger of these domains, creating non-trivial couplings which together act upon a small set of solutions as constraints tighten. It is impractical, if not impossible, to manually determine ideal choices among possibilities that easily exceed billions even in small-size problems. Existing methods to bridge this gap have leveraged theoretical understanding of hardware to f architecture search. However, the assumptions made in computing such theoretical metrics are too idealized to provide sufficient guidance during the difficult search for a practical implementation. Meanwhile, theoretical estimates for many other crucial metrics (like delay) do not even exist and are similarly variable, dependent on parameters of the process design kit (PDK). To address these challenges, we present a study that employs intelligent search using multi-objective Bayesian optimization, integrating both neural network search and ASIC synthesis in the loop. This approach provides reliable feedback on the collective impact of all cross-domain design choices. We showcase the effectiveness of our approach by finding several Pareto-optimal design choices for effective and efficient neural networks that perform real-time feature extraction from input pulses within the individual pixels of a readout ASIC., Comment: 18 pages, 17 figures

This paper introduces Fusion Intelligence (FI), a bio-inspired intelligent system, where the innate sensing, intelligence and unique actuation abilities of biological organisms such as bees and ants are integrated with the computational power of Artificial Intelligence (AI). This interdisciplinary field seeks to create systems that are not only smart but also adaptive and responsive in ways that mimic the nature. As FI evolves, it holds the promise of revolutionizing the way we approach complex problems, leveraging the best of both biological and digital worlds to create solutions that are more effective, sustainable, and harmonious with the environment. We demonstrate FI's potential to enhance agricultural IoT system performance through a simulated case study on improving insect pollination efficacy (entomophily)., Comment: 7 pages, 4 figures, 1 Table

In this thesis, we have studied the evolution of superconductivity in amorphous Molybdenum Germanium ($\textit{a}$-MoGe) thin films. The work can be broken down into two parts. In the first part, we investigate the effect of decreasing thickness on the suppression of superconductivity in $\textit{a}$-MoGe thin films. Thick $\textit{a}$-MoGe thin film is a typical type-II superconductor and follows the conventional Bardeen-Cooper-Schrieffer (BCS) equation. Conventionally, it is believed that decreasing thickness will decrease the effective attractive pairing interaction because of the gradual loss of screening which holds true for large thicknesses in $\textit{a}$-MoGe. But for lower thicknesses, a new mechanism comes into the picture where superfluid density is suppressed making the superconductor vulnerable to phase fluctuations. This is known as the Bosonic mechanism, where superconductivity is destroyed due to the loss of phase coherence of the superconducting state even though the attractive pairing amplitude remains finite above the transition temperature. In the second part, we explore the electromagnetic response of vortices in $\textit{a}$-MoGe thin film by low-frequency two-coil mutual inductance technique. Penetration depth measured from the two-coil technique was earlier used to determine superfluid density. However in the present work, by analyzing the in-field penetration depth data with the help of a mean-field model proposed by Coffey and Clem, we have demonstrated a procedure of extraction of vortex parameters such as pinning restoring force constant or Labusch parameter, vortex lattice drag coefficient and pinning potential barrier for the thermally activated motion of vortices. The temperature variation of vortex parameters suggests the dominant effect of thermal fluctuations., Comment: 178 pages, a thesis submitted to the Tata Institute of Fundamental Research, Mumbai for the PhD degree in Physics

We investigate the low-frequency electrodynamics in the vortex state of two type-II superconducting films, namely, a moderate-to-strongly pinned Niobium Nitride (NbN) and a very weakly pinned amorphous Molybdenum Germanium (a-MoGe). We employ a two-coil mutual inductance technique to extract the complex penetration depth, $\tilde{\lambda}$. The sample response is studied through the temperature variation of $\tilde{\lambda}$ in the mixed state, where we employ a model developed by Coffey and Clem (CC model) to extract the different vortex lattice (VL) parameters such as the restoring pinning force constant (Labusch parameter), VL drag coefficient and pinning potential barrier. We observe that a consistent description of the inductive and dissipative part of the response is only possible when we take the viscous drag on the vortices to be several orders of magnitudes larger than viscous drag estimated from the Bardeen-Stephen model.

Radar is a key component of the suite of perception sensors used for safe and reliable navigation of autonomous vehicles. Its unique capabilities include high-resolution velocity imaging, detection of agents in occlusion and over long ranges, and robust performance in adverse weather conditions. However, the usage of radar data presents some challenges: it is characterized by low resolution, sparsity, clutter, high uncertainty, and lack of good datasets. These challenges have limited radar deep learning research. As a result, current radar models are often influenced by lidar and vision models, which are focused on optical features that are relatively weak in radar data, thus resulting in under-utilization of radar's capabilities and diminishing its contribution to autonomous perception. This review seeks to encourage further deep learning research on autonomous radar data by 1) identifying key research themes, and 2) offering a comprehensive overview of current opportunities and challenges in the field. Topics covered include early and late fusion, occupancy flow estimation, uncertainty modeling, and multipath detection. The paper also discusses radar fundamentals and data representation, presents a curated list of recent radar datasets, and reviews state-of-the-art lidar and vision models relevant for radar research. For a summary of the paper and more results, visit the website: autonomous-radars.github.io.

We extract the vortex lattice parameters using low-frequency two-coil mutual inductance measurements in a 20-nm-thick superconducting a-MoGe thin film. We fit the temperature dependence of ac penetration depth in the mixed state using a model developed by Coffey and Clem and demonstrate a procedure for extracting vortex lattice parameters such as pinning constant, vortex lattice drag coefficient, and pinning potential barrier. We show that the extracted parameters follow the magnetic field variation expected for a weakly pinned 2-dimensional vortex lattice., Comment: 21 pages, 6 figures

A line driver with configurable pre-emphasis is implemented in a 65 nm CMOS process. The driver utilizes a three-tap feed-forward equalization (FFE) architecture. The relative delays between the taps are selectable in increments of 1/16th of the unit interval (UI) via an 8-stage delay-locked loop (DLL) and digital interpolator. It is also possible to control the output amplitude and source impedance for each tap via a programmable array of eight source-series terminated (SST) drivers. The entire design consumes 9 mW from a 1.2 V supply at 1 Gb/s., Comment: Submitted to JINST

The paper describes a radio frequency (RF) spectrometer for 14N nuclear quadrupole resonance (NQR) spectroscopy that uses a detector coil cooled to 77 K to maximize measurement sensitivity. The design uses a minimally-intrusive network of active duplexers and mechanical contact switches to realize a digitally reconfigurable series/parallel coil tuning network that allows transmit- and receive-mode performance to be independently optimized. The design is battery-powered and includes a mixed-signal embedded system to monitor and control secondary processes, thus enabling autonomous operation. Tests on an acetaminophen sample show that cooling both the detector and sample increases the signal-to-noise ratio (SNR) per scan by a factor of approximately 88 (in power units), in good agreement with theoretical predictions., Comment: Submitted to Review of Scientific Instruments

Millimeter wave communications require multibeam beamforming in order to utilize wireless channels that suffer from obstructions, path loss, and multi-path effects. Digital multibeam beamforming has maximum degrees of freedom compared to analog phased arrays. However, circuit complexity and power consumption are important constraints for digital multibeam systems. A low-complexity digital computing architecture is proposed for a multiplication-free 32-point linear transform that approximates multiple simultaneous RF beams similar to a discrete Fourier transform (DFT). Arithmetic complexity due to multiplication is reduced from the FFT complexity of $\mathcal{O}(N\: \log N)$ for DFT realizations, down to zero, thus yielding a 46% and 55% reduction in chip area and dynamic power consumption, respectively, for the $N=32$ case considered. The paper describes the proposed 32-point DFT approximation targeting a 1024-beams using a 2D array, and shows the multiplierless approximation and its mapping to a 32-beam sub-system consisting of 5.8 GHz antennas that can be used for generating 1024 digital beams without multiplications. Real-time beam computation is achieved using a Xilinx FPGA at 120 MHz bandwidth per beam. Theoretical beam performance is compared with measured RF patterns from both a fixed-point FFT as well as the proposed multiplier-free algorithm and are in good agreement., Comment: 22 pages, 8 figures, 3 tables. Fixed typo in Table 1

Cutting edge detectors push sensing technology by further improving spatial and temporal resolution, increasing detector area and volume, and generally reducing backgrounds and noise. This has led to a explosion of more and more data being generated in next-generation experiments. Therefore, the need for near-sensor, at the data source, processing with more powerful algorithms is becoming increasingly important to more efficiently capture the right experimental data, reduce downstream system complexity, and enable faster and lower-power feedback loops. In this paper, we discuss the motivations and potential applications for on-detector AI. Furthermore, the unique requirements of particle physics can uniquely drive the development of novel AI hardware and design tools. We describe existing modern work for particle physics in this area. Finally, we outline a number of areas of opportunity where we can advance machine learning techniques, codesign workflows, and future microelectronics technologies which will accelerate design, performance, and implementations for next generation experiments., Comment: Contribution to Snowmass 2021; 27 pages, 6 figures

This paper describes a highly-integrated CMOS system-on-chip (SoC) for active structural health monitoring (SHM). The chip integrates ultrasonic power and bidirectional half-duplex data transfer, a power management unit (PMU), and an ultrasound transceiver to enable wireless ultrasonically-coupled sensor SHM networks on structures. The PMU includes an active bias-flip rectifier with off-delay compensation, high-efficiency dual-path DC-DC converter with inductor time-sharing, and five switched-capacitor DC-DC converters to generate multi-level spectrally band-limited pulses for guided-wave SHM. The chip was fabricated in a standard 180 nm process and has a die area of $2\times 2$ mm$^{2}$. Test results show power conversion efficiency (PCE) $>85\%$ for the active rectifier, $>70$\% for the inductive DC-DC converter, and $>60$\% for the switched-capacitor DC-DC converters. Output pulses have a peak-to-sidelobe ratio (PSL) $>30$~dB and worst-case out-of-band emissions $<-30$~dB, respectively. The SoC was integrated with a low-power microcontroller and passive components to realize miniaturized (15~mm $\times$ 30~mm) wireless SHM nodes. A set of nodes was deployed on an SHM test-bed (carbon fiber reinforced polymer sheet) representing an airframe panel. Tests on this wireless network confirm both long-range ultrasound power/data transfer and the ability to detect structural damage., Comment: Submitted to IEEE Access

The paper describes highly-sensitive passive electric potential sensors (EPS) for non-contact detection of multiple biophysical signals, including electrocardiogram (ECG), respiration cycle (RC), and electroencephalogram (EEG). The proposed EPS uses an optimized transimpedance amplifier (TIA), a single guarded sensing electrode, and an adaptive cancellation loop (ACL) to maximize sensitivity (DC transimpedance $=150$~G$\Omega$) in the presence of power line interference (PLI) and motion artifacts. Tests were performed on healthy adult volunteers in noisy and unshielded indoor environments. Useful sensing ranges for ECG, RC, and EEG measurements, as validated against reference contact sensors, were observed to be approximately 50~cm, 100~cm, and 5~cm, respectively. ECG and RC signals were also successfully measured through wooden tables for subjects in sleep-like postures. The EPS were integrated with a wireless microcontroller to realize wireless sensor nodes capable of streaming acquired data to a remote base station in real-time., Comment: Submitted to the IEEE Transactions on Instrumentation and Measurement

The coaxial cables commonly used to connect RF coil arrays with the control console of an MRI scanner are susceptible to electromagnetic coupling. As the number of RF channel increases, such coupling could result in severe heating and pose a safety concern. Non-conductive transmission solutions based on fiber-optic cables are considered to be one of the alternatives, but are limited by the high dynamic range ($>80$~dB) of typical MRI signals. A new digital fiber-optic transmission system based on delta-sigma modulation (DSM) is developed to address this problem. A DSM-based optical link is prototyped using off-the-shelf components and bench-tested at different signal oversampling rates (OSR). An end-to-end dynamic range (DR) of 81~dB, which is sufficient for typical MRI signals, is obtained over a bandwidth of 200~kHz, which corresponds to $OSR=50$. A fully-integrated custom fourth-order continuous-time DSM (CT-DSM) is designed in 180~nm CMOS technology to enable transmission of full-bandwidth MRI signals (up to 1~MHz) with adequate DR. Initial electrical test results from this custom chip are also presented., Comment: Accepted for publication in the Review of Scientific Instruments

Nuclear magnetic resonance (NMR) spectroscopy usually requires high magnetic fields to create spectral resolution among different proton species. At low fields, chemical shift dispersion is insufficient to separate the species, and the spectrum exhibits just a single line. In this work, we demonstrate that spectra can nevertheless be acquired at low field using a novel pulse sequence called spin-lock induced crossing (SLIC). This probes energy level crossings induced by a weak spin-locking pulse and produces a unique J-coupling spectrum for most organic molecules. Unlike other forms of low-field J-coupling spectroscopy, our technique does not require the presence of heteronuclei and can be used for most compounds in their native state. We performed SLIC spectroscopy on a number of small molecules at 276 kHz and 20.8 MHZ, and we show that SLIC spectra can be simulated in good agreement with measurements.

In the present-day Universe, magnetic fields pervade galaxy clusters, with strengths of a few microGauss obtained from Faraday Rotation. Evidence for cluster magnetic fields is also provided by Megaparsec-scale radio emission, namely radio halos and relics. These are commonly found in merging systems and are characterized by a steep radio spectrum. It is widely believed that magneto-hydrodynamical turbulence and shock-waves (re-)accelerate cosmic rays, producing halos and relics. The origin and the amplification of magnetic fields in clusters is not well understood. It has been proposed that turbulence drives a small-scaledynamo that amplifies seed magnetic fields (primordial and/or injected by galactic outflows, as active galactic nuclei, starbursts, or winds). At high redshift, radio halos are expected to be faint, due to the Inverse Compton losses and dimming effect with distance. Moreover, Faraday Rotation measurements are difficult to obtain. If detected, distant radio halosprovide an alternative tool to investigate magnetic field amplification. Here, we report LOFAR observations which reveal diffuse radio emission in massive clusters when the Universe was only half of its present age, with a sample occurrence fraction of about 50%. The high radio luminosities indicate that these clusters have similar magnetic field strengths to those in nearby clusters, and suggest that magnetic field amplification is fast during the first phases ofcluster formation., Comment: Published in Nature Astronomy on 2 November 2020. The published version is available at this URL https://www.nature.com/articles/s41550-020-01244-5#citeas

Face masks provide effective, easy-to-use, and low-cost protection against airborne pathogens or infectious agents, including SARS-CoV-2. There is a wide variety of face masks available on the market for various applications, but they are all passive in nature, i.e., simply act as air filters for the nasal passage and/or mouth. In this paper, we present a new "active mask" paradigm, in which the wearable device is equipped with smart sensors and actuators to both detect the presence of airborne pathogens in real time and take appropriate action to mitigate the threat. The proposed approach is based on a closed-loop control system that senses airborne particles of different sizes close to the mask and then makes intelligent decisions to reduce their concentrations. This paper presents a specific implementation of this concept in which the on-board controller determines ambient air quality via a commercial particulate matter sensor, and if necessary activates a piezoelectric actuator that generates a mist spray to load these particles, thus causing them to fall to the ground. The proposed system communicates with the user via a smart phone application that provides various alerts, including notification of the need to recharge and/or decontaminate the mask prior to reuse. The application also enables a user to override the on-board control system and manually control the mist generator if necessary. Experimental results from a functional prototype demonstrate significant reduction in airborne particulate counts near the mask when the active protection system is enabled., Comment: 8 pages, 5 figures

Emerging wireless applications such as 5G cellular, large intelligent surfaces (LIS), and holographic massive MIMO require antenna array processing at mm-wave frequencies with large numbers of independent digital transceivers. This paper summarizes the authors' recent progress on the design and testing of 28 GHz and 60 GHz fully-digital array processing platforms based on wideband reconfigurable FPGA-based software-defined radios (SDRs). The digital baseband and microwave interfacing aspects of the SDRs are implemented on single-chip RF system-on-chip (RF-SoC) processors from Xilinx. Two versions of the RF-SoC technology (ZCU-111 and ZCU-1275) were used to implement fully-digital real-time array processors at 28~GHz (realizing 4 parallel beams with 0.8 GHz bandwidth per beam) and 60~GHz (realizing 4 parallel beams with 1.8~GHz bandwidth per beam). Dielectric lenslet arrays fed by a digital phased-array feed (PAF) located on the focal plane are proposed for further increasing antenna array gain., Comment: 6 pages

We investigate the evolution of superconductivity with decreasing film thickness in ultrathin amorphous MoGe (a-MoGe) films using a combination of sub-Kelvin scanning tunneling spectroscopy, magnetic penetration depth measurements and magneto-transport measurements. We observe that superconductivity is strongly affected by quantum and classical phase fluctuations for thickness below 5 nm. The superfluid density is strongly suppressed by quantum phase fluctuations at low temperatures and evolves towards a linear-T dependence at higher temperatures. This is associated with a rapid decrease in the superconducting transition temperature, Tc, and the emergence of a pronounced pseudogap above Tc. These observations suggest that at strong disorder the destruction of superconductivity follows a Bosonic route where the global superconducting state is destroyed by phase fluctuations even though the pairing amplitude remains finite.

This paper discusses early results associated with a fully-digital direct-conversion array receiver at 28~GHz. The proposed receiver makes use of commercial off-the-shelf (COTS) electronics, including the receiver chain. The design consists of a custom 28~GHz patch antenna sub-array providing gain in the elevation plane, with azimuthal plane beamforming provided by real-time digital signal processing (DSP) algorithms running on a Xilinx Radio Frequency System on Chip (RF SoC). The proposed array receiver employs element-wise fully-digital array processing that supports ADC sample rates up to 2~GS/second and up to 1~GHz of operating bandwidth per antenna. The RF mixed-signal data conversion circuits and DSP algorithms operate on a single-chip RF SoC solution installed on the Xilinx ZCU1275 prototyping platform., Comment: 5 pages

Recently, detailed real space imaging using scanning tunneling spectroscopy of the vortex lattice in a weakly pinned a-MoGe thin film revealed that the vortex lattice melts in two steps with temperature or magnetic field, going first from a vortex solid to a hexatic vortex fluid and then from a hexatic vortex fluid to an isotropic vortex liquid. In this paper, we show that the resistance in the vortex fluid states is extremely sensitive to radio-frequency electromagnetic perturbation. In the presence of very low-amplitude excitation above few kilohertz, the resistance increases by several orders of magnitude. On the other hand when the superconductor is well shielded from external electromagnetic radiation, the dissipation in the sample is very small and the resistance is below our detection limit., Comment: pdf file with figures

Quantum fluids refer to a class of systems that remain in fluid state down to absolute zero temperature. In this letter, using a combination of magnetotransport and scanning tunneling spectroscopy down to 300 mK, we show that vortices in a very weakly pinned a-MoGe thin film can form a quantum vortex fluid. Under the application of a magnetic field perpendicular to the plane of the film, the vortex state transforms from a vortex solid to a hexatic vortex fluid and eventually to an isotropic vortex liquid. The fact that the two latter states remain fluid down to absolute zero temperature is evidenced from the electrical resistance which saturates to a finite value at low temperatures. Furthermore, scanning tunneling spectroscopy measurements reveal a soft gap at the center of each vortex, which arises from large zero point fluctuation of vortices., Comment: In view of more recent findings, the data in this (unpublished) preprint has been reanalyzed: Kindly see arXiv:1909.06573 and arXiv:2102.12996 for more rigorous analysis with more extensive data

This paper describes the analysis and practical implementation of synchronized hyperchaotic maps for private communication of digital data. The data is transmitted using chaotic masking and demodulated using a matched filter (integrate and dump) receiver, which is shown to be nearly optimal in this case. Simulation results were validated by implementing two maps on circuit boards using high-speed discrete components. Experimental results show a bit error rate (BER) of 2x10-6 at a bit rate of 10 kbps and a clock frequency of 0.5 MHz, which is sufficient for high-fidelity real-time speech and image transmission without additional error control coding., Comment: Paper under review (International Journal of Bifurcation and Chaos)

The hexatic fluid refers to a phase in between a solid and a liquid which has short range positional order but quasi-long range orientational order. In the celebrated theory of Berezinskii, Kosterlitz and Thouless and subsequently refined by Halperin, Nelson and Young, it was predicted that a 2-dimensional hexagonal solid can melt in two steps: first, through a transformation from a solid to a hexatic fluid which retains quasi long range orientational order and then from a hexatic fluid to an isotropic liquid. In this paper, using a combination of real space imaging and transport measurements we show that the 2-dimensional vortex lattice in a-MoGe thin film follows this sequence of melting as the magnetic field is increased. Identifying the signatures of various transitions on the bulk transport properties of the superconductor, we construct a vortex phase diagram for a two dimensional superconductor., Comment: New Data added in this version