A Variable Output Power, High Efficiency, Power Amplifier for the ...

(39 dBm to 44 dBm). This was somewhat less than the 6 dBexpected from simulations. The achieved PAE during powercontrol is shown in Fig. 8Gain [dB], PAE [%]70605040302010Gain (meas)PAE (meas)Gain (sim)PAE (sim)39 40 41 42 43 44P OUTdBmFig. 8 Measured and simulated gain and PAE during power control atf = 2.45 GHz. V D = 28 V and I DQ(PS) = 123 mA.From this figure it can be seen that a PAE of almost 40 % ismaintained for the two-stage amplifier over the full tuneablerange.IV. DISCUSSIONAlthough this amplifier was designed for heatingapplications at ISM band where power generated at otherfrequencies is of little concern but the topology used may bevery suitable for more frequency sensitive applications [2]within the ISM band. This covers e.g. applications withincommunication and microwave enhanced chemical reactions.Fig. 9 represents the two-tone IMD performance of thedesigned amplifier.Output Power 2-tone [dBm]806040200-20-40-60P3(meas)P2(meas)P1(meas)P3(sim)P2(sim)P1(sim)IMD3 ~65 dBcV. CONCLUSIONSIn this paper the design of a two stage 30 W poweramplifier with controllable gain for the ISM band is presented.Power control and high efficiency over the controllable outputpower range were the main design objectives. A model baseddesign approach was used and verified in the work. High gainrequirement forced it to be a two-stage amplifier where ashigh efficiency over the full controllable power range wasachieved using GaN HEMT technology in the power stageand Si-LDMOS technology in the driver stage. A gain of25 dB was measured for the two stage amplifier at themaximum output power of 30 W. In compression a drainefficiency of 67.8 % and PAE of 67.2 % was achieved. Theamplifier performs well over a full bandwidth of 150 MHzwith a saturated output power of more than 44 dBm at a PAE> 60% for the full band.The output power is controllable within a 5 dB range bysetting the bias of the driver stage. More than 40 % PAE ismaintained over the full controllable output power rangewhich makes the amplifier well suited for the heatingapplication it was designed for.ACKNOWLEDGMENTSThe authors would like to thank Cree for providing themodel for the GaN-HEMT transistor used and Freescale forproviding the model for the Si-LDMOS used.REFERENCES[1] “The ISM Revolution: The Next Big Thing”, By Iboun Taimiya Sylla,Texas Instruments, 9th Feburary, 2009, www.rfdesignline.com[2] Wojciech Wojtasiak, Daniel Gryglewski and Wojciech Gwarek,' “AlOOW ISM-2.45GHz BAND POWER TEST SYSTEM,” *Institute ofRadioelectronics, Warsaw University of Technology, Poland. Journalof telecommunications and information technology, 2005.[3] Isao Takenaka, Hidemasa Takahashi, Kazunori Asano, JunkoMorikawa, Kohji Ishikura, Mikio Kanamori", Masaaki Kuzuhara andHiroaki Tsutsui, “High efficiency S-band 30W power GaAs FETs”ULSI Device Development Laboratories, NEC Corporation. 9-1,Seiran 2-Chome70tsu,Shiga 520,Japan.[4] A. H. Jardnal, “Large signal modelling for GaN devices for high poweramplifier”, PhD., University of Kassel, Germany, Nov. 2006.[5] Nitronex Corporation, “GaN Power HEMT for 2.5 GHz WiMAXApplications”, NPT25100, 2305 Presidential Drive. Durham, NC27703.[6] K. Krishnamurthy, M. J. Poulton, J. Martin, R. Vetury, J. Brown, and J.B. Shealy, “A 250 W S-Band GaN HEMT Amplifier”, InfrastructureProduct Line, RF Micro Devices, Inc., Charlotte, NC 28269, USA.[7] J. Shumaker, M. Ohoka, and N. Ui, “Design of Power AmplifiersUsing High Breakdown GaN HEMT Devices”, Eudyna Devices USAInc, and Eudyna Devices Inc Japan.[8] S. Cripps, “Advanced Techniques in RF Power Amplifier Design”, 1stEd., Artech House, 2002.-20 -10 0 10 20 30Input Power 2-tone [dBm]Fig. 9 Two-tone IMD performance of the amplifier for a tone-spacing of 100MHx at the deigns frequency 2.45 GHz at V D = 28 V, I DQ(DS) = 23 mA andI DQ(PS) = 123 mA.2009 SBMO/IEEE MTT-S International Microwave & Optoelectronics Conference (IMOC 2009) 824