Kenle Chen

Design of Highly Efficient Broadband Class-E Power Amplifier Using Synthesized Low-Pass Matching Networks

A new methodology for designing and implementing high-efficiency broadband Class-E power amplifiers (PAs) using high-order low-pass filter-prototype is proposed in this paper. A GaN transistor is used in this work, which is carefully modeled and characterized to prescribe the optimal output impedance for the broadband Class-E operation. A sixth-order low-pass filter-matching network is designed and implemented for the output matching, which provides optimized fundamental and harmonic impedances within an octave bandwidth (L-band). Simulation and experimental results show that an optimal Class-E PA is realized from 1.2 to 2 GHz (50%) with a measured efficiency of 80%-89%, which is the highest reported today for such a bandwidth. An overall PA bandwidth of 0.9-2.2 GHz (84%) is measured with 10-20-W output power, 10-13-dB gain, and 63%-89% efficiency throughout the band. Furthermore, the Class-E PA is characterized through measurements using constant-envelop global system for mobile communications signals, indicating a favorable adjacent channel power ratio from -40 to -50 dBc within the entire bandwidth.

Design of Broadband Highly Efficient Harmonic-Tuned Power Amplifier Using In-Band Continuous Class-

A novel methodology for designing high-frequency broadband harmonic-tuned power amplifiers (PAs) is presented in this paper. Specifically, a hybrid PA mode, transferring between continuous inverse Class-F and continuous Class-F, is for the first time employed to design PAs with optimal performance over more than-an-octave bandwidth. A GaN PA is designed and realized based on this mode-transferring operation using a three-stage transmission-line-based low-pass matching network. Simulation and experimental results show that an in-band PA-mode transferring between continuous Class- F-1 and continuous Class-F is successfully performed. The implemented PA achieves a measured 87% bandwidth from 1.3 to 3.3 GHz, while exhibiting a state-of-the-art performance of >;10-dB gain, 60%-84% efficiency, and 10-W output power throughout this band. Furthermore, modulated evaluation is carried out using a 300-kHz bandwidth 16-quadrature amplitude-modulation signal. Good linearity performance is measured with adjacent channel power ratio from -20 to -35 dBc and an error vector magnitude of 4%-9% over the entire bandwidth.

{\hbox{F}}^{-1}/{\hbox{F}}

This paper presents a novel adaptive power amplifier (PA) architecture for performing dynamic-load-modulation. For the first time, a dynamically-load-modulated PA design that achieves octave bandwidth, high power and high efficiency simultaneously is experimentally demonstrated. This PA design is based on a commercial GaN HEMT. The output matching scheme incorporates a broadband static matching for high-efficiency at the maximum power level and a wideband dynamic matching for efficiency enhancement at power back-offs. The impedance and frequency tunability is realized using silicon diode varactors with a very high breakdown voltage of 90 V. Experimental results show that a dynamic-load-modulation from maximum power to 10-dB back-off is achieved from 1 to 1.9 GHz, with a measured performance of ≈10-W peak power, ≈10-dB gain, 64%-79% peak-power efficiency, and 30%-45% efficiency at 10-dB power back-off throughout this band.

Mode Transferring

This letter presents the first high-frequency, multi-harmonic-controlled (> 3), Class-F power amplifier (PA) implemented with a packaged GaN transistor. For PA design at high frequencies, parasitics of a packaged transistor significantly increase the difficulty of harmonic manipulation, compared to low-frequency cases. To overcome this issue, we propose a novel design methodology based on a three-stage, low-pass, output matching network, which is realized with transmission lines. This network provides optimal fundamental impedance and allows harmonic control up to the fourth order to enable an efficient Class-F behavior. The implemented PA exhibits a state-of-the-art performance at 3.1 GHz with a 82% PAE, 15 dB gain, and 10 W output power, indicating a clear advantage of this method over the conventional ones with extra parasitic compensators.

Design of Adaptive Highly Efficient GaN Power Amplifier for Octave-Bandwidth Application and Dynamic Load Modulation

This paper presents a new approach for substantially enhancing the linearity and reducing the effects of bias noise for electrostatic RF microelectromechanical systems (MEMS) devices. The proposed method relies on applying bias voltages with opposite polarities to cancel the dynamic vibration of the MEMS structures. In this paper, the method has been applied to a shunt RF MEMS varactor and a MEMS tunable evanescent-mode tunable filter. In the first case, the shunt MEMS varactor is split into two identical parts that are biased with opposite voltages. This results in almost complete cancelation of the odd-order modulation components, leading to 20-28-dB linearity enhancement depending on the noise and the design. Analytical results, a computer-aided design model and measurements validate the proposed approach. In the tunable filter case, opposite bias voltages are applied on the tuners of its resonators. Simulated and measured results are also presented in this case. Measurements show a sideband reduction as high as 13 dB. In both cases, the effectiveness of the proposed method in the presence of fabrication uncertainties are also considered.

A 3.1-GHz Class-F Power Amplifier With 82% Power-Added-Efficiency

This paper reports the first co-design configuration of a power amplifier (PA) in cascade with a high- Q bandpass filter. By matching the filters input port directly to the transistors drain node, the conventional output matching network (OMN) of a PA is entirely eliminated. This leads to smaller size/volume, minimized loss, and enhanced overall performance. To enable this co-design method, the matching-filter synthesis theory is proposed and investigated in detail in this paper. Based on this theory, a 3% bandwidth (centered at 3.03 GHz) two-pole filter, implemented using high- Q evanescent-mode cavity resonators, is designed as the PA OMN to provide optimized fundamental and harmonic impedances for a commercial 10-W GaN transistor. Simulation and measured results show that the co-designed PA-filter module yields a desired Chybeshev filter behavior while maintaining excellent PA performance in the passband with 72% efficiency, 10-W output power, >10-dB gain, and 60-dBm output third-order intercept point. This co-designed module experimentally presents a 8% higher overall efficiency compared to a control group developed using a conventional independent PA and filter, which further validates the effectiveness of this method.

Antibiased Electrostatic RF MEMS Varactors and Tunable Filters

A mode-transferring technique for designing high-frequency high-efficiency broadband power amplifiers is presented in this paper. It is demonstrated, for the first time, that by properly tuning the second and third harmonic impedances, a PA can operate between inverse Class-F and Class-F modes within a 1.5 ∶ 1 bandwidth. A broadband PA is designed by employing this technique with a commercial GaN transistor. The multi-mode PA operation and broadband matching are realized simultaneously using a three-stage, transmission-line-implemented, low-pass network. Simulation and experimental results show that Class-F−1 and Class-F PA modes are successfully performed at 1.8 and 2.8 GHz, respectively, with ≥ 80% measured efficiency. In addition, an overall bandwidth of 1.3–3.3 GHz is achieved by the implemented PA with > 10-dB gain, 60%–85% efficiency, and 10-W output power throughout this band.

Co-Design of Highly Efficient Power Amplifier and High-

This paper presents the first experimental and theoretical investigation of high-power RF gas discharge as applied to RF front-end filters with critical air gaps in the 10s of μm. Specifically, a strongly-coupled high-Q evanescent-mode resonant cavity is utilized as a vehicle in this study. This cavity tends to concentrate the resonant electric field in a small volume between its loading post and top wall. Both experiments conducted up to 45.3 dBm at 6.5 GHz and molecular-dynamics-based modeling suggest that, as the input power is increased, gas ionization leads to increasing gas discharge inside this volume. In addition to the measured RF data, surface analysis of the cavity post and top wall lead to the same conclusion. Besides the observed instantaneous effects on the resonators RF performance, the impact of gas discharge in its long-term performance and potential failure is analyzed.

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A unique GaN power amplifier (PA) with an integrated evanescent-mode resonator as its output matching network is presented in this paper. Instead of matching the output of the GaN transistor to 50 Ω and connecting it to a 50-Ω bandpass filter, the GaN is directly integrated with a one-pole filter thus eliminating the conventionally-employed output matching network after the GaN transistor. This leads to a reduced circuit complexity and higher efficiency. The one-pole filter implemented by a strongly-coupled evanescent-mode cavity resonator with an unloaded quality factor of 320 is experimentally presented as a proof-of-concept demonstration. This design yields a very narrowband PA response from 1.24–1.275 GHz (2.8%), which is comparable to the bandwidth of typical communication signals. The PA exhibits a state-of-the-art performance of > 70% efficiency, > 10 dB gain, > 30 dBm output power, and second and third harmonic levels of < −70 dBc. The presented methodology has the potential to be further extended to a tunable design for multi-band applications.

Output Bandpass Filter

Microwave gas breakdown in strongly-coupled evanescent-mode cavity resonators in atmospheric pressure and room temperature is investigated both numerically and experimentally. This high- Q resonator is widely tunable by changing the gap between its loading post and top wall. In this letter, we study the effect of different gap spacings on breakdown characteristics of this resonator. Good agreement is observed between measured breakdown powers and ones by plasma simulations for resonators with gaps of 14.8-51.2 μm, working in the 6-8.25 GHz frequency range with input breakdown power in the range of 45-48 dBm.