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ABSTRACT: This letter presents a 44 GHz GaAs MMIC-based power amplifier (PA) which uses envelope tracking (ET) techniques for efficiency enhancement. Digital pre-distortion (DPD) is also employed to achieve high linearity. For a 7.6 dB PAPR 64QAM 20 MHz bandwidth signal (data rate 120 Mb/s) at an output power of 23.8 dBm, the measured EVM was 2.0% and ACPR1 was better than -40 dBc. Power efficiency enhancement of more than 5.7 times for the final MMIC stage (from 1.22% to 7%) was measured, using an external drain modulator. To the authors' best knowledge, this is the first time envelope tracking has been applied to PAs in the millimeter wave regime.
IEEE Microwave and Wireless Components Letters 04/2011; · 1.72 Impact Factor
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ABSTRACT: This work discusses wideband high efficiency envelope tracking (ET) power amplifiers using GaN high electron mobility transistors (HEMTs) to achieve high gain and high efficiency with good linearity. The performances of two ET amplifiers using the same GaN RF device and envelope voltages of 30-V peak and 45-V peak are compared experimentally. With the higher dynamic voltage swing (45-V case), a considerably higher PAE was obtained, as well as a higher gain. For a WCDMA signal with 7.7 dB peak-to-average ratio (PAR) and 3.84 MHz bandwidth, the 45-V peak envelope tracking amplifier shows an overall drain efficiency above 50 % at an average output power above 30 W and a gain of 13.7 dB. The result was achieved with a normalized RMS power error below 3 % and an ACPR1 of -45.2 dBc using memory-less digital predistortion. By comparison, the PAE achieved with the 30-V peak envelope tracking amplifier was 45 %, and the gain was 10.8 dB, with a similar linearity performance. The improved results can be understood on the basis of loss minimization from device on-resistance.
Power Amplifiers for Wireless and Radio Applications (PAWR), 2011 IEEE Topical Conference on; 02/2011
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ABSTRACT: A wideband high dynamic range frequency hopping transceiver is presented for the Joint Tactical Radio System (JTRS) project at the University of California, San Diego. The transceiver utilizes radio frequencies (RF) from 200 MHz to 3.2 GHz and provides a 78 dB maximum dynamic range. The rapid frequency hopping local oscillator (LO) is achieved by Direct Digital Synthesis (DDS) and successive frequency multiplications.
MILITARY COMMUNICATIONS CONFERENCE, 2010 - MILCOM 2010; 12/2010
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ABSTRACT: A radial power-combiner design is presented using broadband probes and a radial cavity configuration. The 8:1 combiner (which can also be used as a power divider) is demonstrated experimentally in both single-ended and differential configurations. The broadband probe is composed of cylindrical conductors and dielectric spacers, arranged on a rod for mechanical stability. The proposed radial power combiner provides low loss, broad bandwidth (800-1800 MHz), and high power capability.
IEEE Transactions on Microwave Theory and Techniques 07/2010; · 1.85 Impact Factor
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ABSTRACT: This paper presents a novel envelope amplifier architecture to improve the overall efficiency of wideband high linearity envelope tracking power amplifiers (PAs). We show here a technique to increase the efficiency of the envelope amplifier while maintaining the amplifier's bandwidth. The technique utilizes digital signal processing (DSP) control in conjunction with analog hysteretic feedback. Two high efficiency buck switching stages are coordinated to provide the wideband envelope power to the RF stage; a wide bandwidth linear regulator is also used at low power to maintain the envelope signal accuracy. The technique improves the efficiency of the envelope amplifier, especially for applications requiring high peak-to-average power ratio (PAPR) with wide bandwidth signals. The overall system was demonstrated using a GaAs high voltage HBT PA. For a variety of signals ranging from 6.6dB to 9.6dB PAR and up to 10MHz bandwidth, the overall system PAE reached above 50%, with a normalized power RMS error below 5% and ACLR1 of -50dBc with memory-less digital predistortion, at an average output power above 19W and gain of 10dB. The efficiencies obtained are the best ever reported, to our knowledge, for envelope tracking base station amplifiers for these signals.
Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
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ABSTRACT: An improved very wideband radial waveguide-based power divider/combiner is presented, which uses switching to compensate for cavity resonance. The combiner is implemented with broadband probes composed of cylindrical conductors and dielectric spacers, arranged on a rod for mechanical stability. The proposed switch-controlled radial power combiner provides low loss (<;1 dB), broad bandwidth (400 MHz~2000 MHz), and high power capability.
Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
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ABSTRACT: This paper presents a new technique to reduce the peak-to-average power ratio (PAPR) of the RF input signals used in envelope tracking (ET) power amplifiers without degrading the linearity and efficiency performance of the RF stages. Due to heavy gain compression, ET amplifiers can suffer from inefficient driver stages. The reduced PAPR RF input signal improves the efficiency of the driver amplifier thereby potentially improving the overall efficiency of the ET amplifier. This technique is demonstrated for a single carrier WCDMA signal using a dynamic supply modulator and a RF stage based on a GaAs HVHBT. The measurement shows that a power added efficiency (PAE) of 74% can be maintained for the RF stage while the PAPR of the RF input signal is reduced from 7.6 dB to 5.2 dB. The overall PAE accounting for the supply modulator is greater than 50% with an average output power of greater than 26 W and an adjacent channel leakage ratio of less than -45 and -53 dBc at 5- and 10-MHz frequency offsets, respectively.
Radio and Wireless Symposium (RWS), 2010 IEEE; 02/2010
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ABSTRACT: This paper presents a new technique to reduce the bandwidth of the dynamic power supply waveform used in wideband envelope tracking power amplifiers (PAs). When the envelope tracking technique is applied to broadband signals such as WCDMA and 3GPP LTE, the wide bandwidth of the envelope signal makes it difficult to implement the dynamic supply modulator efficiently and accurately. We show here a technique to reduce the bandwidth of the power supply waveform, thereby allowing better efficiency for the supply modulator; and a linearization method for correcting the nonlinearity caused by the bandwidth reduction. The feasibility of this technique is demonstrated for a single carrier WCDMA signal with a 7.6-dB peak-to-average power ratio using a GaAs high-voltage HBT PA. The bandwidth of the power supply waveform is reduced from 20 to 4 MHz. After linearization, the reduced bandwidth envelope tracking PA exhibits an average output power of 28 W, an average gain of 12 dB and an overall power-added efficiency of 49%. The measured normalized rms error is as low as 0.67% with an adjacent channel leakage ratio of -53.9 and -54.2 dBc at offset frequencies of 5 and 10 MHz, respectively.
IEEE Transactions on Microwave Theory and Techniques 01/2010; · 1.85 Impact Factor
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ABSTRACT: This paper presents an improved broadband balun using a coplanar-waveguide (CPW)-to-slotline field transformation. It operates at very wide frequency, and is of compact size since it does not depend on a resonant structure. The measured results show a passband of 200 MHz to 2 GHz, insertion loss less than 0.75 dB and a size of 20 mm × 14 mm. The amplitude imbalance is approximately 0.3 dB and the phase imbalance is less than 6° over the entire operation range.
Microwave Conference, 2009. EuMC 2009. European; 11/2009
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ABSTRACT: A record high-performance GaAs high-voltage HBT (HVHBT)-based WCDMA base-station power amplifier is presented, which uses an envelope tracking bias system to achieve high efficiency and linearity. A wideband envelope amplifier provides dynamic collector supply biasing to the RF stage. A digital pre-distortion technique is employed to satisfy the linearity specifications of WCDMA. The measured overall power-added efficiency reached 58% with a normalized root-mean-square (RMS) error of 2.9% and an adjacent channel leakage ratio (ACLR) of -49 dBc at 5-MHz offset at an average output power of 42 W and a gain of 10.3 dB for a single carrier WCDMA signal with 6.6-dB peak-to-average power ratio. A memory mitigation algorithm further improves the linearity, resulting in an ACLR of -70 dBc and a normalized RMS error of 0.3%. Measurements were made to quantify separately the efficiency contributions of the HVHBT-based RF stage, and of the envelope amplifier. The measurements show that the RF stage operates at collector efficiency above 85% over most of the instantaneous power range of the WCDMA signal. This remarkably high efficiency is the result of low ldquoon-resistancerdquo and low (and nearly voltage independent) output capacitance of the HVHBT.
IEEE Journal of Solid-State Circuits 11/2009; · 3.23 Impact Factor
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ABSTRACT: Wideband code division multiple access (WCDMA) base-station RF amplifiers using a variety of device technologies including GaN field-effect transistors (FETs), Si LDMOS, and GaAs high-voltage heterojunction bipolar transistors (HVHBTs) are modeled, optimized, and compared for use in wideband envelope tracking (ET) system. A quasi-static approach is employed to effectively model the supply-modulated RF amplifiers, and thus facilitate the design optimization process. A new design methodology for ET RF amplifiers is introduced including identification of optimum fundamental and harmonic terminations. The fundamental and harmonic impedances have been successfully optimized for various RF devices and good agreement has been achieved between the simulation and measurement results. Among the modeled and measured ET RF amplifiers, a GaAs HVHBT exhibits the best overall efficiency of 60% with an average output power of 33 W and a gain of 10 dB for a WCDMA signal with 3.84-MHz bandwidth and 7.7-dB peak-to-average power ratio, while meeting all linearity requirements of the WCDMA standard. Desirable device characteristics for optimum ET operation are also discussed.
IEEE Transactions on Microwave Theory and Techniques 10/2009; · 1.85 Impact Factor
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ABSTRACT: This paper presents a new technique to reduce the bandwidth of the dynamic power supply waveform for use in wideband envelope tracking power amplifiers (PAs). When the envelope tracking technique is applied to the broadband signals such as WiMAX and LTE, the wide bandwidth of the envelope signal makes it difficult to implement the dynamic power supply efficiently and accurately. We show here for the first time a technique to reduce the bandwidth of the dynamic power supply voltage, thereby allowing better efficiency for the dynamic power supply; and a linearization method for correcting the nonlinearity caused by the bandwidth reduction. The feasibility of this technique is demonstrated for a single carrier WCDMA signal with 7.8-dB PAPR using a GaAs HVHBT PA. The bandwidth of the power supply signal is reduced from 20 MHz to 5 MHz. After linearization, the reduced bandwidth envelope tracking PA exhibits an average output power of 25 W, an average gain of 13 dB and an overall power-added efficiency of 50%. The measured normalized RMS error is as low as 3.98% with an adjacent channel leakage ratio of -41 dBc and -48 dBc at offset frequencies of 5 MHz and 10 MHz, respectively.
Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International; 07/2009
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ABSTRACT: Due to dynamic changes of supply voltage, envelope-tracking (ET) power amplifiers (PAs) exhibit very distinct characteristics in different power regions. It is very difficult to compensate the distortion induced by these amplifiers by employing conventional digital predistortion techniques. In this paper, by introducing a new piecewise Volterra model based on a vector threshold decomposition technique, we first set several thresholds in the input power level according to the PA characteristics, and decompose the input complex envelope signal into several sub-signals by using these thresholds. We then process each sub-signal separately by employing the dynamic deviation reduction -based Volterra series, and finally recombine them together to produce the predistorted output. Experimental results show that by using this new decomposed piecewise digital predistorter model, the distinct characteristics of the ET system at different signal power levels can be accurately modeled, and thus, the distortion, including both static nonlinearities and memory effects, caused by the amplifier nonlinear behavior can be effectively compensated.
IEEE Transactions on Microwave Theory and Techniques 11/2008; · 1.85 Impact Factor
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ABSTRACT: In this paper, we propose an efficient open-loop digital predistorter (DPD) derived from the dynamic deviation reduction-based Volterra series that allows compensation for both nonlinear distortion and memory effects induced by RF power amplifiers in wireless transmitters. In this approach, the parameters of the predistorter can be directly extracted from an offline system identification process. This eliminates the usual requirement for a closed-loop real-time parameter adaptation, which dramatically reduces the implementation complexity of the system. It is shown that a further reduction in system complexity can be achieved by applying under-sampling theory in the model extraction and utilizing parameter interpolation in the DPD implementation. Experimental results show that by utilizing this technique with only a small number of parameters, nonlinear distortion induced by the PA can be significantly reduced, as evaluated by both adjacent channel power ratio reduction and normalized root mean square error improvement. A comparison with a memoryless polynomial function based predistorter and an analysis of the impact of decresting are also presented.
IEEE Transactions on Microwave Theory and Techniques 08/2008; · 1.85 Impact Factor
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ABSTRACT: A monolithic SiGe BiCMOS envelope-tracking power amplifier (PA) is demonstrated for 802.11g OFDM applications at 2.4 GHz. The 4-mm<sup>2</sup> die includes a high-efficiency high-precision envelope amplifier and a two-stage SiGe HBT PA for RF amplification. Off-chip digital predistortion is employed to improve EVM performance. The two-stage amplifier exhibits 12-dB gain, <5% EVM, 20-dBm OFDM output power, and an overall efficiency (including the envelope amplifier) of 28%.
IEEE Journal of Solid-State Circuits 07/2007; · 3.23 Impact Factor
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ABSTRACT: A comparison of envelope elimination and restoration (EER) and envelope tracking (ET) is discussed and a "hybrid" wideband EER power amplifier (PA) for the WLAN 802.11g system is proposed. A 60% efficiency (the output envelope signal power/input dc power) DC-20-MHz wideband envelope amplifier is designed for wideband EER and wideband ET (WBET) applications. A design method is developed to optimize the efficiency of the envelope amplifier for a given peak-to-average ratio and average slew rate of the envelope signal. An experimental "hybrid" Class-E EER system shows an overall efficiency (modulated RF output power/envelope amplifier dc input power) of 36% and power-added efficiency (the modulated RF output power/envelope amplifier dc input power plus RF input power) of 28% for a WLAN 802.11g signal at 19-dBm (80 mW) output power at 2.4 GHz. Digital predistortion, time alignment, and memory effect mitigation are implemented. The measured 3% error vector magnitude exceeds the 802.11g specification for 5% for a 54-Mb/s modulation signal
IEEE Transactions on Microwave Theory and Techniques 01/2007; · 1.85 Impact Factor
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ABSTRACT: A high-efficiency wideband code-division multiple-access (W-CDMA) base-station amplifier is presented using high-performance GaN heterostructure field-effect transistors to achieve high gain and efficiency with good linearity. For high efficiency, class J/E operation was employed, which can attain up to 80% efficiency over a wide range of input powers and power supply voltages. For nonconstant envelope input, the average efficiency is further increased by employing the envelope-tracking architecture using a wide-bandwidth high-efficiency envelope amplifier. The linearity of overall system is enhanced by digital pre-distortion. The measured average power-added efficiency of the amplifier is as high as 50.7% for a W-CDMA modulated signal with peak-to-average power ratio of 7.67 dB at an average output power of 37.2 W and gain of 10.0 dB. We believe that this corresponds to the best efficiency performance among reported base-station power amplifiers for W-CDMA. The measured error vector magnitude is as low as 1.74% with adjacent channel leakage ratio of -51.0 dBc at an offset frequency of 5 MHz
IEEE Transactions on Microwave Theory and Techniques 12/2006; · 1.85 Impact Factor
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ABSTRACT: This paper demonstrates a two-stage 1.95-GHz WCDMA handset RFIC power amplifier (PA) implemented in a 0.25-μm SiGe BiCMOS process. With an integrated dual dynamic bias control of the collector current and collector voltage, the average power efficiency of the two-stage PA is improved from 1.9% to 5.0%. The measured power gain is 18.5 dB. The gain variation with dynamic biasing is less than 1.8 dB. An off-chip memoryless digital predistortion linearizer is also adopted, satisfying the 3GPP wideband code division multiple access (WCDMA) linearity specification by a 10 dB improvement of adjacent channel power ratio (ACPR) at +26 dBm average channel output power.
IEEE Journal of Solid-State Circuits 06/2006; · 3.23 Impact Factor
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ABSTRACT: An efficiency-enhanced power-amplifier system design is presented based on wide-bandwidth envelope tracking (WBET) with application to orthogonal frequency-division multiplexing wireless local area network systems. Envelope elimination and restoration (EER) and WBET are compared in terms of the time mismatch sensitivity between the base-band amplitude path and the RF path, and it is demonstrated that WBET is much less sensitive than EER to these effects. An adaptive time-alignment algorithm for the WBET system is developed and demonstrated. The analysis and algorithm are verified by experimental results. The measurement shows that the peak drain efficiency of the complete system was 30% at a 2.4-GHz orthogonal frequency-division multiplexing output power of 20 dBm.
IEEE Transactions on Microwave Theory and Techniques 05/2005; · 1.85 Impact Factor
