Saturated Power Amplifier Research Articles

Broadband High-Efficiency Quasi-Class-J Power Amplifier Based on Nonlinear Output Capacitance Effect

In this brief, a broadband high-efficiency quasi-Class-J power amplifier (PA) based on nonlinear output capacitance effect is proposed. With the influence of the voltage across between drain and source ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{v}_{\mathrm{ DS}}$ </tex-math></inline-formula> ) at the over-driven condition, the negative second harmonic termination has been generated by the nonlinear output capacitance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{C}_{\mathrm{ out}}$ </tex-math></inline-formula> ). Since the proposed PA is driven into saturation, the current magnitude can be increased which improves the output power and efficiency. Meanwhile, the fundamental termination is modulated near the real axis of the Smith chart by the second harmonic termination, which reduces the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> -factor to extend the bandwidth. It is possible to achieve the saturated PA working in the wide frequency band. Finally, the proposed PA shows a relatively high performance of greater than 39.6 dBm saturated output power, and delivers an average of 64 % drain efficiency (DE) from 3.5 to 5.5 GHz.

Tolerance of SCM Nyquist and OFDM signals for heterogeneous fiber-optic and millimeter-wave mobile backhaul links under the effect of power amplifier saturation induced clipping

Extremely high frequency carrier communications such as millimeter-wave (mmW) is considered a promising solution for the future mobile networks. To compensate for the large path loss of the millimeter-wave links, saturated power amplifiers are inevitably used during amplify-and-forward relaying, which potentially causes system degradation due to power saturation induced clipping. In this paper, the tolerance of OFDM and Nyquist subcarrier multiplexing (SCM) signals against power amplifier saturation induced clipping is studied in the context of fiber-optic and millimeter-wave integrated communications for heterogeneous mobile backhaul networks. In the system, 10 Gbaud OFDM and Nyquist SCM signals are converted to an intermediate frequency passband before converted to the optical domain for a radio-over-fiber transmission to a remote antenna unit (RAU). At RAU, the optical radio signals are converted back to the electrical domain at millimeter-wave range. Those are then amplified by an power amplifier prior to a millimeter-wave communication to a remote radio head (RRH) for detection. Since Nyquist SCM signal exhibits a level of lower peak-to-average power ratio (PAPR) than that of OFDM, Nyquist SCM signals are more tolerant against the clipping caused by the power amplifier saturation. For 16 QAM, at clipping ratio (CR) of 4.5 dB, one-band Nyquist SCM signal shows a signal-to-noise ratio (SNR) performance over 10 times higher than that of OFDM. While the increase in the number of Nyquist SCM bands reduces the tolerance, Nyquist SCM signal maintains a better tolerance than OFDM one with respect to 16 QAM, 32 QAM and 64 QAM formats, which suffer severer impact with larger SNR penalty for higher modulation levels.

Power-Efficient Design Techniques for mm-Wave Hybrid/Digital FDD/Full-Duplex MIMO Transceivers

This article describes system and circuit design techniques to enhance power efficiency and incorporate new features in millimeter-wave multi-input–multi-output (MIMO) transceivers. The higher peak-to-average power ratio (PAPR) of the signal transmitted from a digital beamformer (DBF) or a fully connected hybrid beamforming (FC-HBF) transmitter compared with the conventional partially connected hybrid beamforming (PC-HBF) transmitter is identified for the first time. It is then shown that when a power amplifier (PA) with better back-off efficiency than Class-A PA is used, the overall power efficiency of the FC-HBF is superior to the PC-HBF for a given antenna geometry. Second, a new mechanism for built-in dual-band, per-element self-interference cancellation (SIC) is introduced to enable multi-antenna frequency-division-duplex (FDD) and full-duplex (FD) operation. Such SIC can only be supported in the proposed FC-HBF architecture. Several innovative circuit concepts are introduced, including low-loss wideband antenna interface design, dual-band power combining PA, dual-band RF-SIC design, and bidirectional MIMO signal path design. To demonstrate these techniques, a 28-/37-/39-GHz bidirectional two-stream front-end single-element prototype is designed in the 65-nm CMOS. The prototype can be configured as a transmit (TX) or receive (RX) element in DBFs or FC-HBFs which can in turn be configured to support TDD, FDD, or FD operation. The front-end achieves 16-/11-dB RX gain, 6.2-/7-dB NF, 15.8-/16.8-dBm saturated PA output power, and 20%/21.6% peak PA efficiency in the 28-/37-GHz bands. Extensive characterization results are presented to compare the energy efficiencies of the PC-HBF and FC-HBF architectures. The prototype is also characterized in the FDD/FD mode and achieves 36-dB peak RF-domain SIC and better than 26-dB RF-domain SIC across 0.5-GHz modulation bandwidth.

Wideband Techniques for Outphasing Power Amplifiers

In this paper a wideband, high-power amplifier that achieves an output power of 20 W with a bandwidth greater than one octave in the L and S bands is presented. Two ~10 W Class AB PAs are implemented with Gallium Nitride-high electron mobility transistor devices and a low loaded-Q matching network to achieve wideband performance. High power added efficiency (PAE) is achieved by combining outphased saturated power amplifiers using a wideband isolated combiner. We introduce new analysis detailing proper selection of the isolation resistance in isolated outphasing combiners. The impedance transforming Wilkinson combiner is designed to interface the system with a 50- $\Omega $ load. The L-S band (1.2~2.5GHz) amplifier was simulated, fabricated, and characterized. The fabricated HPA provides a peak output power of 43 dBm, gain of >15 dB with a peak PAE of >40% across the band. A 10 MHz, 64 QAM, long-term evolution signal is measured and achieves ACLR < −30 dBc, EVM = 4.8%-rms at an average output power and efficiency of 39.3 dBm and 33.1%, respectively.

Design of MC-CDMA receiver using radial basis function network to mitigate multiple access interference and nonlinear distortion

Multicarrier code division multiple access (MC-CDMA) is a novel wireless communication technology with high spectral efficiency and system performance. However, all multiple access techniques including MC-CDMA were most likely to have multiple access interference (MAI). So, this paper mainly aims at designing a suitable receiver for MC-CDMA system to mitigate such MAI. The classical receivers like maximal-ratio combining and minimum mean square error fail to cancel MAI when the MC-CDMA is subjected to nonlinear distortions, which may occur due to saturated power amplifiers or arbitrary channel conditions. Being highly nonlinear structures, the neural network (NN) receivers such as multilayer perceptron and radial basis function networks could be better alternative for such a case. The possibility NN receiver for a MC-CDMA system under different nonlinear conditions has been studied with respect to both performance and complexity analysis.

MC–CDMA receiver design using recurrent neural networks for eliminating multiple access interference and nonlinear distortion

SummaryMulticarrier code division multiple access (MC–CDMA) is a promising wireless communication technology with high spectral efficiency and system performance. However, all multiple access techniques including MC–CDMA were most likely to have multiple access interference (MAI). So this paper mainly aims at designing a suitable receiver for MC–CDMA system to mitigate such MAI. The classical receivers like maximal ratio combining, minimum mean square error, and iterative block–decision feedback equalization fail to cancel MAI when the MC–CDMA is subjected to severe nonlinear distortions, which may occur due to saturated power amplifiers or arbitrary channel conditions. Being highly nonlinear structures, the neural network receivers such as multilayer perceptron and recurrent neural network could be better alternative for such a case. The feasibility, efficiency, and effectiveness of the proposed neural network receiver are studied thoroughly for MC–CDMA system under different nonlinear conditions.

Multi-Way Lossless Outphasing System Based on an All-Transmission-Line Combiner

A lossless power-combining network comprising cascaded transmission-line segments in a tree structure is introduced for a multi-way outphasing architecture. This architecture addresses the suboptimal loading conditions in Chireix outphasing transmitters while offering a compact and microwave-friendly implementation compared to previous techniques. In the proposed system, four saturated power amplifiers (PAs) interact through an all-TL power-combining network to produce nearly ideal resistive load modulation of the branch PAs over a 10:1 range of output powers. This work focuses on the operation of the combining network, deriving analytical expressions for input-port admittance characteristics and an outphasing control strategy to modulate output power while minimizing reactive loading of the saturated branch amplifiers. A methodology for combiner design is given, along with a combiner design example for compact layout. An experimental four-way outphasing amplifier system operating at 2.14 GHz demonstrates the technique with greater than 60% drain efficiency for an output power range of 6.2 dB. The system demonstrates a W-CDMA modulated signal with a 9.15-dB peak-to-average power ratio with 54.5% average modulated efficiency at 41.1-dBm average output power.

Simulation on high-power tetrode amplifier based on Similink

For a high energy proton radio frequency quadrupole (RFQ) accelerator which requires a RF power source of 324 MHz and 570 kW, 4616V4 tetrode which can output 350 kW is chosen as the main amplifier. Two tetrodes together can provide an RF power of about 700 kW and meet the design requirement. During the construction of the RF source, simulation studies based on Simulink, tetrode's constant current characteristic curve and experimental data are performed for the optimization of the system working conditions, such as anode voltage, input power, working point and output power. Low anode voltage and nearly saturated input power amplifier can effectively increase the operating frequency. The simulation method is verified with the experimental data setup and the conventional 13-point approximate integral method. As a result, the relative error is less than 5%. ©, 2015, Editorial Office of High Power Laser and Particle Beams. All right reserved.

An HBT Saturated Power Amplifier With Minimized Knee Effect for Envelope Tracking Operation

In this letter, a highly efficient saturated power amplifier (PA) based on a heterojunction bipolar transistor (HBT) is employed to maximize the efficiency of an envelope tracking (ET) PA. In this PA, output voltage waveform of the PA is shaped as a half-sinusoidal voltage waveform peaked by a second harmonic. The knee voltage effect is minimized in this voltage waveform due to the large fundamental voltage for a given supply voltage, which is very important for an ET PA with a low average supply voltage. Based on the saturated PA, the ET PA is tested at 1.85 GHz using a long term evolution signal. The ET PA delivers a power-added efficiency of 46.5%, an E- UTRAACLR of -33.4 dBc, and an error vector magnitude of 3.0% at an average output power of 27 dBm.

A Modified Approach Based On SLM for OFDM PAPR Reduction Using Time Domain SubBlock Conversion Matrix

OFDM is a digital transmission method developed to meet the increasing demand for higher data rates in communications which can be used in both wired and wireless environments. This thesis describes the issue of the PAPR in OFDM which is a major drawback, and presents new and variations to existing algorithms to reduce it. The effect on system performance in terms of the BER and Power Spectral Density is simulated for an OFDM transceiver with a saturated High Power Amplifier. A modified SLM approach based on time-domain sub-block conversion matrices to reduce the computational complexity due to multiple IFFTs. This scheme is modified from the conversion matrix scheme. By dividing the frequency-domain signals into multiple sub-blocks, the number of the valid conversion matrices can be increased, and thus more candidate signals are available for PAPR reduction. By applying proposed scheme, the number of candidate signals can be increased from 12 in the original conversion matrix scheme to 28 and 128 for the two sub block and four-sub block cases, respectively. The scheme will provide improved PAPR reduction performance.

CMOS Saturated Power Amplifier With Dynamic Auxiliary Circuits for Optimized Envelope Tracking

A CMOS saturated power amplifier (PA) is developed for optimally implementing the envelope-tracking (ET) transmitter. The CMOS saturated PA is used to maximize the efficiency of the ET PA. The dynamic feedback control and the biasing techniques at the gates of the common-gate stage and the common-source of the cascode structure are proposed to improve the dynamic range, linearity and efficiency. The fully-integrated CMOS PA with a supply modulator is fabricated using a 0.18- μm RF CMOS technology. For a long-term evolution signal at 1.85 GHz with a 10-MHz bandwidth and a 16-quadrature amplitude modulation 7.5 dB peak-to-average power ratio, the ET-based CMOS PA module delivers a power-added efficiency of 37.6%, an error vector magnitude of 2.4%, and an an evolved universal terrestrial radio access adjacent channel leakage ratio (ACLRE-UTRA) of -36.8 dBc at an average output power of 26.5 dBm. The proposed auxiliary circuits enable the ET-based CMOS PA to provide the significantly improved performance.

Four-Way Microstrip-Based Power Combining for Microwave Outphasing Power Amplifiers

A lossless multi-way outphasing and power combining system for microwave power amplification is presented. The architecture addresses one of the primary drawbacks of Chireix outphasing; namely, the sub-optimal loading conditions for the branch power amplifiers. In the proposed system, four saturated power amplifiers interact through a lossless power combining network to produce nearly resistive load modulation over a 10:1 range of output powers. This work focuses on two microstrip-based power combiner implementations: a hybrid microstrip/discrete implementation using a combination of microstrip transmission line sections with discrete shunt elements, and an all-microstrip implementation incorporating open-circuited radial stubs. We demonstrate and compare these techniques in a 2.14 GHz power amplifier system. With the all-microstrip implementation, the system demonstrates a peak CW drain efficiency of 70% and drain efficiency of over 60% over a 6.5-dB outphasing output power range with a peak power of over 100 W. We demonstrate W-CDMA modulation with 55.6% average modulated efficiency at 14.1 W average output power for a 9.15-dB peak to average power ratio (PAPR) signal. The performance of this all-microstrip system is compared to that of the proposed hybrid microstrip/discrete version and a previously reported implementation in discrete lumped-element form.

Fully Integrated CMOS Saturated Power Amplifier With Simple Digital Predistortion

A highly efficient CMOS saturated power amplifier (PA) is implemented. The efficiency is enhanced by the voltage waveform engineering using the second harmonic component generated by the nonlinear output capacitor (C out ). For an improved linearity to satisfy the specification of handset applications, a simple open-loop digital predisortion algorithm is employed. The fully integrated single-stage differential PA including the output transformer is fabricated using a 0.18- μm CMOS process. The PA with 3.5 V supply delivers good performance across the 1.7-2.0 GHz frequency band.

A CMOS Envelope-Tracking Transmitter With an On-Chip Common-Gate Voltage Modulation Linearizer

This letter presents a fully integrated CMOS envelope-tracking transmitter with an on-chip common-gate voltage modulation linearizer that achieves an average output power of 26/23.5 dBm with a PAE of 33/28%, an ACLR of -33 / -32.5 dBc at a frequency of 1.9 GHz for 3.84 MHz BW 3.5 dB PAPR WCDMA and 5 MHz BW 7.5 dB PAPR LTE signals in an 0.18-μm CMOS process. The CMOS ET transmitter is integrated with an envelope amplifier, two pairs of saturated power amplifiers, and an on-chip linearizer. The total chip size is 2.5 × 1.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with the input/output on-chip transformers and matching networks.

Broadband Saturated Power Amplifier With Harmonic Control Circuits

This letter presents a broadband saturated power amplifier (PA) using the harmonic control circuits for base station application. The saturated PA has advantages for broadband operation with high efficiency due to the large tolerance of the second harmonic tuning. However, it is difficult to simultaneously achieve the fundamental and second harmonic impedance matching across a wide bandwidth. To solve the problem, the harmonic control circuits are placed at the input and output of the device's die. These harmonic control circuits play a role of leading the second harmonic impedances to the optimum regions but are specially designed to be insensitive to the following fundamental matching circuit. The saturated PA with the harmonic control circuit is designed using a 120 W GaN device, achieving a high efficiency and wide bandwidth characteristics simultaneously. The measured output power, drain efficiency, and gain are at least 51.0 dBm, 71.0%, and 8.22 dB at the saturation across the 1.75 to 2.17 GHz (21% relative bandwidth) under pulse test (10% duty). This saturated PA also delivers good performances for long term evolution (LTE) and wideband code division multiple access (WCDMA) modulated signals at 1.85 and 2.14 GHz, respectively. These results show that the broadband saturated PA with the harmonic control circuit is suitable to wide bandwidth multimode/multiband applications.

Interplex for Constant Envelope in LEO Satellite Communication System

In modern LEO satellite communication systems, numerous singnals have to be located in a same frequency band because of limited spectrum resources. Thus, a bandwidth-efficient modulation, which has constant envelope characteristics and can alleviate signal distortions when using saturated power amplifiers is necessary to combine several signals to share the frequency resource. This paper presents the analytic interplex modulation expression in LEO satellite spread spectrum communication systems, and obtains the relationship of modulation efficiency, error rate and power ratio. Lastly, the appropriate choice of power radio is obtained in the case of three signals or four signals multiplexing. The work of this paper is an important guideline for constant envelope combined methodologies in LEO satellite spread spectrum communication systems.

Highly Efficient Saturated Power Amplifier

In this article, a high-efficiency saturated amplifier has been presented. This amplifier takes advantage of the nonlinear output capacitor to shape the voltage waveform. The nonlinear capacitor generates substantial second harmonic voltage with small higher order harmonics. Thus, using √2 times larger fundamental load and the proper second harmonic termination, the resultant voltage waveform can be half-sinusoidal. For high efficiency, the PA should be driven by the large input power. Therefore, the current of the PA is bifurcated, resulting in the quasirectangular current shape. The resultant output waveforms are similar to those of class-F1 amplifiers, whose waveforms are optimal for high efficiencies. Based on harmonic source/ load-pull simulation, the saturated amplifier has been designed using Cree's GaN HEMT CGH40006P packaged model. The matching networks for the input and output were optimized using the Momentum simulator. The implemented amplifier delivered a PAE of 80.1% at 3.475 GHz. The simulation and measurement results verify that the saturated amplifier is suitable for a high-efficiency PA over a relatively high frequency band.

Switching Behavior of Class-E Power Amplifier and Its Operation Above Maximum Frequency

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 above maximum frequency, the charging process should be even faster but it cannot follow. Moreover, the discharging process is not sufficiently fast and further degrades the efficiency. The discharging process is assisted by the bifurcated current at saturation. The performance of the Class-E PA above the maximum frequency is enhanced by the nonlinear <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> , which helps to shape the voltage waveform. The bifurcated current itself cannot generate enough of a second-harmonic voltage component to shape the required voltage waveform. The performance of the Class-E PA can be further improved by a second-harmonic tuning and a conjugate matched output load, leading to the saturated PA. Compared with the Class-E PA, the saturated amplifier delivers higher output power and efficiency. A highly efficient saturated amplifier is designed using a Cree GaN HEMT CGH40010 device at 3.5 GHz. It provides a drain efficiency of 75.8% at a saturated power of 40.2 dBm (10.5 W).

A Multimode/Multiband Envelope Tracking Transmitter With Broadband Saturated Amplifier

A multimode/multiband envelope tracking (ET) transmitter consisting of a hybrid switching amplifier (HSA) and a broadband saturated power amplifier (PA) is developed for operation across 1.3 to 2.7 GHz. For the various standard signals with different bandwidth (BW) and peak-to-average power ratio, the HSA efficiently provides supply signals to the PA by changing the reference value of the hysteresis comparator. The saturated amplifier employs the nonlinear output capacitor to shape the voltage waveform, resulting in the half-sinusoidal or rectangular waveform. Since the nonlinear capacitor generates large out-of-phased second harmonic component with small higher order harmonics, the voltage shaping is mainly carried out by the capacitor and slightly supported by the harmonic loading circuit. Thus, with the harmonic load higher than that of output capacitor, the saturated amplifier can operate with high efficiency. This characteristic enables the saturated PA to operate with broadband characteristic and high efficiency because the design is mainly focused on the fundamental matching problem while the harmonics can be easily kept out of a low efficiency region through the subsequent optimization of the matching circuit. The broadband saturated PA is implemented based on load/source-pull methodology. The broadband matching networks for the high efficiency are synthesized using the simplified real frequency technique. For the BW from 1.3 to 2.7 GHz (70% fractional BW), the measured output power, drain efficiency, and power-added efficiency (PAE) performances are between 39.8-42.0 dBm, 55.8-69.7%, and 51.2-65.3%, respectively. The multimode/multiband ET transmitter with the designed broadband saturated PA is demonstrated at 1.8425-GHz long-term evolution (LTE), 2.14-GHz wideband code division multiple access (WCDMA), and 2.6-GHz mobile world wide interoperability for microwave access (m-WiMAX) applications. This transmitter delivers a PAE of 32.16, 37.24, and 28.75% for LTE, WCDMA, and m-WiMAX applications.

Saturated Power Amplifier Optimized for Efficiency Using Self-Generated Harmonic Current and Voltage

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 voltage peaking. These waveforms are similar to those of a class F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The fundamental load at the intrinsic device is resistive with the output capacitance tuned out, which is identical to the class F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> case. However, the required harmonic impedances are just larger than the impedance levels of the output capacitance for both the second and third harmonics. Therefore, the circuit topology is similar to that of a class E amplifier, which is very simple. The PA implemented using a GaN HEMT delivers the expected good performance using the simple circuit topology.