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AN1445
Antenna design guide for MFRC52x, PN51x and PN53x
Rev. 1.2 — 11 October 2010
144512
Document information
Info
Content
Keywords
NFC, MFRC522, MFRC523, PN511, PN512, PN531, PN532, Antenna
Design, RF Design, constant current design
Abstract
This application notes provides guidance on antenna and RF design for
NFC devices MFRC522, MFRC523, PN511, PN512, PN531, PN532
Application note
PUBLIC
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Table of Contents
Related Manuals for NXP Semiconductors MFRC52 Series
Summary of Contents for NXP Semiconductors MFRC52 Series
- Page 1 AN1445 Antenna design guide for MFRC52x, PN51x and PN53x Rev. 1.2 — 11 October 2010 Application note 144512 PUBLIC Document information Info Content Keywords NFC, MFRC522, MFRC523, PN511, PN512, PN531, PN532, Antenna Design, RF Design, constant current design Abstract This application notes provides guidance on antenna and RF design for NFC devices MFRC522, MFRC523, PN511, PN512, PN531, PN532...
- Page 2 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Revision history Date Description 20101011 Update with MFRC522 and MFRC523 2008/02/22 Selection Guide and all topologies added 2007/10/31 Initial Release Contact information For additional information, please visit: http://www.nxp.com For sales office addresses, please send an email to: salesaddresses@nxp.com...
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Page 3: Introduction
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 1. Introduction 1.1 Purpose and Scope This application note is intended to give a practical guide to design and dimension antennas and RF parts for contactless reader as well as NFC devices. The application... -
Page 4: How To Use This Document
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Note: MFRC52x devises are Reader/Writer devises only. So these are not able to operate in target mode. 2. How to use this document The application note is intended to give a practical guide to choose the matching topology, to design antennas and calculate the matching components for the MFRC52x/PN51x/PN53x RF part. - Page 5 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x c. Formulas to calculate the EMC filter and the matching circuit d. Antenna tuning procedure e. Design and calculation of the receiving part f. Example calculations Note: This application note does not replace the relevant datasheets referenced in chapter 9.
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Page 6: Selection Guide
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 3. Selection Guide The following flow chart describes a selection guide for different antenna topologies. The user needs to start from the top rectangle going downwards. Due to different detuning effects on the antenna only one of the following topologies may apply to the type of reader integration. -
Page 7: Fig 1. Block Diagram Of The Complete Rf Part
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4. Antenna Topology I The RF block diagram in Fig 1 shows a recommended circuitry design with all relevant components required to connect an antenna to the MFRC522/MFRC523/PN51x/PN53x. It also ensures the transmission of energy and data to the target device as well as the reception of a target device answer. -
Page 8: Fig 2. Series Equivalent Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4.1 Equivalent circuit 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 9: Fig 3. Parallel Equivalent Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Note: The equivalent circuit (Fig 3) must be determined under final environmental conditions especially if the antenna will be operated in metal environment or a ferrite will be used for shielding. -
Page 10: Fig 5. Definition Of Transformation Impedance Z
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Fig 5. Definition of transformation impedance Z − EMC filter general design rules: = 390 nH - 1 µH Filter resonance frequency f = 14.1 MHz ...14.5 MHz, => C π... - Page 11 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x ω ⋅ − ⋅ ⋅ − ⋅ match ω ⋅ ⋅ ω ω − ⋅ ⋅ ⋅ ⋅ match AN1445_12 All information provided in this document is subject to legal disclaimers.
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Page 12: Fig 6. Measurement Of Matching Impedance
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4.3 Matching circuit design 4.3.1 Component calculation The following formulas apply for the series and parallel matching capacitances: ≈ ⋅ ω ⋅ ... -
Page 13: Fig 7. Calculation Of Matching Impedance
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Fig 7. Calculation of matching impedance Fig 8 shows the smith chart simulation for Z / 2: match Fig 8. Smith chart for matching impedance AN1445_12 All information provided in this document is subject to legal disclaimers. - Page 14 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Conditions for the tuning: R curve symmetric around the operating frequency match X curve conjugate complex symmetric around the operating frequency match Note: All tuning and measurement of the antenna always has to be performed at the final mounting position to consider all parasitic effects like metal influence on quality factor, inductance and additional capacitance.
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Page 15: Fig 9. Smith Charts For C Tuning
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4.4.1 Tuning of series matching capacitance C The smith charts in Fig 9 show the matching impedance Z / 2 vs. frequency. match a. Optimum C1 b. C too low c. -
Page 16: Fig 10. Smith Charts For C Tuning
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4.5 Tuning of parallel matching capacitance C The smith charts show the matching impedance Z / 2 vs. frequency. match d. Optimum C2 e. C too low f. C too high Fig 10. -
Page 17: Tuning Flow Chart
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4.5.1 Tuning flow chart START > 13.56 MHz Zmax Phase = 0 Phase = 0 Decrease C2 Increase C2 (+/- 10°) (+/- 10°) Zmax = 40 - 50 Ohm |Z(13.56 MHz - ∆... -
Page 18: Receiver Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 4.6 Receiver circuit design Next step, after matching and tuning the transmitting antenna, is the design and tuning of the receiver circuit. The investigations need to be carried out for initiator and target mode. -
Page 19: Pn51X/Pn53X Evaluation Board Antenna
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x (11) ⋅ − with the target value of U = 1 V (antenna not detuned) Step 4: After inserting the determined resistor R... - Page 20 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x The parallel equivalent circuit of the antenna including quality factor damping resistors R = 3.3 Ohm is determined with the following values: = 7148 Ohm = 11 pF = 2.9 µH...
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Page 21: Fig 14. Example: Z Match Simulation
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Simulation result: ⋅ 13.56 10 Re Zmatch f ( ) Im Zmatch f ( ) 1.2 . 10 1.25 . 10 1.3 . 10 1.35 . 10 1.4 . 10 1.45 . -
Page 22: Fig 16. C1 Split Topology
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 5. Antenna Topology II This chapter introduces a capacitor split in the matching circuit to improve large voltage drops at the RX-path. The modifications in the antenna topology are show in Fig 17. The... -
Page 23: Fig 17. Measurement Points For C1 Split
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x of the final mounted antenna and use a low capacitance probe for the measurements. Refer also to Fig 17 on where to place the measurement probes. Fig 17. Measurement points for C1 Split... -
Page 24: Emc And Vant
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 30,00 25,00 U_ANT; 24,14 20,00 U_EMC 15,00 U_ANT U_EMC; 10,80 10,00 5,00 U_EMC; 5,10 U_ANT; 4,60 0,00 w ithout detuning w ith detuning (1) The intersection point is calculated with V Fig 18. -
Page 25: Fig 19. The Voltage At Rx Is More Stabilized
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Now choose appropriate values for C and C , such that the back transformation to a series capacitance gives C1 again. Thus, always check if ⋅ ≅ (16) Otherwise the antenna will be mismatched. Replace only the capacitor C in the TX1-path as shown in Fig 17. -
Page 26: Fig 20. Parallel Capacitor To C1
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 5.2 Features and hints of using antenna topology II By using the antenna topology II it is possible to counteract very strong voltage level variations on the RX-path in reader mode. Although there is no disadvantage in regard to communication constraints when using antenna topology II, it is trickier to tune it. -
Page 27: Fig 21. Asymmetric Tuning Of Antenna Topology I And Ii
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 6. Asymmetric tuning of antenna topology I or II The antenna topology I and II was tuned to have a matching of around 50 Ohms and an impedance curve symmetric around the operating frequency. When loaded with a target, the 13.56 MHz point shifts close to the short circuit point of the Smith Chart when... -
Page 28: Fig 22. Smith Charts For C Tuning
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 6.1 Tuning of series matching capacitance C The smith charts in Fig 22 shows the tuning effect on the impedance curve by adjusting Optimum C1 too low too high Fig 22. -
Page 29: Fig 23. Smith Charts For C Tuning
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 6.2 Tuning of parallel matching capacitance C The smith charts in Fig 23 shows the tuning effect on the impedance curve by adjusting Optimum C2 too low too high Fig 23. -
Page 30: Fig 12. Fig
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7. Antenna Topology III Fig 24. Block diagram of the complete RF part Note: Fig 24 shows only the RF part and the related power supply (TVDD and TVSS). - Page 31 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Table 2. Component list for a basic RF Design Abbreviation Explanation External damping resistors to adjust the quality factor. The power dissipation has to be considered. Typically 0402, 0603 or 0805 SMD parts with low tolerance (< ±2%). NP0 dielectric is required for temperature stability reasons.
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Page 32: Fig 25. Detuning Effects Of Old Antenna Topology
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.1 Features and hints of antenna topology III The antenna topology in this document introduces some major advantages w.r.t. to power consumption, detuning effects on the RX-path and the type and amount of targets in the RF field. -
Page 33: Match
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.2 Transmitter matching resistance R match The transmitter (TX) matching resistance R defines the equivalent resistance at the match operating frequency present between the transmitter output pins TX1 and TX2 of the PN51x/PN53x. -
Page 34: Fig 28. Rf Power Vs. Matching Resistance
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Fig 28 shows antenna power (H-field) dissipation in relation to the matching resistance. 180,00 160,00 140,00 120,00 [mW] 100,00 80,00 60,00 40,00 20,00 0,00 10,0 20,0 30,0 40,0 50,0... -
Page 35: Fig 30
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Conclusion A higher matching resistance results in less power consumption but only slightly less available RF power output compared to the maximum available RF power output. A good compromise between available RF power and TX power consumption can be reached by a matching resistance R between 60 and 80 Ohm. - Page 36 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x • 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 at the operating frequency of f = 13.56 MHz.
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Page 37: Fig 31. Simulation Of Matching Impedance
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Note: Due to simplification of the formulas and tolerances of the measured equivalent antenna circuit values, a final tuning of the matching circuit is necessary to achieve the required matching resistance at the transmitter output pins. -
Page 38: Fig 32. Smith Chart For Matching Impedance
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x The smith chart in Fig 32 shows the antenna simulation based on the example values used in chapter 7.7. Fig 32. Smith chart for matching impedance AN1445_12 All information provided in this document is subject to legal disclaimers. -
Page 39: Fig 33. Smith Charts For C Tuning
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.4.1 Tuning of EMC matching capacitance C The smith charts in Fig 33 show the matching impedance Z vs. frequency. match Optimum C0 too low too high Fig 33. Smith charts for C tuning changes the magnitude of the matching impedance. -
Page 40: Fig 34. Smith Charts For C 1 Tuning
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.4.2 Tuning of series matching capacitance C The smith charts in Fig 34 show the matching impedance Z 2 vs. frequency. match Optimum C1 too low too high Fig 34. Smith charts for C... -
Page 41: Fig 35. Tuning Flow Chart
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.4.3 Tuning flow chart START > 13.56 MHz Zmax Phase = 0 Phase = 0 Decrease C1 Increase C1 (+/- 10°) (+/- 10°) Zmax = 60 - 80 Ohm Zmax <... -
Page 42: Fig 36. Receiver Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.5 Receiver circuit design Next step, after matching and tuning the transmitting antenna, is the design and tuning of the receiver circuit. The investigations need to be carried out for initiator and target mode. -
Page 43: Target Mode
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Typically low capacitance probes are terminated with 50 Ohm, thus the scope configuration has to be set correctly! Step 3: The voltage divider resistor R can be calculated by: ... -
Page 44: Fig 37. Mfrc52X/Pn51X/Pn53X Evaluation Board
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 7.7 Example As an example the antenna of the MFRC52x/PN51x/PN53x evaluation board Rev. 1.1 will be matched to the transmitter output (see Fig 37). Fig 37. MFRC52x/PN51x/PN53x evaluation board antenna ≈... -
Page 45: Fig 38. Z Match Simulation
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x = 71.95 pF The EMC capacitances C and C are determined for the values of C and C = -417.62 pF = 618.20 pF The correct values for the matching components are C and C Refer to Fig 31 for a simulation of the magnitude and phase of the final antenna circuit. -
Page 46: Fig 39. Circular Antenna
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 8. Appendix 8.1 Antenna design 8.1.1 Antenna inductance The following two sub-chapters 8.1.2 and 8.1.3 show required formulas to estimate the antenna inductance in free air. Note: Sophisticated simulation software is required to calculate the antennas parameters to estimate antenna values in environments containing metal (such as shielding planes or batteries in devices). -
Page 47: Fig 40. Rectangular Antenna
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 8.1.3 Rectangular antennas Fig 40 shows a typical rectangular antenna. Fig 40. Rectangular antenna Variables: Overall dimensions of the coil Average dimensions of the coil Track thickness Track width... -
Page 48: Fig 41. Ground Current Compensation
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x ⋅ − 8.1.4 Number of turns 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 49: Fig 42. Example Symmetric 4-Turn Antenna
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x virtual ground point which is floating to achieve symmetry of the antenna. Refer also to Fig 41 where center tap is not connected. TVSS Fig 42. Example symmetric 4-turn antenna 8.1.6 Ferrite shielding... -
Page 50: Metal Plane
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Field strength color map 7.5 cm Minimum field strength Hmin=1.5 A/m |H| [A/m] Fig 43. Non disturbed field distribution of a circular antenna Fig 44 shows the field distribution of the defined antenna but a metal plane near to the antenna. -
Page 51: Antenna
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Fig 45 shows a ferrite plane (µ =40) which is positioned between the metal plane and the 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 52 AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x The bandwidth B –pulse width T product is defined as: ⋅ T ≥ (24) With the bandwidth definition (25) the B-T product results to ≤ ⋅ ≤ ⋅ µ...
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Page 53: Fig 47. Series Equivalent Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 8.2 Equivalent circuit 8.2.1 Determination of series equivalent circuit The antenna loop has to be connected to an impedance analyzer to measure the series equivalent components. Note: The equivalent circuit (see Fig 47) must be determined under final environmental conditions especially if the antenna will be operated in metal environment or a ferrite will be used for shielding. -
Page 54: Fig 48. Parallel Equivalent Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 8.2.3 Determination of parallel equivalent circuit The parallel equivalent circuit of the antenna together with the added external damping resistor R has to be measured. The quality factor should be checked again to be sure to achieve the required value of Q=35. -
Page 55: Equivalent Circuit Measurement
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Equivalent circuit measurement 8.3.1 Impedance analyzer with equivalent circuit calculation 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 56: Fig 49. Simulation Results For Characteristic Circuit
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Stop frequency: above self-resonance frequency of the antenna 8.3.3 Series equivalent circuit The following characteristic circuit elements can be determined by measurements at characteristic points (see also Fig 47 for series equivalent circuit). -
Page 57: Fig 50. Series Equivalent Resistance Calculation
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Fig 50. Series equivalent resistance calculation π ⋅ ⋅ ⋅ (30) The parallel equivalent circuit always has to be calculated by means of the series equivalent circuit using equation (28). -
Page 58: Fig 51. Setup To Check The Q-Factor
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x Pulse shape check The following pulse shape checks are a quick way for investigating the shaping of the generated RF-field. The figures in 8.5 always relates to the latest ISO/IEC18092 specification. -
Page 59: Pulse Shape According To Iso/Iec 18092, 106 Kbps
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 8.5 Pulse shape according to ISO/IEC 18092 8.5.1 Bit rate 106kbps Envelope of carrier amplitude 110% 100% 100% 110% Fig 52. Pulse shape according to ISO/IEC 18092, 106 kbps The time t1-t2 describes the time span, in which the signal falls from 90% down below 5% of the signal amplitude. -
Page 60: Pulse Shape According To Iso/Iec 18092, 212 And 424 Kbps
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 8.5.2 Bit rate 212 kbps and 424 kbps Fig 53. Pulse shape according to ISO/IEC 18092, 212 and 424 kbps Table 4. Table 8-1: Pulse shape definitions according to ISO/IEC18092, 212 and 424 kbps... -
Page 61: References
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 9. References Data sheet: PN511 Transmission Module (Doc. No.: 0797xx) Data sheet: PN512 Transmission Module (Doc. No.: 1113xx) Data sheet: PN531 Transmission Module (Doc. No.: 1119xx) Data sheet: PN532 Transmission Module (Doc. No.:1154xx) Ecma 340 NFCIP-1 Interface and protocol ISO/IEC 18092: Near Field Communication –... -
Page 62: Legal Information
In no event shall NXP Semiconductors, its affiliates or their suppliers be consequences of use of such information. -
Page 63: Table Of Contents
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 12. List of figures Fig 1. Block diagram of the complete RF part ..... 7 Fig 44. Field distribution of a circular antenna with a metal plane ............50 Fig 2. -
Page 64: List Of Tables
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 13. List of tables Table 1. Example of C1-Split ........24 Table 2. Component list for a basic RF Design ..... 31 Table 3. Pulse shape definitions according to ISO/IEC18092, 106 kbps ........ -
Page 65: Contents
AN1445 NXP Semiconductors Antenna design guide for MFRC52x, PN51x and PN53x 14. Contents 8.1.1 Antenna inductance .......... 46 Introduction ............3 8.1.2 Circular antennas ..........46 Purpose and Scope ..........3 8.1.3 Rectangular antennas ........47 MFRC52x/PN51x/PN53x features ...... 3 8.1.4...
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