Highly Efficient RF Transmitter Over Broad Average Power Range Using Multilevel Envelope-Tracking Power Amplifier

Jooseung Kim,Dongsu Kim,Yunsung Cho,Daehyun Kang,Byungjoon Park,Kyunghoon Moon,Seungbeom Koo,Bumman Kim IEEE 2015 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS PART 1 R Vol.62 No.6

<P>We present a highly efficient RF transmitter over broad average power range using a multilevel envelope-tracking power amplifier (ML-ET PA). The ML-ET PA delivers enhanced efficiency at a back-off power region for handset applications. The supply modulator consists of a linear regulator and a switching converter. The DC supply of the linear regulator is adjusted according to the average power of the envelope signal, and the power-supply-independent class-AB output stage is employed to avoid the crossover distortion generated by the different DC supply voltages. The switch current level is not optimally adjusted by itself following the power back-off level, because the DC supply voltages of the linear regulator and switching converter are different. For the optimum operation over the entire power region, the switch current level is adjusted by detecting the input envelope voltage level. For a 20-MHz long term evolution signal with a 7.5 dB peak-to-average power ratio, the proposed supply modulator delivers a peak voltage of 4.5 V to a 6.5 Ω load with a measured efficiency of 75.9%. The proposed ET PA delivers a power-added efficiency (PAE) of 40%, gain of 28.8 dB, evolved universal terrestrial radio access adjacent channel leakage ratio of -35.3 dBc, and error vector magnitude of 3.23% at an average output power of 27 dBm and an operating frequency of 1.71-GHz. At a 10 dB back-off point, the PAE is improved from 14.5% to 18.7% compared to the conventional ET PA.</P>

Envelope-Tracking Two-Stage Power Amplifier With Dual-Mode Supply Modulator for LTE Applications

Jooseung Kim,Dongsu Kim,Yunsung Cho,Daehyun Kang,Byungjoon Park,Bumman Kim IEEE 2013 IEEE transactions on microwave theory and techniqu Vol.61 No.1

<P>This paper presents an envelope tracking power amplifier (ET PA) using a dual-mode supply modulator for handset application. The supply modulator has a combined structure with a linear amplifier and a switching amplifier. The dual-mode supply modulator operates in high-power mode and low-power mode by providing the supply voltage of the linear amplifier of 5 and 2.5 V, respectively. For 1.74-GHz long-term evolution signal with 10-MHz bandwidth, 6.44-dB peak-to-average power ratio, and 16-quadrature amplitude modulation, the ET PA delivers a power-added efficiency (PAE) of 39.8%, an evolved universal terrestrial radio access adjacent channel leakage ratio (E-UTRA<SUB>ACLR</SUB>) of - 35.7 dBc, and an error vector magnitude (EVM) of 3.81% at an average output power of 27 dBm. The ET PA also delivers a PAE of 22.6% at an average output power of 18 dBm, which is 6.6% higher than that of the conventional ET PA and 13.1% higher than that of the standalone PA. The supply modulator is connected to a drive stage and a power stage of the PA simultaneously for further enhanced efficiency at a power back-off region. The dual-mode two-stage ET PA delivers a PAE of 38.1%, an E-UTRA<SUB>ACLR</SUB> of - 32.9 dBc, and an EVM of 4.74% at an average output power of 27 dBm. The dual-mode two-stage ET PA also delivers a PAE of 26.3% at an average output power of 18 dBm, which is 7.8% higher than that of the conventional two-stage ET PA and 16.7% higher than that of the standalone PA.</P>

Highly Efficient Dual-Switch Hybrid Switching Supply Modulator for Envelope Tracking Power Amplifier

Dongsu Kim,Daehyun Kang,Jooseung Kim,Yunsung Cho,Bumman Kim IEEE 2012 IEEE microwave and wireless components letters Vol.22 No.6

<P>This letter describes a highly efficient dual-switch hybrid switching supply modulator for an envelope tracking power amplifier (PA). The supply modulator has a combined structure of a linear amplifier and a switching amplifier. For an improved efficiency, the switching amplifier employs two buck converters and realizes an adaptive slew rate control of the switching amplifier's current. An implemented envelope tracking PA delivers an efficiency of 39.1% at an output power of 27 dBm for long term evolution signal with 10 MHz channel bandwidth.</P>

An HBT Saturated Power Amplifier With Minimized Knee Effect for Envelope Tracking Operation

Kyunghoon Moon,Yunsung Cho,Jooseung Kim,Sangsu Jin,Seokhyeon Kim,Bumman Kim THE INSTITUTE OF ELECTRICAL ENGINEERS 2015 IEEE Microwave and Wireless Components Letters Vol. No.

<P>In this letter, a highly efficient saturated power amplifier (PA) based on a heterojunction bipolar transistor (HBT) is employed to maximize the efficiency of an envelope tracking (ET) PA. In this PA, output voltage waveform of the PA is shaped as a half-sinusoidal voltage waveform peaked by a second harmonic. The knee voltage effect is minimized in this voltage waveform due to the large fundamental voltage for a given supply voltage, which is very important for an ET PA with a low average supply voltage. Based on the saturated PA, the ET PA is tested at 1.85 GHz using a long term evolution signal. The ET PA delivers a power-added efficiency of 46.5%, an E- UTRAACLR of -33.4 dBc, and an error vector magnitude of 3.0% at an average output power of 27 dBm.</P>

A Multimode/Multiband Power Amplifier With a Boosted Supply Modulator

Daehyun Kang,Dongsu Kim,Jinsung Choi,Jooseung Kim,Yunsung Cho,Bumman Kim IEEE 2010 IEEE transactions on microwave theory and techniqu Vol.58 No.10

<P>A multimode/multiband power amplifier (PA) with a boosted supply modulator is developed for handset applications. A linear broadband class-F amplifier is designed to have a constant fundamental impedance across 1.7-2 GHz and its second and third harmonic impedances are located at the high-efficiency area. To reduce the circuit size for handset application, the harmonic control circuits are merged into the broadband output matching circuit for the fundamental frequency. An envelope-tracking operation delivers high efficiency for the overall power. The linearity is improved by envelope tracking (ET) through intermodulation-distortion sweet-spot tracking at the maximum output power level. The efficiency and bandwidth (BW) are enhanced by a boosted supply modulator. Multimode operation is achieved by an ET technique with a programmable hysteresis control and automatic switching current adaptation of the hybrid supply modulator. For demonstration purpose, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and a 65-nm CMOS process. For a long-term evolution signal, the envelope-tracking (ET) PA delivers a power-added efficiency (PAE) and an error vector magnitude of 33.3%-39% and 2.5%-3.5%, respectively, at an average power of 27.8 dBm across 1.7-2 GHz. For a wideband code-division multiple-access signal across 1.7-2 GHz, the ET PA performs a PAE, an ACLR1, and an ACLR2 of 40%-46.3%, from -39 to -42.5&nbsp;dBc, and -51 to -58&nbsp;dBc, respectively, at an average output power of 30.1 dBm. The ET PA with an EDGE signal delivers a PAE, an ACPR1, and an ACPR2 of 37%-42%, from -56.5 to -59.3&nbsp;dBc, and -63.5 to -69.5&nbsp;dBc, respectively, at an average power of 28 dBm across the 300-MHz BW. These results show that the proposed design achieves highly efficient and linear power amplification for multimode/multiband wireless communication applications.</P>

A Dual Power-Mode Multi-Band Power Amplifier With Envelope Tracking for Handset Applications

Yunsung Cho,Daehyun Kang,Jooseung Kim,Dongsu Kim,Byungjoon Park,Bumman Kim IEEE 2013 IEEE transactions on microwave theory and techniqu Vol.61 No.4

<P>This paper presents a dual power-mode and multi-band power amplifier (PA) for handset applications that improves the efficiency in low-power regions. This PA operates in two modes through path control by a shunt switched capacitor. The proposed control method provides efficient mode control without any efficiency degrading and bandwidth (BW) limiting. The proposed PA, in conjunction with a boosted supply modulator for envelope tracking (ET) operation not only in the high-power mode, but also in the low-power mode, delivers good performance at all average output power levels. The linearity is improved by ET through a proper envelope-shaping method. For demonstrative purposes, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and AIGaAs/InGaAs enhancement/depletion-mode pseudomorphic high electron-mobility transistor process and a 0.18-μ m CMOS process, respectively. The ET PA is tested across the range of 1.7-2.0 GHz using a long-term evolution signal with 16 quadrature amplitude modulation, a 7.5-dB peak-to-average power ratio, and 10-MHz BW. The proposed dual power-mode multi-band ET PA delivers good performance for high- and low-power modes, indicating that the architecture is promising for handset PA applications.</P>

Investigating Linguistic Differences in Adult EFL Learners’ Writing Test Performance

Kim, Hyun Jung(김현정),Lee, Jooseung(이주승) 한국외국어대학교 영미연구소 2015 영미연구 Vol.35 No.-

Previous research on L2 writing assessment has tended to focus on quantitative analyses of ratings assigned by raters/teachers. Different from previous research, the present study aimed to examine the linguistic features in test-takers’ written responses across different writing task types, focusing on those used for coherence and cohesion in writing. A total of 143 adult EFL learners were presented with two types of writing-compare/contrast and problem/solution-and they were required to write a 300-word essay on one type of their choice. Their written responses (70 compare/contrast and 73 problem/solution) were analyzed using Coh-Metrix to compare the linguistic differences between the two types of writing. Two raters who evaluated both types of writing were further interviewed to examine their perceptions about the discourse organization of the two types. The results indicated that the two types of written responses showed linguistic differences mostly in referential cohesion (e.g., overlap). However, neither of the raters considered referential cohesion when scoring discourse organization; consequently, the use of referential cohesion by the compare/contrast writing group was not reflected in the ratings. The study also suggests the need to consider the time restrictions and task effects on test-takers’ relative difficulty in organizing discourse.

CMOS Linear Power Amplifier with Envelope Tracking Operation

Byungjoon Park,Jooseung Kim,Yunsung Cho,Sangsu Jin,Daehyun Kang,Bumman Kim 한국전자파학회JEES 2014 Journal of Electromagnetic Engineering and Science Vol.14 No.1

A differential-cascode CMOS power amplifier (PA) with a supply modulator for envelope tracking (ET) has been implemented by 0.18 μm RF CMOS technology. The loss at the output is minimized by implementing the output transformer on a FR-4 printed circuit board (PCB). The CMOS PA utilizes the 2<SUP>nd</SUP> harmonic short at the input to enhance the linearity. The measurement was done by the 10MHz bandwidth 16QAM 6.88 dB peak-to-average power ratio long-term evolution (LTE) signal at 1.85 GHz. The ET operation of the CMOS PA with the supply modulator enhances the power-added efficiency (PAE) by 2.5, to 10% over the stand-alone CMOS PA for the LTE signal. The ET PA achieves a PAE of 36.5% and an ACLRE-UTRA of ?32.7 dBc at an average output power of 27 dBm.

Reconfigurable Power Amplifiers for Handset Applications

김범만,Daehyun Kang,Dongsu Kim,Yunsung Cho,Jooseung Kim 에스케이텔레콤 (주) 2010 Telecommunications Review Vol.20 No.5

Flexible and reconfigurable transmitters with multimode and multiband capability are indispensible to handle the evolving wireless communication systems. To meet the stringent requirements of the systems, digitally enhanced linear power amplifiers (PAs) have received considerable attention because of their digital flexibility and capability. In this paper, we review the key architectures in this area: the delta-sigma digitized polar transmitter and the envelope tracking (ET) technique for multimode operation. The broadband PA is also described for multiband operation with an ET transmitter. The multimode and multiband operation of the broadband PA is demonstrated. This paper covers the basic concepts of flexible PA architectures and their current research status.

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노정언(JungEon Noh),장우혁(WooHyeok Jang),최주승(JooSeung Choi),김천곤(ChunGon Kim) 항공우주시스템공학회 2023 항공우주시스템공학회 학술대회 발표집 Vol.2023 No.05