Load Modulation Technique Research Articles

Comparative Study of Multilevel Converters using DQ Current Control

This paper presents a comprehensive comparative analysis of different multilevel converter topologies, including 2-level, Neutral Point-Clamped (NPC), Cascaded H-Bridge (CHB), and T-Type converters using the DQ current control strategy. The study aims to evaluate the performance of these topologies concerning current Total Harmonic Distortion (THD) and ripple in the direct and quadrature components of the current. A mathematical model of the grid is presented to facilitate the simulation study. The DQ current control scheme is implemented to regulate the current in both the direct and quadrature axes. The simulations are conducted under various operating conditions to capture the converters’ performance across different load scenarios and modulation techniques. Results indicate significant variations in the performance metrics among the different converter topologies. The 2-level converter exhibits higher THD and ripple compared to the more complex multilevel topologies.

Ultra-Compact mm-Wave Monolithic IC Doherty Power Amplifier for Mobile Handsets

This work develops a novel dynamic load modulation Power Amplifier (PA) circuity that can provide an optimum compromise between linearity and efficiency while covering multiple cellular frequency bands. Exploiting monolithic microwave integrated circuits (MMIC) technology, a fully integrated 1W Doherty PA architecture is proposed based on 0.1 μm AlGaAs/InGaAs Depletion-Mode (D-Mode) technology provided by the WIN Semiconductors foundry. The proposed wideband DPA incorporates the harmonic tuning Class-J mode of operation, which aims to engineer the voltage waveform via second harmonic capacitive load termination. Moreover, the applied post-matching technique not only reduces the impedance transformation ratio of the conventional DPA, but also restores its proper load modulation. The simulation results indicate that the monolithic drive load modulation PA at 4 V operation voltage delivers 44% PAE at the maximum output power of 30 dBm at the 1 dB compression point, and 34% power-added efficiency (PAE) at 6 dB power back-off (PBO). A power gain flatness of around 14 ± 0.5 dB was achieved over the frequency band of 23 GHz to 27 GHz. The compact MMIC load modulation technique developed for the 5G mobile handset occupies the die area of 3.2 mm2.

Beam-Steerable Transponder Based on Antenna Array and Phased Modulators

This letter presents a novel concept of beam-steerable transponder based on antenna array and phased modulators. The steerability of the beam is achieved by optimally delaying the modulated reflected signal at each antenna element (i.e., changing the phase in frequency domain) with load modulation technique. In this manner, the reflected backscattered signal power can be maximized at one particular direction. The approach makes transponder to collect ambient waves from any direction and further modulate and redirect it to any other direction. The results obtained through experimentation proves the feasibility of omnidirectional transponder and pave way for future lower power smart devices. The transponder functions in the Wi-Fi frequency band of 2.4 GHz.

Load‐modulation technique without using quarter‐wavelength transmission line

A proposed method for achieving active load-modulation technique without using a quarter-wavelength transmission line is discussed and evaluated. The theoretical analysis shows that the active load-modulation can be achieved without using a quarter-wavelength line, where the main amplifier sees a low impedance when the input signal level is low, and this impedance increases in proportion to the amount of current contributed from the peaking amplifier. The peaking amplifier sees an impedance decreasing from infinity to the normalized impedance. To validate the method, a circuit was designed, simulated and fabricated using two symmetrical gallium nitride (GaN) transistors (6 W) to achieve a peak power of 12 W and 6 dB output back-off efficiency. The design operates with 400 MHz bandwidth at 3.6 GHz and showed an average efficiency of 50% at 6 dB back-off and an efficiency of 75% at peak power. The designed circuit was tested with CW and modulated signals, the amplifier showed an Adjacent Channel Power Ratio (ACPR) of 31–35.5 dB when tested with a wideband code division multiple access signal of 6 dB peak-average-power ratio (PAPR) at 35.5 dBm average power. Additional 20 dB of linearity improvement was achieved after adding a lineariser.

High-Efficiency Power Amplifier Employing Minimum-Power Harmonic Active Load Modulator

There is an impedance conflict between the fundamental harmonic of ${f}_{2}$ and the second of ${f}_{1}$ if ${f}_{2}\,\,{=}\,\,{2}{f}_{1}$ . In this brief, a methodology employing the harmonic active load modulation (HALM) technique is utilized for solving this problem. A main power amplifier and an active load modulator constitute the overall circuit. This technique transforms the second harmonic load impedance to the optimum by injecting second harmonic power in the lower band. In order to improve the overall efficiency, a method of searching optimal location parameter is proposed to achieve the minimum extra power in harmonic injection. A power amplifier (PA) working at 1.7 and 3.4 GHz is fabricated for validation. At 1.7 GHz, the HALM technique brings an improvement of 14% in overall efficiency and an increase of 0.7 dB in output power. As for 3.4 GHz, the fabricated PA delivers overall efficiency of 78.5% and output power of 41.3 dBm without HALM.

Harmonic‐tuned continuum mode active load modulation output combiner for the design of broadband asymmetric Doherty power amplifiers

The conventional Doherty output combiner limits the bandwidth of operation in the asymmetric Doherty power amplifiers (DPAs). In this study, an output combiner that is designed using a harmonic-tuned continuum mode active load modulation technique is proposed with the main target of extending the bandwidth of operation in the asymmetric DPAs. Through this methodology, design equations are derived and multiple harmonic impedance solutions are provided. This offers greater freedom for designing the output combiner of the asymmetric DPA which consists of the impedance inverting network and the impedance transforming network. Moreover, enhancements in the efficiencies at back-off and saturation power levels are made possible. The efficacy of the design strategy is demonstrated by the realised broadband asymmetric DPA prototype working within the band of 1.4–2.45 GHz. The experimental results have shown 54.55% bandwidth of operation, accounting for about 0.95–12.55% increment in bandwidth as compared with some recently published DPAs in the literature. Substantially, drain efficiencies within 35.5–52% at 6 dB output power back-off level and 47.5–64.2% at peaking power level are also recorded from the experiments. The maximum output power and gain are recorded at 43.52 dBm and 13.03 dB, respectively.

An $X$ -Band Pulsed Load Modulation Transmitter With Multilevel Envelope Delta–Sigma Modulations

Switched mode RF power amplifiers (PAs) under bitstream modulations, such as bandpass or envelope delta-sigma modulations (EDSMs), have received increasing attentions over the past years. Such amplifiers offer high power efficiencies under power back-off conditions with pulse train voltage waveforms yet maintain their linearity in amplification through digital coding and modulations. This paper presented an X-band switched mode PA based on the pulsed load modulation (PLM) technique with multilevel EDSM to realize broadband efficient amplification of nonconstant-envelope signals. The complete theory of power efficiency for PLM under three-level EDSM is presented. The X-band PA is implemented with 0.25-μm discrete GaN transistors from Triquint. Both two-level and three-level EDSM techniques were tested and compared in regard to their quantization noise levels and power efficiencies. Under the three-level EDSM, the PA delivered 34.6-dBm output power for a WCDMA uplink signal with 100-MHz bandwidth and 5.3-dB peak-to-average power ratio at the carrier frequency of 9.2 GHz. The measured drain efficiency and the power-added efficiency with the modulation were 34.6% and 26.5%, respectively. The adjacent channel leakage power ratio at the output was measured to be 32.2/32.3 dBc at the 100-MHz offsets without using digital predistortion.

High efficiency radio frequency power amplifier with dynamic load modulation for wireless communications

ABSTRACTIn this article, a radio frequency (RF) power amplifier (PA) with high efficiency and high linearity is presented by using dynamic load modulation (DLM) technique. To improve the average efficiency, the load impedance is dynamically modulated according to the input envelop using tunable matching circuit (TMC). The TMC using varactors is located at a low‐impedance region of the output matching network. This reduces the RF voltage swing across the varactors, which minimizes the performance degradation by the varactors. The measurement setup is constructed to generate a control signal for the TMC that is synchronized with an input envelope. For wideband code division multiple access (W‐CDMA) signal with a peak‐to‐average ratio of 7.4 dB and a bandwidth of 3.84 MHz at 1.85 GHz, the fabricated DLM PA shows a power‐added efficiency of 49.7% at an output power of 30.6 dBm with an adjacent channel leakage ratio of <–45 dBc © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2717–2722, 2016

고차 변조를 사용하는 Load-Modulation MIMO 시스템 설계와 성능 평가

In this paper, we analyze LM-MIMO (load-modulation multiple-input multiple-output) system with single RF chain. And then, we confirm that load modulation technique can support generation of high-order m-PSK modulation and m-QAM modulation in LM-MIMO system. Finally we evaluate performance of LM-MIMO system with load modulation. Conventional MIMO system requires a number of RF chains for expansion of MIMO dimension. A number of RF chains can cause various problems. On the other hand, although LM-MIMO system is expanded, LM-MIMO system requires single RF chain only. Therefore, LM-MIMO system has low-complexity and low power consumption. As results, we can confirm that load modulation of T-model can modulate high-order m-PSK and m-QAM singal. Also, we can confirm that LM-MIMO system using load modulation has a similar performance to conventional MIMO system.

A Pulsed Dynamic Load Modulation Technique for High-Efficiency Linear Transmitters

A pulsed dynamic load modulation (PDLM) technique is introduced for a high-efficiency linear transmitter for wideband modulation signals with a large peak-to-average power ratio. By combining the dynamic load modulation technique with the class-S amplifier concept, the pulse-width-modulated envelope signal is applied to the switchable-load matching circuit so that the power amplifier (PA) can operate near optimum efficiencies in the backed-off power region. A comprehensive analysis is presented to prove the circuit concept using the simplified theory, followed by the full circuit simulations using harmonic-balance analysis. The effect of nonideal terminations at the intrinsic device plane is also analyzed to understand the potential issues in the practical implementation. The proof-of-concept circuits are designed and fabricated using a silicon-on-insulator CMOS process, where a two-stage PA, a load switch, a pulse-width modulation circuit, and a switch driver are implemented in two separate chips. The fabricated PDLM PA operating at 837 MHz shows continuous-wave efficiencies in excess of 44% across the 6-dB power back-off region from the saturated output power. A power-added efficiency as high as 43.4% is achieved at the output power of 24.8 dBm using 10-MHz-bandwidth 16 quadrature amplitude modulation long-term evolution (LTE) signals. Unlike the case of the envelope-tracking techniques, the PDLM PA of this work maintains the overall efficiencies as the LTE signal bandwidth increases. The PDLM PA of this work can provide a potential solution for high-efficiency PAs for future mobile terminals using wideband modulation signals.

Optimized Design of a Dual-Band Power Amplifier With SiC Varactor-Based Dynamic Load Modulation

A new methodology for the design of single/multi-band power amplifiers (PAs) with dynamic load modulation (DLM) is presented. First, the topology for the output matching network (OMN) including the control varactor is selected. A comprehensive optimization of the OMN parameters is then developed by which varactor and transistor losses are considered to ensure maximum efficiency enhancement at each frequency. To verify the method, a dual-band PA with DLM is realized. Drain efficiencies of 75% and 60% at 685 MHz and 1.84 GHz, respectively, are measured at peak output power. At 10-dB output power back-off efficiencies of 43.5% and 49.5%, respectively, are obtained. Linearized modulated measurements with a 6.5-dB peak-to-average power ratio WCDMA signal show average drain efficiencies of 56% and 54% at 685 MHz and 1.84 GHz, respectively, at an adjacent channel leakage ratio of $-{\hbox{49}}$ and $- {\hbox{47.5 dBc}}$ , respectively. The proposed method shows the effectiveness of applying an optimization process for the design of single- or multi-band DLM PAs. The results demonstrate that near-optimum performance may be obtained in terms of efficiency enhancement for a given transistor and varactor-based OMN, thus making DLM competitive against other load modulation techniques.

An ultrawideband CMOS power amplifier using two-stage distributed matching techniques

An ultrawideband CMOS power amplifier (PA) with high efficiency, high P1dB, and flat small signal gain is proposed. The CMOS PA uses the distributed amplifier concept to extend the operating bandwidth from 3.1 to 10.6 GHz, and incorporates the active load modulation technique to improve the power-added efficiency (PAE). The active load modulation is realized with two cascode power stages using two different bias classes (class-AB and class-B) to increase the PAE. The experimental results show that the output P1dB is 17.5 dBm with the maximum PAE of 24.6% at 4 GHz. The measured small signal gain is 8 ± 0.3 dB from 3.1 to 10.6 GHz. The proposed PA is implemented in a 0.13-μm CMOS process, and the chip area is 0.64 mm2 including pads. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1757–1759, 2014

A multiband power amplifier with a tunable transmission line for mobile LTE applications

AbstractA power amplifier (PA) for multiband applications implemented with a tunable load modulation technique is presented. The broadband output matching can be done by load modulation implemented by modification of the characteristic impedance (ZC) of the tunable transmission line. The multiband PA delivered a gain of more than 10.5 dB, an adjacent‐channel‐leakage ratio of evolved UMTS terrestrial radio access adjacent channel leakage ratio (E‐UTRA) lower than −30 dBc, and a power added efficiency of 28–31% at the output power of 26‐dBm and the frequency range of 1.5–2.05 GHz with a 10‐MHz 16QAM long‐term evolution signal. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1175–1178, 2014

ISO 14443A active load modulation technology and its integration in the micro-SD card form factor

A more detailed analysis of the market for mobile phones shows that the proportion of Near Field Communication (NFC)-enabled devices for contactless mobile payment in comparison to the total number of non-NFCenabled mobile phones has grown very slowly. It is predicted that approximately 1.3 billion mobile phones will be sold in 2011 but only a very small proportion with NFC interface equipment. Mobile phone manufacturers are hesitant to implement NFC technology (ISO\IEC 14443/13.56 MHz band) into their mobile phones as there is a lack of mobile payment applications and a small payment infrastructure with point of sales terminals. As a result, a typical ‘chicken or egg’ causality dilemma currently exists in this field. In order to make a breakthrough for mobile payment applications, a far greater share of NFC capable handsets is required. One possible way to solve this dilemma can be to use a standard mobile phone with a replaceable memory device (micro-SD card) including active load modulation for ISO\IEC 14443 type A. In this paper the active load modulation technique and the integration in the micro-SD form factor are described.

Efficient multi-stage load modulation radio frequency power amplifier for green radio frequency front end

The road towards the reduction in the carbon footprint associated with power-hungry wireless communication devices will require a holistic design approach to ensure that energy saving can be achieved throughout the entire system. The information and communication technology today accounted for 3 and 2% global power consumption and global CO2 emissions, respectively, where a significant portion is a result of the power consumption in the radio frequency (RF) power amplifier device. Moreover, tomorrow amplifiers will need to be reconfigurable and host a plethora of modulated signals to support effective signal processing. Therefore performance metrics such as linearity, power efficiency and their trade-off should be at the forefront of the RF power amplifier design. This study proposes an energy-efficient power amplifier design based on the Doherty configuration as part of a green RF front end for mobile WiMAX. The authors extend the classical Doherty to incorporate a three-stage load modulation design with a proposed new output power combiner. The performance of the three-stage load modulation RF power amplifier is compared with the legacy two-stage load modulation technique. The experimental results show that 30 dBm output power can be achieved with 67% power-added efficiency, which represents a 14% improvement over the current state-of-the-art system while meeting the power output requirements for mobile WiMAX.

Dynamic Load Modulation With a Reconfigurable Matching Network for Efficiency Improvement Under Antenna Mismatch

This brief presents the application of a reconfigurable matching network (RMN) to improve the efficiency of an RF power amplifier (PA) using dynamic load modulation techniques under different antenna mismatch conditions. By changing the RMN state, a near-optimal output impedance is presented to the PA, achieving high efficiency for all input-driven levels. Simulations show efficiency enhancement, while nonlinear distortion can be mitigated using digital predistortion. It will be also shown that under severe mismatch conditions, using an RMN, significant efficiency and linearity improvements can be achieved.

Data Transmission Using Original Coils in Resonant Wireless Power Transmission

We propose a data transmission method for resonant wireless power transmission systems. In order to transmit data, we use the coils originally designed for power transmission, no additional antennas are required. We focus on uplink data transmission and adopt the load modulation technique. This configuration yields mid-range data transmission without transmitting power. In addition, the proposal enables simultaneous power feeding and uplink data transmission. We make a prototype demonstrating resonant wireless power transmission and measure its S-parameter under some load conditions. The results confirm the potential of load modulation in supporting uplink data transmission. Additionally, the results are elucidated by analyzing an equivalent circuit. Measured S-parameter and equivalent circuit response are found to be similar.

Design of Highly Efficient Load Modulation Transmitter for Wideband Cellular Applications

In this paper, the high potential of varactor-based dynamic load modulation (DLM) techniques for wideband cellular applications is demonstrated. A systematic design procedure is proposed to ensure high-efficiency wideband performance. It incorporates harmonically tuned power amplifier (PA) concepts and tunable matching techniques in an integrated design. A DLM transmitter at 2.65 GHz with a peak output power of 6 W is designed using the proposed procedure. In order to investigate the wideband performance of the implemented demonstrator, WCDMA signals with scaled bandwidths are employed. The signal peak-to-average ratio is 7 dB and the same for all the experiments. For the 38.4-MHz signal, which has a corresponding channel bandwidth of > 40 MHz, an average power added-efficiency (PAE) of 44%, normalized mean square error (NMSE) of -35 dB, and adjacent channel leakage ratio (ACLR) of -43 dBc are measured.

Condensation Detection Using a Wirelessly Powered RF-Temperature Sensor

The formation of condensation on windshields can be counteracted and even prevented through the concerted use of an automobile heating, ventilation, and air-conditioning (HVAC) system. By anticipating the formation of dew, through the temperature of the windshield and dew point in the cabin, a condensation-free windshield can be ensured. A new approach toward a system for condensation detection is reported. It uses an actively powered humidity sensor, as well as a remotely and wirelessly powered temperature sensor system. The wirelessly powered temperature detector, which may be embedded in the windshield of an automobile, obtains its energy via an inductively coupled magnetic field and simultaneously transmits data through a load-modulation technique. Such a system approach offers advantages in terms of cost, system life, and maintenance, in comparison with existing wired systems and other wireless solutions. The system is implemented using off-the-shelf components and is discretely designed around application-specific resonant tanks. The resonant tanks were mathematically characterized and compared with measured values. The read range of the wirelessly powered condensation detector at a frequency of 13.56 MHz is more than 4 cm while consuming a maximum power of approximately 2 mW. The application of this technology as part of a climate-control system is discussed in this paper. System concept, design considerations, and prototype characterization are also included.

Design of Varactor-Based Tunable Matching Networks for Dynamic Load Modulation of High Power Amplifiers

In this paper, the design of varactor-based tunable matching networks for dynamic load modulation of high power amplifiers (PAs) is presented. Design guidelines to overcome the common breakdown, and tunability problems of the varactors for high power applications are proposed. Based on the guidelines, using commercially available abrupt junction silicon varactors, a tunable matching network is built and measured. The matching network is then used for load modulation of a 1-GHz 7-W class-E LDMOS PA. Static measurements of the load modulated PA show that the power-added efficiency of the PA is improved by an absolute value of 10% at 10-dB backoff. This promising result proves, for the first time, the feasibility of load modulation techniques for high-power applications in the gigahertz frequency range.