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NXP Semiconductors PN544 Design Manual
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NXP Semiconductors PN544 Design Manual

NXP Semiconductors PN544 Design Manual

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AN145715
PN544 Antenna Design Guide
Rev. 1.5 — 28th August 2009
Document information
Info
Content
Keywords
NFC, PN544, Antenna Design, RF Design
Abstract
This application notes provides guidance on antenna and RF design for
NFC device PN544.
Application Note

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Summary of Contents for NXP Semiconductors PN544

  • Page 1 AN145715 PN544 Antenna Design Guide Rev. 1.5 — 28th August 2009 Application Note Document information Info Content Keywords NFC, PN544, Antenna Design, RF Design Abstract This application notes provides guidance on antenna and RF design for NFC device PN544.

  • Page 2: Contact Information

    AN145715 NXP Semiconductors PN544 Antenna Design Guide Revision history Date Description 18/02/2008 Initial Release 14/05/2008 Updates on demo board antenna default matching 27/02/2009 Update on antenna topology 12/03/2009 Minor Updates 30/06/2009 Appendix B added 28/08/2009 max changed to 1.7V Contact information For additional information, please visit: http://www.nxp.com...

  • Page 3: Purpose And Scope

    PN544 antenna topology. The PN544 is capable of performing Reader/Writer (R/W) as well as target mode functionalities. This guide is not primarily based on a strong mathematical background but on a practical approach towards PN544 antenna tuning. Therefore it is recommended to read and use this document as described in the chapter 3 “Tuning Procedure”.
  • Page 4 5 1 H 5 1 H 5 0 H used for Reader/Writer-and Card mode. The number of turns for this antenna topology using the PN544 demo board is six. 5 7 B 5 6 B 5 7 B 5 6 B Fig.
  • Page 5 F ig 1). 5 4 H 5 4 H 5 3 H For the sake of simplicity F ig 2 is a sketch of a possible PN544 demo board 5 5 H 5 5 H 5 4 H antenna. Connections MatchTX1, MatchTX2 and ANT1, ANT2 on the provided NXP PN544 demo board are routed differently.

  • Page 6: Tuning Procedure

    Please follow the steps below for tuning the antenna. The antenna is matched without powering the PN544 IC. A detailed description of each step will follow after this chapter. Step 1: At first the antenna has to be matched to the PN544 as described in chapter 4 .
  • Page 7 Step 4: By removing the 10Ohm resistor, the matching circuit is configured for card mode. The PN544 has to be powered and configured as card. The resonance frequency should be in the range of 14.5 to 16Mhz. Further details on tuning can be...
  • Page 8 The RF block diagram shows the circuitry design with all relevant components required to connect an antenna to the PN544. It also ensures the transmission of energy and data to the target device as well as the reception of a target device answer.

  • Page 9: E Quivalent Circuit

    AN145715 NXP Semiconductors PN544 Antenna Design Guide E quivalent circuit 1 2 B 1 2 B The following subchapters describe the matching procedure. It starts with the determination of the antenna parameters and ends with a fine tuning of the antenna circuitry.
  • Page 10 ˆ ⋅ E MC filter design 1 3 B 1 3 B The EMC filter circuit for the PN544 fulfills two functions: the filtering of the signal and impedance transformation block. The main properties of the impedance transformation are: 145715 ©...
  • Page 11 AN145715 NXP Semiconductors PN544 Antenna Design Guide Decreasing the amplitude rise time after a modulation phase Increasing the receiving bandwidth The EMC filter and the matching circuit must transform the antenna impedance to the required TX matching resistance Z (f) at the operating frequency of f = 13.56 MHz.
  • Page 12 AN145715 NXP Semiconductors PN544 Antenna Design Guide Filter resonance frequency f = 15.5MHz ...16MHz, => C π ⋅ ⋅ The EMC filter resonance frequency f has to be higher than the upper sideband frequency determined by the highest data rate (848 kHz sub carrier) in the system.
  • Page 13 AN145715 NXP Semiconductors PN544 Antenna Design Guide 4.2.1 Capacitive tuning of antenna Due to detuning effects in close distance between reader and card antennas a capacitive tuning is recommended. Fig. 8 Smith diagram for capacitive antenna tuning It is accomplished by lowering C0 compared to the design guidelines given for the first generation NFC devices.
  • Page 14 1 5 B 1 5 B The matching circuit elements C and C must be tuned to get the required matching resistance R = 0) at the PN544 TX pins. The matching impedance Z match match match + jX is measured with an impedance or network analyzer. The Z...
  • Page 15 TX1 and TX2 of the PN544. Different equivalent resistive loads lead to different transmitter supply currents. An optimum tuning R for PN544 is 80Ohm match 145715 ©...
  • Page 16 AN145715 NXP Semiconductors PN544 Antenna Design Guide I mpact of the tuning capacitors visualized on Smith chart 1 6 B 1 6 B 4.5.1 E MC capacitance C0 3 1 B 3 1 B The following diagrams show the effect to the impedance curve by changing C0.
  • Page 17 AN145715 NXP Semiconductors PN544 Antenna Design Guide 4.5.2 S eries capacitance C1 3 2 B 3 2 B The following diagrams show the effect to the impedance curve by changing C1. The smith charts in F ig 15 show the matching impedance Z / 2 vs.
  • Page 18 AN145715 NXP Semiconductors PN544 Antenna Design Guide 4.5.3 P arallel matching capacitance C2 3 3 B 3 3 B The following diagrams show the effect to the impedance curve by changing C2. The smith charts show the matching impedance Z / 2 vs.
  • Page 19 Hence, the RX-point must be checked under following conditions: 1. PN544 antenna not detuned 2. PN544 antenna detuned with a card 3. PN544 in card/target mode and U < U for H <= 7.5 A/m RXmax Fig.
  • Page 20 AN145715 NXP Semiconductors PN544 Antenna Design Guide E xample 1 8 B 1 8 B The antenna of the PN544 evaluation board will be matched to the PN544 transmitter output. Fig. 15 PN544 evaluation board antenna ≈ 80Ohm Recommended R...
  • Page 21 AN145715 NXP Semiconductors PN544 Antenna Design Guide Calculation of the matching parts C = 19.73pF → 18pF normalized value = 52.55pF → 47pF normalized value Simulation result: Fig. 16 Example: Z Smith chart match It can be seen from F ig 19 that the resonance point (13.56MHz) is in the capacitive part...
  • Page 22 AN145715 NXP Semiconductors PN544 Antenna Design Guide S tep 2 – Connecting ANT1 and ANT2 pins 4 B B In step 1 we successfully tuned the matching circuit to a resonance frequency at 13.56 MHz at around 80Ohm. The circuit of step one is again outlined in F ig 20.
  • Page 23 Reader/Writer and card mode and available discrete components. S tep 3 – Reader/Writer fine-tuning 5 B 5 B All tuning steps for the PN544 need to be done without powering the chip. P recondition to start measurements 4 9 B 4 9 B 145715 ©...
  • Page 24 In order to simulate the Reader/Writer behavior of the antenna, C2b capacitors need to be shortcut with a 10 Ohm resistor. In the final application this will be taken over by PN544 so do not forget to remove the part after finishing the tuning. What is the effect? When shortening C2b with 10Ohm resistance C2b acts as additional capacitance parallel to C2a and causes a frequency shift.
  • Page 25 S tep 4 – Card mode tuning 6 B 6 B The tuning steps of PN544 circuitry needs to be done without powering the chip. After accomplishing “Step 3” we need to verify the card mode. The 10Ohm resistor has to be removed now! Card mode tuning is measured with the PN544 being not powered and configured as card.
  • Page 26 AN145715 NXP Semiconductors PN544 Antenna Design Guide Fig. 21 Block diagram for card mode tuning with removed 10Ohm resistor The measurement shall show a resonance in the range of 14.5MHz to 16Mhz. M odifications if resonance frequency does not meet the requirements 5 2 B 5 2 B 1.
  • Page 27 AN145715 NXP Semiconductors PN544 Antenna Design Guide A ppendix 7 B 7 B A ntenna design 1 9 B 1 9 B 8.1.1 A ntenna inductance 3 4 B 3 4 B The following two sub-chapters 8 .1.2 and 8 .1.3 show required formulas to estimate the...
  • Page 28 AN145715 NXP Semiconductors PN544 Antenna Design Guide 8.1.3 R ectangular antennas 3 6 B 3 6 B F ig 28 shows a typical rectangular antenna. 7 6 H 7 6 H 7 5 H Fig. 23 Rectangular antenna Variables: Overall dimensions of the coil...
  • Page 29 AN145715 NXP Semiconductors PN544 Antenna Design Guide ⎡ ⎤ ⋅ − ⎢ ⎣ ⎥ ⎦ 8.1.4 N umber of turns 3 7 B 3 7 B Depending on the antenna size, the number of turns has to be chosen in a way to achieve an antenna inductance between 300 nH and 3 µH.
  • Page 30 AN145715 NXP Semiconductors PN544 Antenna Design Guide F ig 30 shows an example of a symmetric 4-turn antenna design. It can be seen that the 7 8 H 7 8 H 7 7 H center tap of the antenna is connected to ground. Basically, we do not recommend grounding the center tap, but leaving it floating.
  • Page 31 AN145715 NXP Semiconductors PN544 Antenna Design Guide negligible if the antenna is very near to interfering material (metal, battery) and the ferrite has low permeability (foils usually µ <10). Field strength color map 7.5 cm Minimum field strength Hmin=1.5 A/m |H| [A/m] Fig.
  • Page 32 AN145715 NXP Semiconductors PN544 Antenna Design Guide F ig 33 shows a ferrite plane (µ =40) which is positioned between the metal plane and the 8 2 H 8 2 H 8 1 H antenna coil itself. The field strength very near to the ferrite increases, but the increasing magnitude does not necessarily result in an increase of the operating distance at H value (vertical doted line).
  • Page 33 AN145715 NXP Semiconductors PN544 Antenna Design Guide T = 3 µs Fig. 29 Pulse width definition The bandwidth B –pulse width T product is defined as: ⋅ T ≥ With the bandwidth definition the B-T product results to ≤ ⋅...
  • Page 34 AN145715 NXP Semiconductors PN544 Antenna Design Guide E quivalent circuit measurement 2 1 B 2 1 B 8.2.1 I mpedance analyzer with equivalent circuit calculation 4 4 B 4 4 B Impedance analyzers like Agilent 4294A or 4395A can determine directly the series or parallel equivalent circuit by measuring the magnitude and the phase of the impedance of the connected antenna.
  • Page 35 AN145715 NXP Semiconductors PN544 Antenna Design Guide connection points) before each measurement. Please refer to device manual on how to carry out these steps. Settings: S11 Chart: Smith Z Start frequency: 1 MHz Stop frequency: above self-resonance frequency of the antenna 8.2.3...
  • Page 36 AN145715 NXP Semiconductors PN544 Antenna Design Guide The series equivalent resistance of the antenna at the operating frequency f 13.56MHz can be calculated out of the characteristic circuit. Fig. 31 Series equivalent resistance calculation fres fres π ⋅ ⋅ ⋅...
  • Page 37 AN145715 NXP Semiconductors PN544 Antenna Design Guide PHILIPS Reader Terminal Antenna Fig. 32 Setup to check the Q-factor CH1: Use a loop with the ground line shortcut at the probe to enable inductive signal coupling. Hold the probe loop closely above the antenna.
  • Page 38 The time t1-t2 describes the time span, in which the signal falls from 90% down below 5% of the signal amplitude. As the pulse length of PN544 is accurate enough, only the time t2 has to be checked: the signal has to remain below 5% for the time t2.
  • Page 39 AN145715 NXP Semiconductors PN544 Antenna Design Guide 8.4.2 B it rate 212 kbps and 424 kbps 4 8 B 4 8 B Fig. 34 Pulse shape according to ISO 18092, 212 and 424 kbps Table 8-1: Pulse shape definitions according to ISO18092, 212 and 424 kbps...
  • Page 40 AN145715 NXP Semiconductors PN544 Antenna Design Guide 9. Appendix B 9.1 How to measure card mode resonance frequency The card-mode resonance frequency and quality factor depends on the H-field strength. As a matter of fact, the chip input resistance and capacitance have a dependency on the antenna voltage.
  • Page 41 AN145715 NXP Semiconductors PN544 Antenna Design Guide A bbreviations 8 B 8 B Electromagnetic compatibility Reader/Writer Receiver Printed Circuit Board Transmitter matching resistance match Transmitter Transmitter matching impedance match 145715 © NXP B.V. 2006. All rights reserved. Application Note Rev. 1.5 — 28th August 2009...

  • Page 42: Legal Information

    11.2 T rademarks Right to make changes — NXP Semiconductors reserves the right to make 2 5 B 2 5 B changes to information published in this document, including without Notice: All referenced brands, product names, service names and limitation specifications and product descriptions, at any time and without trademarks are property of their respective owners.
  • Page 43 AN145715 NXP Semiconductors PN544 Antenna Design Guide C ontents 9 B 9 B 0 B 0 B I NTRODUCTION ............ 7 B 7 B A PPENDIX ............8 9 H 2 4 H 1 1 3 H 1 .1 1 1 B 1 1 B P .........
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