RF Fro nt End Modu les Impro ve ment o f Har mo nic Dis torti on Har monic perf or ma n c e of R F FE M over V SW R a nd pha s e Applic atio n N ote A N 284 Revision: Rev. 1.0 2012-04-10 RF and P r otecti on D evic es Edition 2012-04-10 Published by Infineon Technologies AG 81726 Munich, Germany © 2013 Infineon Technologies AG All Rights Reserved. Legal Disclaimer The information given in this document shall in no event be regarded as a guarantee of conditions or characteristics. With respect to any examples or hints given herein, any typical values stated herein and/or any information regarding the application of the device, Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind, including without limitation, warranties of non-infringement of intellectual property rights of any third party. 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RF Front End Modules RF FEM improvement by Harmonic Termination Application Note AN284 Revision History: 2012-04-10 Previous Revision: prev. Rev. x.x Page Subjects (major changes since last revision) Trademarks of Infineon Technologies AG AURIX™, C166™, CanPAK™, CIPOS™, CIPURSE™, EconoPACK™, CoolMOS™, CoolSET™, CORECONTROL™, CROSSAVE™, DAVE™, DI-POL™, EasyPIM™, EconoBRIDGE™, EconoDUAL™, EconoPIM™, EconoPACK™, EiceDRIVER™, eupec™, FCOS™, HITFET™, HybridPACK™, I²RF™, ISOFACE™, IsoPACK™, MIPAQ™, ModSTACK™, my-d™, NovalithIC™, OptiMOS™, ORIGA™, POWERCODE™, PRIMARION™, PrimePACK™, PrimeSTACK™, PRO-SIL™, PROFET™, RASIC™, ReverSave™, SatRIC™, SIEGET™, SINDRION™, SIPMOS™, SmartLEWIS™, SOLID FLASH™, TEMPFET™, thinQ!™, TRENCHSTOP™, TriCore™. Other Trademarks Advance Design System™ (ADS) of Agilent Technologies, AMBA™, ARM™, MULTI-ICE™, KEIL™, PRIMECELL™, REALVIEW™, THUMB™, µVision™ of ARM Limited, UK. AUTOSAR™ is licensed by AUTOSAR development partnership. Bluetooth™ of Bluetooth SIG Inc. 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Last Trademarks Update 2011-11-11 Application Note AN284, Rev. 1.0 3 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination List of Content, Figures and Tables Table of Content 1 Introduction ........................................................................................................................................ 5 2 2.1 Application Information ..................................................................................................................... 5 Application ............................................................................................................................................ 5 3 Measurement Procedure ................................................................................................................... 7 4 4.1 4.1.1 4.1.2 4.1.3 4.1.4 4.2 4.2.1 4.2.2 4.2.3 Measurement Results ........................................................................................................................ 8 Measurement results with f0 = 824 MHz .............................................................................................. 8 Worst case harmonic results ................................................................................................................ 8 H2 optimised harmonic results ............................................................................................................. 9 H3 optimised harmonic results ............................................................................................................. 9 Summary of measurement results with f0 = 824 MHz ........................................................................ 10 Measurement results at f0 = 915 MHz ................................................................................................ 12 Worst case harmonic results .............................................................................................................. 12 Best case harmonic results ................................................................................................................ 12 Summary of measurement results at f0 = 915 MHz ........................................................................... 13 5 Antenna matching influences the harmonic performance .......................................................... 15 6 Conclusion ........................................................................................................................................ 16 Authors 17 List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Application Diagram ............................................................................................................................. 5 Harmonic Distortion Test setup ............................................................................................................ 5 Measurement Procedure ...................................................................................................................... 7 Example of high impedance termination at Tx port.............................................................................. 8 H2 optimized impedance termination of Tx port .................................................................................. 9 H3 optimized impedance termination of Tx port .................................................................................. 9 2 nd Harmonic Results at f0 = 824MHz .............................................................................................. 10 3 rd Harmonic Results at f0 = 824MHz ............................................................................................... 11 High impedance termination of Tx port .............................................................................................. 12 Low impedance termination of Tx port ............................................................................................... 12 2 rd Harmonic Results at f0 = 915MHz ............................................................................................... 13 3 rd Harmonic Results at f0 = 915MHz ............................................................................................... 14 Proposal for an antenna matching ..................................................................................................... 15 Impact of the Antenna Matching ........................................................................................................ 15 2 nd Harmonic improvement by low harmonic termination of the Tx path ......................................... 16 List of Tables Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Test Setup Equipment .......................................................................................................................... 6 Worst case harmonics with f0 = 824 MHz ............................................................................................ 8 H2 optimized harmonics at f0 = 824 MHz ............................................................................................. 9 H3 optimized harmonics at f0 = 824 MHz ............................................................................................. 9 Summary of the harmonic measurements at f0 = 824 MHz ............................................................... 10 Worst case harmonics at f0 = 915 MHz .............................................................................................. 12 Best case harmonic at f0 = 915 MHz .................................................................................................. 12 Summary of harmonic measurements at f0 = 915 MHz ..................................................................... 13 Application Note AN284, Rev. 1.0 4 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Introduction 1 Introduction This application note shows the possibilities to reduce harmonic products of a RF Front End Module over VSWR antenna port mismatch with arbitrary phase by tuning the impedance termination at the RF CMOS switch input and output. Infineon`s BGS18D RF CMOS SP8T antenna switch has been used as an example. 2 Application Information 2.1 Application The block diagram on Figure 1 shows a typical Front End Module application in RF environments of mobile phones or Base stations. The FEM is connecting the Rx path to the antenna or the antenna to Tx path. Figure 1 Application Diagram This application describes the importance of the harmonic impedance terminations in a RF FEM. The impedances at input and output of the switch have great influences on the performance. To achieve best possible distortion results low impedance harmonic termination has to be offered at the high-power ports of the switch. To find out the perfect port conditions to reach best harmonic performance at VSWR mismatch a test setup has been developed (Figure 2, Table 1). Figure 2 Harmonic Distortion Test setup The test bench includes two phase shifters, one at the input and another at the output of the DUT (BGS18D, chip on evaluation board) to tune the phase of the impedance at the second (H2) and third harmonics (H3). The Application Note AN284, Rev. 1.0 5 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Application Information reflections in the stopband (H2, H3) between the filter (bandpass or lowpass possible) at the TX input and the antenna at output of the DUT influence the harmonic generation in the switch itself. Table 1 Test Setup Equipment Description Manufacturer Identification number Function Signal Generator Rohde & Schwarz SMIQ 06B Power Amplifier Mini Circuits ZHL-30W-252-S+ Circulator MTC C163FFF For proper matching of the PA Directional Coupler PULSAR CS20-22-436/3 Enable power measurement during the test Attenuator Lucas Wenschel 33-3-34 3dB/50W Establishment of a 50 Ohm environment behind directional coupler Power Meter Agilent E4419B Lowpass Filter Wainwright WLK1.0/18G-10SS TX Phase Shifter ATM PNR P1213D Filtering the harmonics of PA and providing mismatch at H2 and H3 Phase tuning of the H2,H3 impedance Highpass Filter Wainwright WLK1.3/15G-10SS Prevents overload of the spectrum analyser Spectrum Analyser Rohde & Schwarz FSIQ26 ANT Phase Shifter ARRA D4428C Application Note AN284, Rev. 1.0 Phase tuning at VSWR conditions 6 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Procedure 3 Measurement Procedure 1. Set low Impedances (only for 2f0 and 3f0) at the lowpass filter to reduce reflections by changing the phase of the TX phase shifter. The best way, to reach a good harmonic performance is to bring the Input Matching of the lowpass filter (2f0 and 3f0) together on the left side of the Smith chart. 2. Measure 2f0 and 3f0 products concerning several phase conditions by the ANT phase shifter 1. Step 2. Step Vary -180 to 180° Figure 3 Measurement Procedure Harmonic Frequencies: (2 examples) f0 = 824 MHz, 2f0 = 1648 MHz, 3f0 = 2472 MHz f0 = 915 MHz, 2f0 = 1830 MHz, 3f0 = 2745 MHz All measurements are done at nominal operation conditions of the switch (25° room temperature). PIN = 35 dBm, VDD = 3.5V Application Note AN284, Rev. 1.0 7 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results 4 Measurement Results The measurement results manifest the dependence of the harmonic degeneration and input / output VSWR including phase. As an example for such a harmonic improvement both corners of GSM850 and GSM900 have been chosen (824MHz and 915MHz). 4.1 Measurement results with f0 = 824 MHz 4.1.1 Worst case harmonic results Table 2 Worst case harmonics with f0 = 824 MHz Phase (°)* -180 H2 (dBm) -57 H3 (dBm) -54 -150 -120 -90 -30 0 30 60 90 120 150 180 -61 -49,5 -54 -44 -42,1 -35,1 -25,6 -25,8 -26,2 -25,6 -29 -23,7 -32,6 -21,8 -34,6 -28,4 -34,7 -34,1 -41 -37 -57 -54 *2 phase shifter in front of antenna Bad harmonic performance due to the high impedance harmonic termination of the Tx port of the switch Figure 4 Example of high impedance termination at Tx port Application Note AN284, Rev. 1.0 8 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results 4.1.2 Table 3 H2 optimised harmonic results H2 optimized harmonics at f0 = 824 MHz Phase (°)* -180 H2 (dBm) -56 H3 (dBm) -150 -65 -32 -35,4 -120 -49,8 -33,1 -90 -30 0 -48 -40,5 -50,5 -38,9 -50 -35 30 60 90 120 150 180 -47 -40,4 -43,6 -45,2 -39,9 -41,3 -40,8 -35,8 -47,2 -36,7 -56 -35,4 *2 phase shifter in front of antenna Figure 5 4.1.3 Table 4 H2 optimized impedance termination of Tx port H3 optimised harmonic results H3 optimized harmonics at f0 = 824 MHz Phase (°)* -180 H2 (dBm) -50,3 H3 (dBm) -35,4 -150 -120 -90 -30 0 30 60 90 120 150 180 -52,1 -32 -52,4 -33,1 -47 -40,5 -35,3 -38,9 -30,1 -35 -30,1 -40,4 -35,7 -45,2 -41,4 -41,3 -46,6 -35,8 -52,5 -36,7 -50,3 -35,4 *2 phase shifter in front of antenna Figure 6 H3 optimized impedance termination of Tx port Application Note AN284, Rev. 1.0 9 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results 4.1.4 Summary of measurement results with f0 = 824 MHz Table 5 Summary of the harmonic measurements at f0 = 824 MHz -180 -150 -120 -90 -30 0 30 60 90 120 150 180 H3 -50,3 optimized H2 High Tx -57 (dBm) impedance H2 -56 optimized -52,1 -52,4 -47 -35,3 -30,1 -30,1 -35,7 -41,4 -46,6 -52,5 -50,3 -61 -54 -42,1 -25,6 -26,2 -29 -32,6 -34,6 -34,7 -41 -57 -65 -49,8 -48 -50,5 -50 -47 -43,6 -39,9 -40,8 -47,2 -56 Phase (°)* 50 ohm -57 -62 -54 -41,7 -26 -27 -29,5 -32 -34 -33 -41 -57 Phase (°)* -180 -150 -120 -90 -30 0 30 60 90 120 150 180 H3 -35,4 optimized H3 High Tx -54 (dBm) impedance H2 -33,9 optimized -32 -33,1 -40,5 -38,9 -35 -40,4 -45,2 -41,3 -35,8 -36,7 -35,4 -49,5 -44 -35,1 -25,8 -25,6 -23,7 -21,8 -28,4 -34,1 -37 -54 -28,4 -35,4 -35,3 -31,8 -35,9 -39,9 -37,5 -32,3 -35,7 -36,2 -33,9 -53 -43 -32,9 -26 -25 -22,2 -22 -29 -32 -33 -44 50 ohm Figure 7 -44 2 nd Harmonic Results at f0 = 824MHz Application Note AN284, Rev. 1.0 10 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results Figure 8 3 rd Harmonic Results at f0 = 824MHz Application Note AN284, Rev. 1.0 11 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results 4.2 Measurement results at f0 = 915 MHz 4.2.1 Worst case harmonic results Table 6 Worst case harmonics at f0 = 915 MHz Phase (°)* -180 H2 (dBm) -33 H3 (dBm) -30 -150 -35 -30 -120 -37 -29 -90 -30 -36 -37 0 -40 -45 -51 -56 30 -60 -44 60 -54 -45 90 -40 -41 120 -29 -29 150 -30 -28 180 -33 -30 *2 phase shifter in front of antenna Bad harmonic performance due to high impedance termination of Tx path Figure 9 High impedance termination of Tx port 4.2.2 Best case harmonic results Table 7 Best case harmonic at f0 = 915 MHz Phase (°)* -180 H2 (dBm) -36 H3 (dBm) -43 -150 -41 -45 -120 -48 -41 -90 -56 -35 -30 0 -62 -40 -55 -42 30 -51 -39 60 -53 -36 90 -49 -43 120 -43 -44 150 -38 -38 180 -36 -43 *2 phase shifter in front of antenna Figure 10 Low impedance termination of Tx port Application Note AN284, Rev. 1.0 12 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results 4.2.3 Summary of measurement results at f0 = 915 MHz Table 8 Summary of harmonic measurements at f0 = 915 MHz Phase (°)* -180 -150 -120 -90 -30 0 30 60 90 120 150 180 High Tx H2 impedance (dBm) Low Tx impedance -33 -35 -37 -36 -40 -51 -60 -54 -40 -29 -30 -33 -36 -41 -48 -56 -62 -55 -51 -53 -49 -43 -38 -36 50 ohm -34 -39 -44 -48 -52 -53 -51 -52 -45 -39 -33 -34 Phase (°)* -180 -150 -120 -90 -30 0 30 60 90 120 150 180 High Tx H3 impedance (dBm) Low Tx impedance -30 -30 -29 -37 -45 -56 -44 -45 -41 -29 -28 -30 -43 -45 -41 -35 -40 -42 -39 -36 -43 -44 -38 -43 -29 -28 -29 -34 -39 -45 -56 -45 -37 -29 -28 -29 50 ohm Figure 11 2 rd Harmonic Results at f0 = 915MHz Application Note AN284, Rev. 1.0 13 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Measurement Results Figure 12 3 rd Harmonic Results at f0 = 915MHz Application Note AN284, Rev. 1.0 14 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Antenna matching influences the harmonic performance 5 Antenna matching influences the harmonic performance To avoid the worst case phase condition at the antenna port of the module a properly chosen matching circuit is recommend. Simple example is given on Figure 13. The results of such an antenna matching are shown on Figure 14. Proposal for an antenna matching The antenna matching network can transform the VSWR circle to lower impedances to avoid the worst case harmonic performance phase SP2.SP.S(1,1) SP1.SP.S(1,1) SP1.SP.S(2,2) Figure 13 lower impedances freq (1.648GHz to 1.648GHz) freq (2.472GHz to 2.472GHz) Figure 14 Impact of the Antenna Matching Application Note AN284, Rev. 1.0 15 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Conclusion 6 Conclusion The overall harmonic performance of a RF Front End Module has been improved in this example by well chosen termination impedances of the TX filter Figure 15. ≈ 20 dB Figure 15 2 nd Harmonic improvement by low harmonic termination of the Tx path An additional improvement of the harmonic distortion could be achieved by an antenna matching network in the module or on PCB transforming the VSWR impedance in order to reduce VSWR high impedance seen from the RF switch at the critical phase angle. Application Note AN284, Rev. 1.0 16 / 18 2012-04-10 RF Front End Modules RF FEM improvement by Harmonic Termination Authors Authors Nikolay Ilkov, RF CMOS Switch Product Development André Dewai, Application Engineer of Business Unit “RF and Protection Devices” Klaus Hoenninger, RF CMOS Switch Product Development Application Note AN284, Rev. 1.0 17 / 18 2012-04-10 w w w . i n f i n e o n . c o m Published by Infineon Technologies AG AN284