Batteryless sensor nodes, powered solely by energy harvesting, are a promising alternative to battery-powered sensor nodes. However, energy harvesting rates being very low, unreliable, and time-varying, nodes cannot sustain a continuous operation, making them intermittently powered. As a result, these nodes incur unpredictable wakeup times due to continuously varying off-times. To perform tasks like distributed sensing, time synchronization, and communication for intermittently powered nodes, timely execution and robust coordination is vital. To achieve robust coordination, nodes must guarantee to be ON at a coordinated target time regardless of harvesting variations. To ensure robust coordination of on-times, we propose PAIL, a novel hardware-software approach where the hardware component enforces a constant off-time, with small variations. The software component dynamically corrects for those variations. We fabricated a PAIL sensor node and validated its ability to discover neighboring nodes. Using extensive simulations calibrated from experimental measurements, we observe that PAIL maintains nearly 99.3% coordination at steady state. In the context of pairwise communication, we show that leveraging PAIL coordination, nodes improve packet tail latency by 99%.

Most modern-day communication systems require the use of baluns to interface between differential and single-ended components. Using an example of a concurrent dual-band switch-mode push-pull power amplifier, this paper establishes that distributed baluns designed using traditional strategies, focusing solely on a balun's center frequency, lead to reduced efficiency due to the imperfect termination of the intermodulation components of their common mode signal. For solving this problem, a wide-band mixed-mode S-parameter analysis is employed to derive the common mode termination requirements of distributed baluns for concurrent dual-band operation; based on which, a generalized design procedure is developed to modify traditional balun designs. The modification provides the required termination to prevent common mode power loss while preserving the balun's performance in terms of input port matching, insertion loss, and amplitude and phase balance. The newly developed theory is tested by designing a modified concurrent dual-band tapped stepped-impedance balun. Measurement results are provided to validate the feasibility of the approach.

Ions play a significant role in biological, industrial, and agricultural processes. Noninvasive, real-time detection of their presence and concentration has become of vital importance in a multitude of processes. In this paper, we present a lumped-element circuit model for an Archimedean spiral inductor based resonant sensor which accurately detects and quantifies ionic concentration of aqueous solutions. The development of the model is guided by observed physical phenomena caused by changing a solution's ionic concentration. The system's response to different concentrations of aqueous potassium chloride is measured, and the model parameters are extracted from measured data. The model parameters are extrapolated to obtain expressions that model the system's response over a wide range of concentrations. There is good agreement between the model and measured data, making it valid for concentrations ranging from 1.66 mmol/L to 1 mol/L. The model helps generate insight into the behavior of the physical system, could be used to systematically optimize the sensor design, and could be extended to other analytes.

This paper investigates a multi-band harvesting (EH) schemes under cognitive radio interweave framework. All secondary users are considered as EH nodes that are allowed to harvest energy from multiple bands of Radio Frequency (RF) sources. A win-win framework is proposed, where SUs can sense the spectrum to determine whether the spectrum is busy, and hence they may harvest from RF energy, or if it is idle, and hence they can use it for transmission. Only a subset of the SUs can sense in order to reduce sensing energy, and then machine learning is used to characterize areas of harvesting and spectrum usage. We formulate an optimization problem that jointly optimize number of sensing samples and sensing threshold in order to minimize the sensing time and hence maximize the amount of energy harvested. A near optimal solution is proposed using Geometric Programming (GP) to optimally solve the problem in a time-slotted period. Finally, an energy efficient approach based on multi-class Support Vector Machine (SVM) is proposed by involving only training SUs instead of all SUs.

The optimum bias point for an inverse class-F power amplifier is discussed in this paper from a time-domain point of view. It is shown that the inverse class-F power amplifier should be biased in shallow triode region where the bias current is slightly higher than DC current when driven into compression. Lower bias currents can cause significant efficiency degradation due to peaking in the drain-source voltage. Simulation results show that drain efficiency at 6dB over drive drops from 83.4% to 65.2% when bias current is reduced by 34% from optimum bias current. Moreover, it is shown that if the bias current is too high, then the efficiency under power back off is reduced.

Concurrent dual-band switch-mode power amplifiers require high common-mode impedance at their intermodulation frequencies. Baluns utilizing quarter-wave effects only have perfect open common-mode impedance at their design frequency. Attempting to use a balun without taking the new dual-band requirements for common-mode impedance into account will result in efficiency loss. However, the addition of some transmission lines can add impedance at those specific frequencies by rotation of the common-mode impedance without affecting the differential mode match.

This paper introduces a quadrature oscillator for LTE/LTE-A standards with an improved quadrature mode stability using transformers. In Inductor-based (L-based) quadrature voltage controlled oscillators (QVCO), there exist two stable quadrature modes. When a transformer is used in place of an inductor in a QVCO, it is shown that the selected quadrature mode of oscillation is different from and more stable than the L-based QVCO. This additional stability ensures that only one mode of oscillation in T-based QVCOs is selected whereas in L-based QVCOs, cascode transistors are commonly used for this purpose. This is demonstrated using an oscillator designed in a commercially available 130 nm CMOS process. The oscillator provides a tuning range of 40.6% (2620-3033, 3423-4446 MHz), a phase noise of -112 dBc/Hz at an offset of 2.5 MHz from 3033 MHz, and a maximum power consumption of 26.4 mW from a 1.2 V supply.

Recently concurrent dual-band receivers are being investigated to help improve data rates and ease roaming across different network standards. Traditionally, nonlinear behavior has been confined to two-tone tests where the tone spacing is relatively small. In concurrent dual-band systems, however, two bands must be received simultaneously with an arbitrary spacing between the bands. In this paper, the intermodulation issues between bands and between the signals within a given band are analyzed. It is found that there are certain band spacings that must be avoided because of significant intermodulation distortion. Based on this analysis, a frequency plan to avoid inter-band nonlinear distortion is proposed. These results are then verified with Matlab simulations.

A complete analysis of a new tunable matching network utilizing a transformer-capacitor network that exploits magnetic tuning is presented. The performance of this matching network is explored in the presence of non-idealities and an example matching network capable of continuous tuning from 3 to 8 GHz is presented.

Symmetric multi-tap transformers are designed, modeled, and characterized. Simple mathematical calculations are utilized to estimate the inductances and coupling coefficients from the physical parameters of a multi-tap transformer, which reduces the time required to develop an initial design. A broadband lumped-element model is then presented and its accuracy is demonstrated by comparing the extracted inductances from the model to Momentum simulation results. A concentric and an interleaved symmetric multi-tap transformer are designed in 0.13μm CMOS RF process and their self-inductances, coupling coefficients, and quality factors are evaluated.

This paper studies how the reflected impedance impacts the quality factor and noise performance of transformer-based resonators. The analysis shows that in oscillators employing transformer-based resonators, the improved noise performance does not primarily come from an increase in Q, but instead from a decrease in the bandwidth of the resonator as compared to that of an equivalent inductor-based resonator.

This paper presents a reconfigurable multimode matching network employing a multi-tap transformer designed in 130 nm CMOS. By combining a multi-tap transformer and a bank of switched capacitors, it is shown that frequency matching in 2.4 GHz, 5 GHz, or 5-10 GHz bands, is achievable and thus supports multiple standards such as Bluetooth, 802.11a/b/g/n, WiMAX, and UWB.

An area-efficient U-shaped slow-wave coplanar waveguide (U-SCPW) in a standard 0.18 μm CMOS process is presented. Compared to a conventional straight line CPW (S-CPW), it provides a more compact layout because of its approximate 1:1 aspect ratio. Measured results show that it has a quality factor and phase velocity comparable to its straight-line counterpart with measured Q ~ 30 at 23 GHz.

As CMOS technologies and their respective supply voltages continue to scale downwards, new methods for designing RF analog and mixed-signal circuits must be found. A promising technique that has emerged is the use of monolithic transformers. Unfortunately, due to parasitic magnetic coupling, there can be a substantial amount of cross-talk between transformers and other, nonrelated, devices resulting in the requirement for large separation distances and hence, wasted silicon. This paper presents a new winding scheme that reduces the parasitic magnetic coupling by approximately 1000X (32 dB) and allows the separation distance between transformers to be reduced by 10X.

Dynamic spectrum access (DSA) is a promising approach for the more effective use of existing spectrum. Of fundamental importance to DSA is the need for fast and reliable spectrum sensing over a wide bandwidth. A model for two-stage sensing is described based on an analysis of the mean time to detect an idle channel. Simulation results show that it provides significantly faster idle channel detection than conventional single-stage random searching. Several system-level issues are also investigated including the settling time of the phase-locked loop (PLL) in the frequency synthesizer, which determines the channel switching time. Effects of the bandwidth of the coarse sensing block and the integration duration of the energy detector are also presented.

A parallel, multi-resolution spectrum sensing technique that is amenable to multiple-antenna cognitive radios is introduced. The authors show that for energy-detector-type spectrum sensors, the total sensing time due to FFT latency is reduced by 100 times using the proposed method versus the fixed-resolution, serial detection method employed in single-antenna systems. System-level tradeoffs such as the number of antennas, sensing bandwidth, and FFT size are also explored.