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NFC Forum Measurements

NFC Forum Measurements. Objective. Suite of standard tests to qualify Readers and Tags Ensure Interoperability Present discussion limited to certain aspects of ‘Analog Specifications’ only RF Power and Signal Interface. Accessories defined by NFC Forum.

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NFC Forum Measurements

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  1. NFC Forum Measurements

  2. Objective • Suite of standard tests to qualify Readers and Tags • Ensure Interoperability • Present discussion limited to certain aspects of ‘Analog Specifications’ only • RF Power and Signal Interface

  3. Accessories defined by NFC Forum • Reference Polling Devices (i.e. Reader) • Used to characterize Tags • Reference Listening Devices (i.e. Tag) • Used to characterize Readers

  4. NFC Forum Reference Polling Devices PD 0 72 mm f antenna 4T uncompensated/compensated PD 3 47 X 38 mm antenna 4T uncompensated/compensated PD 6 25 X 20 mm antenna 4T uncompensated/compensated

  5. Reference Polling Device - Simplified Schematic C1 J1 Antenna L1 C2 J2 ~1 W Antenna: Uncompensated modestandard. Compensated mode possible J1: RF (13.56 MHz) excitation J2: Monitor antenna current (e.g. Load modulation) C1,C2 used to match to 50 ohm at J1

  6. Thevenize and R-C transformation C1 ≈ (C1+C2) ≈C1 R0 ≡ <R0 ≡ C2 C2 • Alternative Methods • Smith Chart • Analytically

  7. Example: PD-3 is matched to 50W C1, C2 match 50Wto ~ [C1/(C1+C2)]2.50W = 3.6W (3.4W by exact calculation) Therefore, Coil resistance = 3.6 – 1 = 2.6W Reactance at 13.56 MHz = 1/(w.(208+76)pF) = 41.3W Therefore, Q of inductor (same reactance as capacitor at resonance) = 41.3/2.6 = 15.9 And inductance = 485 nH (494.5nH by exact calculation)

  8. NFC Forum Reference Listening Devices LD 1 72 X 42 mm 4T LD 3 47 X 32 mm 5T LD 6 25 X 20 mm 5T All antennas are uncompensated

  9. Reference Listening Device - Simplified Schematic J1 Detected output J5 J2 Load modulation Used for: Qualifying Readers Calibrating specified magnetic field generated by NFC Forum Polling Devices

  10. Setting up Specified Magnetic Field Example – Setting PD-3 up for specified magnetic field • LD-1 is placed at 5mm from PD-3 • RF excitation is adjusted to PD-3 (J1) till detected output from LD-1 (at J1) is 4.72 V. This sets up for the ‘nominal’ field. • For ‘minimum’ field detected output should be 4.24 V • For ‘maximum’ field detected output should be 2.22 V using LD-3 instead of LD-1 • Nominal field = 7.3 A/m from independent measurements J1 LD-1 RF Sig Gen PD-3 J1

  11. Magnetic Field from Readers

  12. TTF Tag under test RF Signal Generator (13.56 MHz) J1 Voltage doubling rectifier J2 PCI Bus 20 Ms/s DAS PC with Software PD-X Example: Tag-talk-first (TTF) Tag Testing TTF does not require query command e.g. SENS_REQ Set up specified magnetic field for a particular NFC Forum test using LD-X Replace LD-X by Tag Under Test and perform tests Analysis of received frames done in software Detect logic level Manchester decoding CRC check

  13. DAS Waveforms

  14. Examples of some NFC Forum Tests

  15. TTF Tag under test RF Signal Generator (13.56 MHz) J1 Voltage doubling rectifier J2 PCI Bus 20 Ms/s DAS PC with Software PD-X Tag ‘Functioning Properly’ Objective: How the Tag functions in a specified field generated by a given Polling Device? Pass criterion: Return serial ID and CRC correctly for three independent frames

  16. Nominal NFC Field: Field according to settings specified by NFC Forum Tag1,Tag2: Minimum field at which test Tags ‘function correctly’

  17. Influence of Tag on Operating Field (Loading) Objective: Tag loading on the Reader should be within specified limits Tag under test RF Signal Generator J1 Oscilloscope J2 PD-X Pass criterion: Change in RF voltage at J2 (i.e. Reader antenna current) cannot exceed specified value for Tag at a certain distance e.g. 0.3V for PD-3 set up for minimum magnetic field and test Tag placed at 5mm

  18. ~1/w02.M L1-M R1 C1 Vi M ~w02.M2/R2 (w0.M)/R2>>1 +jw.M -jw.M ~ Loading test - continued Loading occurs due to the ‘Choking’ effect of parallel resonance Strong coupling phenomenon I1

  19. TTF Tag under test RF Signal Generator (13.56 MHz) J1 Voltage doubling rectifier J2 PCI Bus 20 Ms/s DAS PC with Software PD-X Tag Requirement for Carrier Frequency Objective: Tag should ‘function properly’ for 13.55 to 13.57 MHz Pass Criterion : Return serial ID and CRC correctly for three independent frames

  20. Tag under test J1 RF Signal Generator J2 Scope AM In Sync PD-X Pulse Generator Tag Requirement for Power-On Objective: Tag should respond within specified time after field is applied

  21. Pulsed RF Waveform – can be used for query commands also

  22. Tag Requirement for Load Modulation Objective: Load modulation to be maintained within specified limits Tag under test RF Signal Generator J1 Oscilloscope J2 PD-X Magnetic field set up for nominal value. Pass Criterion: Signal at J2 should have a subcarrier = fc/16 (847.5 KHz) and specified P-P amplitude (Vpp) of the load modulation, e.g. between 9.5 and 53 mV for PD-3

  23. Signal at J2

  24. Thank You!

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