L o w C o s t F M R a d i o L NA u s i n g BFR460 L3 Mobile Phone Applications App lication No te 2 01 Revision 1.1, 2010-08-18 RF and Protect i on Devi ces Edition 2010-08-18 Published by Infineon Technologies AG 81726 Munich, Germany © 2010 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. Information For further information on technology, delivery terms and conditions and prices, please contact the nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements, components may contain dangerous substances. For information on the types in question, please contact the nearest Infineon Technologies Office. Infineon Technologies components may be used in life-support devices or systems only with the express written approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure of that life-support device or system or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered. Low Cost FM Radio LNA BFR460L3 Application Note 201 Revision History: 2010-08-18, Revision 1.1 Previous Revision:1.0 Page Subjects (major changes since last revision) 11 ESD Appendix updated Trademarks of Infineon Technologies AG A-GOLD™, BlueMoon™, COMNEON™, CONVERGATE™, COSIC™, C166™, CROSSAVE™, CanPAK™, CIPOS™, CoolMOS™, CoolSET™, CONVERPATH™, CORECONTROL™, DAVE™, DUALFALC™, DUSLIC™, EasyPIM™, EconoBRIDGE™, EconoDUAL™, EconoPACK™, EconoPIM™, E-GOLD™, EiceDRIVER™, EUPEC™, ELIC™, EPIC™, FALC™, FCOS™, FLEXISLIC™, GEMINAX™, GOLDMOS™, HITFET™, HybridPACK™, INCA™, ISAC™, ISOFACE™, IsoPACK™, IWORX™, M-GOLD™, MIPAQ™, ModSTACK™, MUSLIC™, my-d™, NovalithIC™, OCTALFALC™, OCTAT™, OmniTune™, OmniVia™, OptiMOS™, OPTIVERSE™, ORIGA™, PROFET™, PRO-SIL™, PrimePACK™, QUADFALC™, RASIC™, ReverSave™, SatRIC™, SCEPTRE™, SCOUT™, S-GOLD™, SensoNor™, SEROCCO™, SICOFI™, SIEGET™, SINDRION™, SLIC™, SMARTi™, SmartLEWIS™, SMINT™, SOCRATES™, TEMPFET™, thinQ!™, TrueNTRY™, TriCore™, TRENCHSTOP™, VINAX™, VINETIC™, VIONTIC™, WildPass™, X-GOLD™, XMM™, X-PMU™, XPOSYS™, XWAY™. Other Trademarks AMBA™, ARM™, MULTI-ICE™, PRIMECELL™, REALVIEW™, THUMB™ of ARM Limited, UK. AUTOSAR™ is licensed by AUTOSAR development partnership. Bluetooth™ of Bluetooth SIG Inc. CAT-iq™ of DECT Forum. COLOSSUS™, FirstGPS™ of Trimble Navigation Ltd. EMV™ of EMVCo, LLC (Visa Holdings Inc.). EPCOS™ of Epcos AG. FLEXGO™ of Microsoft Corporation. FlexRay™ is licensed by FlexRay Consortium. HYPERTERMINAL™ of Hilgraeve Incorporated. IEC™ of Commission Electrotechnique Internationale. IrDA™ of Infrared Data Association Corporation. ISO™ of INTERNATIONAL ORGANIZATION FOR STANDARDIZATION. MATLAB™ of MathWorks, Inc. MAXIM™ of Maxim Integrated Products, Inc. MICROTEC™, NUCLEUS™ of Mentor Graphics Corporation. Mifare™ of NXP. MIPI™ of MIPI Alliance, Inc. MIPS™ of MIPS Technologies, Inc., USA. muRata™ of MURATA MANUFACTURING CO. OmniVision™ of OmniVision Technologies, Inc. Openwave™ Openwave Systems Inc. RED HAT™ Red Hat, Inc. RFMD™ RF Micro Devices, Inc. SIRIUS™ of Sirius Sattelite Radio Inc. SOLARIS™ of Sun Microsystems, Inc. SPANSION™ of Spansion LLC Ltd. Symbian™ of Symbian Software Limited. TAIYO YUDEN™ of Taiyo Yuden Co. TEAKLITE™ of CEVA, Inc. TEKTRONIX™ of Tektronix Inc. TOKO™ of TOKO KABUSHIKI KAISHA TA. UNIX™ of X/Open Company Limited. VERILOG™, PALLADIUM™ of Cadence Design Systems, Inc. VLYNQ™ of Texas Instruments Incorporated. VXWORKS™, WIND RIVER™ of WIND RIVER SYSTEMS, INC. ZETEX™ of Diodes Zetex Limited. Last Trademarks Update 2009-10-19 Application Note 201 3 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Introduction 1 Introduction FM Radio has a long history to its credit starting from its development in 1933. Today, FM radio is an integral part of almost all mobile phones, including the ultra low cost models. Till recently, the headset served as the antenna for FM Radio reception, wherein the antenna size is a bit relaxed and the antenna performance is satisfactory. A new trend has emerged to be able to use FM radio also without the headset, wherein the antenna has to be embedded into the phone. But in this case, the space constraint poses a challenge on the antenna design. Shrinking the size of the antenna reduces antenna gain and bandwidth, which introduces a high loss into the system which deteriorates the receiver performance, namely the receiver sensitivity. This application note presents Infineon solution to the aforementioned challenges leading to the design of a high performance RF front end with lowest power consumption. A general topology for the RF front-end of FM Radio is as shown in Figure 1. Variations of the given application schematic are possible based on the complete system design and concept. These may include systems with only external headset antenna, only internal embedded antenna or both antennas co-existing. In all cases a ESD protection circuit is needed at the antenna to protect the front-end system from ESD strikes, as the antenna is susceptible to ESD events. More details and Infineon solutions for ESD protection can be found later in this document. A Single Pole Double Throw or SPDT RF switch is used to toggle between the headset and embedded antenna. The switch being in front of the LNA and in the vicinity of strong cellular signals should introduce minimal loss to the system and prove high linearity. To know more about Infineon solutions for RF Switches, please refer to Reference [2]. Headset Antenna ESD Protection SPDT LNA FM Transceiver IC Rx Embedded Antenna Figure 1 ESD Protection FM_Application _Diagram .vsd FM Radio RF Front-End schematic A Low Noise Amplifier or LNA follows the switch, which significantly reduces the noise figure of the whole receiver chain, thereby improving the receiver sensitivity. However, there are a few challenges in the design of the LNA for this purpose. Using it in a hand held device demands low current consumption and high linearity due to the coexistence of cellular bands. In a system with internal antenna, due to the very small size, the antenna impedance is very high and thus the LNA has to be matched to this high impedance and in addition offer a low noise figure. Infineon offers its LNA solution using a low cost discrete transistor BFR460L3, which fulfills all these performance criteria. The LNA is designed for worldwide FM band (76-108 MHz). The LNA finds its application in all kinds of mobile devices like mobile phones, PDAs, portable FM radio, MP3 players etc. Application Note 201 4 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Performance Overview 2 Performance Overview The following table gives a quick overview on the performance of the FM Antenna LNA described in this application note. Table 1 Electrical characteristics at TA = 25°C, VCC = 1.8V, ICCq =2.9 mA, f = 100MHz Measurements done in a 50 Ohm system Parameter Symbol Values Min. |S21| Insertion power gain 1) Typ. 2 Unit Max. 13.5 dB Input return loss RLIN 1.2 dB Output return loss RLOUT 16 dB ISO 40 dB F50ohm 1.0 dB Input 1dB gain compression point P-1dB,in -26 dBm Output 1dB gain compression point P-1dB,out -12.5 dBm Input 3rd Order Intercept Point3) IIP3 -15.5 dBm -2 dBm Isolation Noise figure (Zs=50Ohm) 2) Output 3rd Order Intercept OIP3 Point4) 1) LNA presents a high input impedance match over the 76-108 MHz FM radio band. 2) Does not include PCB and SMA connector losses 3) IP3 value depends on termination of all intermodulation frequency components. Termination used for the measurement is 50 Ω from 0.1 to 6 GHz 4) IP3 value depends on termination of all intermodulation frequency components. Termination used for the measurement is 50 Ω from 0.1 to 6 GHz Application Note 201 5 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Application Circuit 3 Application Circuit The FM Radio application schematic for the BFR460L3 is shown in Figure 2 and the function of each component is explained in Table 2. Vc c 1. 8V R3 56Ω C3 R1 RFin 47n 33kΩ R2 56Ω BFR460 L3 C1 B 330 p E C R4 C2 10Ω 330 p RFout N1 Appl_Ckt.vsd Figure 2 Application schematic for FM Radio Table 2 Bill of material Component Value Manufacturer / Type Function N1 BFR460L3 Transistor Infineon Technologies / TSLP-3-1 LNA Active device C1 330 pF Various / 0402 DC blocking C2 330 pF Various / 0402 DC blocking C3 47 nF Various / 0402 DC stabilization R1 33 kOhm Various / 0402 Biasing R2 56 Ohm Various / 0402 Biasing, Matching, Stability R3 56 Ohm Various / 0402 Biasing and DC operating point stabilization over temperature & transistor hfevariation R4 10 Ohm Various / 0402 RF Stability Application Note 201 6 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Evaluation Board 4 Evaluation Board To enable a fast and stand alone evaluation of the Application circuit described in this document, Infineon offers an application board, which is as shown in the Figure 3. PCB.vsd Figure 3 Evaluation Board The PCB cross-section of the evaluation board is shown in Figure 4. Copper Top FR4, 0.2mm Copper Middle Cu 35µm FR4, 0.8 mm Copper Bottom Figure 4 PCB_Cross_Section.vsd PCB Cross-section Application Note 201 7 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Measurement Results 5 Measurement Results This section presents the measurement results of the aforementioned application circuit on the evaluation board. The measurements were performed at 25°C and include the losses of both SMA connectors and the PCB microstrip lines. 5.1 Narrowband Results NB_Gain 15 14 13 12 11 10 9 8 7 6 5 70 Figure 5 80 90 Frequency (MHz) 100 110 NB_ Gain.vsd Power Gain (dB) RL 0 -5 DB(|S(1,1)|) BFR460L3_FMR_LNA -10 DB(|S(2,2)|) BFR460L3_FMR_LNA -15 -20 70 Figure 6 80 90 Frequency (MHz) 100 110 RL.vsd Input and Output Reflection Coefficient (dB) Application Note 201 8 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Measurement Results Most of the internal antennas for FM Radio are high ohmic and vary in their impedance value based on the antenna design. Therefore, the LNA in this AN is designed to have high impedance at the input, which can be easily matched to the desired antenna. The input impedance of the LNA is shown in Figure 7 for the FMR frequency range. Input_RL 2. 0 6 0. 0.8 1.0 Swp Max 110MHz 0. 4 0 3. 72.438 MHz r 156.919 Ohm x -299.091 Ohm 0 4. 5.0 0.2 10.0 5.0 4.0 3.0 2.0 1.0 0.8 0.6 0.4 0 0.2 10.0 -10. 0 109.9 MHz r 80.8962 Ohm x -222.09 Ohm -3 .0 .0 -2 Input-Smith.vsd Swp Min 70MHz -1.0 -0.8 -0 .6 .4 -0 Figure 7 4 .0 -5. 0 2 -0. Input Reflection Coefficient Isolation 0 -10 -20 -30 -40 -50 70 Figure 8 80 90 Frequency (MHz) 100 110 Iso.vsd Input to Output Isolation (dB) Application Note 201 9 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Measurement Results 5.2 Wide-Band Results Below is a graph depicting wide-band LNA Gain up to 6 GHz. BB_Gain 14 12 10 8 6 4 2 0 -2 -4 -6 -8 -10 0 Figure 9 1000 2000 3000 Frequency (MHz) 4000 5000 6000 WB_Results.vsd Wide-Band: Gain, Input/Output Matching, Isolation Stability 5 K() BFR460L3_FMR_LNA 4 B1() BFR460L3_FMR_LNA 3 2 1 0 0 Figure 10 2000 4000 6000 Frequency (MHz) 8000 10000 Stability.vsd Stability Factor (necessary and sufficient condition for “Unconditional Stability”: k>1 & B1>0) Application Note 201 10 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Appendix 1: ESD protection circuit for system level ESD robustness Appendix 1: ESD protection circuit for system level ESD robustness Introduction With the advancement in miniaturization of semiconductor structures, ESD handling capability of the devices is becoming a concern. Increasing ESD handling capability of the I/O ports costs additional chip size and affects the I/O capacitance significantly. This is very important for high frequency devices, especially when high linearity is required. Therefore, tailored and cost effective ESD protection devices can be used to build up an ESD protection circuit. To handle ESD events during assembly, devices normally have on-chip ESD protection according to the device level standards e.g. “Human Body Model” JEDEC 22-A-115. To fulfill the much more stringent system level ESD requirements according to IEC61000-4-2 as shown in Figure 11, the external ESD protection circuit has to handle the majority of the ESD strike. The best external ESD protection is achieved using a TVS diode assisted by additional passive components. ESD_current, A 60 m6 Reference Pulse 15kV contact discharge according IEC61000-4-2 40 m6 time=1.507nsec ESD_current=57.68 A m7 time=30.01nsec ESD_current=29.43 A m7 m8 20 m8 time=60.01nsec ESD_current=15.18 A 0 0 20 40 60 80 100 120 time, nsec Figure 11 140 160 180 200 ESD_Pulse .vsd ESD test pulse according to system level specification IEC61000-4-2 – Contact Discharge 15kV Some examples of RF applications addressed by the Infineon ESD protection proposal are given below: • • • • • • FM Radio (76 MHz -110 MHz) WLAN 802.11b/g/n (2.4 GHz, Tx ~ +20 dBm) Bluetooth (2.4 GHz, Tx ~ +20 dBm) Automatic Meter Reading, AMR (900 MHz, TX ~ +20 dBm) Remote Keyless Entry, RKE (315 MHz - 434 MHz - 868 MHz - 915 MHz, Tx~13 dBm) GPS (1575 MHz, Rx only but can be affected by RF interferer) For an ESD protection device tailored for medium power RF signals (=< +20 dBm), following requirements are essential: 1. RF requirements a) Bidirectional characteristic to handle DC free signals without clipping / signal distortion b) A highly symmetrical behavior of the ESD device for positive and negative voltage swings is mandatory to keep the power level of even Harmonics low c) Breakdown voltage of 5 V-10V, to avoid signal distortion at high RF voltage swing applied at the TVS diode, located close to the antenna d) High linearity e) Low leakage current and stable diode capacitance vs. RF voltage swing f) Ultra low diode capacitance is mandatory Application Note 201 11 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Appendix 1: ESD protection circuit for system level ESD robustness 2. ESD requirements: a) Lowest dynamic resistance Rdyn to offer best protection for the RFIC; Rdyn is characterized by Transmission Line Pulse (TLP) measurement b) Very fast switch-on time (<<1nsec) to ground the initial peak of an ESD strike according to IEC61000-4-2 c) No performance degradation over a large number of ESD zaps (>1000 Two-step ESD Protection approach General structure for a 2-step ESD approach according to Figure 12 enables to split the entire ESD current between the internal and external ESD protection device. The external device is much more robust and handles the majority of the ESD current. To avoid any impact on the RF behavior of the system and to minimize non linearity effects, the TVS diode should possess an ultra low device capacitance. Therefore the bi-directional (symmetrical) Infineon TVS Diode ESD0P2RF is well suited, which provides a diode capacitance as low as 0.2 pF and a Rdyn of only 1 Ohm. The additional insertion loss in the 50 Ohm environment caused by the ESD0p2RF is less than 0.05dB up to 3Ghz. + Vcc Figure 12 PCB line or Resistor ESD current Main ESD curr ent Internal ESD protection External ESD Pprotection U_ cla mp e xtern LNA/ Switch/ Filter V_Clamp Internal OUT Residual ESD current ESD strike PCB- line ESD_protection_1.vsd Smart 2-step ESD protection approach based on external and internal ESD protection structure For further ESD improvement it is highly recommend to add a serial capacitor (C1). The capacitor cuts off most of the high energy created by the ESD strike. For an improved ESD robustness, C1 should be as small as possible, but has to match to the intended application frequency as well. For a broadband ESD protection (80MHz…3GHz) C1 should be about 150pF…50pF. Optional matching can be implemented with a serial inductor L1 for a dedicated frequency. In combination with L1, C1 can be reduced significantly which improves the ESD performance further more. The serial inductor should be a low Q type serving a (small) serial resistor which is helpful for the ESD performance. An serial resistor of e.g. 2.2 Ohm costs 0.2dB IL, but limits the residual ESD current significant to reduce the ESD stress for the IC input. OUT LNA/ Switch/ Filter Internal ESD Protection RF IC input C1 R1 Residual ESD current ESD_protection_2b.vsd Figure 13 RX antenna Low Q inductor or optional Resistor L1 ESD Diode Vcc ESD current Standard ESD protection topology with optional ESD resistor, blocking capacitor and a serial inductor Application Note 201 12 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 Appendix 1: ESD protection circuit for system level ESD robustness Alternatively another TVS diode (ESD5V3L1U-02LRH/LS, unidirectional) can be used for ESD performance improvement in order to reduce the residual stress for the IC (FM-LNA) in case of high IEC61000-4-2 ESD strikes. The ESD5V3L1U-02LRH/LS provides a dynamic resistance of 0.31 Ohm only (1 Ohm for ESD0P2RF) and a diode capacitance of 1pF typically. For the FM radio frontend the low diode capacitance of 1pF is not affecting the circuit matching performance, the very low dynamical resistance (0.31 Ohm) makes the serial resistor (2.2 Ohm in Figure 2/3) obsolete. However designers have to obey that in packed design with possible high RF interference level e.g. from the TX path of GSM the unidirectional ESD5V3L1U could clip the signal in the negative direction. In a more "non hostile" environment the ESD5V3L1U-02LRH/LS works very fine and provides lower R_dynamic/lower clamping voltage, resulting in in a lower residual ESD stress for the FM radio LNA. For hostile interfering environment, the bidirectional ESD0P2RF is the preferred ESD solution for FM radio, for other FM radio environments, the ESD5V3L1U-02LRH/LS is the better alternative. Application Note 201 13 Revision 1.1, 2010-08-18 Low Cost FM Radio LNA BFR460L3 References References [1] BFR460L3 Datasheet, Infineon Technologies AG. [2] Application Note AN175, RF CMOS SPDT Switches, Infineon Technologies AG Authors 1. Ralph Kuhn, Senior Staff Engineer of the Business Unit “RF and Protection Devices” 2. Deepak Bachu, Senior Application Engineer of the Business Unit “RF and Protection Devices” Application Note 201 14 Revision 1.1, 2010-08-18 w w w . i n f i n e o n . c o m Published by Infineon Technologies AG AN201