1. NFC Forum Measurements

2. Suite of standard tests to qualify Readers and Tags
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 SchematicJ1
Antenna L1
Device
Nominal cap pF C2 C1
PD-0
103 67
PD-3
208 76
PD-6
485
115 C2 J2
~1 W
Antenna: Uncompensated mode standard. 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 ≡ ≡ Alternative Methods Smith Chart
≈ (C1+C2)
≈C1 R0 ≡ ≡
<R0 C2 C2
Alternative Methods
Smith Chart
Analytically

7. Example:
PD-3 is matched to 50W
C1, C2 match 50W to ~ [C1/(C1+C2)]2.50W = 3.6W (3.4W by exact calculation)
Therefore, Coil resistance = 3.6 – 1 = 2.6W
Reactance at 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 SchematicJ1
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
RF Sig
Gen
PD-3
LD-1 J1

11. Magnetic Field from Readers

12. Example: Tag-talk-first (TTF) Tag TestingJ2
RF Signal Generator
(13.56 MHz) J1
PD-X
Voltage doubling rectifier
20 Ms/s DAS
PC with Software
PCI Bus
TTF Tag under test
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. 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 J2
RF Signal Generator
(13.56 MHz) J1
PD-X
Voltage doubling rectifier
20 Ms/s DAS
PC with Software
PCI Bus
TTF Tag under test

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

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

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

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 J2
Oscilloscope
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!