The auxiliary envelope tracking RF power amplifier system

The advancement of the mobile communication industry increases the need for RF power amplifier (RFPA) to be more efficient and linear. The communication network that is shifting towards smaller micro-cell or nano-cell network has also motivated the design of the RF power amplifier to be simple, compact and cost efficient. In this research work, a novel technique for efficiency and linearity improvement of the RFPA is presented. A simplistic approach in the technique called ‘Auxiliary Envelope Tracking' (AET) system has promoted the design for small and straightforward AET tracking generator, a key component in the system. The use of low cost components in the AET tracking generator has made the technique commercially attractive. The AET technique proposes a separation in generating DC and AC components of the AET signal that biases the drain of the RFPA. The separation eases the generation of the signals resulting in low power consumption that leads to efficiency improvement. The investigation of the gain characteristic of gallium nitride (GaN) RFPA has shown an important RFPA attribute where the gain varied substantially as the drain voltage increases. By using the AET technique, the gain characteristic is harnessed to get linearity improvement. In order to validate the technique, AET measurement systems for two-carrier and WCDMA signals were developed and experimented. A special Class AB RFPA is designed and implemented to use dedicatedly for this investigation. In two-carrier signal measurement, a tracking generator is developed that consists of an envelope amplifier (EA) and a diplexer. The RFPA and the tracking generator are then combined to be an integrated AET block. In order to accommodate the high peak-toaverage ratio (PAR) and high bandwidth WCDMA signal, a broadband RF transformer was designed as part of the AET tracking generator to replace the diplexer. The two-carrier and WCDMA signals measurement results have proven that the AET technique is a valid technique for efficiency and linearity improvement. The improvements were achieved with simple, compact and cost-effective implementation.

[1]  Peter M. Asbeck,et al.  RF and Microwave Power Amplifier and Transmitter Technologies — Part 4 , 2003 .

[2]  Rowan. Gilmore,et al.  Practical RF Circuit Design for Modern Wireless Systems: Active Circuits and Systems, Vol. 2 , 2003 .

[3]  David R. Cox,et al.  Linear Amplification with Nonlinear Components , 1974, IEEE Trans. Commun..

[4]  J. Moon,et al.  High-Efficiency Hybrid EER Transmitter Using Optimized Power Amplifier , 2008, IEEE Transactions on Microwave Theory and Techniques.

[5]  A. Sedra Microelectronic circuits , 1982 .

[6]  M. Marchetti,et al.  A 90-W Peak Power GaN Outphasing Amplifier With Optimum Input Signal Conditioning , 2009, IEEE Transactions on Microwave Theory and Techniques.

[7]  Jangheon Kim,et al.  Power Efficiency and Linearity Enhancement Using Optimized Asymmetrical Doherty Power Amplifiers , 2011, IEEE Transactions on Microwave Theory and Techniques.

[8]  P. J. Tasker,et al.  An efficient, linear, broadband class-J-mode PA realised using RF waveform engineering , 2009, 2009 IEEE MTT-S International Microwave Symposium Digest.

[9]  Joy Laskar,et al.  Comparison between Si-LDMOS and GaN-based microwave power transistors , 2002, Proceedings. IEEE Lester Eastman Conference on High Performance Devices.

[10]  S. Dimitrijev Principles of semiconductor devices , 2005 .

[11]  Frederick H. Raab,et al.  RF and Microwave Power Amplifier and Transmitter Technologies — Part 1 , 2003 .

[12]  Steve C Cripps,et al.  Rf power amplifier for wireless communications , 2014 .

[13]  W.H. Doherty,et al.  A New High Efficiency Power Amplifier for Modulated Waves , 1936, Proceedings of the Institute of Radio Engineers.

[14]  Manabu Kawabe,et al.  A Polar Loop Transmitter with Digital Interface including a Loop-Bandwidth Calibration System , 2007, 2007 IEEE International Solid-State Circuits Conference. Digest of Technical Papers.

[15]  Peter B. Kenington,et al.  High-Linearity RF Amplifier Design , 2000 .

[16]  Shawn P. Stapleton Adaptive FeedForward Linearization For RF Power Amplifiers , 2000, 55th ARFTG Conference Digest.

[17]  P. J. Tasker,et al.  Linearity improvement in RF power amplifier system using integrated Auxiliary Envelope Tracking system , 2011, 2011 IEEE MTT-S International Microwave Symposium.

[18]  P. J. Tasker,et al.  Linearity enhancement of GaN HEMTs under complex modulated excitation by optimizing the baseband impedance environment , 2011, 2011 IEEE MTT-S International Microwave Symposium.

[19]  F.H. Raab,et al.  Split-band modulator for Kahn-technique transmitters , 2004, 2004 IEEE MTT-S International Microwave Symposium Digest (IEEE Cat. No.04CH37535).

[20]  J.C. Pedro,et al.  An MMIC linearized amplifier using active feedback , 1993, IEEE 1993 Microwave and Millimeter-Wave Monolithic Circuits Symposium Digest of Papers.

[21]  H. B. Wood,et al.  Linear amplification using envelope feedback , 1971 .

[22]  F.H. Raab,et al.  Drive modulation in Kahn-technique transmitters , 1999, 1999 IEEE MTT-S International Microwave Symposium Digest (Cat. No.99CH36282).

[23]  Jinsung Choi,et al.  Optimization for Envelope Shaped Operation of Envelope Tracking Power Amplifier , 2011, IEEE Transactions on Microwave Theory and Techniques.

[24]  Richard C. Davis,et al.  An experimental M-QAM modem using amplifier linearization and baseband equalization techniques , 1982 .

[25]  T. Rahkonen,et al.  Design of a Linearly Assisted Switcher for a Supply Modulated RF Transmitter , 2006, 2006 NORCHIP.

[26]  M.N. Moghaddasi,et al.  Power amplifier linearization using feedforward technique for wide band communication system , 2009, 2009 IEEE International Symposium on Radio-Frequency Integration Technology (RFIT).

[27]  P. J. Tasker,et al.  Highly efficient operation modes in GaN power transistors delivering upwards of 81% efficiency and 12W output power , 2008, 2008 IEEE MTT-S International Microwave Symposium Digest.

[28]  Stanley H. Johnson,et al.  Use of Hammerstein Models in Identification of Nonlinear Systems , 1991 .

[29]  P. J. Tasker,et al.  The effect of baseband impedance termination on the linearity of GaN HEMTs , 2010, The 40th European Microwave Conference.

[30]  Youngoo Yang,et al.  Analog predistortion linearizer for high-power RF amplifiers , 2000, IMS 2000.

[31]  Jangheon Kim,et al.  Efficiency Enhancement of Doherty Amplifier Through Mitigation of the Knee Voltage Effect , 2011, IEEE Transactions on Microwave Theory and Techniques.

[32]  Narisi Wang,et al.  60% efficient 10-GHz power amplifier with dynamic drain bias control , 2004, IEEE Transactions on Microwave Theory and Techniques.

[33]  Michael Faulkner,et al.  Amplifier linearization using RF feedback and feedforward techniques , 1998 .

[34]  P. Asbeck,et al.  High-Efficiency Envelope-Tracking W-CDMA Base-Station Amplifier Using GaN HFETs , 2006, IEEE Transactions on Microwave Theory and Techniques.

[35]  D. C. Cox,et al.  Improving the Power-Added Efficiency of FET Amplifiers Operating with Varying-Envelope Signals , 1983 .

[36]  U. Mishra,et al.  AlGaN/GaN HEMTs-an overview of device operation and applications , 2002, Proc. IEEE.

[37]  Jau-Horng Chen,et al.  A Polar Transmitter Using Interleaving Pulse Modulation for Multimode Handsets , 2011, IEEE Transactions on Microwave Theory and Techniques.

[38]  Feipeng Wang,et al.  An Improved Power-Added Efficiency 19-dBm Hybrid Envelope Elimination and Restoration Power Amplifier for 802.11g WLAN Applications , 2006, IEEE Transactions on Microwave Theory and Techniques.

[39]  J. Lees,et al.  The benefit of GaN characteristics over LDMOS for linearity improvement using drain modulation in power amplifier system , 2011, 2011 Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits.

[40]  H. Chireix High Power Outphasing Modulation , 1935, Proceedings of the Institute of Radio Engineers.

[41]  Edward J. Powers,et al.  A new Volterra predistorter based on the indirect learning architecture , 1997, IEEE Trans. Signal Process..

[42]  Steve C. Cripps,et al.  Advanced Techniques in RF Power Amplifier Design , 2002 .

[43]  L.E. Larson,et al.  Design of wide-bandwidth envelope-tracking power amplifiers for OFDM applications , 2005, IEEE Transactions on Microwave Theory and Techniques.

[44]  Francois T. Assal,et al.  A technique for the maintenance of FET power amplifier efficiency under backoff , 1989, IEEE MTT-S International Microwave Symposium Digest.

[45]  Chul Soon Park,et al.  High-Efficiency Envelope-Tracking Transmitter With Optimized Class-${\hbox{F}}^{-1}$ Amplifier and 2-bit Envelope Amplifier for 3G LTE Base Station , 2011, IEEE Transactions on Microwave Theory and Techniques.

[46]  P. Draxler,et al.  Wideband Envelope Tracking Power Amplifiers With Reduced Bandwidth Power Supply Waveforms and Adaptive Digital Predistortion Techniques , 2009, IEEE Transactions on Microwave Theory and Techniques.

[47]  B. Vassilakis,et al.  Comparative analysis of GaAs/LDMOS/GaN high power transistors in a digital predistortion amplifier system , 2005, 2005 Asia-Pacific Microwave Conference Proceedings.

[48]  Michael Murray. Elliott Single sideband transmission by envelope elimination and restoration. , 1953 .

[49]  Changsoo Eun,et al.  Design for Nonlinearity Preceded by a System a Memory-less Dynamic Linear , 1995 .

[50]  J.A. Cobos,et al.  Switching capacities based envelope amplifier for high efficiency RF amplifiers , 2010, 2010 Twenty-Fifth Annual IEEE Applied Power Electronics Conference and Exposition (APEC).

[51]  Lawrence E. Larson,et al.  Design of linear RF outphasing power amplifiers , 2003 .

[52]  D. Pozar Microwave Engineering , 1990 .

[53]  Risto Kaunisto,et al.  A 20-W Chireix Outphasing Transmitter for WCDMA Base Stations , 2007, IMS 2007.

[54]  Dai Qingyun Power Amplifier Linearization Technique based on Pre-distortion Principle and Wiener model , 2010 .