Showing papers on "RF power amplifier published in 2013"

Ambient RF Energy Harvesting in Urban and Semi-Urban Environments

Abstract: RF harvesting circuits have been demonstrated for more than 50 years, but only a few have been able to harvest energy from freely available ambient (i.e., non-dedicated) RF sources. In this paper, our objectives were to realize harvester operation at typical ambient RF power levels found within urban and semi-urban environments. To explore the potential for ambient RF energy harvesting, a city-wide RF spectral survey was undertaken from outside all of the 270 London Underground stations at street level. Using the results from this survey, four harvesters (comprising antenna, impedance-matching network, rectifier, maximum power point tracking interface, and storage element) were designed to cover four frequency bands from the largest RF contributors (DTV, GSM900, GSM1800, and 3G) within the ultrahigh frequency (0.3-3 GHz) part of the frequency spectrum. Prototypes were designed and fabricated for each band. The overall end-to-end efficiency of the prototypes using realistic input RF power sources is measured; with our first GSM900 prototype giving an efficiency of 40%. Approximately half of the London Underground stations were found to be suitable locations for harvesting ambient RF energy using our four prototypes. Furthermore, multiband array architectures were designed and fabricated to provide a broader freedom of operation. Finally, an output dc power density comparison was made between all the ambient RF energy harvesters, as well as alternative energy harvesting technologies, and for the first time, it is shown that ambient RF harvesting can be competitive with the other technologies.

Per-Antenna Constant Envelope Precoding for Large Multi-User MIMO Systems

Abstract: We consider the multi-user MIMO broadcast channel with M single-antenna users and N transmit antennas under the constraint that each antenna emits signals having constant envelope (CE). The motivation for this is that CE signals facilitate the use of power-efficient RF power amplifiers. Analytical and numerical results show that, under certain mild conditions on the channel gains, for a fixed M, an array gain is achievable even under the stringent per-antenna CE constraint. Essentially, for a fixed M, at sufficiently large N the total transmitted power can be reduced with increasing N while maintaining a fixed information rate to each user. Simulations for the i.i.d. Rayleigh fading channel show that the total transmit power can be reduced linearly with increasing N (i.e., an O(N) array gain). We also propose a precoding scheme which finds near-optimal CE signals to be transmitted, and has O(MN) complexity. Also, in terms of the total transmit power required to achieve a fixed desired information sum-rate, despite the stringent per-antenna CE constraint, the proposed CE precoding scheme performs close to the sum-capacity achieving scheme for an average-only total transmit power constrained channel.

A Dual-Band Rectenna Using Broadband Yagi Antenna Array for Ambient RF Power Harvesting

Abstract: This letter presents a dual-band rectenna that can harvest ambient RF power of GSM-1800 and UMTS-2100 bands efficiently. The novel rectenna is based on a broadband 1 × 4 quasi-Yagi antenna array with bandwidth from 1.8 to 2.2 GHz and high gains of 10.9 and 13.3 dBi at 1.85 and 2.15 GHz, respectively. Also, a dual-band rectifier that can sufficiently enhance the RF-to-dc power conversion efficiency (PCE) at ambient RF power level is designed for the rectenna. Measurement results show that a PCE of 40% and an output dc voltage of 224 mV have been achieved over a 5-k Ω resistor when the dual-tone input power density is 455 μW/m 2. Additionally, output dc voltage varying between 300-400 mV can be obtained by collecting the relatively low ambient RF power.

A Batteryless 19 $\mu$ W MICS/ISM-Band Energy Harvesting Body Sensor Node SoC for ExG Applications

Abstract: This paper presents an ultra-low power batteryless energy harvesting body sensor node (BSN) SoC fabricated in a commercial 130 nm CMOS technology capable of acquiring, processing, and transmitting electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG) data. This SoC utilizes recent advances in energy harvesting, dynamic power management, low voltage boost circuits, bio-signal front-ends, subthreshold processing, and RF transmitter circuit topologies. The SoC is designed so the integration and interaction of circuit blocks accomplish an integrated, flexible, and reconfigurable wireless BSN SoC capable of autonomous power management and operation from harvested power, thus prolonging the node lifetime indefinitely. The chip performs ECG heart rate extraction and atrial fibrillation detection while only consuming 19 μW, running solely on harvested energy. This chip is the first wireless BSN powered solely from a thermoelectric harvester and/or RF power and has lower power, lower minimum supply voltage (30 mV), and more complete system integration than previously reported wireless BSN SoCs.

Wireless inductive power transfer

Abstract: A wireless power transfer system includes a power receiver (105) and a power transmitter (101) generating a wireless inductive power transfer signal for powering the power receiver (105) during a power transfer phase. An apparatus, often the power transmitter (101) comprises a first communication unit (305) communicating with a second communication unit of an entity using an electromagnetic communication signal. The entity may typically be the power receiver (105). The apparatus comprises a reference processor (307) for measuring and storing a reference value of a characteristic of the communication signal and a measurement unit (309) which repeatedly during the power transfer phase determines a measured value of the characteristic. A comparator (311) compares the measured values to the reference value and an initiator (313) triggers an entity detection process if the comparison indicates that a measured value and the reference value do not meet a similarity criterion. The entity detection process detect a presence of another entity.

Flat panel, stationary or mobile, spatially beam-formed wireless energy delivery system

Abstract: Methods and systems are provided for achieving delivery of power wirelessly using a highly beam-formed array of radio frequency (RF) transmitters as a source and a spatially beam-formed array of receivers that collect the impinged RF power and feed a multistage RF to direct current (RF-DC) conversion circuit that, for example, increases output voltage by doubling the voltage at each stage, while power delivery remains constant. One or more embodiments may provide energy wirelessly and—unlike conventional systems where the power flux density may be too low for applications where an energy density (specific energy) on the order of several mega-Joules per kilogram (MJ/Kg) is desired—may provide sufficient power flux density for many practical applications.

A 60-GHz Dual-Mode Class AB Power Amplifier in 40-nm CMOS

Abstract: A 60-GHz dual-mode power amplifier (PA) is implemented in 40-nm bulk CMOS technology. To boost the amplifier performance at millimeter-wave (mmWave) frequencies, a new transistor layout is proposed to minimize the device and interconnect parasitics while the neutralized amplifier stage is co-optimized with input transformer to improve the power gain and stability. The transformer-based power-combining PA consists of two unit amplifiers, operating in Class AB for better back-off efficiency. To further reduce the power consumption and hence extend battery lifetime, one unit PA is tuned off in low-power mode. A switch is used to short the output of this non-operating unit PA to reduce the combiner loss and improve the efficiency. The PA achieves a measured saturated output power (PSAT) of 17.0 dBm (12.1 dBm) and 1-dB compressed power (P1dB) of 13.8 dBm (9.1 dBm) in the high-power (low-power) mode. The power-added efficiencies (PAEs) at PSAT and P1dB are 30.3% and 21.6% respectively for the high-power mode. Compared to Class A, the PA operating in Class AB shows 5.3% improvement in measured PAE at P1dB with no compromise in linearity. The PA with the power combiner only occupies an active area of 0.074 mm 2. The reliability measurements are also conducted and the PA has an estimated lifetime of 80613 hours.

A Modified Doherty Power Amplifier With Extended Bandwidth and Reconfigurable Efficiency

Abstract: This paper derives the theory and presents measurements of a new power amplifier based on the Doherty power amplifier topology. It is theoretically shown that the proposed amplifier can simultaneously provide high efficiency at both full output power and at output power back-off, over a much improved bandwidth compared to the conventional Doherty power amplifier. It is also shown that the proposed amplifier allows reconfiguration of the efficiency in power back-off without the need of tunable elements.

Method for forming film by plasma-assisted deposition using two-frequency combined pulsed RF power

Abstract: A method for forming a dielectric film on a substrate by plasma-assisted deposition, includes: introducing a Si-containing process gas to a reaction space wherein a substrate having a surface with patterned recesses is placed; and applying RF power to the process gas in the reaction space to form a dielectric film on the surface by plasma reaction. The RF power is comprised of pulses of high-frequency RF power and pulses of low-frequency RF power, which overlap and are synchronized.

Multiband accelerated spin-echo echo planar imaging with reduced peak RF power using time-shifted RF pulses.

Abstract: Purpose: To evaluate an alternative method for generating multibanded radiofrequency (RF) pulses for use in multiband slice-accelerated imaging with slice-GRAPPA unaliasing, substantially reducing the required peak power without bandwidth compromises. This allows much higher accelerations for spin-echo methods such as SE-fMRI and diffusion-weighted MRI where multibanded slice acceleration has been limited by available peak power. Theory and Methods: Multibanded “time-shifted” RF pulses were generated by inserting temporal shifts between the applications of RF energy for individual bands, avoiding worst-case constructive interferences. Slice profiles and images in phantoms and human subjects were acquired at 3 T. Results: For typical sinc pulses, time-shifted multibanded RF pulses were generated with little increase in required peak power compared to single-banded pulses. Slice profile quality was improved by allowing for higher pulse bandwidths, and image quality was improved by allowing for optimum flip angles to be achieved. Conclusion: A simple approach has been demonstrated that significantly alleviates the restrictions imposed on achievable slice acceleration factors in multiband spin-echo imaging due to the power requirements of multibanded RF pulses. This solution will allow for increased accelerations in diffusion-weighted MRI applications where data acquisition times are normally very long and the ability to accelerate is extremely valuable. Magn Reson Med 69:1261–1267, 2013 Wiley Periodicals, Inc.

Method for controlling cyclic plasma-assisted process

Abstract: A method for processing a substrate in a reactor by pulsing RF power, includes: applying RF power in pulses in the reactor to process the substrate; monitoring data from the reactor indicative of anomalous pulses of RF power, including data from a photo sensor equipped in the reactor; counting the number of anomalous pulses of RF power in the monitored data; determining whether or not the number of anomalous pulses of RF power is acceptable; and initiating a pre-designated sequence if the number of anomalous pulses of RF power is determined to be unacceptable.

A Class-G Switched-Capacitor RF Power Amplifier

Abstract: A switched-capacitor power amplifier (SCPA) that realizes an envelope elimination and restoration/polar class-G topology is introduced. A novel voltage-tolerant switch enables the use of two power supply voltages which increases efficiency and output power simultaneously. Envelope digital-to-analog conversion in the polar transmitter is achieved using an SC RF DAC that exhibits high efficiency at typical output power backoff levels. In addition, high linearity is achieved and no digital predistortion is required. Implemented in 65 nm CMOS, the measured peak output power and power-added efficiency (PAE) are 24.3 dBm and 43.5%, respectively, whereas when amplifying 802.11g 64-QAM OFDM signals, the average output power and PAE are 16.8 dBm and 33%, respectively. The measured EVM is 2.9%.

Envelope power supply calibration of a multi-mode radio frequency power amplifier

Abstract: The present disclosure relates to envelope power supply calibration of a multi-mode RF power amplifier (PA) to ensure adequate headroom when operating using one of multiple communications modes. The communications modes may include multiple modulation modes, a half-duplex mode, a full-duplex mode, or any combination thereof. As such, each communications mode may have specific peak-to-average power and linearity requirements for the multi-mode RF PA. As a result, each communications mode may have corresponding envelope power supply headroom requirements. The calibration may include determining a saturation operating constraint based on calibration data obtained during saturated operation of the multi-mode RF PA. During operation of the multi-mode RF PA, the envelope power supply may be restricted to provide a minimum allowable magnitude based on an RF signal level of the multi-mode RF PA, the communications mode, and the saturation operating constraint to provide adequate headroom.

AlGaN Channel HEMT With Extremely High Breakdown Voltage

Abstract: Enhanced performance of RF power modules is required in a next-generation information society. To satisfy these requirements, we designed a novel high-electron mobility transistor (HEMT) structure employing wider bandgap AlGaN for a channel layer, which we called AlGaN channel HEMT, and investigated it. The wider bandgap is more effective for higher voltage operation of HEMTs and contributes to the increase of output power in RF power modules. As a result, fabricated AlGaN channel HEMTs had much higher breakdown voltages than those of conventional GaN channel HEMTs with good pinchoff operation and sufficiently high drain current density without noticeable current collapse. Furthermore, specific on-state resistances of fabricated AlGaN channel HEMTs were competitive with the best values of reported GaN- and SiC-based devices with similar breakdown voltages. These results indicate that the proposed AlGaN channel HEMTs are very promising not only for an information-communication society but also in the power electronics field.

Millimeter-Wave CMOS Power Amplifiers With High Output Power and Wideband Performances

Abstract: In this paper, we propose a design method of multi-way combining networks with impedance transformation for millimeter-wave (MMW) power amplifiers (PAs) to achieve high output power and wideband performance simultaneously in millimeter-wave frequency. Based on the proposed methodology, three power amplifiers are designed and fabricated in V-band, W-band, and D-band using 65-nm CMOS technology. With 1.2-V supply, the saturation powers of these power amplifiers are 23.2 dBm, 18 dBm and 13.2 dBm at 64 GHz, 90 GHz, and 140 GHz, with 25.1-GHz, 26-GHz, and 30-GHz 3-dB bandwidth, respectively. Compared with the published MMW amplifiers, these PAs achieve high output power and wide band performances simultaneously, and the ouput power levels is the state-of-the-art performance at these frequencies.

Linearization Circuits And Methods For Multilevel Power Amplifier Systems

Abstract: Circuits and methods for achieving high linearity, high efficiency power amplifiers, including digital predistortion (DPD) and pulse cancellation in switched-state RF power amplifier systems are described.

Electrical switching dynamics and broadband microwave characteristics of VO2 RF devices

Abstract: Vanadium dioxide is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate a large resistance modulation of the same magnitude (>10^3) in both electrically (i.e. by bias voltage, referred to as E-MIT) and thermally (T-MIT) driven transitions. We examine transient switching characteristics of the E-MIT and observe two distinguishable time scales for switching. We find an abrupt jump in conductivity with a rise time of the order of 10 ns followed by an oscillatory damping to steady state on the order of several {\mu}s. We characterize the RF power response in the On state and find that high RF input power drives VO2 further into the metallic phase, indicating that electromagnetic radiation-switching of the phase transition may be possible. We measure S-parameter RF properties up to 13.5 GHz. Insertion loss is markedly flat at 2.95 dB across the frequency range in the On state and sufficient isolation of over 25 dB is observed in the Off state. We are able to simulate the RF response accurately using both lumped element and 3D electromagnetic models. Extrapolation of our results suggests that optimizing device geometry can reduce insertion loss further and maintain broadband flatness up to 40 GHz.

RF amplifier architecture and related techniques

Abstract: A radio frequency (RF) power amplifier system or transmitter includes one or more power amplifiers and a controller that is configured to adjust amplitudes and phases of RF input signals of the one or more power amplifiers and supply voltages applied to the one or more power amplifiers. In embodiments where multiple power amplifiers are used, a combiner may be provided to combine outputs of the power amplifiers. In at least one implementation, amplitude adjustment of the RF input signals of the one or more power amplifiers may be used to provide transmit power control and/or power backoff.

Integrated Self-Healing for mm-Wave Power Amplifiers

Abstract: Self-healing as a technique for improving performance and yield of millimeter-wave power amplifiers (PAs) against process variation and transistor mismatch, load impedance mismatch, and partial and total transistor failure is described and investigated. A 28-GHz PA is presented with three types of sensors, two types of actuators, data converters, and a digital algorithm block that are all integrated on a single chip to show the validity of the technique. Two algorithms are implemented to either maximize output power or to minimize dc power for a desired output power. Measurements from 20 chips show increased RF output power up to 3 dB or reduced dc power by 50% in backoff with a 50-Ω load. Self-healing with up to 4-1 voltage standing-wave ratio load impedance mismatch is verified and linear operation under nonconstant envelope modulation is shown to improve with healing. Self-healing after laser cutter induced transistor failure is verified and increases RF output power by up to 5.4 dB. The aggregate yield of the PA across several representative specifications is increased from 0% to 80% with self-healing.

Photonic-band-gap traveling-wave gyrotron amplifier.

Abstract: We report the experimental demonstration of a gyrotron traveling-wave-tube amplifier at 250 GHz that uses a photonic band gap (PBG) interaction circuit. The gyrotron amplifier achieved a peak small signal gain of 38 dB and 45 W output power at 247.7 GHz with an instantaneous $\ensuremath{-}3\text{ }\text{ }\mathrm{dB}$ bandwidth of 0.4 GHz. The amplifier can be tuned for operation from 245--256 GHz. The widest instantaneous $\ensuremath{-}3\text{ }\text{ }\mathrm{dB}$ bandwidth of 4.5 GHz centered at 253.25 GHz was observed with a gain of 24 dB. The PBG circuit provides stability from oscillations by supporting the propagation of transverse electric (TE) modes in a narrow range of frequencies, allowing for the confinement of the operating ${\mathrm{TE}}_{03}$-like mode while rejecting the excitation of oscillations at nearby frequencies. This experiment achieved the highest frequency of operation for a gyrotron amplifier; at present, there are no other amplifiers in this frequency range that are capable of producing either high gain or high output power. This result represents the highest gain observed above 94 GHz and the highest output power achieved above 140 GHz by any conventional-voltage vacuum electron device based amplifier.

Electrical switching dynamics and broadband microwave characteristics of VO2 radio frequency devices

Abstract: Vanadium dioxide (VO2) is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate a large resistance modulation of the same magnitude (>103) in both electrically (i.e., by bias voltage, referred to as E-MIT) and thermally (T-MIT) driven transitions. We examine transient switching characteristics of the E-MIT and observe two distinguishable time scales for switching. We find an abrupt jump in conductivity with a rise time of the order of 10 ns followed by an oscillatory damping to steady state on the order of several μs. We characterize the RF power response in the On state and find that high RF input power drives VO2 further into the metallic phase, indicating that electromagnetic radiation-switching of the phase transition may be possible. We measure S-parameter RF properties up to 13.5 GHz. Insertion loss is markedly flat at 2.95 dB across the frequency range in the On state, and sufficient isolation of over 25 dB is observed in the Off state. We are able to simulate the RF response accurately using both lumped element and 3D electromagnetic models. Extrapolation of our results suggests that optimizing device geometry can reduce insertion loss further and maintain broadband flatness up to 40 GHz.

Fully Integrated ASK Receiver MMIC for Terahertz Communications at 300 GHz

Abstract: An ASK receiver MMIC operating at 300 GHz for future terahertz communications is presented. In the receiver IC, we fully integrated all necessary components-a receiving dipole antenna, high gain RF amplifier, envelop detector for demodulating ASK signal and output differential data amplifier-in a 1000×2500 μm2 area. A silicon lens was used to compensate for the small gain of the on-chip antenna. To ensure reliable and stable operation, we designed the MMIC with a thin-film microstrip line, which is expected to suppress crosstalk between the on-chip antenna and the RF amplifier through the substrate and silicon lens. The packaged receiver module with the silicon lens is expected to provide approximately 24-dBi beam directivity. Measured RF and baseband bandwidths are around 30 and 15 GHz, respectively, when a single bias of 3.3 V and total current of around 86 mA are applied. With the receiver module, simple wireless data transmission was conducted for up to 24 Gbps in the 300-GHz band. At 12.5 Gbps, error-free data transmission (bit error rate <; 10-9) over 0.3 m was achieved with the transmission power of - 16-dBm and a 25-dBi transmitting antenna. With -10-dBm transmission power, measured Q-factors of the received eye patterns were larger than 6 for up to 20 Gbps, which implies that the bit error rate will be less than 10-9.

Power loop control based envelope tracking

Abstract: Configuration-feedback circuitry and transceiver circuitry are disclosed. The configuration-feedback circuitry regulates an output power from a radio frequency power amplifier based on a difference between a target output power from the radio frequency power amplifier and a measured output power from the radio frequency power amplifier. The transceiver circuitry regulates a modulated power supply voltage, which is used by the radio frequency power amplifier to provide power for amplification, based on the difference between the target output power from the radio frequency power amplifier and the measured output power from the radio frequency power amplifier.

An Analysis of Band-limited Communication Systems from Amplifier Efficiency and Distortion Perspective

Abstract: Considering growing concerns toward green communications, not only their bandwidth efficiency but also their power consumption is expected to gain increasing importance for future communication systems. A power amplifier (PA) is one of the most power consuming analog devices at the transmitter in communication systems and a precise estimation of the power consumption at the transmitter circuit requires the knowledge of its efficiency that depends on the distribution of input signal envelope and the amount of input back-off. In this paper, we develop a simple analytical model that can be used for estimating achievable efficiency of a linear PA as well as the amount of resulting nonlinear distortion for a given modulated signal exclusively from its envelope distribution. Based on this model, the trade-off relationships between the efficiency and signal-to-distortion power ratio for several spectrally efficient linear modulations are examined. It is also shown that in some special cases of Gaussian input and memoryless nonlinearity PA models, the results can be represented in simple closed-form expressions.

A 77-GHz CMOS Power Amplifier With a Parallel Power Combiner Based on Transmission-Line Transformer

Abstract: This paper presents a 77-GHz CMOS power amplifier (PA) with a parallel power combiner based on a transmission-line transformer (TLT). An inter-stage matched cascode power cell structure is applied to obtain high output power and efficiency, where a simple matching network between the common-gate and common-source stage is introduced. The parallel power combiner based on a broadside-coupled TLT is analyzed and compared with a series power combiner. The PA is fabricated using a 65-nm RF CMOS process. It achieves the saturated output power of 15.8 dBm, the power-added efficiency of 15.2%, and the power gain of 20.9 dB with a supply voltage of 2.0 V at 77 GHz.

Scalable periphery tunable matching power amplifier

Abstract: A scalable periphery tunable matching power amplifier is presented. Varying power levels can be accommodated by selectively activating or deactivating unit cells of which the scalable periphery tunable matching power amplifier is comprised. Tunable matching allows individual unit cells to see a constant output impedance, reducing need for transforming a low impedance up to a system impedance and attendant power loss. The scalable periphery tunable matching power amplifier can also be tuned for different operating conditions such as different frequencies of operation or different modes.

5.2-GHz RF Power Harvester in 0.18- $\mu$ m CMOS for Implantable Intraocular Pressure Monitoring

Abstract: A first fully integrated 5.2-GHz CMOS-based RF power harvester with an on-chip antenna is presented in this paper. The design is optimized for sensors implanted inside the eye to wirelessly monitor the intraocular pressure of glaucoma patients. It includes a five-stage RF rectifier with an on-chip antenna, a dc voltage limiter, two voltage sensors, a low dropout voltage regulator, and MOSCAP based on-chip storage. The chip has been designed and fabricated in a standard 0.18- $\mu$ m CMOS technology. To emulate the eye environment in measurements, a custom test setup is developed that comprises Plexiglass cavities filled with saline solution. Measurements in this setup show that the proposed chip can be charged to 1 V wirelessly from a 5-W transmitter 3 cm away from the harvester chip. The energy that is stored on the 5-nF on-chip MOSCAP when charged to 1 V is 2.5 nJ, which is sufficient to drive an arbitrary 100- $\mu$ W load for 9 $\ \mu$ s at regulated 0.8 V. Simulated efficiency of the rectifier is 42% at ${-}$ 7 dBm of input power.

A Generalized Architecture for the Frequency- Selective Digital Predistortion Linearization Technique

Abstract: This paper presents a new architecture for the frequency-selective digital predistortion (DPD) for two- and three-band power amplifier (PA) linearization. Also, largely spaced-signal DPD using a digital intermediate frequency (IF) technique is demonstrated. The algorithm used accounts for differential memory effects up to fifth order for bands that can be arbitrarily spaced. The simulation and experimental studies are performed using various signal sets; two- and three-band multitone signals with various tone spacing, band separation, and complementary cumulative distribution function. An improvement of 10 dB over third-order linearization is demonstrated in simulation for more than 20 dB of adjacent channel power ratio reduction. The test signal and the linearization algorithm were implemented on a field-programmable gate array. The linearization algorithm was applied to an RF amplifier at 700-900 MHz. For the two-band case, more than 15 dB on the in-band, 13 dB on the third, and 5 dB on the fifth intermodulation distortion (IMD) cancellation were achieved. For the three-band case, more than 12 dB of IMD cancellation was observed. For largely spaced signal DPD, more than 15 dB of IMD cancellation was achieved. In the three-band case, the linearization of intermodulation byproducts overlapping with the in-band distortion is found to be of critical importance.

An UHF RFID Energy-Harvesting System Enhanced by a DC-DC Charge Pump in Silicon-on-Insulator Technology

Abstract: An RF-DC converter enhanced by a DC-DC voltage booster in silicon-on-insulator technology for UHF radio frequency identification (RFID) energy harvesting is presented in this letter. When the received RF power level is -14 dBm or higher, the system, fabricated on an FR4 substrate using off-the-shelf low-cost discrete components and connected to a flexible dipole antenna, is able to produce 2.4 V DC voltage to power general-purpose electronic devices. As a simple proof of concept, a device comprising microcontroller, temperature sensor, and EEPROM is considered in this work. The experimental results demonstrate the capability of the system to autonomously perform temperature data logging up to a distance of 5 m from a conventional UHF RFID reader used as an RF energy source.

Envelope-Tracking Two-Stage Power Amplifier With Dual-Mode Supply Modulator for LTE Applications

Abstract: This paper presents an envelope tracking power amplifier (ET PA) using a dual-mode supply modulator for handset application. The supply modulator has a combined structure with a linear amplifier and a switching amplifier. The dual-mode supply modulator operates in high-power mode and low-power mode by providing the supply voltage of the linear amplifier of 5 and 2.5 V, respectively. For 1.74-GHz long-term evolution signal with 10-MHz bandwidth, 6.44-dB peak-to-average power ratio, and 16-quadrature amplitude modulation, the ET PA delivers a power-added efficiency (PAE) of 39.8%, an evolved universal terrestrial radio access adjacent channel leakage ratio (E-UTRAACLR) of - 35.7 dBc, and an error vector magnitude (EVM) of 3.81% at an average output power of 27 dBm. The ET PA also delivers a PAE of 22.6% at an average output power of 18 dBm, which is 6.6% higher than that of the conventional ET PA and 13.1% higher than that of the standalone PA. The supply modulator is connected to a drive stage and a power stage of the PA simultaneously for further enhanced efficiency at a power back-off region. The dual-mode two-stage ET PA delivers a PAE of 38.1%, an E-UTRAACLR of - 32.9 dBc, and an EVM of 4.74% at an average output power of 27 dBm. The dual-mode two-stage ET PA also delivers a PAE of 26.3% at an average output power of 18 dBm, which is 7.8% higher than that of the conventional two-stage ET PA and 16.7% higher than that of the standalone PA.