NFC Forum Measurements
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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
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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
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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
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Reference Polling Device - Simplified Schematic
J1
C1
L1
Antenna
Device
C2
C1
PD-0
103
67
PD-3
208
76
PD-6
485
115
C2
J2
~1 W
Nominal cap pF
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
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Thevenize and
R-C transformation
C1
≈ (C1+C2)
≈C1
R0
≡
≡
C2
<R0
C2
Alternative Methods
• Smith Chart
• Analytically
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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 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)
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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
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Reference Listening Device - Simplified Schematic
J1
J5
Detected output
J2
Load modulation
Used for:
Qualifying Readers
Calibrating specified magnetic field generated by NFC Forum Polling Devices
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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
RF Sig
Gen
J1
PD-3
LD-1
J1
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Magnetic Field from Readers
10
8
6
H A/m
minimum@14443
PD-3 min
PD-3 nom
Nexus 5
4
2
0
0
5
10
15
20
25
30
35
Distance m m
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Example: Tag-talk-first (TTF) Tag Testing
TTF Tag under test
RF Signal
Generator
(13.56 MHz)
J1
J2
TTF does not
require query
command e.g.
SENS_REQ
Voltage
doubling
rectifier
20 Ms/s PCI Bus PC with
DAS
Software
PD-X
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
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DAS Waveforms
2.6
2.4
2.2
2
1.8
1.6
1.4
0
50
100
150
200
250
300
350
400
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Examples of some NFC Forum Tests
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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
TTF Tag under test
RF Signal
Generator
(13.56 MHz)
J1
J2
Voltage
doubling
rectifier
20 Ms/s PCI Bus PC with
DAS
Software
PD-X
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Minm activation field for RT using NFC PD-3
8.0
7.0
6.0
Tag1
H A/m
5.0
Nom NFC field
4.0
Tag2
3.0
ISO 14443
minm
2.0
1.0
0.0
0
5
10
15
20
25
30
35
Range mm
Nominal NFC Field: Field according to settings specified by NFC Forum
Tag1,Tag2: Minimum field at which test Tags ‘function correctly’
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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
J2
Oscilloscope
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
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Loading test - continued
Loading occurs due to the ‘Choking’ effect of parallel resonance
Strong coupling phenomenon
I1
R1
Vi
~
C1
~1/w02.M
L1-M
M
+jw.M
~w02.M2/R2
-jw.M
(w0.M)/R2>>1
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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
TTF Tag under test
RF Signal
Generator
(13.56 MHz)
J1
J2
Voltage
doubling
rectifier
20 Ms/s PCI Bus PC with
DAS
Software
PD-X
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Tag Requirement for Power-On
Objective: Tag should respond within specified time after field is applied
Tag under test
RF Signal
Generator
J1
J2
AM In
Scope
Sync
PD-X
Pulse Generator
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Pulsed RF Waveform – can be used for query commands also
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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
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Signal at J2
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Thank You!
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