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NXP Semiconductors

AN11740

PN5180 Antenna design

AN11740

All information provided in this document is subject to legal disclaimers.

Application note
COMPANY PUBLIC

Rev. 1.1 — 19 June 2018

345311

54 of 62

5. Annex

This annex describes some basics about impedance measurement and the related
measurement tools.

5.1 Vector Network Analyzer

The impedance measurement must be done with a vector network analyzer, e.g. as
shown in Fig 49.

a. Rohde & Schwarz ZVL (refer to [11])

b. MiniVNA Pro (refer to [12])

Fig 49. Examples of Vector Network Analyzers

For the miniVNA Pro the recommendation is to use the VNA/J SW tool (refer to [13]), as
shown in Fig 50.

Содержание PN5180

Страница 1: ...Rev 1 1 19 June 2018 345311 Application note COMPANY PUBLIC Document information Info Content Keywords PN5180 Antenna design Antenna tuning Abstract This document describes the standard antenna desig...

Страница 2: ...is subject to legal disclaimers NXP B V 2018 All rights reserved Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 2 of 62 Contact information For more information please visit http www nxp...

Страница 3: ...d transfer function The DPC antenna design and the specifics of the DPC are described in detail in 14 and 15 2 NFC Reader Antenna design For the NFC operation three different communication modes are s...

Страница 4: ...following details see 2 specifies the contactless interface as widely being used with contactless smartcards The ISO IEC 14443 defines the communication between a reader proximity coupling device PCD...

Страница 5: ...PUBLIC Rev 1 1 19 June 2018 345311 5 of 62 1 k coupling coefficient 2 magnetic flux Fig 2 Magnetic coupling between reader PCD and card PICC According to the ISO IEC 14443 the PICC antenna coils can...

Страница 6: ...all different sizes of antenna coils from a few 10 mm2 up to 20cm diameter can be found in various shapes The ISO IEC 14443 does not specify an operating volume The reader manufacturer needs to guaran...

Страница 7: ...Cs which are commercially available e g Fig 5 are pre calibrated and equipped with several jumper options to address the most relevant tests with a single ReferencePICC 1 The jumper settings allow the...

Страница 8: ...send the related pulse s It may send an ISO IEC 14443 REQA and or REQB with the required bit rate as e g specified in 5 Any other command fits the purpose too Note For the test of higher bit rates it...

Страница 9: ...rresponding contactless payment cards in 6 This interface is very similar to the one defined ISO IEC 14443 but it uses its own set of requirements and specification details The EMVCo test equipment an...

Страница 10: ...age level which can be measured in all of the given positions needs to be between the minimum and maximum limit as given in 6 Due to the operating volume it can become challenging to meet the EMVCo re...

Страница 11: ...loscope with a measurement bandwidth of 500Msamples or higher and 5 a tool that filters and transforms the oscilloscope data into the envelope signal according to the EMVCo test requirement The tool n...

Страница 12: ...nput either from the field or from the PCD itself The voltage level of the load modulation input signal for each test case must be set according to 6 The PCD must be able to receive all the responses...

Страница 13: ...the antenna system is optimized based on the parallel operation of smart cards on top of the PCD antenna The optimization is derived for the operating distance i e the target is to show the optimum PC...

Страница 14: ...le antenna coils with a single turn can be used as well as antenna coils with many turns The only remaining parameter to optimize the coupling is the antenna radius r i e the antenna size and will be...

Страница 15: ...e 2018 345311 15 of 62 1 Green area target area for standard antenna matching Fig 10 Inductance examples versus coil radius On the other hand the number of turns defines the relationship of voltage le...

Страница 16: ...optimum antenna size 1 Green at a distance of x 4 cm 2 Blue at a distance of x 6 cm 3 Black at a distance of x 8 cm 4 The coupling coefficient scaling in this diagram is relative only The absolute va...

Страница 17: ...ed to the optimum antenna size 1 The absolute scale of k might not be correct due to simplifications Fig 13 Maximum coupling vs antenna size Theoretical example The Fig 14 shows the field strength ver...

Страница 18: ...the detuning and loading effect of the reader antenna The Fig 15 shows the simulation result of three different square antennas The magnitude of the field strength is shown versus the distance from th...

Страница 19: ...ndividually to achieve the maximum allowed field strength for each antenna 3 2 Layout recommendations The connection between the TX output pins TX1 and TX2 and the EMC low pass filter has to be as sho...

Страница 20: ...ormation provided in this document is subject to legal disclaimers NXP B V 2018 All rights reserved Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 20 of 62 1 Part of the top layer 2 Middl...

Страница 21: ...N5180 Layout Reference Board Bottom layer 4 PN5180 hardware design The PN5180 is optimized to support the NFC ISO and EMVCo with a minimum of additional components The PN5180 simply requires the anten...

Страница 22: ...apted 2 Tbd to be defined need to be defined using this document 3 CXx CAntx C0x C1x and C2x must be NP0 Fig 18 Typical PN5180 analog circuit 1 Names to be adapted 2 Tbd to be defined need to be defin...

Страница 23: ...e EMVCo operating volume Therefore the Tx output can drive up to ITVDD 250mA Based on a power supply voltage VBAT TVDD 5V that means a possible total power consumption for the total antenna circuit of...

Страница 24: ...g and matching of the symmetrical antenna tuning is very similar using the same tuning steps However the detailed specifics related to the symmetrical antenna tuning and especially to the related DTC...

Страница 25: ...antenna together with the PN5180 The blocks and components are used as shown in Fig 21 1 This circuit only covers the Tx part Fig 21 PN5180 Reader only antenna matching circuit 4 2 1 1 Measure the an...

Страница 26: ...2018 All rights reserved Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 26 of 62 1 Measurement with R S ZVL Fig 22 Measurement 1 Antenna coil of PN512 Blueboard 1 Measurement with miniVNA...

Страница 27: ...mples show the design for a maximum power transfer e g for an EMVCo POS design The quality factor Q depends on the overall system requirements and frame conditions The overall system requires the Q to...

Страница 28: ...e following calculation is more accurate i e the calculation result gets closer to the measured result 4 2 1 3 Define the EMC filter The EMC filter can be a second order low pass filter as shown in Fi...

Страница 29: ...able with the PN5180 like with any other NXP Reader IC and shown in the following sections too Based on this the following EMC filter values are chosen L0 L0A L0B 470nH C0 C0A C0B 56pF 68pF fCutoffasy...

Страница 30: ...he symmetrical antenna tuning can be found in 14 For symmetrical antenna tuning the following EMC filter values are chosen L0 L0A L0B 470nH C0 C0A C0B 220pF 33pF fCutoffsym 14 6MHz Note This EMC filte...

Страница 31: ...ching capacitors are calculated C1 C1A C1B C1C C1D 41 6pF 33pF 8 2pF 0 4pF less C2 C2A C2B C2C C2D 125 6pF 68pF 56pF 1 6pF less 4 2 1 5 Simulate the matching The measurement of the antenna coil itself...

Страница 32: ...C filter inductors L0 are far from being ideal RFSIM99 allows to use physical models which requires to enter e g the self resonant frequency and the Q factor measured at a certain frequency With these...

Страница 33: ...information provided in this document is subject to legal disclaimers NXP B V 2018 All rights reserved Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 33 of 62 a L0 ideal component b L0 u...

Страница 34: ...simple 2 pin connector is soldered between TX1 and TX2 to simplify the impedance measurement Fig 28 Impedance measurement example The measurement result is shown in Fig 29 The circuit does not meet th...

Страница 35: ...retuned Fig 29 Measurement result of first assembly 4 2 1 7 Impedance adaptation in simulation The easiest and fastest way to fine tune the antenna is to first of all adapt the simulation in such a wa...

Страница 36: ...MPANY PUBLIC Rev 1 1 19 June 2018 345311 36 of 62 c Impedance first step d Impedance after adaptation Fig 30 Impedance adaptation in the simulation result a Circuit first step b Circuit after adaptati...

Страница 37: ...cation note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 37 of 62 4 2 1 8 Impedance correction and assembly The tuning of the impedance is now corrected with the values of C1 and C2 as shown in Fig 32 a...

Страница 38: ...DD might even exceed the specification limits and therefor reduce the life time of the PN5180 So in any case it is strongly recommended to check the loading and detuning of the antenna The first step...

Страница 39: ...nder normal operating conditions see 4 2 2 3 Note The loading with the ReferencePICC typically turns the impedance circle in the smith chart clockwise At the same time the overall Q factor drops so th...

Страница 40: ...he ReferencePICC shows a slightly different behavior than in the real test case Therefore the passive loading measurement can only show the trend of loading and detuning but does not allow a 1 1 calcu...

Страница 41: ...ption must be as low as possible For impedances higher than 50 it might be better to target a parallel resonance as shown in Fig 36b a Serial resonance low impedance b Parallel resonance high impedanc...

Страница 42: ...345311 42 of 62 1 10 22pF for simulation of the PN5180 ANT1 and ANT2 in RM Fig 37 NFC antenna in RM The Fig 38 shows the simulation and measurement result Note The measurement must be done with 10 br...

Страница 43: ...l rights reserved Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 43 of 62 1 4k 22pF for simulation of the PN5180 ANT1 and ANT2 in CM Fig 39 NFC antenna in CM The simulation and measuremen...

Страница 44: ...h the TX_RESIDUAL_CARRIER in the RF_CONTROL_TX register On top it might be helpful to adapt the rise and fall times of the Tx envelop signal to match the pulse shapes to the timing requirements of the...

Страница 45: ...ter allows to change the TX output stage behavior during the modulation pulses The Fig 41 shows an example with the default setting as well as the setting where the TX output stages are open drain and...

Страница 46: ...0 Disabled TX overshoot protection TX_OVERSHOOT_PROT_ENABLE 0 Disabled TX Shaping TX_BYPASS_SC_SHAPING 1 TX_CLK_MODE_RM 0x1 default or 0x5 low side pull More details refer to 14 and 15 4 5 Optimizing...

Страница 47: ...5mm x 65mm evaluation board antenna Some of these settings typically must be adjusted and optimized for other antenna designs 4 5 1 External Rx components The RxP and RxN are connected to the antenna...

Страница 48: ...UX2 can be used for analog test signals the IRQ AUX1 AUX2 and GPIO1 can be used for the digital test signal Note Be aware that some of those test pins might be used for other purpose already like IRQ...

Страница 49: ...ncePICC The left part starts with falling edge of the trigger signal blue derived from the digital test signal using the TX_ACTIVE The green signal shows the LMA input at the ReferencePICC In the cent...

Страница 50: ...ng the RxGain in combination with RX_HPCF can directly be seen in the unfiltered I or Q channel signal The Fig 45 shows the same test case with the same LMA level and the same bandwidth HPCF but just...

Страница 51: ...F 0 g Green LMA RefPICC input h Blue TX_ACTIVE Trigger i Yellow unfiltered Q Channel j Orange BPSK_SUM Fig 45 Test signals for Type B comparison of RxGain a RxGain 3 HPCF 0 b Green LMA RefPICC input c...

Страница 52: ...noise ratio Min_Level_P can be seen as a threshold for the decoded BPSK signal BPSK_SUM The BPSK signal must exceed the Min_Level_P to be taken into account be the PN5180 data decoder Note The Min_Le...

Страница 53: ...roperly received in Fig 48a where no noise applies In Fig 48b the card response together with the noise is shown The noise spikes which are much larger than the sub carrier signal itself introduce som...

Страница 54: ...f 62 5 Annex This annex describes some basics about impedance measurement and the related measurement tools 5 1 Vector Network Analyzer The impedance measurement must be done with a vector network ana...

Страница 55: ...asurement b VNA J Smith chart example Fig 50 VNA J from DL2SBA refer to 13 In Fig 51 the result of the same measurement is shown for the R S ZVL as well as for the VNA J using the miniVNAPro The accur...

Страница 56: ...0MHz is sufficient enough to do the antenna tuning The standard VNA provides an unbalanced 50 measurement port which is used here to measure a balanced impedance The mismatch due to this setup error c...

Страница 57: ...Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 57 of 62 1 The mismatch due to the unbalanced measurement of a balanced impedance can be ignored Fig 52 Measurement connector and calibrati...

Страница 58: ...rt 2 PICC and Part 4 PCD https www bsi bund de DE Home home_node html 6 EMV Contactless Specifications for Payment Systems Book D https www emvco com 7 https www rohde schwarz com 8 http miniradiosolu...

Страница 59: ...s applications and products planned as well as for the planned application and use of customer s third party customer s Customers should provide appropriate design and operating safeguards to minimize...

Страница 60: ...urement 1 Antenna coil of PN512 Blueboard 26 Fig 23 Measurement 2 Antenna coil of PN512 Blueboard 26 Fig 24 Tuning options 29 Fig 25 Antenna matching calculation asymmetrical tuning 31 Fig 26 RFSIM99...

Страница 61: ...All information provided in this document is subject to legal disclaimers NXP B V 2018 All rights reserved Application note COMPANY PUBLIC Rev 1 1 19 June 2018 345311 61 of 62 9 List of tables Table 1...

Страница 62: ...ader mode 24 4 2 1 Antenna matching 24 4 2 1 1 Measure the antenna coil 25 4 2 1 2 Define target impedance and Q factor 27 4 2 1 3 Define the EMC filter 28 4 2 1 4 Calculate the matching components 30...

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