Class-D RF Research Articles

Nonlinear Analytical Model for Switched-Capacitor Class-D RF Power Amplifiers

This paper presents a nonlinear analytical model for an inverter-based switched-capacitor Class-D RF power amplifier (SCDPA). The root causes of the SCDPA AMAM and AMPM nonlinearities are studied. The major factors affecting SCDPA nonlinearities are identified as the unequal on-resistances of selected cell and unselected cell. Specifically, time-varying resistance of the switch, different transistor responses during the transition and parasitic resistance on the supply path (IR drop) are analyzed. Then, the system-level result, like EVM and power spectral density, can be obtained with nonlinear behavior of PA. The results of model calculation, schematic simulation, and measurement are presented and compared with validate the model both on transistor level and system level. This paper, for the first time, provides an accurate design guidance to enable fast architecture study and quick circuit-level prototype with close-to-optimum component initial parameters. It can be expanded to more architectures, therefore helps to pave the path to future design automation for highly linear SCDPAs.

Techniques for Power Dynamic Range and Back-Off Efficiency Improvement in CMOS Digitally Controlled Polar Transmitters

Techniques to extend the power dynamic range and to reduce the dc power consumption in back-off for a multiband CMOS digitally controlled polar transmitter are described. The techniques are applied to a transmitter comprising a digitally controlled buck converter and a current-mode class-D RF amplifier with digitally controlled unit cells. The power dynamic range is improved by using tri-state unit-cells (rather than the customary “on–off” controlled cells) to reduce the feed-through power. The measured overall power dynamic ranges are 91 and 85 dB, at 0.85 and 1.75 GHz, respectively. DC power consumption at low power was reduced by introducing a new charge-sampling mode of operation for the buck converter in addition to the customary pulse-width modulation operation. Experimental results showed dc power consumption reduced by 30% at low power.

Optimized Current-Mode Class-D RF Power Amplifier for Software Defined Radio

Optimized Current-Mode Class-D RF Power Amplifier for Software Defined Radio

Design of High-Efficiency Voltage-Mode Class-D RF Power Amplifier for Class-S Transmitter Using Signal Analysis and Additional Multi-Section Bandpass Filter

This paper proposes a high-efficiency voltage-mode class-D (VMCD) RF power amplifier (PA) for class-S transmitter, which includes additional multi-section bandpass filter (BPF). For an accurate analysis of class-S transmitter, the output signals of band pass delta sigma modulator (BPDSM) are described with probability distribution functions (PDF) versus pulse widths of quantized signals. Usually, the results show that magnitudes of sub-harmonic terms increases for high peak-to-average power ratio signal such as long term evolution (LTE) signal. For a high efficiency and appropriate linearity of class-S transmitter, we propose a VMCD PA utilizing a multi-section BPF. The proposed architecture effectively improves the linearity without deterioration the efficiency. For the LTE signal, the efficiency is 25.82% and adjacent channel power ratio (ACPR) is -52.44dBc when using a one-section BPF. By using the multi-section BPF, ACPR and efficiency have been improved up to 11.88dB and 13.44% respectively. The effectiveness of the proposed design is demonstrated for various input signals.

Development of Wireless Energy Transfer Module for Solar Energy Harvesting

A module of wireless energy transfer (WET) has been developed to interact with the ambient solar energy. The main idea of the module development is to distribute the collected electrical energy from a solar panel module to in house loads appliances wirelessly. The solar panel module has been identified to have 240W, 30 V, Poly Crystalline Silicon Photovoltaic solar panel with 60 cells. The design of WET module is based on magnetic resonance technology, which employed two sub-unit modules development; driving circuit and two coils mutually inducted to transfer energy in a suitable resonant frequency. Class-D RF power amplifier has been used as the driving circuit for transmitted coil switching which has an advantage of nearly 99% efficiency theoretically. Three types of coils have been developed; there are circular coil, flat spiral coil and flat Rodin coil. High quality factor Q (>100) of each coil is designed to minimize the power dissipation in coil. With the highest efficiency of the wireless energy transfer module, the energy collected by photovoltaic solar panel can be transferred with nearly zero of its losses and higher wireless transmission distance. Results have shown that, flat spiral coil have higher efficiency with longer distance of transmission that can be achieved compare to the other designs. The maximum distance of transmission is 26 cm with an efficiency of 80% at quality factor 272.62. Based on the results it has been proven that using the coil with a high factor Q and coupling coefficient at matched resonant frequency leads to a bigger energy transfer with a greater distance. Experimental results show that, optimal efficiency of the designed system can be achieved with circular loop coil is 45.25% at factor Q 413.62, while 36.5% at factor Q 264.63.

Inverse Class-F 기법을 이용한 900 MHz 전류 모드 Class-D RF 전력 증폭기 설계

본 논문에서는 900 MHz 대역에서 동작하는 전류 모드 Class-D(Current-Mode Class-D: CMCD) 전력 증폭기를 설계 및 제작하고 특성을 분석하였다. 차동 구조에 의해 짝수차 고조파 성분이 제거된다는 점에 착안하여 출력단의 일반적인 CMCD 회로의 병렬 공진기를 제거하고 inverse class-F 전력 증폭기를 push-pull 구조로 연결하여 CMCD 전력 증폭기를 설계하였다. 로드-풀 기법을 이용하여 GaN 소자 기반의 inverse class-F 및 이를 적용한 CMCD 전력 증폭기를 설계 및 제작하였다. 제작한 CMCD는 34.2 dBm의 출력과 64.5 %의 드레인 효율을 가지며, 이는 출력측에 공진기 구조를 가지는 일반적인 CMCD 전력 증폭기의 드레인 효율과 비교했을 때 13.6 %의 효율 향상을 가진다. In this paper, Current-Mode Class-D(CMCD) RF Power Amplifier(PA) is designed and implemented at 900 MHz. Conventional CMCD PA has output parallel resonator to reconstruct a fundamental frequency component of the output signal. However the resonator can be removed by connecting inverse class-F PAs because even-harmonic components can be removed by CMCD PA's push-pull structure. Using load-pull, inverse class-F PA with GaN transistors is designed, and CMCD PA with the inverse class-F PA is implemented. The CMCD PA has 64.5 % drain efficiency, 34.2 dBm output power. Comparing with the drain efficiency of a CMCD PA with parallel resonator, the CMCD with the inverse class-F technology has 13.6 % improved drain efficiency.

Highly efficient switched-mode transmitter using a current mode class-D RF amplifier

This article presents a switched-mode transmitter architecture using a current mode class-D (CMCD) amplifier. To achieve high average efficiency for a modulated signal the envelope of the complex baseband signal is transformed into pulses such that the CMCD amplifier is operated either at its peak efficiency or completely switched off. The CMCD amplifier has been designed based on single-tone active harmonic load-pull measurements to achieve a power-added efficiency (PAE) of 61.5% with 25 W output power at 900 MHz using LDMOS FETs. Removing the losses of the demodulation filter and of the amplifier a 10% higher efficiency than in an ideal class-B amplifier can be obtained for burst-mode operation with a peak-to-average power ratio of 10 dB. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.

Design of high-efficiency RF Class-D power amplifier

In this paper, the losses in a Class-D RF switching power amplifier and their frequency dependence are described. The losses analyzed are the switching, conduction, and gate drive losses. A 300 W, 13.56 MHz, Class-D circuit is designed in the traditional manner to illustrate the magnitude of the different types of loss. A circuit using the ZVS equations developed in this paper is designed. An experimental circuit is built using standard IRF540 devices in TO220 packages. That circuit does not meet its performance goals because of the package inductance. A new low inductance half-bridge package is introduced to solve this problem. Techniques for circuit layout and power measurements for RF applications are also presented in the experimental section. A low loss gate drive circuit is also presented using a Class-E circuit to provide the drive power. The experimental results confirm the accuracy of the design equations derived in this paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

MOS-FETを使用した広帯域D級電力増幅器の周波数特性

MOS-FETを使用した広帯域D級電力増幅器の周波数特性