Hyunuk Kang

Optimized Current of the Peaking Amplifier for Two-Stage Doherty Power Amplifier

This paper presents a method of improving efficiency for the two-stage Doherty power amplifier (DPA) using the optimized current of the peaking amplifier. The DPA has a two-stage structure for both the carrier and peaking amplifiers. The first stage of the peaking amplifier has an adjusted bias condition for a near Class-B operation, while the first stage of the carrier amplifier has a higher Class-AB operation. The gain expansion of the first stage due to its lower gate bias helps the second stage of the peaking amplifier to be biased for light Class-C operation and to have steeper turn-ON characteristics, which leads higher peak output power and higher back-off efficiency. The two-stage DPA was designed for the 2.655-GHz band. Using a downlink long-term evolution signal with a signal bandwidth of 10 MHz and a peak-to-average power ratio of 6.5 dB, the overall power gain of 25 dB and a peak output power of 54.2 dBm are experimentally obtained. Using an optimized shape of the peaking amplifier’s current, a drain efficiency (DE) of 53% and an adjacent channel leakage power ratio of −30 dBc were obtained at an average output power of 47.8 dBm. A DE of 56.8% and an adjacent channel leakage power ratio of −25 dBc were also obtained at an average output power of 49.5 dBm.

Doherty Power Amplifier Based on the Fundamental Current Ratio for Asymmetric cells

This paper presents a Doherty power amplifier (DPA) based on asymmetric cells using an even input power drive and an appropriate peak fundamental current ratio (FCR) between the peaking amplifier and the carrier amplifier. Using an appropriate output combiner and an even input power drive for the DPA, not only better load modulation but also enhanced power gain can be achieved. After providing an analysis for the fundamental currents, a design guide for the proposed DPA using the peak FCR is presented. For verification, conventional and proposed DPAs were designed using GaN-HEMTs for the 2.14-GHz band. Using a downlink long-term evolution signal having a peak-to-average power ratio of 6.5 dB, comparably better performances were achieved than the conventional DPAs, such as a high power-added efficiency of 55.7% and a power gain of as high as 16.6 dB, at an average output power level of 36.9 dBm.

Symmetric Three-Way Doherty Power Amplifier for High Efficiency and Linearity

This brief presents a three-way Doherty power amplifier (DPA) with a symmetric structure in terms of the output power capacities between the carrier and peaking amplifiers for high efficiency and linearity. Based on the analysis for the efficiency peak at the output power back-off, a symmetric structure was adopted to have higher overall efficiency for the modulated signal. Through the optimized bias condition for the two peaking amplifiers, the proposed three-way DPA can be linearized in the wide output power range. To validate the proposed scheme, a three-way DPA was designed and implemented using a 60 W GaN–HEMT for the carrier amplifier and two 30 W GaN–HEMTs for the peaking amplifiers. Using a 2.14 GHz long-term evolution downlink signal with a peak-to-average power ratio of 6.5 dB, the implemented symmetric three-way DPA exhibited a drain efficiency (DE) of 33.7% and an ACLR of −38 dBc at an average output power of 41.4 dBm. Compared to the condition with the same bias for the peaking amplifiers, the DE and average output power were improved by 8.0% and 2.4 dB for the given ACLR of −38 dBc, respectively.

2.6 GHz GaN-HEMT Doherty power amplifier integrated circuit with 55.5% efficiency based on a compact load network

This paper presents a GaN-HEMT DPA IC based on a compact load network for LTE small cells. The gate widths of the transistors for the carrier and peaking amplifiers are optimized to have the same load impedance of 100 Ω. A shunt inductor is added to compensate for the output capacitor of each transistor with parallel resonance. A x-type high-pass impedance transformer based on lumped components is used to modulate the load impedance. Parallel inductors from the resonant circuit and the impedance transformer are merged for further simplification. As a result, only two inductors remain in the load network. For verification, a 2.6 GHz DPA IC with an on-chip load network and input matching networks was designed and fabricated using a 0.4 μm GaN-HEMT process. The DPA IC exhibited a peak output power of 43.9 dBm. For an LTE signal with a signal bandwidth of 10 MHz and a PAPR of 6.5 dB, a high drain efficiency of 55.5% with an ACLR of −30 dBc was obtained at an average output power of 37.4 dBm.

2.6 GHz GaN-HEMT Power Amplifier MMIC for LTE Small-Cell Applications

This paper presents a two-stage power amplifier MMIC using a 0.4 μm GaN-HEMT process. The two-stage structure provides high gain and compact circuit size using an integrated inter-stage matching network. The size and loss of the inter-stage matching network can be reduced by including bond wires as part of the matching network. The two-stage power amplifier MMIC was fabricated with a chip size of 2.0×1.9 mm² and was mounted on a 4×4 QFN carrier for evaluation. Using a downlink LTE signal with a PAPR of 6.5 dB and a channel bandwidth of 10 MHz for the 2.6 GHz band, the power amplifier MMIC exhibited a gain of 30 dB, a drain efficiency of 32%, and an ACLR of -31.4 dBc at an average output power of 36 dBm. Using two power amplifier MMICs for the carrier and peaking amplifiers, a Doherty power amplifier was designed and implemented. At a 6 dB back-off output power level of 39 dBm, a gain of 24.7 dB and a drain efficiency of 43.5% were achieved.

Design of a 2.6 GHz GaN-HEMT Doherty Power Amplifier IC for Small-Cell Base Station Systems

This paper presents a 2.6 GHz Doherty power amplifier IC to enhance the back-off efficiency. In order to apply to small-cell base stations, the Doherty power amplifier was fabricated using GaN-HEMT process for high power density. In addition, the implemented Doherty power amplifier was mounted on a QFN package. The implemented GaN-HEMT Doherty power amplifier was measured using LTE downlink signal with 10 MHz bandwidth and 6.5 dB PAPR for verification. A power gain of 15.8 dB, a drain efficiency of 43.0 %, and an ACLR of -30.0 dBc were obtained at an average output power level of 33.9 dBm.

2.6 GHz 4 watt GaN-HEMT two-stage power amplifier MMIC for LTE small-cell applications

This paper presents a two-stage PA MMIC using 0.4-μm GaN-HEMT. Two-stage structure is adopted to take its high gain property and simple inter-stage matching network. The size and loss of the inter-stage matching network can be reduced by including bond wires as a part of the shunt inductors in the matching network. The two-stage PA MMIC was fabricated with a size of 2.0×1.9 mm2 and was mounted on the 4×4 QFN package for evaluation. Using a downlink LTE signal with a PAPR of 6.5 dB and a channel bandwidth of 10 MHz at the 2.6 GHz band, the PA MMIC exhibited a gain of 30 dB, a DE of 32%, and an ACLR of -31.4 dBc at an average output power of 36 dBm. Using two PA MMICs for carrier and peaking amplifiers, DPA was designed and evaluated. At a 6-dB back-off output power level of 39 dBm, a gain of 24.7 dB and a DE of 43.5% were achieved.

Power amplifier based on 50 Ω Load impedance using boost DC-DC converter for APT

This paper presents a power amplifier (PA) based on a boosted supply voltage using a boost DC-DC converter to eliminate the load impedance matching network for handset applications. With appropriate transistor size and boosted collector/drain voltage, the optimum load impedance of the PA can be around 50 Ω to have a required output power level. As a result, loss and bandwidth limitation from the output matching network can be greatly mitigated. In addition, efficiency improvement at low output power level can be obtained by decreasing the output voltage of the boost DC-DC converter, which is an average power tracking (APT) operation. To prove the proposed concept, the PA with a boost DC-DC converter was implemented for the 1.88 GHz band. Using a 16-QAM uplink LTE signal with a peak-to-average power ratio (PAPR) of 7.2 dB and a channel bandwidth of 5 MHz, the PA with a drain supply voltage of 12 V exhibited an output power of 27.8 dBm, a power-added efficiency (PAE) of 41.3%, and power gain of 12.5 dB for the given adjacent-channel leakage power ratio (ACLR) of -30 dBc. For a supply voltage of 4 V from the DC-DC converter, a high PAE of 33.8% is maintained for a back-off output power of 18.3 dBm.

High-Efficiency GaN-HEMT Doherty Power Amplifier with Compact Harmonic Control Networks

본 논문에서는 long term evolution(LTE) 통신을 위한 2.6 GHz 대역에서 동작하는 고효율 Doherty 전력증폭기를 설계하였다. 2차 및 3차 고조파 임피던스를 조정하기 위한 간단한 구조의 정합 네트워크를 통해 전력증폭기의 고효율 동작을 달성하였다. Doherty 전력증폭기는 다양한 측면에서 장점을 갖는 GaN-HEMT 소자를 이용하여 제작되었으며, 10 MHz의 대역폭 및 6.5 dB 첨두 전력 대 평균 전력비(PAPR)의 특성을 갖는 LTE downlink 신호를 이용하여 측정되었다. 평균 전력 33.4 dBm에서 13.1 dB의 전력 이득, 57.6 %의 전력부가효율(PAE) 및 ?25.7 dBc의 인접채널누설비(ACLR) 특성을 갖는다.This paper presents a Doherty power amplifier(DPA) operating in the 2.6 GHz band for long term evolution(LTE) systems. In order to achieve high efficiency, second and third harmonic impedances are controlled using a compact output matching network. The DPA was implemented using a gallium nitride high electron mobility transistor(GaN-HEMT) that has many advantages, such as high power density and high efficiency. The implemented DPA was measured using an LTE downlink signal with a 10 MHz bandwidth and 6.5 dB PAPR. The implemented DPA exhibited a gain of 13.1 dB, a power-added efficiency(PAE) of 57.6 %, and an ACLR of —25.7 dBc at an average output power of 33.4 dBm.