Optimized Envelope Shaping for Hybrid EER Transmitter of Mobile WiMAX— Optimized ET Operation

Ildu Kim,Jungjoon Kim,Junghwan Moon,Bumman Kim IEEE 2009 IEEE microwave and wireless components letters Vol.19 No.5

<P>The envelope signal of a Hybrid Envelope Elimination and Restoration (H-EER) technique is optimally reshaped to improve linearity and efficiency, resulting in an Envelope Tracking (ET) architecture. The bias V<SUB>ds</SUB> of the ET is adjusted to be a higher value than that of the conventional H-EER technique to enhance the output power and power-added efficiency (PAE). Furthermore, the bias is shifted above the knee region of the PA to reduce the AM/AM and AM/PM distortions at the low bias region. For the verification, the Mobile WiMAX signal with 8.2 dB peak-to-average power ratio and 5-MHz signal bandwidth is used. In the interlock experiment, the PAE of the transmitter is 40% at an output power of 42.04 dBm. By using the digital predistortion technique, the Relative Constellation Error has satisfied the specification of - 33.6 dB. These results clearly show that the H-EER transmitter with ET shaping is the most suitable architecture for the highly linear and efficient Base Transceiver Station transmitter.</P>

The linearity and efficiency enhancement using 3-way Doherty amplifier with uneven power drive

Ildu Kim,Jangheon Kim,Jeonhyeon Cha,YoungYun Woo,Sungchul Hong,Bumman Kim 대한전자공학회 2005 ITC-CSCC :International Technical Conference on Ci Vol.2005 No.1

IEEE 802.16e Mobile WiMAX용 고효율 고출력 하이브리드 포락선 제거 및 복원 전력 송신기

김일두(Ildu Kim),문정환(Junghwan Moon),김장헌(Jangheon Kim),김정준(Jungjoon Kim),김범만(Bumman Kim) 한국전자파학회 2008 한국전자파학회논문지 Vol.19 No.8

본 논문에서는 효율이 특화된 전력 증폭기를 이용하여 IEEE 802.16e Mobile WiMAX용 고출력 하이브리드 포락선 제거 및 복원 전력 송신기에 대해 기술하였다. Nitronex사의 100-W PEP를 갖는 GaN HEMT 소자를 이용하여 중요한 전력 생성 Vds 구간에 대하여 최대 PAE를 가질 수 있도록 전력 증폭기를 설계하였다. 고출력 응용을 위해서 하이브리드 포락선 제거 및 복원 전력 송신기는 전력 증폭기의 bias fluctuation 문제 및 바이어스 변조기의 stability 문제에 의한 regenerative 오실레이션 문제를 반드시 고려하여 설계되어야 한다. 연동 실험을 위하여, 8.5 ㏈의 PAPR을 갖는 포락선 신호에 대해 바이어스 변조기는 30 V의 최대 출력 전압 크기를 가지면서 72 %의 높은 효율을 유지하도록 구현되었다. WiMAX 신호를 목표로 구현된 하이브리드 포락선 제거 및 복원 전력 송신기는 41.25 ㏈m의 출력 전력에서 38.8 %의 높은 PAE 성능을 얻었다. 또한, 디지털 전치 왜곡 기술을 적용함으로써 전력 송신기의 RCE 성능은 -34.5 ㏈를 기록하여 WiMAX 신호의 선형화 지표를 만족시킬 수 있었다. 본 연구는 2.655 ㎓ 주파수 대역에서 처음으로 구현된 WiMAX용 고출력 하이브리드 포락선 제거 및 복원 전력 송신기에 관한 것이다. We have described a high power hybrid envelope elimination and restoration(H-EER) transmitter for IEEE 802.16e Mobile World Interoperability for Microwave Access(WiMAX) using an efficiency optimized power amplifier(PA). The PA has been designed to have maximum PAE at the important power generation Vds region using Nitronex 100-W PEP GaN HEMT. For the high power application, H-EER transmitter should be considered the regenerative oscillation problem due to the PA’s bias fluctuation effect and bias modulator stability issue. Therefore, the bias modulator for H-EER transmitter has been designed to suppress the regenerative oscillation. For the interlock experiment, the bias modulator has been built with the efficiency of 72 % and peak output voltage of 30 V for the envelope signal with a PAPR of 8.5 ㏈. The H-EER transmitter for WiMAX application has been achieved a high PAE characteristic, 38.8 % at an output power of 41.25 ㏈m. By using digital predistortion(DPD) technique, the Relative Constellation Error (RCE) has been satisfied the specification of -34.5 ㏈. This is the first work at 2.655 ㎓ high power H-EER transmitter for WiMAX application.

효율 향상을 위해 포락선 추적 기술을 이용한 비대칭 포화 3-Stage 도허티 전력 증폭기

김일두(Ildu Kim),지승훈(Seunghoon Jee),문정환(Junghwan Moon),손정환(Junghwan Son),김정준(Jungjoon Kim),김범만(Bumman Kim) 한국전자파학회 2009 한국전자파학회논문지 Vol.20 No.8

본 논문에서는 1:2:2의 비대칭 3-stage 도허티 전력 증폭기의 동작을 살펴보고, Freescale사의 4 W, 10 W LDMOSFET을 이용하여 1 GHz에서 구현하였다. 두 번의 최대 효율 특성을 갖는 N-way 도허티 전력 증폭기와 비교하였을 때, 비대칭 3-stage 도허티 전력 증폭기는 세 번의 최대 효율 특성을 갖도록 함으로써 백 오프된 출력 전력영역에서의 심각한 효율 저하를 극복할 수 있고, 주어진 변조 신호에서의 평균 효율을 최대화 할 수 있다. 효율 특성을 더욱 최적화하기 위해, 역 F급 전력 증폭기를 캐리어 및 피킹 전력 증폭기로 설계하였다. 또한, 적절한 로드 모듈레이션 동작을 이끌어내기 위해, 포락선 추적 방법에 근거한 적응 게이트 바이어스 조절 신호를 두 개의 피킹 전력 증폭기에 인가하였다. 8.5 ㏈의 PAPR을 갖는 802.16e Mobile WiMAX 신호에 대해 제안된 비대칭 도허티 전력 증폭기는 36.85 ㏈m에서 55.46 %의 높은 효율 특성을 얻었고, ?37.23 ㏈의 우수한 RCE 특성을 유지하였다. 본 논문에서는 처음으로 포화 증폭기와 적응 게이트 바이어스 조절 신호를 비대칭 3-stage 도허티 전력 증폭기에 적용하였으며, 이를 통해 기지국용 고효율 전력 송신기의 설계가 구현 가능함을 성공적으로 검증하였다. We have investigated operation of a 1:2:2 asymmetric 3-stage Doherty PA(Power Amplifier) and implemented using the Freescale’s 4 W, 10 W PEP LDMOSFETs at 1 GHz. By employing the three peak efficiency characteristics, compared to the two peak N-way Doherty PA, the asymmetric 3-stage Doherty can overcome the serious efficiency degradation along the backed-off output power region and maximize the average efficiency for the modulation signal. To maximize the efficiency characteristic, the inverse class F PA has been designed as carrier and peaking amplifiers. Furthermore, to extract the proper load modulation operation, the adaptive gate bias control signal has been applied to the two peaking PAs based on the envelope tracking technique. For the 802.16e Mobile WiMAX(World Interoperability for Microwave Access) signal with 8.5 ㏈ PAPR(Peak to Average Power Ratio), the proposed Doherty PA has shown 55.46 % of high efficiency at an average output power of 36.85 ㏈m while maintaining the ?37.23 ㏈ of excellent RCE(Relative Constellation Error) characteristic. This is the first time demonstration of applying the saturated PA and adaptive gate bias control technique to the asymmetric 3-stage Doherty PA for the highly efficient transmitter of the base-station application.

Saturated Power Amplifier Optimized for Efficiency Using Self-Generated Harmonic Current and Voltage

Jungjoon Kim,Jangheon Kim,Junghwan Moon,Jungwhan Son,Ildu Kim,Seunghoon Jee,Bumman Kim IEEE 2011 IEEE transactions on microwave theory and techniqu Vol.59 No.8

<P>A saturated power amplifier (PA) optimized for efficiency is described. As a PA is driven into saturated operation, the current source of the device generates a large third harmonic current, which creates a quasi-rectangular current waveform. The large nonlinear output capacitor of the transistor generates a second harmonic voltage with a very small third harmonic component. The second harmonic voltage is in-phase with the fundamental voltage, making a half-sine wave voltage waveform with voltage peaking. These waveforms are similar to those of a class F<SUP>-1</SUP> . The fundamental load at the intrinsic device is resistive with the output capacitance tuned out, which is identical to the class F<SUP>-1</SUP> case. However, the required harmonic impedances are just larger than the impedance levels of the output capacitance for both the second and third harmonics. Therefore, the circuit topology is similar to that of a class E amplifier, which is very simple. The PA implemented using a GaN HEMT delivers the expected good performance using the simple circuit topology.</P>

Analysis of a Fully Matched Saturated Doherty Amplifier With Excellent Efficiency

Jangheon Kim,Junghwan Moon,Young Yun Woo,Sungchul Hong,Ildu Kim,Jungjoon Kim,Bumman Kim IEEE 2008 IEEE transactions on microwave theory and techniqu Vol.56 No.2

<P>A saturated Doherty amplifier based on class-F amplifiers is analyzed in terms of its load modulation behavior, efficiency, and linearity. Simulations included the amplitude ratio and phase difference between the fundamental and third harmonic voltages, the current/voltage waveforms, load lines, and the third-order intermodulation amplitudes/phases of the carrier and peaking amplifiers. The saturated doherty power amplifier was implemented using two Eudyna EGN010MK GaN HEMTs with a 10-W peak envelope power. For a 2.14-GHz forward-fink wideband code-division multiple-access signal, the doherty amplifier delivers an excellent efficiency of 52.4% with an acceptable linearity of -28.3 dBc at an average output power of 36 dBm. Moreover, the amplifier can provide the high linearity performance of -50 dBc using the digital feedback predistortion technique.</P>

Optimized Design of a Highly Efficient Three-Stage Doherty PA Using Gate Adaptation

Ildu Kim,Junghwan Moon,Seunghoon Jee,Bumman Kim IEEE 2010 IEEE transactions on microwave theory and techniqu Vol.58 No.10

<P>We demonstrate an optimized design of a highly efficient three-stage Doherty power amplifier (PA) for the 802.16e mobile world interoperability for microwave access (WiMAX) application at 2.655 GHz. The “three-stage” Doherty PA is the most efficient architecture among the various Doherty PAs for achieving a high peak to average power ratio (PAPR) signal. However, it has a problem in that the carrier PA has to maintain a saturated state with constant output power when the other peaking PAs are turned on. We solved the problem using a gate envelope tracking (ET) technique. For the proper load modulation, the gate biases of the peaking PAs were adaptively controlled, and the peak power and maximum efficiency characteristics along the backed-off output power region were successfully achieved. Using Agilent's Advanced Design System and Matlab simulations, the overall behavior of the three-stage Doherty PA with the ET technique employed was fully analyzed, and the optimum design procedure is suggested. For the WiMAX signal with a 7.8-dB PAPR, the measured drain efficiency of the proposed three-stage Doherty PA is 55.4% at an average output power of 42.54 dBm, which is an 8-dB backed-off output power. Digital predistortion was used to linearize the proposed PA. After linearization, a -33.15 dB relative constellation error performance was achieved, satisfying the system specifications. This is the best performance of any 2.655-GHz WiMAX application ever reported, and it clearly shows that the proposed three-stage Doherty PA is suitable as a highly efficient and linear transmitter.</P>

Advanced Doherty Architecture

Kim, Bumman,Kim, Ildu,Moon, Junghwan IEEE 2010 IEEE microwave magazine Vol.11 No.5

<P>For modulated signals with a high peak-to-average power ratio (PAPR), the transmitter has to be operated with its average output power backed off for an acceptable linearity at the expense of low efficiency. To achieve high efficiency and high linearity at the same time, both an efficiency enhancement technique and a linearization technique should be utilized. A powerful and reliable linearization technique, digital predistortion (DPD), is currently the most favored method for the linearization of base-station amplifiers [1]–[3]. Possible efficiency enhancement techniques are the hybrid envelope elimination and restoration/envelope tracking technique (H-EER/ET) and the Do-herty technique.</P>

Efficiently Amplified

Bumman, Kim,Junghwan, Moon,Ildu, Kim IEEE 2010 IEEE microwave magazine Vol.11 No.5

<P>Modern wireless communication systems have evolved to support increasing numbers of subscribers and provide higher data rate services within the limited frequency resources. As part of this evolution, many transmitted signals in the new standards, such as WCDMA, long term evolution (LTE), and worldwide interoperability for microwave access (WiMAX), now utilize a high peak-to-average power ratio (PAPR) caused by complex modulation schemes, generating the rapid change in the magnitude of signal as shown in Figure 1(a). In particular, as depicted in Figure 1(b), the PAPRs of the signals exceed 9 dB at 0.01% level of complementary cumulative distribution function. Use of high PAPR signals result in the power amplifier (PA) operating at a large enough back-off to satisfy the stringent linearity requirement. However, in this region, efficiency of the PA is very low. To bolster low efficiency in the back-off region, various efficiency boosting techniques have been considered over time. Recently, due to high-efficiency capabilities [1]–[13], supply voltage modulated PAs, such as envelope elimination and restoration (EER), hybrid-EER (H-EER), and envelope tracking (ET) technique, have received a lot of attention. Excellent experimental results have been reported using the various device technologies and modulated signals, as summarized in Table 1.</P>

An optimum design of high-power amplifier with high efficiency using a realizable harmonic loading circuit

Moon, Junghwan,Kim, Jangheon,Kim, Jungjoon,Kim, Ildu,Kim, Bumman Wiley Subscription Services, Inc., A Wiley Company 2010 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol.52 No.4

<P>An optimum design approach for a highly efficient power amplifier (PA) using a packaged high-power device is described.Large fundamental load impedance assisted by a simple second harmonic manipulation is explored to improve the efficiency when maintaining the power density. For demonstration of the performance, the PA is implemented using GaN HEMT device at 2.655 GHz. In the experiment, the fabricated PA achieves power-added efficiency (PAE) of 64.3% at the saturated output power of 49.2 dBm. For 802.16e mobile worldwide interoperability for microwave access signal, the PA delivers the PAE of ∼31% and ACLR of −49 dBc at the 10 dB backed-off power of 40 dBm after the digital feedback predistortion linearization. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:818–822, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25032</P>