B GS F18 D Op ti mizin g the P erf or manc e of S P8 T Ant enna S witch Mod ule G S M/ U MT S Mo bile Applic atio ns Applic atio n N ote A N 247 Revision: Rev. 1.0 2010-10-13 RF and P r otecti on D evic es Edition 2013-08-05 Published by Infineon Technologies AG 81726 Munich, Germany © 2013 Infineon Technologies AG All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. 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Last Trademarks Update 2009 10 19 Application Note AN247, Rev. 1.0 3 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance List of Content, Figures and Tables Table of Content 1 Introduction ........................................................................................................................................ 5 2 BGSF18D Schematic .......................................................................................................................... 5 3 Configuration of ports ....................................................................................................................... 6 4 4.1 4.2 Optimizing Harmonics of GSM Low Band ....................................................................................... 8 Optimizing Harmonic Filter characteristic ............................................................................................ 8 rd Optimizing 3 Harmonic generation of the Switch ............................................................................. 10 5 PCB Design Guide Lines ................................................................................................................. 11 Appendix: Switch Controller Unit ...................................................................................................................... 12 Author 14 List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 BGSF18D Application Schematic ........................................................................................................ 5 Effect of Lext on Filter Curve ................................................................................................................. 8 Switch and Filter Response with Lext=1.6nH ........................................................................................ 9 nd 2 Harmonic Generation ................................................................................................................... 10 rd 3 Harmonic Generation .................................................................................................................... 10 ASM Package: Top View ................................................................................................................... 11 PCB Layout Proposal ......................................................................................................................... 11 Switch Controller Unit Board .............................................................................................................. 12 List of Tables Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 GSM/EDGE Frequencies ..................................................................................................................... 6 UMTS Frequencies .............................................................................................................................. 6 Port Configuration Proposals ............................................................................................................... 6 BGSF18D Port to Port Isolation (in dB)................................................................................................ 7 Variation in Insertion Loss by changing Lext ......................................................................................... 9 Active RF Path ................................................................................................................................... 13 Application Note AN247, Rev. 1.0 4 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Introduction 1 Introduction The BGSF18D is a Single Pole Eight Throw (SP8T) switch module optimized for wireless applications up to 2.7GHz. The switch module is designed to meet the evolving challenges due to the continuous advancement in mobile phone technologies. The convergence of GSM, EDGE and UMTS standards, leads to the design handsets capable of multiband multimode operation which poses a great challenge on the system designer. To meet the requirements of today’s multiband multimode handsets, the ASM (Antenna Switch Module) has two exclusive GSM/EDGE transmit paths including harmonic filters and six identical RF ports which can be flexibly used as GSM/EDGE receive or UMTS transmit receive paths. This document is a guide to help the system designer to get the optimum performance out of the ASM. Scope of this document: 1. Configuration of ports: Insertion Loss and Port to Port Isolation considerations 2. Optimizing Harmonics and Insertion Loss of GSM Low Band 3. PCB design guidelines 2 BGSF18D Schematic Below is the application schematic of BGSF18D. There is only one optional external component (Lext), which gives the designer flexibility to further optimize the performance of the ASM. ANT BGSF18D ESD Protection TRx_1 TRx_2 Tx_LB TRx_3 Harmonic Filters TRx_4 TRx_5 Tx_HB TRx_6 SP8T Gnd_LB Figure 1 Gnd VDD Lext SPI-VDD SPI-CLK SPI-DATA SPI-FRM SPI Controller BGSF18D Application Schematic Application Note AN247, Rev. 1.0 5 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Configuration of ports 3 Configuration of ports Before we start with the port configuration of BGSF18D, it is valuable to have an insight into the list of frequencies recognized by 3GPP for GSM/EDGE and UMTS as shown in Table 1 and Table 2. Table 1 GSM/EDGE Frequencies Band Tx (MHz) Rx(MHz) GSM850 824 to 849 869 to 894 GSM900 890 to 915 935 to 960 DCS 1710 to 1785 1805 to 1880 PCS 1850 to 1910 1930 to 1990 Tx(MHz) Rx(MHz) I 1920 to 1980 2110 to 2170 II 1850 to 1910 1930 to 1990 III 1710 to 1785 1805 to 1880 IV 1710 to 1755 2110 to 2155 V 824 to 849 869 to 894 Table 2 UMTS Frequencies Band VI 830 to 840 875 to 885 VII 2500 to 2570 2620 to 2690 VIII 880 to 915 925 to 960 IX 1749.9 to 1784.9 1844.9 to 1879.9 X 1710 to 1770 2110 to 2170 XI 1427.9 to 1447.9 1475.9 to 1495.9 XII 698 to 716 728 to 746 XIII 777 to 787 746 to 756 XIV 788 to 798 758 to 768 XIX 830 to 845 875 to 890 XX 832 to 862 791 to 821 XXI 1447.9 to 1462.9 1495.9 to 1510.9 Based on the system design, different band combinations from the above listed frequency bands can be used. From the table above, we can see that some of the transmit frequencies of one band overlap with the receive frequencies of the other. Therefore, care should be taken to have good port to port isolation between these bands. Below are the most critical combinations 1. Band I Tx and Band II/PCS Rx 2. Band II/PCS Tx and Band III/DCS Rx Therefore, it should be taken into account that they are not routed through adjacent ports. Table 3 shows two such recommended combinations, to get the best possible isolation between the different paths. All TRx ports on the BGSF18D are identical, which gives designer the flexibility to configure other ports to different bands. Table 3 Port Configuration Proposals UMTS / GSM Band Option 1 Option 2 Band I TRx2 TRx3 Band II / PCS TRx4 TRx1 Band III / DCS TRx6 TRx5 Application Note AN247, Rev. 1.0 6 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Configuration of ports The port to port isolation values are tabulated in a table below. It is to be observed that the isolation between adjacent ports is lower than other combinations. Table 4 BGSF18D Port to Port Isolation (in dB) Freq TRx1 TRx2 TRx3 TRx4 TRx5 TRx6 LB HB 0.85 37.1 45.1 56.4 51.4 50.1 35.4 49.3 1.71 30.8 38.2 43.3 39.8 39.7 36.4 38.5 1.91 29.7 36.9 41.7 37.7 38.8 37 37.7 29.3 (GHz) TRx1 1.98 TRx2 TRx3 TRx4 TRx5 TRx6 LB HB 36.5 41.2 37.1 38.2 38.9 37.4 0.85 36 35.4 47.6 49.2 52.7 35.4 48.4 1.71 29.3 29.3 39.4 38.4 40.2 36.4 39.2 1.91 28.1 28.3 38 36.5 38.8 36.7 38.8 1.98 27.7 27.9 37.5 36 38.2 38.4 38.6 0.85 39.1 33.9 39.8 44.3 51.8 35.4 47.8 1.71 31.9 27.7 33.5 35.9 39.7 36.2 41.6 1.91 30.6 27 32.4 34.2 37.9 36.4 42.5 1.98 30.2 26.4 32 33.8 37.4 38.1 42.9 0.85 51.8 46.2 38.9 36.3 43.7 35.4 44.6 1.71 39.1 39 33 30 36.3 35.9 38.9 1.91 37.4 37.6 32 28.8 34.5 36.1 39.5 1.98 36.8 37.2 31.6 28.5 34.3 37.7 39.9 0.85 51.4 53.9 46 36.1 36.8 35.5 43.3 1.71 38.8 41.6 38.9 30 30.6 36 37.8 1.91 37.1 40 37.5 28.9 29 36.1 38.2 1.98 36.5 39.4 37.2 28.6 28.9 37.7 38.5 0.85 49.4 54.2 56.3 43.6 39.7 35.8 41.9 1.71 39 42.4 44.6 37.1 32.3 36 36.4 1.91 37.5 41 42.8 35.7 30.8 36.2 36.7 1.98 37 40.3 42.2 35.4 30.4 37.7 36.9 0.85 47 47.2 47.6 48.4 43 43.5 39.6 1.71 50.1 51.2 52.3 55 42.6 46 38.9 1.91 49.9 51.5 53.1 52.5 44.5 48 38.6 1.98 45.8 47.2 48.3 47.8 43.6 45.5 0.85 49.1 52.7 53.1 49 48.8 47.5 35.1 1.71 34.7 37.8 39.6 39 37.7 37.7 35.6 1.91 32.3 35.4 37.2 37 35.5 36.3 36 1.98 31.5 34.5 36.3 36.3 34.7 35.5 37.4 Application Note AN247, Rev. 1.0 7 / 15 38.1 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Optimizing Harmonics of GSM Low Band 4 Optimizing Harmonics of GSM Low Band As shown in the application schematic earlier, an external inductor L ext can be used to optimize the Harmonic behavior of the ASM. The external inductor gives system designer the flexibility to improve the Harmonic performance of the ASM by adapting to the peripheral components. The inductor plays two roles 1. It helps to shape the filter curve as required 2. It influences the harmonic generation of the switch Let us now see the two effects in detail. 4.1 Optimizing Harmonic Filter characteristic In Figure 2, we see the effect of varying the inductor (Lext) value on the filter response. The measurements are done on application board using Murata LQP03xx inductors. The inductor value is varied between short and rd 2nH. It is observed that there is a significant effect on the 3 harmonic suppression and also an impact on the nd 2 harmonic suppression. The filter curve can thus be tuned as to fit to the system performance. The short is achieved using a jumper which normally has a certain inductance too. A perfect short can be achieved using vias directly at the GND pad. DB(|S(2,1)|) 0N8 DB(|S(2,1)|) 1N6 DB(|S(2,1)|) OPEN DB(|S(2,1)|) 1N2 DB(|S(2,1)|) 2N0 DB(|S(2,1)|) SHORT Forward Transmission GSM LB 0 -5 -10 -15 -20 -25 -30 -35 -40 0 Figure 2 1 2 3 4 5 Frequency (GHz) 6 7 8 8.5 Effect of Lext on Filter Curve Application Note AN247, Rev. 1.0 8 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Optimizing Harmonics of GSM Low Band DB(|S(2,1)|) 1N6.$FPRJ From the graph above, it can be seen that filter notches can be fine tuned to achieve a good trade off between nd rd 2 and 3 harmonic suppression for low and high side of the GSM850/900 bands. System measurements at Infineon have shown that 1.6nH inductor provides an optimum solution. The forward transmission curve with a 1.6nH inductor is shown in the figure below. 0.824 GHz -1.051 dB 0.915 GHz -1.091 dB IL GSM LB 1n6 0 -5 2nd Harmonics 1.65 GHz 1.83 GHz -20.57 dB -26.43 dB -10 -15 -20 -25 -30 2.47 GHz -25.53 dB -35 2nH 2.745 GHz -20.06 dB 3rd Harmonics -40 0 Figure 3 1 2 3 4 5 Frequency (GHz) 6 7 8 8.5 Switch and Filter Response with Lext=1.6nH It is to be noted that using the inductor slightly deteriorates the Insertion Loss of the Switch. The variation in Insertion Loss can bee seen in Table 5. It can be seen that going from short to 2nH, the Insertion Loss of the RF path increases by 0.05dB. Table 5 Variation in Insertion Loss by changing Lext Lext (nH) Short 1.2 1.6 2.0 Application Note AN247, Rev. 1.0 IL (dB) 824 MHz IL (dB) 850 MHz IL (dB) 915 MHz 1.03 1.05 1.05 1.08 1.04 1.06 1.06 1.09 1.07 1.08 1.09 1.12 9 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Optimizing Harmonics of GSM Low Band 4.2 Optimizing 3rd Harmonic generation of the Switch As we know, the harmonic generation of an active device depends on the source and load terminations. The inductor Lext changes the impedance of the filter as seen by the Switch input and thus has an effect on the nd harmonic generation of the Switch. Little impact is seen in 2 harmonic generation (Figure 4) but significant rd impact can be seen in the 3 harmonics. From the graph below, we can see that by using a 2nH inductor we rd can gain up to 10dB margin in the 3 harmonic generation with a Switch input power of 35dBm. 2nd Harmonics -40 -50 -60 -70 PlotCol(3,7) SHORT.$FPRJ -80 19.97 Figure 4 nd 2 PlotCol(3,7) 0n8.$FPRJ PlotCol(3,7) 1n2.$FPRJ 24.97 PlotCol(3,7) 1n6.$FPRJ PlotCol(3,7) 2n0.$FPRJ 29.97 34.97 37.96 Harmonic Generation 3rd Harmonics 0 PlotCol(3,8) SHORT.$FPRJ -10 PlotCol(3,8) 0n8.$FPRJ PlotCol(3,8) 1n2.$FPRJ PlotCol(3,8) 1n6.$FPRJ PlotCol(3,8) 2n0.$FPRJ -20 -30 -40 -50 -60 -70 -80 -90 -100 20 Figure 5 22 24 26 28 30 32 34 36 38 rd 3 Harmonic Generation Application Note AN247, Rev. 1.0 10 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance PCB Design Guide Lines 5 PCB Design Guide Lines Figure 6 shows the package outline. The ASM has 16 pads with 1 big center pad, which is a Ground pad and also acts as a heat sink. Figure 6 ASM Package: Top View As we know, the performance of RF devices is strongly influenced by the PCB design. Here are a few points to realize a good PCB layout for the BGSF18D: 1. The center pad should be grounded using several vias directly under the pad to provide a good RF grounding. Improper grounding of this pad can have negative effects on the filter curve and isolation. 2. All other ground pads should be connected to the center ground as shown in the PCB proposal below. 3. General guidelines for a good RF board to be applied, namely, right characteristic line impedance, optimum spacing between lines, short line lengths etc. ANT Figure 7 PCB Layout Proposal Application Note AN247, Rev. 1.0 11 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Appendix: Switch Controller Unit Appendix: Switch Controller Unit The BGSF18D is controlled via SPI interface and Infineon offers a SPI controller unit to ease the evaluation of its BGSF18D on application board. The unit is very simple to use with a few buttons to select the right device and different states. This section helps as a short user guide for the controller unit shown in Figure 8. The controller unit requires a DC supply of 5.5V with a current capability of 50mA. G VG N CN D CD to BGSF18D P3 P2 GND GND Vcc LVdd FRM Figure 8 GND GND NC SPI CLK P1 Switch Controller Unit Board Please observe the following steps to use the controller unit: 1. Step1: Attach the power supply and “OK” appears on the display. 2. Step2: Set the control mode: a. Press and hold “P1” and “P3” simultaneously until “8A” appears on the display b. “P2” can be used to set the Vdd to the switch between 1.8V, 3.5V (default) and 4.0V c. To use 4V, please connect to 6V power supply instead of 5.5V d. “8A” addresses BGSF18D device 3. Step3: Connect the control unit to the switch with an appropriate cable according to the connector pinout shown in Figure 8. 4. Step4: Set the switch state to measure using “P1” and “P3”. The active paths corresponding to the state displayed are tabulated in Table 6. Application Note AN247, Rev. 1.0 12 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Appendix: Switch Controller Unit Table 6 Active RF Path Display Active RF Path LB ANT – GSM LB Tx HB ANT – GSM HB Tx P1 ANT – TRx1 P2 ANT – TRx2 P3 ANT – TRx3 P4 ANT – TRx4 P5 ANT – TRx5 P6 ANT – TRx6 AO All OFF, Device is ON but all ports in isolation mode GW Global Stand-by (Power Down) DS Switch Stand-by (Power Down) Application Note AN247, Rev. 1.0 13 / 15 2010-10-13 BGSF18D Optimizing BGSF18D Perfromance Author Author Deepak Bachu, Senior Application Engineer of the Business Unit “RF and Protection Devices” Application Note AN247, Rev. 1.0 14 / 15 2010-10-13 w w w . i n f i n e o n . c o m Published by Infineon Technologies AG AN247