Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117576, Singapore Center for Intelligent Sensors and MEMS, National University of Singapore, Singapore, 117608, Singapore Hybrid-Integrated Flexible (Stretchable) Electronic Systems Program, National University of Singapore, Singapore, 117608, Singapore NUS Suzhou Research Institute (NUSRI), Suzhou, 215123, China NUS Graduate School for Integrative Science and Engineering, National University of Singapore, Singapore, 117456, Singapore

Progress in wearable electronics/photonics—Moving toward the era of artificial intelligence and internet of things

This paper presents the first 28-/37-/39-GHz linear Doherty power amplifier (PA) in silicon for broadband fifth-generation (5G) applications. We introduce a new transformer-based on-chip Doherty power combiner that can reduce the impedance transformation ratio (ITR) in power back-off (PBO) and, thus, improve the bandwidth and power-combining efficiency. We also devise a “driver-PA co-design” method that creates power-dependent uneven feeding in the Doherty PA and enhances the Doherty operation without any hardware overhead or bandwidth compromise. For the proof of concept, we implement a 28-/37-/39-GHz PA fully integrated in a standard 130-nm SiGe BiCMOS process, which occupies 1.8 mm $^{\mathbf {2}}$ . The PA achieves a 52% −3-dB small-signal $\text{S}_{\mathbf {21}}$ bandwidth and a 40% −1-dB large-signal saturated output power ( $\text{P}_{\mathbf {sat}}$ ) bandwidth. At 28/37/39 GHz, the PA achieves +16.8−/+17.1−/+17-dBm $\text{P}_{\mathbf {sat}}$ , +15.2−/+15.5−/+15.4-dBm $\text{P}_{\mathbf {1\,dB}}$ , and superior 1.72/1.92/1.62 times efficiency enhancement over class-B operation at 5.9-/6-/6.7-dB PBO. Moreover, the PA demonstrates multi-gigabit-per-second data rates with excellent efficiency and linearity for 64-quadrature amplitude modulation (64-QAM) in three millimeter-wave (mm-wave) 5G bands. This PA advances the state of the art for Doherty, wideband, and 5G silicon PAs in mm-wave bands. It supports drop-in upgrade for current PAs in existing mm-wave systems and opens doors to compact system solutions for future multiband 5G massive multiple-input multiple-output (MIMO) and phased-array platforms.

A 28-/37-/39-GHz Linear Doherty Power Amplifier in Silicon for 5G Applications

In order to satisfy the power thirst of communication devices in the imminent fifth generation era, wireless charging techniques have attracted much attention both from the academic and industrial communities Although the inductive coupling and magnetic resonance-based charging techniques are indeed capable of supplying energy in a wireless manner, they tend to restrict the freedom of movement By contrast, radio frequency (RF) signals are capable of supplying energy over distances, which are gradually inclining closer to our ultimate goal—charging anytime and anywhere Furthermore, transmitters capable of emitting RF signals have been widely deployed, such as TV towers, cellular base stations, and Wi-Fi access points This communication infrastructure may indeed be employed also for wireless energy transfer (WET) Therefore, no extra investment in dedicated WET infrastructure is required However, allowing RF signal-based WET may impair the wireless information transfer (WIT) operating in the same spectrum Hence, it is crucial to coordinate and balance WET and WIT for simultaneous wireless information and power transfer, which evolves to integrated data and energy communication networks (IDENs) To this end, a ubiquitous IDEN architecture is introduced by summarizing its natural heterogeneity and by synthesizing a diverse range of integrated WET and WIT scenarios Then the inherent relationship between WET and WIT is revealed from an information theoretical perspective, which is followed by the critical appraisal of the hardware enabling techniques extracting energy from RF signals Furthermore, the transceiver design, resource allocation, and user scheduling as well as networking aspects are elaborated on In a nutshell, this treatise can be used as a handbook for researchers and engineers, who are interested in enriching their knowledge base of IDENs and in putting this vision into practice

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Integrated Data and Energy Communication Network: A Comprehensive Survey

This article reviews the state-of-the-art millimeter-wave (mm-wave) power amplifiers (PAs), focusing on broadband design techniques. An overview of the main solid-state technologies is provided, including Si, gallium arsenide (GaAs), GaN, and other III–V materials, and both field-effect and bipolar transistors. The most popular broadband design techniques are introduced, before critically comparing through the most relevant design examples found in the scientific literature. Given the wide breadth of applications that are foreseen to exploit the mm-wave spectrum, this contribution will represent a valuable guide for designers who need a single reference before adventuring in the challenging task of the mm-wave PA design.

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A Review of Technologies and Design Techniques of Millimeter-Wave Power Amplifiers

GaN technology is not only gaining traction in power and RF electronics but is also rapidly expanding into other application areas including digital and quantum computing electronics. This paper provides a glimpse of future GaN device technologies and advanced modeling approaches that can push the boundaries of these applications in terms of performance and reliability. While GaN power devices have recently been commercialized in the 15–900 V classes, new GaN devices are greatly desirable to explore both higher-voltage and ultra-low-voltage power applications. Moving into the RF domain, ultra-high frequency GaN devices are being used to implement digitized power amplifier circuits, and further advances using the hardware–software co-design approach can be expected. On the horizon is the GaN CMOS technology, a key missing piece to realize the full-GaN platform with integrated digital, power, and RF electronics technologies. Although currently a challenge, high-performance p-type GaN technology will be crucial to realize high-performance GaN CMOS circuits. Due to its excellent transport characteristics and ability to generate free carriers via polarization doping, GaN is expected to be an important technology for ultra-low temperature and quantum computing electronics. Finally, given the increasing cost of hardware prototyping of new devices and circuits, the use of high-fidelity device models and data-driven modeling approaches for technology-circuit co-design are projected to be the trends of the future. In this regard, physically inspired, mathematically robust, less computationally taxing, and predictive modeling approaches are indispensable. With all these and future efforts, we envision GaN to become the next Si for electronics.

Emerging GaN technologies for power, RF, digital, and quantum computing applications: Recent advances and prospects

This paper presents the combination of two back-off efficiency enhancement techniques, the voltage-mode Doherty and the class-G switched-capacitor power amplifier (PA), to achieve efficiency peaking at both 6 and 12 dB back off without introducing the mode-switching glitches present in previous architectures. The proposed technique enables transmission of high peak-to-average-power ratio (PAPR) signals with high efficiency while maintaining excellent linearity. The PA is fabricated in 45-nm CMOS SOI with integrated balun for power combining and matching. At 3.5 GHz a saturated output power of 25.3 dBm is measured with 30.4%/25.3%/17.4% power added efficiency (PAE) at 0/6/12 dB back off. With memoryless, non-adaptive linearization, the PA achieves 19.2% PAE with −35.8 dB error vector magnitude (EVM) while transmitting a 40 MHz 256-QAM 10.1 dB PAPR 802.11ac modulation. Significant efficiency improvement compared to class-B and EVM better than −34 dB is maintained over more than 1 GHz bandwidth.

A Class-G Voltage-Mode Doherty Power Amplifier

This paper presents a new wideband Doherty amplifier technique that can achieve high efficiency while maintaining excellent linearity. By modifying a “forgotten” topology originally proposed by Doherty, a new Doherty amplifier architecture is realized with two voltage mode power amplifiers (PAs) and transformers, thus eliminating a narrowband impedance inverter. The voltage mode PA is implemented using switched capacitor PA techniques. The PA is fabricated in 65-nm low-leakage CMOS and achieves 24-dBm saturated power (at the standard supply voltage) with PAE of 45% at peak power and 34% at 5.6-dB back-off over 750 to 1050 MHz 1 dB bandwidth. With memory-less linearization, the PA can transmit 40 MHz 256-QAM 9 dB peak-to-average power ratio 802.11ac modulation centered at 900 MHz meeting the spectral mask with measured EVM of −34.8 dB and 22% PAE without backing off or equalization.

Voltage Mode Doherty Power Amplifier

DOI: 10.1002/admt.201700279 rubrene-based transistors with microstructured gate electrodes,[2] microelectromechanical systems with strain gauges,[3] and other methods.[4,5] With the introduction of force sensing into mobile handheld devices, it becomes critical to develop force sensing solutions that are scalable, thin, light, and cost-effective. Force sensing functionality has been pursued using various methods that include strain sensors,[6] light emitters and detectors,[7] and surface acoustic wave sensors among others.[8–11] A powerful approach in pressure sensor development is the incorporation of both pressure sensing and switching functionalities into a single array element.[12] This allows the use of miniature sensor elements with high sensitivity and scalability to large areas. Zinc oxide (ZnO) is semiconducting, suitable for transistor fabrication in a vertically integrated process, transparent, and has a high piezoelectric coefficient that confers excellent pressure sensitivity,[13,14] positioning it as a forefront candidate for integration into in-cell touchscreen technologies.[15] A large portion of the emerging display technologies use materials based on ZnO, such as indium gallium zinc oxide (IGZO).[16,17] In addition, amenability to low temperature processing allows the ZnO pressure sensor arrays to be seamlessly integrated into pressure display technologies. When pressure is applied on top of a sputtered ZnO film, the net dipole moment in the c-direction is distorted, leading to accumulation or depletion of free charge carriers at the surface of the device.[18] The pressure-induced free charge carriers lead to a change in the drain current, with the magnitude of change being proportional to the applied pressure. In a field-effect transistor (FET) configuration, small pressures applied to the gate can lead to large drain current changes, especially when the transconductance of the ZnO FET is high. Vishniakou et al. reported the fabrication of 8×8 ZnO thin film transistor (TFT) arrays on rigid glass, with good pressure sensing characteristics.[12] However, their Ion/Ioff ratio was lower than 103, and the piezoelectric properties of the films were not explored in detail. For good transistor performance, the unintentionally doped ZnO films, usually n-type due to O2 vacancies and impurity donors, need to be compensated to achieve low leakage currents. Further, the film grains in the ZnO layers need to be A zinc oxide thin film transistor is developed and optimized that simultaneously functions as a transistor and a force sensor, thus allowing for scalable integration of sensors into arrays without the need for additional addressing elements. Through systematic material deposition, microscopy, and piezoelectric characterization, it is determined that an O2 rich deposition condition improves the transistor performance and pressure sensing characteristics. With these optimizations, a sensitivity of 4 nA kPa−1 and a latency of below 1 ms are achieved, exceeding the criteria for successful commercialization of arrayed pressure sensors. The functionality of 16 × 16 pressure sensor arrays on thin bendable glass substrates for integrated low weight and flexible touchscreen displays is fabricated and demonstrated and read-out electronics to interface with the arrays and to record their response in real-time are developed. Finally, the application of these sensors for mobile displays via their operation with an existing commercial touch integrated circuit controller is demonstrated.

Improved Performance of Zinc Oxide Thin Film Transistor Pressure Sensors and a Demonstration of a Commercial Chip Compatibility with the New Force Sensing Technology

Distributed amplifiers (DAs) feature large bandwidth but relatively low gain and power efficiency. This paper presents a supply-scaling technique to improve the efficiency of a mm-wave DA while maintaining a broadband $50\Omega $ match. An analysis of interstage load modulation and the effects of shunt dc-feed inductors on distributed operation is provided. A single-ended, eight-stage DA is designed in a 90 nm SiGe BiCMOS process. The fabricated amplifier has a gain of 12 dB over a 3 dB bandwidth from 14–105 GHz. The measured peak output power is 17 dBm with a peak power-added efficiency (PAE) of 12.6% at 50 GHz and 3 dB power bandwidth greater than 70 GHz. The DA occupies an area of 2.65 mm $\times 0.57$ mm, and total dc power consumed from four scaling voltage supplies is 297 mW.

Supply-Scaling for Efficiency Enhancement in Distributed Power Amplifiers

CMOS RF switches support watt-level RF output power while enabling signal processing with high speed. Typically, RF FET switches offer a tradeoff between a power handling and modulation bandwidth. This paper investigates the cause of compression in a FET switch, and the analysis suggests the optimization of the gate driving impedance for a stacked-FET switch. A design methodology is presented to realize watt-level power handling with high fractional bandwidth (FBW). The measurements demonstrate a BPSK modulator that can handle up to 10 W with wide FBW. The high-power, low-insertion loss, and high-modulation bandwidth demonstrate record performance.

Cooper S. Levy

Papers

A Class-G Voltage-Mode Doherty Power Amplifier

Voltage Mode Doherty Power Amplifier

Improved Performance of Zinc Oxide Thin Film Transistor Pressure Sensors and a Demonstration of a Commercial Chip Compatibility with the New Force Sensing Technology

Supply-Scaling for Efficiency Enhancement in Distributed Power Amplifiers

RF Watt-Level Low-Insertion-Loss High-Bandwidth SOI CMOS Switches