The linearity of phase interpolators (PIs) is enhanced by pre-distorting the PI control weights, instead of increasing the number of clock phases. This approach shifts the design complexity from the analog to the digital domain, resulting in a PI with high linearity, low power consumption, low clock jitter, compact area. The optimized pre-distorted control weights effectively suppress the phase nonlinearity stemming from deterministic sources across PVT corners. Post-layout simulation results demonstrate that a 65-nm implementation of a 7-bit PI with 4-phase input has a peak-to-peak integral nonlinearity better than 1.6 LSB across PVT corners and under circuit mismatch at 7 GHz, with a power consumption of 4.0 mW, and a circuit area of 0.0085 mm2. This performance is competitive with more complex PI designs.

Communication systems across a variety of applications are increasingly using the angular domain to improve spectrum management. They require new sensing architectures to perform energy-efficient measurements of the electromagnetic environment that can be deployed in a variety of use cases. This paper presents the Directional Spectrum Sensor (DSS), a compressive sampling (CS) based analog-to-information converter (CS-AIC) that performs spectrum scanning in a focused beam. The DSS offers increased spectrum sensing sensitivity and interferer tolerance compared to omnidirectional sensors. The DSS implementation uses a multi-antenna beamforming architecture with local oscillators that are modulated with pseudo random waveforms to obtain CS measurements. The overall operation, limitations, and the influence of wideband angular effects on the spectrum scanning performance are discussed. Measurements on an experimental prototype are presented and highlight improvements over single antenna, omnidirectional sensing systems.

Injection-locked ring oscillators (ILROs) are widely used for quadrature clock generators (QCG) in multi-lane wireline or optical transceivers because of their low power, low area, and technology scalability. However, locking a four-stage I/Q oscillator with a two-phase injection signal generates imbalances in amplitude and phase, resulting in I/Q phase errors and degraded jitter performance. This paper proposes a modified frequency-domain analysis with amplitude constraint for even-phase ILROs. Combining theoretical derivations with simulation results in 28nm CMOS technology, the behaviors of ring oscillators with partial injection and ILRO-based QCG are discussed and concluded.

The frequency-domain analysis method by Mirzaeiet al.(2012) offers a systematic way to analyze the RF input impedance of$M$-phase bandpass high-Q filters. The article also provides the mathematical expressions of the RF input impedance for$M$-phase filters in both single-ended and differential realizations. However, the expression for the differential RF input impedance is off by a factor of two compared to simulations. In this article, we derive the corrected expression.

A double-conversion, noise-cancelling receiver architecture is presented that consists of a double-layer mixer-first branch and two quadrature-modulated LNTA branches. The two layers of passive mixing in the mixer-first branch up-convert the low-pass, baseband impedance and create concurrent, narrowband impedance matching at (FLO±FIF), as well as concurrently receive signals around these two RF carriers while rejecting spurious responses without using any IF filters. To improve the noise performance, quadrature-modulated LNTA branches are incorporated to allow frequency-translational, noise cancellation for better receiver sensitivity. Double conversion is achieved in the LNTA branches by periodically varying the LNTA transconductance and current-mode, passive mixing. A generalized, linear time-varying (LTV) analysis of the receiver is presented and verified with behavioral-model simulation results.

With the prevalence of smartphones, pedestrians and joggers today often walk or run while listening to music. Since they are deprived of their auditory senses that would have provided important cues to dangers, they are at a much greater risk of being hit by cars or other vehicles. In this paper, we build a wearable system that uses multichannel audio sensors embedded in a headset to help detect and locate cars from their honks, engine, and tire noises, and warn pedestrians of imminent dangers of approaching cars. We demonstrate that using a segmented architecture consisting of headset-mounted audio sensors, a front-end hardware platform that performs signal processing and feature extraction, and machine learning-based classification on a smartphone, we are able to provide early danger detection in real time, from up to 60 m away, and alert the user with low latency and high accuracy. To further reduce power consumption of the battery-powered wearable headset, we implement a custom-designed integrated circuit that is able to compute delays between multiple channels of audio with nW power consumption. A regression-based method for sound source localization, angle via polygonal regression, is proposed and used in combination with the IC to improve the granularity and robustness of localization.

This paper considers compressed sensing (CS) in the context of RF spectrum sensing and presents an efficient approach for learning hardware nonidealities in an analog-to-information converter (A2IC). The proposed methodology is based on the learned iterative shrinkage-thresholding algorithm (LISTA), which enables co-optimization of the hardware and the reconstruction algorithm and leads to a model-free recovery approach that is optimally tuned for the unique computational constraints and hardware nonidealities present in the RF frontend. To achieve this, we devise a training protocol that employs a dataset and neural network of minimal sizes. We demonstrate the effectiveness of our methodology on simulated data from a model of a well-established CS A2IC in the presence of linear impairments and noise. The recovery process extrapolates from training on 1-sparse signals to recovering the support of signals whose sparsity runs up to the theoretical optimum for l1-based algorithms across a range of typical operating SNRs.

This paper presents an on-chip technique for calibrating static and dynamic DAC errors in a multibit continuous-time (CT) Delta-Sigma (ΔΣ) modulator. Dynamic errors such as inter-symbol-interference (ISI) affect the DAC output at every data transition and significantly deteriorate the in-band noise floor in high-speed applications. In the proposed technique, a compensation current is injected in the loop at every up-transition of input data to cancel the ISI error of each unit cell, thus improving its dynamic linearity. High linearity merged-input-feedback Gm-C integrators have been shown to enhance the converter's linearity and reduce power but require that the feedback DAC common mode matches the input-signal common mode. A biasing circuit for the current-steering feedback DAC is proposed to match its output common mode to the input signal common mode across PVT. Simulation results for a 70 MHz bandwidth, 3rdorder modulator, operating at a 2.8 GHz sampling rate, show a 2.8dB improvement in the in-band noise with the proposed dynamic calibration technique as well as maintaining the common-mode matching requirements across PVT.

This paper demonstrates the use of very high DC gain of a VCO based OTA to break the trade-off between the conversion gain (CG) and the power consumption in a passive mixer direct-conversion receiver for a given noise and linearity performance. A process for selecting the parameters of a VCO-OTA based TIA is highlighted with an example where the receiver delivers 20MHz of RF bandwidth at various CG settings. Simulation results demonstrate up to 38dB and 18dB improvement in CG and operational dynamic range compared to an inverter based OTA and a two-stage OTA respectively for a given linearity, NF and power consumption. Up to 17.5dB and 7.7dB improvement in the LNTA P1dB is demonstrated for a given CG, NF and power consumption. Up to two orders of magnitude reduction in the effect of TIA output 3rd order non-linearity on the overall linearity performance of the receiver is demonstrated with a VCO-OTA TIA.

This paper presents a 0.2V VCO-based OTA (VCO-OTA) for low-voltage, low-power applications. The VCO-OTA processes information in the time domain, which makes it possible to scale down supply to really low voltages. The proposed architecture eliminates current sources used in the charge pump to design a 0.2V VCO-OTA. Simulations show that in unity gain configuration, the proposed architecture achieves 60kHz unity gain bandwidth and 207μVRMs input referred noise while consuming 492nW.

A reconfigurable and scalable architecture called the Direct Space-to-Information Converter (DSIC) is presented for rapid and energy-efficient direction-of-arrival (DoA) finding. In conventional delay-and-sum beamformers (CBF), the tradeoff between scan time, resolution and energy consumption is fixed due to the Nyquist sampling theorem. To accurately detect the DoA of an interferer, many scan angles and complex energy intensive calculations are needed. In contrast, the proposed DSIC directly converts an incoming wavefront to spatial information and generates only a few compressed sensing (CS) measurements by forming random projections of the spatial signal consecutively in time. The DoA of the wavefront is then rapidly found from these CS measurements. The energy consumption of the DSIC is 16x lower than the CBF for a realistic scenario where the DoA of only one large interferer needs to be found. Compared to other recently proposed CS DoA finders, the DSIC delivers significant reconfigurability and scalability advantages especially when the number of interferers is unknown.

This paper presents a VCO-integrator-based high-efficiency low-dropout voltage regulator (LDO). Due to the integrator based architecture the LDO has higher efficiency, lower input voltage and better load regulation than traditional operational-amplifier based implementations. The proposed LDO was fabricated in 180nm CMOS technology along with a traditional operational-amplifier based design for comparison. The proposed LDO consumes a power of 3.7μW at 0.8V input and can achieve a drop-out voltage of 100mV and a load regulation of 8.8μV/mA. The proposed LDO is capacitor-free.

This paper presents performance improvement techniques for VCO-based OTAs (VCO-OTAs). An on-off charge pump(CP) topology is used as an alternative to power-hungry current-steering charge pump used in earlier VCO-OTAs. This brings down the power consumption of the CP and also the phase frequency detector (PFD) used in VCO-OTAs. The paper also presents the use of inherent low pass filtering in VCO-OTAs for out-of-band spur reduction. The techniques have been demonstrated by prototyping a 4-MHz 4th order active-RC filter using VCO-OTAs. The filter prototype, fabricated in 180nm CMOS technology, shows a power reduction of 41% in the CP and 25% in the PFD, achieved by trading off in-band IIP3 from 21dBm to 19dBm and noise from 0.71mVrms to 0.75mVrms.

An inverter-transconductor-based continuous-time analog 4th-order low-pass Butterworth filter was described entirely in Verilog hardware description language (HDL) using only standard cells. The physical design was synthesized with automated digital logic place-and-route (APR) CAD tools. APR was achieved in less than a minute making for an enormous improvement compared to traditional manual analog chip layout. A test chip was fabricated in a 0.18um CMOS technology and its performance was experimentally verified. The experimental results document excellent measured performance and a huge physical design timesaving thereby validating the proposed automated design methodology.

Next-generation (Next-G) wireless terminals need to sense their ambient and adapt to the diverse deployment scenario requirements on the fly while leveraging technology scaling. Several key circuit and system innovations are required to make the realization of this vision possible. We discuss how compressed sampling can be exploited to design a rapid, GHz-wide and energy-efficient interferer detector using a quadrature analog-to-information converter. A family of field-programmable receiver front ends demonstrating two linearity enhancement techniques including interferer-reflecting loops and hybrid Class-AB-C low noise transconductors is discussed. The technology scalable and out-of-band blocker robust switched-capacitor RF front end is then presented.

With the prevalence of smartphones, pedestrians and joggers today often walk or run while listening to music. Since they are deprived of their auditory senses that would have provided important cues to dangers, they are at a much greater risk of being hit by cars or other vehicles. In this demonstration we present SEUS, a wearable system aimed at Sense Enhancement for Urban Safety. SEUS uses a three-stage architecture, consisting of headset mounted audio sensors, an embedded front-end for signal processing and feature extraction, and machine learning based classification on a smartphone, to provide early danger detection for pedestrians in real-time.

This article focuses on a new type of wireless devices in the domain between RFIDs and sensor networks—Energy-Harvesting Active Networked Tags (EnHANTs). Future EnHANTs will be small, flexible, and self-powered devices that can be attached to objects that are traditionally not networked (e.g., books, furniture, toys, produce, and clothing). Therefore, they will provide the infrastructure for various tracking applications and can serve as one of the enablers for the Internet of Things. We present the design considerations for the EnHANT prototypes, developed over the past 4 years. The prototypes harvest indoor light energy using custom organic solar cells, communicate and form multihop networks using ultra-low-power Ultra-Wideband Impulse Radio (UWB-IR) transceivers, and dynamically adapt their communications and networking patterns to the energy harvesting and battery states. We describe a small-scale testbed that uniquely allows evaluating different algorithms with trace-based light energy inputs. Then, we experimentally evaluate the performance of different energy-harvesting adaptive policies with organic solar cells and UWB-IR transceivers. Finally, we discuss the lessons learned during the prototype and testbed design process.

This paper focuses on a new type of wireless devices in the domain between RFIDs and sensor networks - Energy Harvesting Active Networked Tags (EnHANTs). Future EnHANTs will be small, flexible, and self-powered devices that can be attached to objects that are traditionally not networked (e.g., books, toys, clothing), thereby providing the infrastructure for novel tracking applications. We present the design considerations for the EnHANT prototypes, developed over the past 3 years. The prototypes harvest indoor light energy using custom organic solar cells, communicate and form multihop networks using ultralow-power Ultra-Wideband Impulse Radio (UWB-IR) transceivers, and adapt their communications and networking patterns to the energy harvesting and battery states. We also describe a small scale EnHANTs testbed that uniquely allows evaluating different algorithms with trace-based light energy inputs.

The modern computing landscape increasingly requires a range of skills to successfully integrate complex systems. Project-based learning is used to help students build professional skills. However, it is typically applied to small teams and small efforts. In this paper, we describe our experience in engaging a large number of students in research projects within a multi-year interdisciplinary research effort. The projects expose the students to various disciplines in Electrical Engineering (circuit design, wireless communications, hardware prototyping), Computer Science (embedded systems, algorithm design, networking) and Applied Physics (thin-film battery design, solar cell fabrication). While a student project is usually focused on one discipline area, it requires interaction with at least two other areas. Over 4 years, 115 semester-long projects have been completed. The students were a diverse group of high school, undergraduate, and M.S. Computer Science, Computer Engineering, and Electrical Engineering students. Some of the approaches we have taken to facilitate student learning are real-world system development constraints, regular cross-group meetings, and extensive involvement of Ph.D. students in student mentorship and knowledge transfer. To assess our approaches, we conducted a survey among the participating students. The results demonstrate the effectiveness of our methods. For example, 70% of the students surveyed indicated that working on their research project improved their ability to function on multidisciplinary teams more than coursework, internships, or any other activity.

Energy Harvesting Active Networked Tags (EnHANTs) are a new class of devices in the domain between RFIDs and sensor networks. EnHANTs will be small, flexible, and energetically self-reliant. Their development is enabled by advances in ultra-low-power ultra-wideband (UWB) communications and in organic semiconductor-based energy harvesting materials. In this demo, we present UWB-enabled EnHANT prototypes. Each prototype is based on a MICA2 mote integrated with a UWB Transceiver and an energy harvesting module (EHM) that allows demonstrating energy harvesting-adaptive communications. Additional information about EnHANTs is available at [2] and http://enhants.ee.columbia.edu.

Energy Harvesting Active Networked Tags (EnHANTs) will be a new class of devices in the domain between RFIDs and sensor networks. Small, flexible, and energetically self-reliant, EnHANTs will be attached to objects that are traditionally not networked, such as books, furniture, toys, produce, and clothing. More information about the EnHANTs project is available at http://enhants.ee.columbia.edu. In this demo we present a small network of EnHANT prototypes. The current EnHANT prototypes are integrated with novel custom in-house-developed energy harvesting and communications hardware, namely organic solar cells and ultra-wide-band impulse radio (UWB-IR) transceivers. The demo showcases prototypes communicating using the novel UWB-IR transceivers and adapting their communications and networking parameters to the available environmental energy harvested by the organic solar cells.

With the convergence of ultra-low-power communications and energy-harvesting technologies, networking self-sustainable ubiquitous devices is becoming feasible. Hence, we have been recently developing new devices, referred to as Energy Harvesting Active Networked Tags (EnHANTs). These small, flexible, and energetically self-reliant tags can be seen as a new class of devices in the domain between RFIDs and sensor networks. EnHANTs are made possible by advances in ultra-lowpower ultra-wideband (UWB) communications and in organic semiconductor-based energy harvesting materials. They will enable novel tracking applications, such as continuous monitoring of objects and locating misplaced items. In this demo, we present phase I EnHANT prototypes. These prototypes are much larger than the envisioned EnHANTs and do not include custom-made UWB and organic electronic components. Yet, they serve as platforms for preliminary experiments and allow demonstrating energy harvesting-adaptive EnHANT communications. Each prototype is based on a MICA2 mote and includes a custom-designed sensor board with a light sensor and a solar cell, which are used to determine the light energy received from the environment. We have also designed a monitoring system which is used in the demo to show how the EnHANT prototypes adjust their communications patterns based on their energy harvesting parameters.

This paper presents the design challenges posed by a new class of ultra-low-power devices referred to as Energy-Harvesting Active Networked Tags (EnHANTs). EnHANTs are small, flexible, and self-reliant (in terms of energy devices that can be attached to objects that are traditionally not networked (e.g., books, clothing, and produce), thereby providing the infrastructure for various novel tracking applications. Examples of these applications include locating misplaced items, continuous monitoring of objects (items in a store, boxes in transit), and determining locations of disaster survivors. Recent advances in ultra-low-power wireless communications, ultra-wideband (UWB) circuit design, and organic electronic harvesting techniques will enable the realization of EnHANTs in the near future. In order for EnHANTs to rely on harvested energy, they have to spend significantly less energy than Bluetooth, Zigbee, and IEEE 802.15.4a devices. Moreover, the harvesting components and the ultra-low-power physical layer have special characteristics whose implications on the higher layers have yet to be studied (e.g., when using ultra-low-power circuits, the energy required to receive a bit is an order of magnitude higher than the energy required to transmit a bit). These special characteristics pose several new cross-layer research problems. In this paper, we describe the design challenges at the layers above the physical layer, point out relevant research directions, and outline possible starting points for solutions.

Device variability is receiving a lot of interest recently due to its important impact on the design of digital integrated systems. In analog integrated circuits, the variability of identically designed devices has long been a concern since it directly affects the attainable precision. This paper reviews the mismatch device models that are widely used in analog design as well as the fundamental impact of device mismatch on the trade-off between different performance parameters.

In this paper we present an ultra-low voltage gate-input operational transconductance amplifier using pMOS input devices and nMOS load devices with local common-mode feedback. This topology has a good intrinsic common-mode rejection. Simulations for a two-stage, 0.5 V fully differential operational transconductance amplifier (OTA) with a gain of 55 dB and a common-mode rejection ratio of 61 dB are reported. The amplifier consumes 77 /spl mu/W and has a gain-bandwidth product of 8.7 MHz when designed in 0.18 /spl mu/m CMOS technology.

A delay-based time-domain model is used to predict the locking dynamics in injection-locked non-harmonic oscillators, such as ring or relaxation oscillators. The locking dynamics predicted by the model are verified against simulations and measurements of a four-stage ring oscillator circuit built using discrete components.

We present a broadband digital pulse generation technique for use in ultra-wideband pulse radio transceivers. The pulse shape and frequency spectrum is digitally controlled. A quadrature-DAC based transmitter architecture is used to achieve reduction of the sampling images. A pulse generator test-chip fabricated in a 0.25 mum BiCMOS process is reported and generates broadband pulses in the public safety band (below 800 MHz)

In this paper we demonstrate that an intrinsic amplitude detector exists in negative resistance CMOS LC oscillators. The DC bias on the common-mode node in CMOS VCOs depends on the oscillation amplitude. Amplitude control loops can thus be built without a separate amplitude detector. Insights in possible AM to PM noise mechanisms are also derived

This paper presents the CMOS realisation of a programmable cellular neural network. An analogue programmable synapse circuit was designed that allows a large dynamic range for the template weights. Tuning circuits transform the digital values specified by the user to the corresponding analogue tuning voltages. A chip containing a 4x4 programmable CNN has been fabricated in a 2.4 /spl mu/m CMOS process.>