AP09_2.vp 1 Introduction Efficiency is a more and more critical issue when design- ing transmitters, both to save energy costs at the base station and to reduce the power consumption of mobile terminals to increase battery life. Efficiency boosting techniques tend to rely on switch-mode amplifiers (SMA). Conventional ampli- fier classes like A, AB, which offer high linearity at the cost of efficiency are avoided. The non-linearities caused by these amplifiers are compensated using envelope elimination and restoration (EER)[2] or vector addition (LINC) [1] techniques or both (CLIER) [5]. For implementation of a CLIER amplifier architecture a Class E amplifier is well suited both for the LINC and for the EER part. LINC consists of two non-linear amplifiers. The in- put signal, containing both amplitude a(t) and phase �(t) is transformed into two solely phase modulated signals with constant envelopes. Both non-linear amplified signals are vector combined at the output, resulting in an amplified rep- lica of the original time varying envelope signal. Additionally, the supply of the amplifiers is modulated with a slowly varying signal. This reduces the dynamics of the LINC signal and thereby increases the efficiency of the entire system. This paper focuses on the implementation of class E amplifiers. 2 Theory For lossless operation of the Class E amplifier there are two criteria that have to be met: First, zero voltage across the transistor terminals when the switch closes [4] u t ts c( )� �� � 0. (1) And, second, no voltage building across the transistor terminals while the switch is closed d d u t t ts c( )� �� � 0. (2) To obtain this non overlapping between voltage and cur- rent a complex load impedance is imposed on the switch output terminals, which results in a phase shift between cur- rent and voltage of the output signal. Fig. 1 shows a typical Class E circuit. The transistor is ideally replaced with a switch. The load network consists of a parallel capacitor C and an inductance L in series with a tuned output network L0C0 and load resistance R. When using a real transistor the capacitor C can comprise the intrin- sic transistor capacitance Cds and an external capacitance. An RF choke at the supply voltage enforces a DC supply current. The output tuning network L0C0 forces the current through the load resistance R to be a sinusoidal function of �t angular time and phase shift �. The current can be described as i t I tR R( ) sin ( )� � �� � . (3) Because the RF choke enforces a DC current IDC, the difference between output- and DC current flows into the switch-capacitance network. Initially, when the switch S is closed, the switch current is zero i ts( )� � �0 0. With (3), the DC current can then be described as I IDC R� � sin( )� . (4) While the switch S is closed the capacitor C has zero volt- age across and consequently all current starts flowing through S for � t � 0. The current flowing the switch S i ts( )� can be described as � �i t I I t I ts DC R R( ) sin ( ) sin ( ) sin ( )� � � � � �� � � � � � . (5) At the time � � � �t t k� � �0 2 the switch S opens and the difference current i t t i t tc s( ) ( )� � � �� � �0 0 flows into capacitor C which starts charging. The build up of the voltage u ts( )� across the switch S is determined by the charging of capacitor C, which can be described as u t C i t ts c t t ( ) ( )� � � � � � � � 1 0 d . (6) 90 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 49 No. 2–3/2009 2.45 GHz Class E Power Amplifier for a Transmitter Combining LINC and EER M. Dirix, O. Koch A 10 W class-E RF power amplifier (PA) is designed and fabricated using a Cree GaN HEMT. The proposed PA uses an innovative input circuit to optimize band with. At 2.45 GHz the PA achieves a PAE of 60 % at an outputpower of 40 dBm. The resulting amplifier is simu- lated and constructed using a transmissionline topology. Two of these amplifiers are fabricated on a single board for outphasing application. Their suitability for outphasing application and supply modulation is investigated. Keywords: Class E, power amplifier, CLIER. Fig. 1: Class E circuit with lumped elements With (5) it follows that � �u t I C t ts R( ) cos ( ) cos ( ) sin� � � � � � � �� � � � � � . (7) With the first criteria for Class E operation Eq. (1) and Eq. (7) it follows that for optimal operation the phase angle � can be defined as � � � � � � � � � �tan .1 2 32 482 deg. (8) With these equations the resulting normalized voltage can easily be obtained. The normalized voltage and current tran- sients are shown in Fig. 2. As can be seen, there is no overlap between switch current and voltage waveforms, resulting in 100 % switch efficiency. A common design approach for high frequency Class E PAs is to design a lumped element amplifier [4] and then re- place each component with an equivalent transmission line. This however makes the design and optimization both tedious and time-consuming because only the slightest change in a transmission line parameter will change the load network radically, losing Class E operating conditions. A better approach is found in [3]. Consider Fig. 3. Class E operation in this circuit depends on the load network pro- viding a phase angle � � 49.05 deg. This complex output impedance, using tan � � X R, can be written as Z R j f nf nE E � � � � � � � ( . ) , . 1 1152 1 at at 0 0 (9) The optimum value for the load resistance RE at the fun- damental frequency f0 is given by R f CE s � 1 34 225 0. . (10) By choosing a moderate to high impedance for transmis- sion lines ZTL1 and ZTL2 and defined output load impedance RL, circuit parameters can be further obtained by keeping the absolute value of the reflection parameter on both sides of TL1 equal � �E G� . The total admittance combining the load admittance GL and transmission lines TL2 and TL3 can be written as Y G jBG L� � , (11) where B is B Y G Y GE TL L TL L E � � � � � � � � 2 2 2 2 1 1 1 ( ) ( ) (12) Because the load resistance is real, the imaginary part of YG has to comprise both transmission lines TL2 and TL3. With the already chosen parameter ZTL2, ZTL 3 can be ob- tained with Z B Z TL TL 3 2 1 1 30� � � tan( deg) . (13) With �E being the reflection factor at the transistor output terminals �E E TL E TL Z Z Z Z � � � 1 1 (14) and �G the reflection factor at the end of transmission line TL1 �G G TL G TL Y Z Y Z � � � 1 1 1 1 (15) the electrical length of ZTL1 can be calculated with l j TL E G1 4� � � � � � � � � ln � � . (16) Because this implementation only provides a high imped- ance at the second and third harmonics across the transistor output terminals, output current and voltage waveforms are not completely separated resulting in less than 100 % maxi- mum efficiency. Hence the transmissionline circuit should only be used for applications where it is not possible to use © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 91 Acta Polytechnica Vol. 49 No. 2–3/2009 0 100 200 300 0 1 2 3 4 �t Fig. 2: Switch current (light) and voltage (dark) transient Fig. 3: Class E circuit with transmission lines lumped elements, or the insertion losses are greater than the efficiency restraints due to harmonic termination problems. 2.1 Input network To meet the demands that Class E imposes on the used transistor for this project a GaAS HEMT transistor of type CREE CGH4010F is chosen. This transistor allows for a maximum collector voltage of 120 V . The input impedance for this transistor is 4�j 4 � at 2.4 GHz which needs to be adapted to the 50 � output of the pre-amplifier. While this can be easily be achieved using a � 4 transmission line limit- ing bandwidth, a binomial input filter is chosen. The main advantage of using a binomial matching transformer is that the passband response is maximally flat near the design fre- quency. The order N also determines the number of sections in the transformer [7]. 2.2 Simulation and Measurement Results In this section, the Class E amplifier structure is modeled and simulated in the Agilent Advanced Design System (ADS). Then simulation results are compared to measurement of the implemented amplifier. The Cree CGH4010F GaN HEMT has an output capacitance CGS of typically 1.3 pF [6]. Using Eqs. (10) and (9) the required load impedance ZE can be calculated. Further following the advice of [3] a medium to high characteristic impedance has been chosen for TL1 � 75 � and TL2 � 50 �. Further parameters can easily be attained us- ing equations presented in Section 2. First, the circuit output network is simulated using two real ports, to review the location of the second and third harmonic in a Smith chart. As already mentioned, the output network should impose a 40.5 deg phase shift on the transistor output terminals for the target frequency and impose a high imped- ance at the second and third harmonic. Fig. 4 shows the frequency response of the output network as seen by the tran- sistor output terminals. Fig. 5 shows the frequency response of the amplifier. In red the measurement, and in blue the simulated values. Remarkable for this amplifier is that the measurement results are well above the simulation results. In addition, the real amplifier performs best with 28 dBm input power, while the simulation is carried out with 30 dBm input power. These differences can be explained given that the simulation model of the transistor is optimized for Class AB operation. The output frequency response of the pre-amplifier is shown in turquoise. Fig. 6 shows the resulting amplifier efficiency. Fig. 7 shows that the two amplifiers, Yellow and Blue, are put together on a single circuit board for implementation in 92 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 49 No. 2–3/2009 Fig. 4: Smithchart of the output load network Fig. 5: Frequency response of the measured and simulated ampli- fier, and pre-amplifier using a 20 V DC supply voltage Fig. 6: Power added efficiency the CLIER system. In the following figures the two amplifiers can be compared. Figs. 8 and 9 show that the differences between the two amplifiers are small. This makes them ideally suited for fur- ther implementation in the LINC part of the CLIER amplifier architecture, as a LINC transmitter requirers a small phase and amplitude imbalance between the two paths. Figure 10 depicts the linearity between the DC supply voltage and the output voltage. As can be seen good linearity is de- livered up to 20 V DC. The non-linearity in the higher voltage range must be compensated using pre-distorting or with the LINC part of the architecture. 3 Conclusion A Class E Power Amplifier has been presented and its effi- ciency simulated and measured. Its suitability for a CLIER transmitter has been demonstrated. References [1] Cox, D. C.: Linear Amplification with Nonlinear Com- ponents. IEEE-TC, Vol. 41 (1974), No. 4, p. 1942–1945. [2] Kahn, L. R.: Signal-Sideband Transmission by Envelope Elimination and Restoration. Radioengineering, Vol. 40 (1952), p. 803–806. [3] Negra, R., Fadhel, M., Ghannouchi, M., Bachtold, W.: Study and Design Optimization of Multiharmonic Transmission-Line Load Networks for Class-E and Class-FK-Band MMIC Power Amplifiers. IEEE Transac- tions on Microwave Theory and Techniques, 207, Vol. 55, No. 6, p. 1390–1394. [4] Raab, F. H.: Idealized Operation of the Class E Tuned Power Amplifier. IEEE Transactions on Circuits and Sys- tems, Vol. 24 (1977), No. 12, p. 725–735. [5] Rembold, B., Koch, O.: Increasing Power Amplifier Effi- ciency by Combining LINC and EER, Proceedings of the 12th International Student Conference on Electrical Engineer- ing POSTER 2008.ue (Czech Republic), 2008. [6] Cree Inc.: CGH40010 Datasheet 2007, Rev 1.5 Preliminary [7] Pozar, D. M.: Microwave Engineering, John Wiley & Sons, Inc., 2005. Marc Dirix e-mail: marc@ihf.rwth-aachen.de Olivier Koch e-mail: koch@ihf.rwth-aachen.de Institute of High Frequency Technology RWTH Aachen University Melatener Strasse 25 52074 Aachen, Germany © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 93 Acta Polytechnica Vol. 49 No. 2–3/2009 Fig. 7: The two Linc Class E amplifiers on a circuitboard 2 2.2 2.4 2.6 2.8 3 10 20 30 40 50 Frequency (GHz) O u tp u t P o w e r (d B m ) 10V 15V 20V 25V Fig. 8: Frequency response of the blue and the yellow amplifier with 10, 15, 20 and 25 V supply voltage, DC supply 2 2.2 2.4 2.6 2.8 3 �4 �2 0 2 4 Frequency (GHz) P h a s e s h if t (d e g ) 5V 10V 15V 20V Fig. 9: Phase difference of the two ouput signals B21-Y21 5 0 � in to Fig. 10: Comparison of the output voltage of the yellow (light) and the blue (dark) amplifier Table of Contents Multi-Condition Training for Unknown Environment Adaptation in Robust ASR Under Real Conditions 3 J. 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Bauer A New Buck-Boost Converter for a Hybrid-Electric Drive Stand 70 P. Mašek Transformation of Commercial Flows into Physical Flows of Electricity – Flow Based Method 75 M. Adamec Implementation of a Power Combining Network for a 2.45 GHz Transmitter Combining LINC and EER 80 F. Wang, O. Koch Importance of Peaceful Utilization of Nuclear Energy 86 J. Frydryšková 2.45 GHz Class E Power Amplifier for a Transmitter Combining LINC and EER 90 M. Dirix, O. Koch << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends true /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /CZE /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. 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