Zhijiang Dai

A New Distributed Parameter Broadband Matching Method for Power Amplifier via Real Frequency Technique

A general matching method is presented in this paper for broadband power amplifier (PA) design. A novel cost function is proposed for the real frequency technique (RFT), which could straightforwardly describe PA optimal impedance along with frequency change. The new function is also developed to design a broadband transformer for the PA output matching network (MN). Based on Richard transformation, a commensurate transmission line is deployed so that the PA matching could be convenient expressed by a real positive function. More important is that the function could be directly implemented with a distributed MN through synthesis theory. Therefore, this method is practical for computer-aided design and has less calculation amount with new function for the RFT. To verify the method, a step-by-step design of a broadband PA is given. For large signals, power gain is 14.2-16.8 dB across 0.9-2.8 GHz, while output power is around 39.5 dBm. The maximum power-added efficiency is from 52.2% to 85.1%.

A Post-Matching Doherty Power Amplifier Employing Low-Order Impedance Inverters for Broadband Applications

This paper presents a modified Doherty configuration with extended bandwidth. The narrow band feature of the conventional Doherty amplifier is discussed in the view of the broadband matching. To extend the bandwidth, the post-matching architecture is employed in the proposed design. Meanwhile, broadband low-order impedance inverters are adopted to replace the quarter-wavelength transmission lines. Low-pass filter topologies are used to realize both the post matching network and the impedance inverters. A modified Doherty Power amplifier was designed and fabricated based on commercial GaN HEMT devices to validate the broadband characteristics of this configuration. The 6-dB backoff efficiencies of 47%-57% are obtained from 1.7 to 2.6 GHz (41.9% fractional bandwidth) and the measured maximum output power ranges from 44.9 to 46.3 dBm in the designed band. In particular, more than 40% efficiencies are measured at 10-dB backoff throughout the operation band.

Design of a Post-Matching Asymmetric Doherty Power Amplifier for Broadband Applications

In this letter, the design of a broadband asymmetric Doherty power amplifier (ADPA) with an 800 MHz (41% fractional) bandwidth is presented. The post-matching structure and low-order impedance transformation networks (ITN) are employed to achieve the broadband performance. Meanwhile, different drain biases on the main and peaking devices are used to run the asymmetric operation. The proposed ADPA shows high-efficiency performance at 8-9 dB output power back-off (OBO) throughout the whole 800 MHz band. The ADPA has been designed and implemented using commercial GaN HEMTs to validate the OBO and broadband characteristics. Maximum output power ranges from 43.7 to 45.2 dBm, 50.4%-56.2% efficiencies at 8-9 dB OBO are measured from 1.55 to 2.35 GHz.

A Novel Design of Concurrent Dual-Band High Efficiency Power Amplifiers With Harmonic Control Circuits

A methodology for designing concurrent dual-band high efficiency power amplifiers (PAs) is presented in this letter. Load-pull simulations based on active device model are performed in two different bands to find the optimal required impedance conditions. A novel matching network with up to third order harmonic control is proposed to realize the high-efficiency mode matching in the two designed bands. A 1.9/2.6 GHz GaN PA is then designed to verify this method. The realized dual-band PA delivers above 10 W output power with more than 74% drain efficiency in the both operation bands.

Digital Predistortion for Power Amplifier Based on Sparse Bayesian Learning

In this brief, a sparse-Bayesian-learning algorithm is applied to estimate the coefficients of the power amplifier (PA) behavioral models and inverse models from the view of probability. With this sparse learning method, the needed number of samplings can be reduced significantly. In addition, it also provides researchers with ideas that obtain the needed subspace of the preselected model. The performance of the algorithm is validated experimentally on a gallium nitride (GaN) PA, and the signal used to test the proposed approach is an Long Term Evolution (LTE) signal. A comparison with the state-of-the-art estimation algorithm in an open-loop digital-predistortion system is also presented, and the vast majority of tests show that the number of model coefficients is reduced by at least 50%.

Extend the Class-B to Class-J Continuum Mode by Adding Arbitrary Harmonic Voltage Elements

An extended Class-B to Class-J continuum mode is presented and a power amplifier(PA) based on this theory is realized in this paper. The enhanced voltage waveform formulation, which gives multiple impedances solutions of the fundamental and harmonics for the target performance by adding the harmonic elements, has been described mathematically. Unlike conventional continuous Class-J mode, the optimal impedance solutions of the new mode can contain real and imaginary parts of arbitrary even harmonics. To verify this theory, a high-efficiency PA from 2.85-4.25 GHz is designed at the package plane. The measurement results illustrate that the fabricated PA outputs 11.7-15.8 W saturation power with drain efficiency(DE) of 58% to 78% and PAE of 54.5%-74% across the entire band. For a 5 MHz WCDMA signal with a peak-to-average ratio (PAR) of 8.6 dB, an adjacent channel leakage ratio (ACLR) of -31.5 to -38 dBc is measured at an average DE of 38%-48% when the output power (Pout) is 36 dBm from 2.85-4.25 GHz.

A Semianalytical Matching Approach for Power Amplifier With Extended Chebyshev Function and Real Frequency Technique

In this paper, an extended Chebyshev function is proposed to adapt the matching condition of the power amplifier (PA) by introducing a new factor. A set of impedance functions can be directly calculated along with the variation of a new variable, and the first element extracted from the functions is distributed in a wide range. In addition, the impedance function whose first element is the closest to the output capacitance of the transistor can be easily read out and selected as the original matching network. The fundamental impedance of the selected function will be reached a good matching state, and the impedances out of band will be on the edge of Smith chart. To achieve better performances, the real frequency technique is applied to adjust the harmonic impedances preventing it from falling into the low-efficiency region. Two PAs with a relative bandwidth of 34% and 75% are implemented to validate the proposed approach.

A 80W high gain and broadband Doherty power amplifier for 4/5G wireless communication systems

This paper presents a 80W high gain and broadband Doherty power amplifier (DPA) with symmetrical devices, employing Wolfspeeds CGHV27030S GaN HEMT. A novel architecture is used to eliminate the complex interaction of varying second harmonic impedances caused by active load modulation and provide high efficiency at output back-off (OBO) region and saturation point. Under a 10% duty cycle pulse excitation from 3.35-3.50 GHz, experimental results show the proposed DPA delivers 49.1-49.5 dBm output power with a drain efficiency (DE) of 50.2%-55.1% at 8 dB OBO and achieves a gain of 14.6-14.9 dB at an output power of 41 dBm. When extend the bandwidth to 3.3-3.6 GHz, the DPA can attain a measured DE higher than 40.9% at an OBO of 8 dB with a saturated power of 48.5-49.5 dBm. For a 2-carrier 40-MHz long-term evolution (LTE) signal with a peak-to-average power ratio (PAPR) of 8 dB, the adjacent channel leakage ratio (ACLR) is -30 dBc at 41 dBm average output power at 3.45 GHz.

A Simplified Sparse Parameter Identification Algorithm Suitable for Power Amplifier Behavioral Modeling

In this letter, a simplified sparse parameter identification algorithm is proposed to estimate the coefficients of the power amplifier (PA) behavioral model. The main idea is to select the kernel one by one from the complete model, where the criteria of selection are according to the projection of the residual vector on each kernel. By using this kernel selection method, all sparse parameters can be obtained quickly without any matrix inversion operation. The proposed algorithm is applied to prune dynamic deviation reduction-based Volterra model for a gallium-nitride (GaN) PA. Moreover, the performance and computation complexity of the proposed method are analyzed and compared with existing algorithms.

Novel design of highly-efficient concurrent dual-band GaN Doherty power amplifier using direct-matching impedance transformers

A novel methodology for designing concurrent dual-band Doherty power amplifier (DPA) is presented in this paper. The required impedance conditions of the carrier amplifier to achieve high-efficiency performance at back-off region are discussed from a new perspective. A novel combine network with direct-matching impedance transformers is then presented to support the load modulation conditions for concurrent dual-band operations. A 1.8-2.6 GHz dual-band Doherty amplifier employing commercial GaN devices is then designed and implemented to validate the proposed method. The fabricated power amplifier (PA) achieves 72% and 60% efficiency for saturation operation at 1.8 and 2.6 GHz, respectively. For the 6 dB back-off region, the measured efficiencies are 63% and 51% in the two designed bands.