Broadband Power Amplifier Research Articles

Unbalanced Power Amplifier: An Architecture for Broadband Back-Off Efficiency Enhancement

In this article, we present a new broadband power amplifier (PA) architecture with a back-off efficiency enhancement that supports very wide modulation bandwidths. The unbalanced PA is composed of two cooperating sub-PAs using the Lange couplers as input power splitter and output power combiner. The PA operation is controlled by the transistors' width ratio and coupling coefficients of the Lange couplers. The output power back-off (OPBO) level is given by the transistors' width ratio and coupling coefficient of the output coupler, while the maximum efficiency is achieved at the back-off point. These features provide more design flexibility compared with the conventional Doherty PA, where the OPBO can be set only by the transistors' width ratio, and the maximum efficiency is achieved at the peak power. Using broadband harmonic matching networks, the main and auxiliary sub-PAs operate in the continuous mode to improve efficiency over a broad bandwidth. A fully integrated unbalanced PA, implemented in a 250-nm GaN-on-SiC process, achieves 32.2-34.3-dBm output power, 27%-37% efficiency at peak power, and 27%-40% at 5-6-dB back-off, across 4.5-6.5 GHz. The PA provides 3.7/4.5% (-28.6/-26.9 dB) rms error vector magnitude (EVMrms) and 30% average efficiency for a 256-QAM signal with 100-/200-MHz bandwidth, 7.2-dB PAPR, and 25.5-dBm average output power, without using any predistortion.

Design of a Broadband Power Amplifier Based on Power and Efficiency Contour Estimation

This letter presents the design of a broadband power amplifier (PA) that achieves, over the 0.45-3.4-GHz frequency band, an output power between 41.5 and 44.3 dBm and a power added efficiency (PAE) higher than 54%. A four-section transformer has been adopted as the output-matching network in order to target the impedance region defined by a simplified prediction of the power and efficiency contours. The designed PA can find application in flexible hardware for 5G applications, as well as in broadband radar and countermeasure systems.

Extended Inverse Class-F Continuum for Designing Broadband Power Amplifier

The impedance space of the continuous inverse class-F power amplifier (PA) is extended in this paper. Traditionally, for extending impedance space, a reactive term is introduced into the current waveform of the continuous inverse class-F PA. In this paper, two reactive terms are introduced into the current and voltage waveforms simultaneously. The proposed method results in an expansive impedance space for designing broadband continuous inverse class-F PAs. For validating the proposed theory, a broadband PA working over 1.2–4.0[Formula: see text]GHz is designed and fabricated. Experimental results indicate that the fabricated broadband PA delivers a saturation power of 40.2–42.8[Formula: see text]dBm and a drain efficiency of 50.7–69%.

A Methodology and a Metric for the Assessment of the Linearizability of Broadband Nonlinear Doherty Power Amplifiers

This letter proposes a novel methodology and a metric for the assessment of the linearizability of broadband nonlinear power amplifiers (PAs). Validation of the proposed methodology and the proposed metric on two linearized Doherty PAs (DPAs) using digital predistortion (DPD) technique was carried out and it demonstrated the suitability and appropriateness of the new metric. Different from the iterative optimization procedure between the PA circuit design and the DPD algorithm compensation, the proposed method aims to provide a quantitative criterion on the PA linearizability based on its frequency-dependent amplitude modulation (AM)/AM and AM/phase modulation (PM) characteristics. To verify the effectiveness of the metric, two DPAs were characterized before and after a DPD-based linearization. The average correlation coefficients between the values of the metric and the adjacent channel power ratio after DPD were 0.8763 and 0.9156, and that between the values of the metric and the error vector magnitude after DPD were 0.8618 and 0.7200 for PA1 and PA2, respectively, indicating that the evaluation method and the linearizability metric can be used as a good measure to assess the linearizability of broadband PAs.

A Broadband High-Efficiency Continuous Class-AB Power Amplifier for Millimeter-Wave 5G and SATCOM Phased-Array Transmitters

A broadband and compact harmonic-tuned power amplifier (PA) is presented for 5G and mobile satellite communication (SATCOM). A noninverting 1:1 transformer is the core of the output matching and provides an embedded second harmonic trap in a compact layout. The proposed PA is fabricated by the BiCMOS SiGe-8XP technology. At $P_{1\,\text {dB}}$ , an output power of 11 dBm and a collector efficiency of more than 30% from 30 to 39 GHz are achieved. The PA has a single-ended topology with electrostatic discharge (ESD) protection, which is well suited for deployment in the output stage of the multichannel beamformer transmitter (TX) monolithic microwave integrated circuit (MMICs). Detailed analysis, design methodology, and experimental results are presented.

A Robust and Scalable Harmonic Cancellation Digital Predistortion Technique for HF Transmitters

High frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) enables long-distance communication and has strong survivability. However, it is faced with the problem of harmonics because of the nonlinearity of the PA. We first consider canceling the harmonics using a harmonic cancellation digital predistortion (HC-DPD) technique, instead of lossy and bulky analog filter banks. A uniform complex-valued Hilbert transform-based polynomial (HTBP) function is proposed for the modeling of the harmonics, as well as the fundamental component in the real-valued input and output signals. In order to validate this idea, detailed experiments were performed for carrier frequencies located at 5 and 10 MHz, respectively. After the proposed HC-DPD, the harmonics were all canceled to satisfy the linearization requirements. In particular, the improvement of the second harmonic is more than 40 dB, which is nearly 20 dB better than that of the memoryless polynomial (MLP) model. Furthermore, the experimental results demonstrate that the proposed technique is scalable, in which the model coefficients extracted at a specific power level, signal bandwidth, and carrier frequency can be extended to other scenarios. Both the second and third harmonics were canceled for being below −45 dBc after the HC-DPD.

Approach for the Design of a Broadband Microwave Power Amplifier in Microstrip Technology for Mobile Communications Systems

This work presents a broadband power amplifier in S-band in microstrip technology. The proposed power amplifier is modeled with a single-stage architecture based on a field effect transistor ATF13786 of Agilent Technologies (hp) ® . The used transistor has been polarized with transmission lines and it has been adapted with matching networks in the form of λ /4 transformers filters at the input and at the output. This amplifier has been studied and optimized using the Advanced Design System (ADS ® ) software. The simulation results of the output power and S parameters show excellent characteristics with a satisfactory gain greater than 10.9 dB, low reflections, a saturated output power of 16.4 dBm with a 1 dB compression point at an input power level of about 5 dBm, a maximum PAE of 25.3% and unconditional stability in the desired frequency band. The modeled amplifier can be integrated into mobile communications systems namely LTE mobile networks (2500 to 2690 MHz) and wireless networks using Wi-Fi protocol (2400 to 2485 MHz).

Generalized Hybrid Continuous Mode for Designing Broadband Power Amplifiers

It has been widely validated that continuous working modes are powerful theories for designing broadband power amplifier (BPA). Theoretically, the conduction angle of all continuous-mode power amplifiers (PAs) is 180∘ (class-B-biased). However, in practice, these PAs are always biased in class-AB condition. Thus, continuous-mode PAs biased in class-AB condition should be researched. This paper generalizes the theory of hybrid continuous mode (HCM) for implementing broadband power amplifiers. The intrinsic drain current waveform of HCM biased above the pinch-off point (conduction angle is larger than 180∘) is first derived. Then, the impedance space of the generalized HCM (class-AB-biased) is explored and analyzed. The conclusion is that the generalized HCM possesses a shifted fundamental impedance space along with the enlargement of conduction angle. For validating the proposed theory, a broadband PA working over 1.6–3.0[Formula: see text]GHz is implemented. Experimental results indicate that the designed BPA achieves a saturation power of 40.3–42.7[Formula: see text]dBm and a drain efficiency of 64.3–74.4%.

Co-Design of Second Harmonic-Tuned Power Amplifier and a Parallel-Coupled Stub Loaded Resonator

This brief presents a co-design of the second harmonic-tuned broadband power amplifier (PA) in cascade with a stub loaded parallel-coupled lines microstrip bandpass filter. These coupled microstrip lines are bilaterally connected with the shorted stub. Filter parameters are determined by an even-odd mode impedance analysis to ensure the high-selectivity and anti-interference bandpass response. Hence, a proper fundamental and second harmonic impedance matching is realized in the desired regions of the Smith chart. Moreover, an overall circuit size is significantly reduced with easy integration. For validation, the proposed structure is manufactured and tested for a commercial 10-W GaN transistor across 1.6-2.8 GHz (54.5%), with 49.1%-65% measured drain efficiency (DE) and 38-41 dBm of measured output power has been obtained. Also, when this PA-filter circuit is driven by a 5 MHz long term evolution signal with a peak to average power ratio of 8.2 dB, an adjacent channel leakage ratio of lower than -55 dBc is achieved.

Linear-Decomposition Digital Predistortion of Power Amplifiers for 5G Ultrabroadband Applications

This article proposes a novel linear-decomposition digital predistortion (LD-DPD) for the linearization of power amplifiers (PAs) in ultra broadband applications. LD-DPD is able to perform excellently with low complexity at the oversampling rate of only 1.5×. It combines leading terms with a linear decomposition of cross-terms, which can reduce the spectrum aliasing even when sampling rates are insufficient. The model complexity of the proposed model is quantified by floating-point operations. Experiments on broadband PAs at both sub-6-GHz and millimeter-wave frequencies have provided effective validations of the proposed model by employing the 5G New Radio (NR) waveforms. Particularly, the linearization of a signal with modulated bandwidth (BW) 800 MHz at 28 GHz was demonstrated. LD-DPD achieved a normalized root-mean-square error (NRMSE) of 3.34% for continuous 800-MHz modulated signal at the sampling rate of only 1.2 GHz. Compared with the already published DPDs, the proposed method is featured by high accuracy with limited available sampling rates to significantly reduce the system BW requirements. Also, it presents much lower complexity that will reduce expenses on hardware, which is very suitable for 5G ultra broadband applications.

A broadband and excellent flatness power amplifier with novel‐designed band‐pass filter based on composite right/left‐handed unit cell

AbstractIn this paper, a broadband and excellent flatness power amplifier (PA) with a novel‐designed band‐pass filter based on composite right/left‐handed (CRLH) unit cell structure is proposed. On studying the structure of CRLH unit cell, a way to enhance PA bandwidth, gain flatness, and power‐added efficiency (PAE) flatness is explored. The novel‐designed CRLH unit cell structure is studied and applied in PA design. The measurements show that the PA has an output power of greater than 40 dBm, a gain flatness of 0.5 dB, and a PAE flatness of 4.4% within 1.7‐3.1 GHz bandwidth.

A broadband RLC matched GaN power amplifier using interposer‐MMIC technology

AbstractIn this article, we report a compact and low‐profile GaN‐based broadband power amplifier using silicon interposer‐MMIC (iMMIC) technology. The iMMIC technology enables a GaN HEMT to be embedded in the silicon substrate, and passive circuit elements such as metal‐insulator‐metal (MIM) capacitors, spiral inductors, and thin film resistors to be implemented on the high‐resistivity silicon (HRS) substrate using standard integrated passive device (IPD) process, so that the final power amplifier is almost indistinguishable from a single GaN MMIC power amplifier. The RLC matched all‐pass network and LC ladder type low‐pass network are employed as the input matching network and output matching network, respectively. The proposed power amplifier has a Psat of 39.1 to 39.2 dBm with a power‐added efficiency (PAE) of 40% to 50.5% in the frequency range of 2.1 to 3.5 GHz under continuous wave (CW) input signal. The proposed iMMIC power amplifier occupies only 9.9 mm2.

A trade-off design of microstrip broadband power amplifier for UHF applications

In this paper, the design of a Broadband Power Amplifier for UHF applications is presented. The proposed BPA is based on ATF13876 Agilent active device. The biasing and matching networks both are implemented by using microstrip transmission lines. The input and output matching circuits are designed by combining two broadband matching techniques: a binomial multi-section quarter wave impedance transformer and an approximate transformation of previously designed lumped elements. The proposed BPA shows excellent performances in terms of impedance matching, power gain and unconditionally stability over the operating bandwidth ranging from 1.2 GHz to 3.3 GHz. At 2.2 GHz, the large signal simulation shows a saturated output power of 18.875 dBm with an output 1-dB compression point of 6.5 dBm of input level and a maximum PAE of 36.26%.

Broadband power amplifier using hairpin bandpass filter matching network

This Letter presents a new combination of a broadband power amplifier (PA) and an output microstrip hairpin bandpass filter. The filter is designed based on the fifth-order Chebyshev low-pass prototype element values. Even-odd mode impedance analysis is used to calculate the filter parameters. Meanwhile, only the fundamental impedance matching is considered for this design. Therefore, a highly selective bandpass response is obtained to provide a spurious-free fundamental impedance matching. For verification, a broadband PA-filter component across 1.9-3.1 GHz (48%) is designed and fabricated. Measurements have shown a drain efficiency of 48-56.6% with 39.3-40.5 dBm of maximum output power.

Broadband High-Efficiency Power Amplifier With Quasi-Elliptic Low-Pass Response

This paper presents a broadband high-efficiency harmonic-tuned power amplifier (PA) with quasi-elliptic low-pass responses. A combination of continuous Class-F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> and extended continuous Class-F PA modes is employed to significantly expand the design space. A quasi-elliptic low-pass matching network is proposed, which can realize a broadband impedance matching in the predefined optimal impedance region desired by the combination of PA modes. Furthermore, two transmission zeros are generated near the passband, exhibiting high skirt selectivity and providing rapid impedance transition from the passband to the stopband. A wide stopband covering up to the third harmonic is achieved which shows good harmonic suppression. Design procedures of the proposed broadband PA are presented. To verify the proposed methodology, the broadband PA is fabricated and measured. The implemented PA achieves a bandwidth of 145.2% from 0.5 to 3.15 GHz. Over this frequency range, the drain efficiency is measured as 58–74.9% with the output power of greater than 39.03 dBm and a large signal gain ranging from 8.43 to 15.67 dB. A wide stopband is realized from 3.4 to 10 GHz, showing excellent quasi-elliptic low-pass responses. The measured adjacent leakage ratios (ACLRs) using a 20-MHz LTE signal with digital pre-distortion are below −45.06 dBc.

Broadband Power Amplifier Based on a Generalized Step-Impedance Quasi-Chebyshev Lowpass Matching Approach

In this article, a 1.7–2.6-GHz broadband power amplifier (PA) was proposed using the generalized quasi-Chebyshev lowpass matching approach, which was directly composed of step-impedance transmission lines (SITLs). First, the complete design theory for the introduced step-impedance matching network was provided with the detailed design equations. The impedance of the SITLs can be calculated directly based on the specified bandwidth, maximum allowable return loss, and impedance-transforming ratio. The electrical length of SITLs was utilized to adjust the harmonic impedances to perform a PA high-efficiency region. For demonstration, a PA using the 10-W gallium nitride high electron mobility transistor (GaN HEMT) with the measured drain efficiency (DE) of 65%–78% from 1.7 to 2.6 GHz was achieved. A good agreement between the simulated and measured results can be observed.

The Nested-Mode Power Amplifiers for Highly Efficient Multi-Octave Applications

In this article, a novel nested-mode power amplifier (NMPA) is proposed for highly efficient multi-octave applications. By introducing a group of nested guaranteed regions (GRs) at the fundamental and harmonic frequencies as the target design space, the difficulties caused by frequency overlapping in harmonically tuned multi-octave power amplifiers (PAs) can be overcome, leading to a self-consistent theory of multi-octave PAs. Furthermore, the methodology of constructing the proposed nested GRs is demonstrated based on a simplified numerical model. According to the methodology, the desired nested GRs can be constructed by following several well-defined closed-form steps. In addition, a feasible design methodology of the NMPA is established based on a simplified deembedding technique of packaged devices. Based on the proposed theory and design method, a 1–3100-MHz NMPA is designed and measured. According to the measured results, the designed PA exhibits 57.5–73.9% drain efficiency and 39–42.6-dBm output power across the band. Moreover, the linearity and linearizability of the designed NMPA are verified using up to 20-MHz-bandwidth-modulated signals across the designed band accompanied with a digital predistortion (DPD) procedure. To the best of our knowledge, this is the state-of-the-art performance of multi-octave broadband PAs.

Sampling Rate Reduction for Digital Predistortion of Broadband RF Power Amplifiers

In this article, we present a novel technique to build digital predistorters that can linearize broadband power amplifiers (PAs) using reduced sampling rates. In contrast to conventional digital predistortion (DPD) where oversampling is necessary to avoid aliasing effect, the proposed method cancels the aliasing distortion using a sliced multistage cancellation scheme. A large reduction of sampling rate can be achieved in digital implementation of DPD, significantly reducing power consumption and implementation cost. Experimental results show that a DPD with a sampling rate of merely 1.5×, instead of 5×, signal bandwidth, can still produce satisfactory performance within the linearization bandwidth but consume only one-third of power, compared with that using the conventional approaches. The proposed technique provides a promising solution for the next-generation 5G systems, where large signal bandwidths are required.

High‐power multi‐octave laterally diffused metal–oxide–semiconductor power amplifier with resistive harmonic termination

In this study, a broadband high-power amplifier with resistive harmonic matching is introduced. The analytical formulations for the drain voltage, output power, optimum load resistance, and efficiency are derived for this type of amplifier under class-B bias conditions. The design is based on a linear model of a laterally diffused metal–oxide–semiconductor transistor. In contrast to the conventional linear method that is based on an equivalent output circuit, the output matching circuit is designed in the presence of the dependent current source and intrinsic elements of the transistor. The design technique permits a broadband amplifier to be realised without load–pull measurement. The broadband power amplifier is intended for operation in the frequency range of 30–1000 MHz and covers the very high-frequency (HF) and ultra-HF bands. The power amplifier delivers 100 W to a 50 Ω load with efficiencies of 38–56%. To validate the design concept, the measured performance of the power amplifier is compared with simulations that incorporate a non-linear model of the transistor. The power amplifier is not driven into saturation and exhibits 2nd and 3rd harmonics of <−20 and <−10 dBc, respectively.

Design of High Efficiency Linear Power Amplifier with a Continuous Broadband Based on Two-Tone Signal Analysis

In this paper, an innovative approach to achieve broadband linear power amplifier (PA) with a continuous broadband is presented. The proposed method mainly depends on the theory of control of intermodulation products and harmonics. This method results in a continuous sweet spots over a wide bandwidth. Based on the continuous sweet spots, a suboptimal solution is derived for improving the efficiency and linearity of broadband PAs. To verify the effectiveness of this method, one broadband PA operating over 4.5–5.5[Formula: see text]GHz is developed and measured, it indicates that the peak output power of the PA is 35–57[Formula: see text]dBm for a small signal input with a gain of 12[Formula: see text]dB, and the peak drain efficiency (DE) of the PA is larger than 57% over the whole working band. However, when the PA is stimulated by a 5[Formula: see text]MHz two-tone signal input, we observe that the DE keeps above 38% under the condition of the measured third-order intermodulation distortion (IMD3) is not larger than [Formula: see text][Formula: see text]dBc.