Conventional Power Amplifier Research Articles

High-Efficiency Hybrid EER Transmitter Using Optimized Power Amplifier

This paper describes a new design approach for a power amplifier (PA) of the highly efficient hybrid envelope elimination and restoration (H-EER) transmitter. Since the PA operates mostly at the average power region of the modulation signal, power-added efficiency (PAE) of the PA at the average drain voltage is very important for the overall transmitter PAE. Accordingly, the PA is designed to have a maximum PAE in that region. The performances of the proposed PA and a conventional PA under H-EER operation are evaluated via ADS and MatLab simulations using a behavioral large-signal model of a silicon LDMOSFET, which verifies that the proposed PA has significant advantages for the H-EER transmitter in both PAE and output power. A saturated amplifier, inverse class F, has been implemented using a 5-W peak envelope power LDMOSFET for 3GPP forward-link single-carrier wideband code-division multiple-access at 1 GHz with a peak-to-average power ratio of 9.8 dB. An envelope amplifier is built that has an efficiency of above 68% and peak output voltage of 31 V for an interlock experiment. The overall PAE of the transmitter with a conventional PA is 35.5% at an output power of 29.2 dBm. On the other hand, the transmitter with the proposed PA delivers significantly improved performances: PAE increased by 4% and output power by 2.5 dB. The H-EER transmitter has been linearized by the digital feedback predistortion technique. The measured error vector magnitude is reduced to 1.47% from 6.4%. These results clearly show that the proposed architecture is a good candidate for efficient linear transmitters.

Novel Tracking Power Supply for Linear Power Amplifiers

Conventional linear power amplifiers (LPAs) show a high output voltage quality but are characterized by high power losses and/or low power density. Therefore, there is a growing interest in increasing the efficiency of LPAs, e.g., for the realization of high power testing voltage sources. In this paper, a high-frequency isolated boost-type tracking power supply (TPS) system is proposed for the conditioning of the input voltage of an LPA. The output voltage of the TPS is varied according to the voltage to be formed by the LPA so that the voltage drop across the power amplifier output transistors is reduced to low values. This results in a significant increase of the total system efficiency. The operating principle of the proposed system is described. A design method for the output filter using the power supply rejection ratio of the LPA is proposed. This method ensures that the amplifier output voltage has minimal switching frequency components. Furthermore, a control system design method is presented that ensures good performance in the control of the constant inductor current of the switch-mode tracking stage. Finally, the theoretical considerations are verified by measurements on a 1-kW laboratory prototype.

A 2-GHz GaAs HBT RF Pulsewidth Modulator

RF pulsewidth modulation (PWM) has been proposed as an efficiency improving technique for power amplifiers (PAs) handling varying envelope signals. The core idea is to modulate the varying envelope into a square-wave signal such that the width of each pulse is varied according to the envelope, and any phase information is contained in the timing of the pulses. The square wave signal can give a theoretical efficiency of 100% for the subsequent PA. Such a system differs significantly from a conventional up-conversion and PA and, therefore, a significant design challenge results. The first important step is to generate the PWM signal. This paper demonstrates a functional modulator for Universal Mobile Telecommunications System operating at 2 GHz. The modulator is designed in a GaAs HBT process and uses low-frequency feedback combined with predistortion to obtain a high spectral purity. Measurements show a Universal Mobile Telecommunications System PWM signal with more than 10-dB margin to the modulation mask and an error vector magnitude of less than 1.5% rms (requirement: 17.5%).

Application notes - Broadband and compact impedance transformers for microwave circuits

Most microwave circuits and antennas use impedance transformers. In a conventional power amplifier, large number of inductors and capacitor or transmission line sections are use to realize an impedance transformer. This article presents an asymmetric broadside-coupled microstrip TLT (transmission line transformer) on the GaAs substrate. This matching network can be easily implemented using any monolithic microwave integrated circuit (MMIC) process supporting multilevel metallization

A new adaptive delay method for wideband wireless Kahn's RF power amplifiers

This paper presents an adaptive delay control method used in wideband Kahn's envelope elimination and restoration (EER) RF power amplifiers (PAs). Besides control circuits, envelope and phase signals are also implemented by baseband digital signal processing (DSP) technique. It avoids using not only nonlinear limiter and envelope detector, but also difficult RF delay module or complicated feedback loop, each of which is necessary in conventional EER PA's structure. With the help of applying phase detector, counter, and latch register, the delay varies adaptively with circuit parameters, and then the new PA maintains performance at all times. With the application of this method we can realize a PA applicable to IEEE 802.11b standard with 11 MHz signal bandwidth, of which adjacent channel power ratio (ACPR) is better than -40 dBc at the first side lobe

A novel diode linearizer for SiGe HBT power amplifier

In this paper, a novel diode linearizer to keep the base voltage of SiGe HBT power amplifier (PA) constant in the large-signal region is introduced. The results show that the output P1dB, and power-added efficiency (PAE) are improved by 4.9 dBm and 22.8%, respectively. At an input power of 20 dBm, the gain compression and phase distortion of the linearized PA is 2.1 dB and 1.1°, respectively, compared with 5.0 dB and 20.4° for the conventional PA. Also, the improved ACPR is given.© 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1535–1537, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21681

Novel Band-Reconfigurable High Efficiency Power Amplifier Employing RF-MEMS Switches

A novel scheme for a multi-band power amplifier (PA) that employs a low-loss reconfigurable matching network is presented and discussed. The matching network basically consists of a cascade of single-stub tuning circuits, in which each stub is connected to a transmission line via a Single-Pole-Single-Throw (SPST) switch. By controlling the on/off status of each switch, the matching network works as a band-switchable matching network. Based on a detailed analysis of the influence of non-ideal switches in the matching network, we conceived a new design perspective for the reconfigurable matching network that achieves low loss. A 900/1900-MHz dual-band, 1 W class PA is newly designed following the new design perspective, and fabricated with microelectro mechanical system (MEMS) SPST switches. Owing to the new design and sufficient characteristics of the MEMS switches, the dual-band PA achieves over 60% of the maximum power-added efficiency with an output power for each band exceeding 30dBm. These results are comparable to the estimated results for a single-band PA. This shows that the proposed scheme provides a band-switchable highly efficient PA that has superior performance compared to the conventional multi-band PA that has a complex structure.

Power amplifier with low average current and compact output matching network

A power amplifier with a compact output matching network and a high average operating efficiency owing to its control circuits which enable the dynamic control of the quiescent current is presented. The microwave monolithic integrated circuit of the power amplifier was designed and implemented, in order to verify the output matching network and control circuits for the 1.88-GHz band. The power-added efficiency for an average power-usage of the proposed amplifier is almost twice that of conventional power amplifiers (3.74% versus 6.86%) in urban areas.

Transceive surface coil array for magnetic resonance imaging of the human brain at 4 T

As the static magnetic field strength used in human magnetic resonance imaging increases, the wavelength of the corresponding radiofrequency field becomes comparable to the dimensions of the coil and volume of interest. The dielectric resonance effects that arise in this full wavelength regime may be partially compensated for through the use of surface coils. A novel high-field (4 T) transceive surface coil array is presented that allows arbitrary surface coil placement and size while maintaining the ability to independently transmit and/or receive through conventional 50-ohm power amplifiers and preamplifiers, respectively. A ninefold signal-to-noise ratio (SNR) increase is shown in close proximity to the transceive array and there is an overall 38% increase throughout the entire brain volume in comparison to the standard hybrid birdcage coil. Furthermore, the ability to independently transmit and receive through each surface coil within this array enables transmit and/or receive-only fast parallel imaging techniques to be employed while maintaining the increased SNR sensitivity inherent to surface coil designs.

Noise properties of a NMR transceiver coil array

The use of multiple radiofrequency (RF) surface coil elements has applications in both fast parallel imaging and conventional imaging techniques. Through implementation of a simple magnetic decoupling network, 50 Ω matching can be achieved in both the transmitter and receiver chains, enabling the use of conventional RF power amplifiers and preamplifiers for transceive applications. Unlike phased array coil arrangements using low impedance preamplifiers for decoupling, the noise correlation between 50 Ω coils decoupled with discrete components has not been characterized. We have measured the dependence of coil quality factor (Q-factor) and noise correlation on coil separation and shown these quantities to be consistent with theoretical arguments, at least at 4 T (170 MHz). Our results suggest that a coil system for transmission and reception of NMR signals with 50 Ω coils can be built to take advantage of all the benefits of conventional array coils and with the added advantages of using conventional amplifiers.

Improved doubly electromagnetic periodic structure (DEPS) for microwave power amplifier application

AbstractIn this paper, we propose an improved doubly electromagnetic periodic structure (DEPS) and apply it in a power amplifier for harmonic tuning. The DEPS power amplifier shows an improvement of 0.5 dB and 8% in output power and power‐added efficiency (PAE), respectively, compared with the conventional EPS power amplifier. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 342–344, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11209

Thin-film inductor for gigahertz band with CoFeSiO-SiO/sub 2/2 multilayer granular films and its application for power amplifier module

The thin-film power amplifier module for wide-band code division multiple access was designed and fabricated using the magnetic thin film as magnetic core of choke inductors. CoFeSiO-SiO/sub 2/ multilayer granular films showing high resistivity and good magnetic properties were applied to the module. Inductance value increased about 30% by application of magnetic films, and occupation area and series resistance were also reduced by 20%. The obtained module size was 3.0 mm /spl times/ 3.5 mm, which was much smaller than the conventional power amplifier module, since the bias circuit was formed on the same silicon substrate.

Power-amplifier module with digital adaptive predistortion for cellular phones

This paper describes a new type of power amplifier (PA) module with a predistortion function and can be applied to a N-CDMA (narrow-band CDMA system defined in IS-95B Standard) handset terminals. Distortion compensation technology to improve the efficiency of the PA is discussed, quantitatively. Various parameters to be considered in designing are investigated in detail. The predistortion technology proposed is based on the lookup-table method using the input and output signal envelopes and can operate independently from the baseband block. By omitting adaptative predistortion for amplitude/phase modulation and integrating the main controlling functions on a single CMOS integrated-circuit chip, the predistortion capability has been realized in a PA module. The PA module has a power-added efficiency (PAE) of 48% at an output power of 27.5 dBm. This PAE is very high in comparison with that of the conventional PA module for N-CDMA.

Special Issue Ceramics Integration. Advanced Microwave Integrated Circuits with Ceramic Integration Technologies.

The highly integrated monolithic microwave power amplifier module for W-CDMA (wideband code division multiple access) cellular phones were designed and fabricated taking advantage improvements in microwave materials and new developments in processing methods of thin films for applications in decoupling capacitors and choke inductors. The obtained module is ultimately downsized into 3.0mm by 3.5mm with 0.5mm in thickness. The volume is about 10 times smaller than that of the ceramic chip components assembled conventional power amplifier module.

Arbitrary wave-form-pulsed power source for flash-lamp-pumped solid-state lasers

An arbitrary wave-form-pulsed power source for driving pulsed flash lamps electrically to pump quasi-continuous-wave Nd:YAG lasers has been developed. It is based on a high-frequency switching converter as opposed to conventional pulse-forming network or linear power amplifier circuit-based pulse generators. The system can generate rectangular pulses through the flash lamp with fine adjustment in pulse parameters over a wide range. The system can also generate an arbitrary-shaped pulsed current within a bandwidth of 500 Hz. The design of the system and the results in the form of rectangular- and arbitrary-shaped pulsed-current wave forms with different pulse parameters are presented. In addition, a burst of consecutive pulses with different arbitrary shapes can also be generated as desired or as programed. The developed pulsed power source offers advantages of more flexibility in control and adjustment of output pulse parameters, arbitrary-shaped pulse generation, better efficiency, compactness, and higher reliability as compared to the pulsed power sources based on normal schemes. The electronic system developed is of immense value in studying the dependence of flash-lamp impedance, spectral output, and energy-transfer efficiency on pulse parameters as well as optimization of these parameters for use in various laser material processing applications.

Intermodulation distortion in Kahn-technique transmitters

The Kahn Envelope Elimination and Restoration (EER) technique implements a linear RF power amplifier (PA) by combining nonlinear, but efficient, RF and AF power amplifiers. For signals with high peak-to-average ratios, the average efficiency of a Kahn-technique transmitter can be three to four times that of a transmitter that employs conventional linear RP PAs. Since switching-mode amplifiers are employed, the linearity of an EER transmitter depends upon parameters such as the bandwidth of the envelope modulator and the differential delay between envelope and phase signals. This paper determines the relationship between these parameters and IMD levels and verifies the predictions by laboratory measurements. The results can be used to determine the requirements for the components of a Kahn-technique transmitter.

Efficiency of Doherty RF Power-Amplifier Systems

A Doherty system combines the outputs of two or more linear RF power amplifiers (PAs) through an impedance-inverting coupler such as a quarter-wave transmission line. At low output levels, the first PA operates linearly, reaching saturation (and maximum efficiency) at some transition voltage below the system peak-output voltage. At higher output levels, the first PA remains saturated and the second PA operates linearly. The instantaneous efficiency and power characteristics of a Doherty system are derived using ideal class-B RF PAs so that the results can easily be scaled for use with real-world PAs. The average efficiency and maximum-efficiency transition points are then determined for a variety of amplitude-modulated signals. The Doherty amplifier can be considerably more efficient than a conventional class-B linear PA. For example, the 28-and 8.9-percent average efficiencies of a class-B PA with Rayleigh-distri buted envelopes with 10-and 20-dB peak-to-average ratios are improved to 60 and 48 percent, respectively, by a two-stage Doherty system. The addition of a third stage further improves the efficiencies to 70 and 66 percent, respectively.

A High-Efficiency Audio Power Amplifier Using a Self-Oscillating Switching Regulator

A new high-efficiency audio power amplifier has been developed. This amplifier consists of a conventional power amplifier and a self-oscillating switching power supply which is arranged to vary the power supply output voltage according to the input signal voltage. The new amplifier achieves a higher efficiency than the conventional amplifier, by making the collector voltage of the emitter-follower-transistor follow the waveform of the output signal. Applying this idea to class A amplifiers, a one-third power dissipation can be achieved compared with the conventional class A amplifier. A power MOSFET is used as a switcher. The switching frequency is from 150 kHz to 300 kHz. The new amplifier shows sufficient favorable characteristics. Switching noise is suppressed to a low noise level, which has no influence on the AM tuner or other audio equipment. By stabilizing the single-ended push-pull (SEPP) output transistors, the amplifier can reproduce high quality tone. The present idea is also applicable to dass B power amplifiers and may be suitable for PA or car audio power amplifiers.

The Super-Soc

A new concept in cyclic particle accelerators is described in which time harmonic accelerating fields are produced without recourse to conventional power amplifiers. Instead, the accelerating fields are produced by extracting energy from a bunched beam of particles. In essence the new machine consists of two intimately connectbd Separated Orbit Cyclotrons, one of which is operated in the decelerating mode. The decelerating particles obtain their energy initially from a D. C. high voltage supply.