Jeonghyeon Cha

A fully matched N-way Doherty amplifier with optimized linearity

This paper presents a new fully matched N-way Doherty amplifier. The basic principles of operation and important features are described. For the experimental verification, 2.14-GHz Doherty amplifiers having two-, three-, and four-way structures are implemented using silicon LDMOSFETs and tested using down-link WCDMA signal. The linearity performances of the two-, three-, and four-way Doherty amplifiers are optimized for better efficiency versus linearity by a bias adjustment of the peaking amplifiers. For simultaneously improving the efficiency and linearity to achieve maximum efficiency versus linearity, the gate biases of the peaking amplifiers for the N-way Doherty amplifier are optimized. As a result, the efficiency versus linearity characteristics are drastically improved by N-way extension of the Doherty amplifier.

Optimum operation of asymmetrical-cells-based linear Doherty power Amplifiers-uneven power drive and power matching

We developed a Doherty amplifier with uneven input drive and optimized individual matching for the carrier and peaking cells. In the proposed amplifier, higher input power is delivered to the peaking cell rather than the carrier cell for optimized linear power operation, especially for appropriate load modulation. Both cells are matched differently to further optimize the performance. We analyzed the efficiency of the proposed amplifier as a function of the input drive ratio for the two cells. To interpret the linearity related to the load modulation and harmonic cancellation mechanisms, we simulated the third-order intermodulation amplitude and phase of each cell of the proposed amplifier. For verification, we implemented the asymmetric power amplifier with uneven drive and optimized power matching using Motorolas MRF281SR1 LDMOSFET with a 4-W peak envelope power. For a 2.14-GHz forward-link wireless code-division multiple-access signal, the measured drain efficiency of the amplifier is 40%, and the measured average output power is 33 dBm at an adjacent channel leakage ratio (ACLR) of -35 dBc, while those of the comparable class-AB amplifier are 21% and 30.6 dBm at the same ACLR level, respectively.

The Doherty power amplifier

In this article, we show that the Doherty amplifier is capable of delivering the stringent requirements of the base station power amplifiers. We explain the operation principles, including both linearity and efficiency improvements, and the basic circuit configuration of the amplifier. Advanced design methods to operate across wide bandwidth and improve the linearity are also described. For verification, the Doherty amplifier is implemented using laterally diffused metal oxide semiconductor (LDMOS) transistors and measured using a WCDMA 4FA signal. These results show that the Doherty amplifier is a promising candidate for base station power amplifiers with wide bandwidth, high efficiency, and linearity

A microwave Doherty amplifier employing envelope tracking technique for high efficiency and linearity

In this letter, we demonstrate a microwave Doherty amplifier employing an input signal envelope tracking technique. In the amplifier, the gate bias of the peaking amplifier is controlled according to the magnitude of the envelope. A 2.14-GHz Doherty amplifier is implemented using 4-W PEP LDMOSFETs, and an adaptive controlled gate bias circuit is constructed and the control shape is optimized experimentally. The performance of the microwave Doherty amplifier is compared with that of a class AB amplifier using one-tone, two-tone, and forward-link wideband code-division multiple access (WCDMA) signals. For a forward-link WCDMA signal, the measured power added efficiency (PAE) of the microwave Doherty amplifier is 39.4% at -30 dBc adjacent channel leakage ratio (ACLR), while that of the comparable class AB amplifier is 24.2% at the same ACLR level.

Linear power amplifier based on 3-way Doherty amplifier with predistorter

This paper presents a 3-way Doherty amplifier with predistorter (PD) for a repeater application. It is implemented using three 60 Watts PEP silicon LDMOSFETs and tested using two-tone and one- and two-carrier down-link WCDMA signals. For the two-carrier downlink WCDMA signal, the amplifier provides -49.1 dBc adjacent-channel-leakage-ratio (ACLR) and 10.3% power-added efficiency (PAE) at an output power 40 dBm which is an improvement of 8.5 dBc in linearity and 2% in efficiency compared to a similar class-AB amplifier.

Optimum design of a predistortion RF power amplifier for multicarrier WCDMA applications

This paper provides a design guide for optimum design of an RF power amplifier with a predistortion linearizer. For a two-tone signal, three performance degradation factors, higher order terms, amplitude, and phase mismatches are analyzed quantitatively. The results are implemented to the design of optimized predistortion power amplifier for a WCDMA signal application. For the experiments, a 2.4-GHz class-AB power amplifier is fabricated using an LDMOSFET with a 30-W peak envelope power. A simple third-order predistorter is used to measure the relative phases of the harmonics, as well as to linearize the amplifier. The performance of the optimized predistortion power amplifier is excellent for an IS-95 code-division-multiple-access signal. Finally, a method for reducing the memory effects of the amplifier is devised to get a good cancellation performance for a wide-band signal, and the performance degradation caused by the memory effects is analyzed. For a forward-link four-carrier WCDMA signal, the predistortion power amplifier delivers an adjacent channel leakage ratio of -46 dBc at a 4-W average output power with a cancellation of 13.4 dB.

An adaptive bias controlled power amplifier with a load-modulated combining scheme for high efficiency and linearity

This paper presents a highly efficient linear power amplifier with an adaptive bias control circuit. In the amplifier, two amplifiers are power-combined using load modulation networks and then gate biases are controlled according to the input signal envelope. The gate voltage shapes of the two amplifiers have been optimized by envelope simulation to maximize the power added efficiency for the ACLR of -30 dBc. For verification, an adaptively controlled power amplifier has been implemented at 2.14 GHz using 4 watts PEP LDMOSFETs and its bias circuit were constructed based on simulated control shapes. The performances of the amplifier were compared with the class AB and Doherty amplifiers using a one-tone and forward-link WCDMA signals. The measured PAE of the amplifier is 41 % at -30 dBc ACLR, while those of the class AB and Doherty amplifiers are 24.5 % and 28.1 %, respectively.

Weighted Polynomial Digital Predistortion for Low Memory Effect Doherty Power Amplifier

We have proposed a simple and effective weighted polynomial digital predistortion algorithm, which consists of weighting, least square polynomial fit, and de-weighting. The weighting factor is introduced to describe the signal distribution statistics and high harmonic generation at a high power region to improve accuracy of the error function. A low memory linear Doherty power amplifier (PA) has been realized with two 90-W peak envelope power LDMOSFETs using memory effect reduction techniques, and the proposed algorithm has been applied to the PA. For the forward-link wideband code division multiple access 3FA signal, the adjacent channel leakage ratio performance at 5-MHz offset is -56 dBc with power-added efficiency of 20.78% at an average power of 40 dBm. The proposed weighting polynomial algorithm provides a significantly reduced error power and superior convergence behavior with improved linearization capability than the conventional polynomial. Moreover, the low memory Doherty amplifier could be linearized for a wideband signal using the simple algorithm without any memory effect compensation

Highly linear three-way Doherty amplifier with uneven power drive for repeater system

We have demonstrated a high linear three-way Doherty amplifier by applying uneven power drive and optimizing the peaking biases and load impedances. The amplifier has been implemented at 2.14GHz using 190-W peak envelope power laterally diffused metal-oxide-semiconductor field-effect transistors. For comparison, a class AB biased amplifier is tested as its counterpart. The two-tone signal and forward-link wideband code-division multiple access (WCDMA) signal have been selected as test signals. At 42dBm (12.5-dB backed-off output power), there are large improvements in the third- and fifth-order intermodulation distortions. For the forward-link four-carrier WCDMA signal, the adjacent channel leakage ratio (ACLR) performances at 5-MHz and 10-MHz offsets are -52.5dBc and -53.4dBc, respectively, and satisfy the generally medium high power amplifier linearity target without using any other linearization circuits. In comparison with the class AB amplifier, the three-way Doherty amplifier with uneven power drive has 9.8-dB lower ACLR at 5-MHz offset while maintaining a comparable drain efficiency of 10.2%.

Microwave Doherty Power Amplifier for High Efficiency and Linearity

This paper explains the basic circuit configuration of microwave Doherty amplifier and additional design methods for wide bandwidth and high power applications. This paper also presents the recent experimental results of the group using the uneven power drive. Most of the previous works about microwave Doherty amplifier have employed identical input drives. In this works, two 1:1(2-way) and a 1:2(3-way) Doherty amplifiers are implemented at 2.14GHz center frequency using LDMOS with a peak envelope power of 180 watt and 285 watt, respectively. The 2-way Doherty amplifiers are optimized at 25 watt average output power for high efficiency and linearity and the 3-way Doherty amplifier at 16 watt average output power for high linearity. The amplifiers are tested using WCDMA 4FA signal. The performances of the 2-way Doherty amplifier are compared with that of the comparable class AB amplifier and the Doherty amplifier with even power drive. The performances of the 3-way Doherty amplifier are compared with that of the comparable class AB amplifier. The experimental results show the superior performances of our Doherty amplifiers