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S m a r t L E W I S TM R X + BDTIC TDA524 0/35 /25 Sensitivity Improvement by using the Automatic Frequency Control (AFC) for FSK App lication No te V1.3, 2013-10-11 Wireless Sense & Control www.BDTIC.com/infineon BDTIC Edition 2013-10-11 Published by Infineon Technologies AG Am Campeon 1 - 12, 85579 Neubiberg, Germany © 2013-10-11 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. www.BDTIC.com/infineon Sensitivity Improvement using AFC TDA5240 Enhanced Sensitivity Receiver TDA5240 Revision History: 2013-10-11, V1.3 Previous Revision: V1.1 Page Subjects (major changes since last revision) --- Keywords added in document Page 8 Min values for analog bandwidth added BDTIC 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 www.BDTIC.com/infineon 3 V1.3, 2013-10-11 Sensitivity Improvement using AFC Table of Contents Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Receiver and FSK Demodulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Bandwidth considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4 4.1 AFC configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 AFC frequency overshoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5 Sensitivity Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6 7 BDTIC Blocking Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Application Note www.BDTIC.com/infineon 4 V1.3, 2013-10-11 Sensitivity Improvement using AFC List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Double down conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Single down conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 System BW measurement using RSSI voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Input power = -80 dBm; K1 = K2; 25% overshoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Input power = -80 dBm; K2 = K1/10; no overshoot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Input power at sensitivity level; K1 = K2; 25% overshoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Input power at sensitivity level; K2 = K1/10; no overshoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Sensitivity Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Blocking Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 BDTIC Application Note www.BDTIC.com/infineon 5 V1.3, 2013-10-11 Sensitivity Improvement using AFC Introduction 1 Introduction The Automatic Frequency Control (AFC) can be used to decrease the used Channel Filters to the given theoretical occupied bandwidth of the transmitted signal. By doing this, the sensitivity of the receiver system which is defined by the front end noise figure and the used receive channel bandwidth can be increased significantly. This application note describes the technical background of the AFC and the techniques how to setup the channel filters and AFC loop constants of the receiver. In general it can be stated that the described techniques are only valid for FSK modulation. In the Chapter 5 and Chapter 6 some measurements shows the significant sensitivity improvement by using the AFC in combination with wide possible frequency offsets of the transmitter counterpart. 2 Receiver and FSK Demodulation BDTIC The receiver is realized as a superheterodyne architecture with single or double down conversion to the 274kHz IF frequency. The pictures below shows the principle of single and double down conversion: match + SAW CERF MIX1 fc=10.7MHz fo=10.7MHz 150~300kHz BPF fc=274Hz MIX2 50, 80, 125, fo=274kHz 200, 300kHz LIM fc=274kHz DIGMIX fo=0Hz PDF 33~283kHz LNA FSK FSK 10.974 MHz 274kHz SDPLL Figure 1 AFC Double down conversion match + SAW MIX1 fo=274kHz BPF fc=274Hz 50, 80, 125, 200, 300kHz LIM fc=274kHz DIGMIX fo=0Hz PDF 33~283kHz LNA FSK FSK 274kHz SDPLL Figure 2 AFC Single down conversion The local oscillator frequency of the receiver is derived out of the on-chip fully integrated Sigma-Delta Fractional N PLL Synthesizer which enables a high frequency resolution. The functionality of the digital programmable Application Note www.BDTIC.com/infineon 6 V1.3, 2013-10-11 Sensitivity Improvement using AFC Bandwidth considerations Synthesizer is used by the AFC circuitry to adjust the receiver local oscillator to the transmitted center frequency. In reality all transmitters and receivers have a frequency drift over temperature and supply voltage. Due to this frequency drift of the system, receivers without AFC need to take this frequency drift into account by selecting the appropriate receiver channel filter (occupied bandwidth of Signal + receiver / transmitter frequency inaccuracy). The architecture of the IFX receiver which uses a analog bandpass filter after the down conversion and a additional digital predemodulation filter where the bandwidth of both filters can be selected independently, enables a wide frequency offset in combination with good jammer behavior and outstanding sensitivity performance. In parallel to the predemodulation filter (PDF) a second FSK demodulator is used to derive the control signal for the Automatic Frequency Control Unit, which is actually the DC value of the FSK demodulated signal. This makes the AFC loop independent from signal path filtering and allow a wider frequency capture range of the AFC. Since the digital FSK demodulator determines the exact frequency offset between the received input frequency and the programmed input center frequency of the receiver, this offset can be corrected through the sigma delta control of the PLL. As shown in Figure 1 and Figure 2, for AFC purposes a parallel demodulation path is implemented. This path does not contain the digital low pass filter (PDF). The entire IF bandwidth, filtered by the analog bandpass filter only, is processed by the AFC demodulator. BDTIC The maximum frequency offset removed by the AFC can be limited to avoid the tracking of unwanted signal too far away from the selected channel. 3 Bandwidth considerations The minimal bandwidth for the expected signal is defined by the carson rule: (1) BW min = 2 × ( f DRmax + f deviation ) • • fDRmax = max frequency in baseband data fdeviation = deviation of FSK modulation To achieve the best sensitivity the reception bandwidth of the receiver should be equal or just slightly bigger then the minimal bandwidth. That means that the digital predemodulation filter (PDF) of the receiver should be set to the minimum bandwidth as calculated by the carson rule. As mentioned before, due to tolerances on the receiver and transmitter side the caption range of the AFC must be large enough to cover those frequency offsets. With the two filter approach the analog bandpass filter (BPF) can be adjusted to cover the frequency tolerances and the PDF can be set to the minimal required occupied carson bandwidth. With such a technique the receiver is setup for highest possible sensitivity in combination with wide frequency tolerances of the transmitter / receiver. The best way to define the analog system bandwidth is to measure the RSSI voltage by applying a continuous wave (CW) signal at the RF input of the receiver. The measurement shall be done by changing the frequency of the CW and collect at each point a RSSI measurement value. The 3dB reference value should be taken at the center frequency by decreasing the CW signal power by 3dB. In the following picture such a measurement was done and the resulting system bandwidth is calculated. Application Note www.BDTIC.com/infineon 7 V1.3, 2013-10-11 Sensitivity Improvement using AFC AFC configuration RSSI [V] System Bandwidth measured at analog RSSI 1.6 1.55 1.5 1.45 1.4 1.35 1.3 1.25 1.2 1.15 1.1 1.05 BDTIC 1 -300 -200 -100 0 0.95 200 300 Thousands 100 Signal frequency offset [kHz] Signal -90dBm - BPF50kHz Figure 3 Signal -90dBm - BPF125kHz Signal -90dBm - BPF300kHz System BW measurement using RSSI voltage The analog system bandwidth for different bandpass filter settings are shown in the table below: Table 1 Analog system bandwidth (related to a CW input signal) BPF setting BWana (typ.) BWana (min.) 50 kHz 50 kHz (DDC/SDC) 20 kHz (DDC/SDC) 80 kHz 80 kHz (DDC/SDC) 47 kHz (DDC/SDC) 125 kHz 120 kHz (DDC/SDC) 88 kHz (DDC/SDC) 200 kHz 180 kHz (DDC/SDC) 140 kHz (DDC/SDC) 1) 300 kHz 230 kHz (DDC ) 180 kHz (DDC) 240 kHz (SDC2)) 200 kHz (SDC) 1) DDC .. Double Down Conversion 2) SDC .. Single Down Conversion 4 AFC configuration A general rule to setup the right AFC limit for Run Mode Slave (always on) is: (2) BW ana f AFClimit ≤ ----------------- + f deviation 4 This rule maintains that the frequency change done by the AFC will never push the center frequency out of the analog frontend system bandwidth. Application Note www.BDTIC.com/infineon 8 V1.3, 2013-10-11 Sensitivity Improvement using AFC AFC configuration This has the advantage that the receiver functionality at the presence of a possible interferer which is out of band is not significantly degraded due to the AFC frequency de tuning. (See Figure 9 “Blocking Comparison” on Page 14) The receiver has also the functionality of Self Polling which means autonomous changing from Sleep Mode to Run Mode. If the receiver is configured in self polling mode, the AFC is initialized after each change from Sleep Mode to Run Mode. This means also, that a possible interferer is not able to de tune the AFC which enables a even higher AFC limit. A general rule to setup the right AFC limit for Self Polling Mode is: (3) BW ana f AFClimit ≤ ----------------- + f deviation 2 BDTIC The AFC bandwidth (and thus the settling time) of the AFC loop is programmed by means of the integrator gain coefficients K1 and K2 (x_AFCK1CFG and x_AFCK2CFG register) K1 mainly determines the AFC bandwidth (AFCBW). K2 influences the dynamics/damping (overshoot) - smaller K2 means smaller overshoot, but slower dynamics. (4) AFC BW = f DR ⋅ K1 ⋅ 1, 3 To avoid residual FM, limiting the AFCBW to 1/20 ~ 1/80 of the data rate is suggested, therefore K1 must be set to approximately 1/25 ~ 1/100 of the data rate. Table 2 settings available in the Explorer tooling: AFC tool setting K1 factor AFC bandwidth ultra fast Data Rate / 10 Data Rate / 7.7 fast Data Rate / 25 Data Rate / 20 normal Data Rate / 50 Data Rate / 38.5 slow Data Rate / 75 Data Rate / 57.7 very slow Data Rate / 100 Data Rate / 80 Application Note www.BDTIC.com/infineon 9 V1.3, 2013-10-11 Sensitivity Improvement using AFC AFC configuration 4.1 AFC frequency overshoot The overshoot of the frequency which is mainly influenced by the K2 factor should be reduced as much as possible. Due to the fact that the digital filter is very tight, a overshoot in the frequency domain would result in a extended settling time of the receiver at low input power levels. In the picture below the output of the FSK demodulator (magenta curve) and the corresponding baseband data of the transmitter (blue curve) are shown at -80dBm input level and 40kHz center frequency offset. In addition the digital channel D1 shows the clock recovered data (CHIP_DATA) and the digital channel D0 shows the analog slicer output (DATA). BDTIC Figure 4 Input power = -80 dBm; K1 = K2; 25% overshoot Application Note www.BDTIC.com/infineon 10 V1.3, 2013-10-11 Sensitivity Improvement using AFC AFC configuration BDTIC Figure 5 Input power = -80 dBm; K2 = K1/10; no overshoot It can be seen that at high input level the overshoot effect has no influence on the settling time. The next pictures were taken with input power levels at the sensitivity boarder and 40kHz center frequency offset. Figure 6 Input power at sensitivity level; K1 = K2; 25% overshoot Application Note www.BDTIC.com/infineon 11 V1.3, 2013-10-11 Sensitivity Improvement using AFC AFC configuration This figure shows that the overshoot results in a degradation of the FSK output signal and corresponding to that also a degradation of the sensitivity by a given constant settling time of the receiver. BDTIC Figure 7 Input power at sensitivity level; K2 = K1/10; no overshoot By avoiding the overshoot the signal stays always within the digital PDF filter and therefore no degradation of the sensitivity is expected. Application Note www.BDTIC.com/infineon 12 V1.3, 2013-10-11 Sensitivity Improvement using AFC Sensitivity Comparison 5 Sensitivity Comparison In this section of the application note we will show, how the sensitivity of the system can be improved by using the AFC and the tight predemodulation filter. The measurement was packet based using the on chip FIFO and the message error rate limit was set to 10%. 2.4kBit, FSK, 5k Dev, Message Error Rate -116 -114 BDTIC Sen s [d B m ] -112 -110 -108 -106 -104 Thousands -102 -100 -100 -80 -60 -40 -20 0 20 40 60 80 100 frequency offset [kHz] AFC ON 125kBPF 33kPDF 42kAFCLIM Figure 8 AFC ON 300kBPF 33kPDF 64kAFCLIM AFC OFF 125kBPF 132kPDF AFC OFF 300kBPF 282kPDF Sensitivity Comparison It can be seen by using the AFC a sensitivity improvement of ~5dB can be achieved with 125kHz BPF and ~7dB improvement by using the 300kHz BPF setting. The following formula shows the theoretical sensitivity improvement by reducing the PDF filter bandwidth. (5) Sens diff = 10 × log ( BW diff ) Example: (6) 120kHz Sens diff = 10 × log ( BW diff ) = 10 × log ⎛ --------------------⎞ = 5, 6dB ⎝ 33kHz ⎠ (7) 230kHz Sens diff = 10 × log ( BW diff ) = 10 × log ⎛⎝ --------------------⎞⎠ = 8, 4dB 33kHz As can be seen the calculation follows roughly the measurements. Application Note www.BDTIC.com/infineon 13 V1.3, 2013-10-11 Sensitivity Improvement using AFC Blocking Comparison 6 Blocking Comparison The setup for the blocking measurement: Two Signal Generators where used and combined to the RF input of the receiver. The wanted signal was set to 3 dB above the sensitivity limit at the center of the channel and the jammer power level was increased as long the message error rate of 10% was reached again. The difference between jammer level and wanted signal power level for different BPF bandwidth settings and AFC configurations are plotted in the figure below. Blocking 20 BDTIC 10 0 S/J [dB] -10 -20 -30 -40 -50 -60 -500 -400 -300 -200 -100 0 100 200 300 125kBPF 33kPDF AFCON Figure 9 Blocking Comparison 7 Conclusion 300kBPF 33kPDF AFCON 125k BPF 132kPDF AFCOFF 400 500 Thousands Jam m er frequency offset [kHz] 300kBPF 283kPDF AFCOFF It can be seen that usage of the AFC has a slight impact on the blocking performance. The curves using the AFC are wider according to the used AFC limit. A trade off between the wider blocking curve and the enhanced sensitivity needs to be done. In general it can be seen, by using the AFC a significant sensitivity improvement can be achieved which approximately doubles the range of the system. Application Note www.BDTIC.com/infineon 14 V1.3, 2013-10-11 BDTIC w w w . i n f i n e o n . c o m www.BDTIC.com/infineon Published by Infineon Technologies AG