Seung-Hoon Ji

In this paper, an extensive review of the most up-to-date papers on microwave Doherty power amplifiers is presented. The main applications are discussed, together with the employed semiconductor technologies. The different research trends, all aimed to improve the advantages of the Doherty scheme and to solve its inherent drawbacks, are presented. The first considered topic is the maximization of efficiency and/or linearity, where analog and digital techniques are exploited. Another important tr

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 tu

Operational behaviors of the class-F and class-F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> amplifiers are investigated. For the half-sinusoidal voltage waveform of the class-F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> amplifier, the amplifier should be operated in the highly saturated region, in which the phase relation between the fundamental and second harmonic currents a

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 voltag

A power amplifier (PA) for a femto-cell base station should be highly efficient and small. The efficiency for amplification of a high peak-to-average power ratio (PAPR) signal is improved by designing an asymmetric Doherty power amplifier (DPA). From the simulation result for a long-term evolution (LTE) signal with 7.2-dB PAPR, the DPA delivers the highest efficiency with 1:1.4 cell size ratio for the carrier and peaking PAs. A small size is achieved by designing the DPA using a GaN monolithic m

A novel 2.14-GHz Doherty power amplifier (PA) was designed and fabricated using a 0.25- μm GaN on SiC monolithic microwave integrated circuit (MMIC), to build small-cell base stations. To reduce the size and loss, lumped passive elements were employed in a manner of minimizing the device count. The core components of the PA were integrated on the MMIC die to reduce the area, and low-loss chip inductors were mounted around the die to enhance the efficiency. An unconventional uneven power splittin

The switching behavior of Class-E power amplifiers (PAs) is described. Although the zero voltage switching can be performed properly, the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> charging process at the switch-off transition cannot be abrupt and the waveform deviates from the ideal shape, degrading the efficiency. For the operation abo

We have proposed two methods of enhancing efficiency of an envelope tracking power amplifier (ET PA) from an interlock operation. The first is the utilization of sinking current. The sinking current is a critical efficiency reduction factor since it is a wasted power. To reduce the sinking current, the gate bias of the power amplifier (PA) is increased so that the sinking current is delivered to the PA and is utilized for amplification. The other one is the RF input shaping method. The input sig

This paper presents an approach to maximize the gain and power-added efficiency (PAE) of a Doherty power amplifier (PA) using a 0.25 μm GaN pHEMT. The conventional carrier PA has an input matching for the R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OPT</sub> load and does not deliver the 3 dB higher gain with 2R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OPT</sub> load due to the mismatch and

A Doherty amplifier assisted by a supply modulator is presented using 2.14 GHz GaN HEMT saturated power amplifier (PA). A novel envelope shaping method is applied for high power-added efficiency (PAE) over a broad output power range. Experimental comparison with the Doherty and saturated PAs with the supply modulator is carried out. For the 8 dB crest factor WCDMA 1FA signal, the Doherty PA supported by the modulator presents the improved PAE over the broad output power region compared to the st

This letter presents an approach to maximize the output power and efficiency of a Doherty power amplifier (PA). The conventional carrier PA having 2R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OPT</sub> match, used in a symmetric Doherty PA, does not deliver the saturated high efficiency at the 6 dB back-off power but at the 5.5 dB back-off power due to the knee voltage effect. To solve the problem, the gate biases of the carrier and peaking PA

A power amplifier (PA) for a femto-cell base station should be highly efficient, linear and small. The efficiency for amplification of a high peak-to-average power ratio (PAPR) signal is improved by designing an asymmetric Doherty PA (DPA). The linearity is improved by applying third-order inter-modulation (IM3) cancellation method. For dual-band operation, a tunable switched capacitor is applied. A small size is achieved by designing the DPA using GaN MMIC process. The implemented dual-band DPA

Recently, several red-green-blue-white (RGBW) color filter arrays (CFAs), which include highly sensitive W pixels, have been proposed. However, RGBW CFA patterns suffer from spatial resolution degradation owing to the sensor composition having more color components than the Bayer CFA pattern. RGBW CFA demosaicing methods reconstruct resolution using the correlation between white (W) pixels and pixels of other colors, which does not improve the red-green-blue (RGB) channel sensitivity to the W ch

This work proposes a new offset line of carrier PA for Doherty power amplifier (PA). The carrier PA of conventional Doherty PA (DPA) delivers lower efficiency at back-off output power than at peak output power due to the phase mismatch of the carrier offset line in implementation, because the efficiency at back-off power is very sensitive to the output impedance change. To solve the problem, a new offset line for the carrier PA is adopted optimizing the efficiency performance at back-off output

A quarter-wavelength transformer, phase compensation network, offset line are the bandwidth limiting factors of Doherty PAs. In this paper, we expand the bandwidth of the Doherty PA by employing a new structure. The conventional phase compensation network is merged into an input matching circuit and the offset line is resonated-out by an inductor. The quarter wavelength transformer has a low-Q characteristic compared to that of conventional one. With the proposed topology, a broadband Doherty PA