A.H. Yang

Bio: A.H. Yang is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Amplifier & Power-added efficiency. The author has an hindex of 4, co-authored 5 publications receiving 429 citations.

An Improved Power-Added Efficiency 19-dBm Hybrid Envelope Elimination and Restoration Power Amplifier for 802.11g WLAN Applications

Abstract: A comparison of envelope elimination and restoration (EER) and envelope tracking (ET) is discussed and a "hybrid" wideband EER power amplifier (PA) for the WLAN 802.11g system is proposed. A 60% efficiency (the output envelope signal power/input dc power) DC-20-MHz wideband envelope amplifier is designed for wideband EER and wideband ET (WBET) applications. A design method is developed to optimize the efficiency of the envelope amplifier for a given peak-to-average ratio and average slew rate of the envelope signal. An experimental "hybrid" Class-E EER system shows an overall efficiency (modulated RF output power/envelope amplifier dc input power) of 36% and power-added efficiency (the modulated RF output power/envelope amplifier dc input power plus RF input power) of 28% for a WLAN 802.11g signal at 19-dBm (80 mW) output power at 2.4 GHz. Digital predistortion, time alignment, and memory effect mitigation are implemented. The measured 3% error vector magnitude exceeds the 802.11g specification for 5% for a 54-Mb/s modulation signal

Highly Efficient and Linear Class E SiGe Power Amplifier Design

Abstract: This paper discusses the design of monolithic RF broadband Class E SiGe power amplifiers (PAs) that are highly efficient and linear. Load-pull measurement data on IBM 7HP SiGe power devices have been made at 900MHz and 2.4GHz and monolithic class E PAs have been designed using these devices to achieve highest power-added-efficiency (PAE) at these frequencies. It is found that high PAE can be achieved for monolithic single-stage Class E PAs designed using high-breakdown SiGe transistors at ~65% (900MHz) and ~40% (2.4GHz), respectively, which are roughly ~10% lower than the device's maximum PAE values obtained by load-pull tests under optimal off-chip matching conditions. We have also demonstrated that monolithic SiGe class E PAs can be successfully linearized using an open-loop envelope tracking (ET) technique as their output spectra pass the stringent EDGE transmit mask with margins, achieving overall PAE of 44.4% for the linearized PA system that surpasses the < 30% PAE with commercially available GaAs Class AB PAs for EDGE applications. These promising results indicate the feasibility of realizing true single-chip wireless transceivers with on-chip RF SiGe PAs for spectrally-efficient non-constant-envelope modulation schemes

The limitations in applying analytic design equations for optimal class E RF power amplifiers design

Abstract: The power efficiency of the final stage power amplifier (PA) in a RF transmitter is critical for the overall power consumption, size, lifetime, and reliability of RF transceiver products, especially for portable low-power highly-integrated RF-SoC applications. This paper discusses the limitations and issues in applying the analytic design equations for designing highly efficient RF class E PAs. The main focus of this work is on the validation of the previously published analytic design equations for optimal class E PAs design, as we implemented the PA designs using both discrete RF transistors and monolithic RF ICs at 300 to 2400 MHz. It is found that these analytic design equations available in the literature for RF class E PAs design largely ignored some important physical factors such as the bias sensitivity for the transistor, the undesired device parasitics at RF frequencies, the finite inductance and the low quality factor of the RF choke and/or tank inductors, the time-varying input impedance, and PA stability, etc. They are therefore in general not adequate for predicting the optimal class E PA performance at RF frequencies.

Monolithic Class E SiGe Power Amplifier Design with Wideband High-Efficiency and Linearity

Abstract: This paper discusses and compares the design of monolithic RF broadband Class E SiGe power amplifiers (PAs) centered at 900MHz that are highly efficient and linear. It is found that high power-added-efficiency (~65%) can be achieved with PAs designed using either high-breakdown or high-fT SiGe transistors. The PAs designed with high-breakdown devices can provide ~3% better efficiency at higher supply voltages but with worse bias sensitivity, inferior broadband frequency response, and slightly lower gain than those designed with high-fT devices. However, the Class E PAs designed using high-breakdown devices can be successfully linearized using an open-loop envelope tracking (ET) technique as their output spectra pass the stringent EDGE transmit mask with margins, achieving an overall system PAE of 44.4% that surpasses the ~30% PAE obtainable using commercial GaAs Class AB PAs. These promising results indicate the feasibility of realizing true single-chip wireless transceivers with on-chip RF SiGe PAs for spectrally-efficient non-constant-envelope modulation schemes.

Design of highly efficient and linear class E SiGe power amplifier for highly-integrated multifunctional wireless transmitters

Abstract: This paper discusses the design of highly efficient and monolithic linear RF Class E SiGe power amplifiers (PAs) at both 900 MHz and 24 GHz for various wireless applications Without needing off-chip on-board matching, we achieved very high power-added-efficiency (PAE) for the single-stage Class E SiGe PAs at -70% (900 MHz) and -60% (24 GHz), respectively, which performance rivals that of commercially-available III-V PA modules These switch-mode PAs can be successfully linearized using polar modulation and a hybrid Envelope Tracking (ET) technique, resulting in impressive high PAE suitable for implementing future highly-integrated multifunctional wireless transceivers systems

High-Efficiency Envelope-Tracking W-CDMA Base-Station Amplifier Using GaN HFETs

Abstract: A high-efficiency wideband code-division multiple-access (W-CDMA) base-station amplifier is presented using high-performance GaN heterostructure field-effect transistors to achieve high gain and efficiency with good linearity For high efficiency, class J/E operation was employed, which can attain up to 80% efficiency over a wide range of input powers and power supply voltages For nonconstant envelope input, the average efficiency is further increased by employing the envelope-tracking architecture using a wide-bandwidth high-efficiency envelope amplifier The linearity of overall system is enhanced by digital pre-distortion The measured average power-added efficiency of the amplifier is as high as 507% for a W-CDMA modulated signal with peak-to-average power ratio of 767 dB at an average output power of 372 W and gain of 100 dB We believe that this corresponds to the best efficiency performance among reported base-station power amplifiers for W-CDMA The measured error vector magnitude is as low as 174% with adjacent channel leakage ratio of -510 dBc at an offset frequency of 5 MHz

A Monolithic High-Efficiency 2.4-GHz 20-dBm SiGe BiCMOS Envelope-Tracking OFDM Power Amplifier

Abstract: A monolithic SiGe BiCMOS envelope-tracking power amplifier (PA) is demonstrated for 802.11g OFDM applications at 2.4 GHz. The 4-mm2 die includes a high-efficiency high-precision envelope amplifier and a two-stage SiGe HBT PA for RF amplification. Off-chip digital predistortion is employed to improve EVM performance. The two-stage amplifier exhibits 12-dB gain, <5% EVM, 20-dBm OFDM output power, and an overall efficiency (including the envelope amplifier) of 28%.

A Switched-Capacitor RF Power Amplifier

Abstract: A fully integrated switched-capacitor power amplifier (SCPA) utilizes switched-capacitor techniques in an EER/Polar architecture. It operates on the envelope of a nonconstant envelope modulated signal as an RF-DAC in order to amplify the signal efficiently. The measured maximum output power and PAE are 25.2 dBm and 45%, respectively. When amplifying an 802.11g 64-QAM orthogonal frequency-division multiplexing (OFDM) signal, the measured error vector magnitude is 2.6% and the average output power and power-added efficiencies are 17.7 dBm and 27%, respectively.

High-efficiency envelope tracking systems and methods for radio frequency power amplifiers

Abstract: Envelope tracking (ET) methods and systems for controlling the delivery of power to radio frequency power amplifiers (RFPAs). An exemplary ET system includes an RFPA and a wide bandwidth capable and power efficient envelope modulator that includes a first power supplying apparatus and a second power supplying apparatus. The first power supplying apparatus includes a switch-mode converter and a regulator. The first mode converter is operable to dynamically step down a fixed power supply voltage according to amplitude variations in an envelope signal received by the regulator, and use the resulting dynamic power supply signal to power the regulator. The second power supplying apparatus is connected in parallel with the first power supplying apparatus. Depending on a power of an output signal to be generated at an output of the power amplifier, power is supplied to the power amplifier from either or both of the first and second power supplying apparatuses.

High-Frequency PWM Buck Converters Using GaN-on-SiC HEMTs

Abstract: GaN high electron mobility transistors (HEMTs) are well suited for high-frequency operation due to their lower on resistance and device capacitance compared with traditional silicon devices. When grown on silicon carbide, GaN HEMTs can also achieve very high power density due to the enhanced power handling capabilities of the substrate. As a result, GaN-on-SiC HEMTs are increasingly popular in radio-frequency power amplifiers, and applications as switches in high-frequency power electronics are of high interest. This paper explores the use of GaN-on-SiC HEMTs in conventional pulse-width modulated switched-mode power converters targeting switching frequencies in the tens of megahertz range. Device sizing and efficiency limits of this technology are analyzed, and design principles and guidelines are given to exploit the capabilities of the devices. The results are presented for discrete-device and integrated implementations of a synchronous Buck converter, providing more than 10-W output power supplied from up to 40 V with efficiencies greater than 95% when operated at 10 MHz, and greater than 90% at switching frequencies up to 40 MHz. As a practical application of this technology, the converter is used to accurately track a 3-MHz bandwidth communication envelope signal with 92% efficiency.