NFC Forum Measurements
description
Transcript of NFC Forum Measurements
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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PD 072 mm antenna4T uncompensated/compensated
PD 347 X 38 mm antenna4T uncompensated/compensated
PD 625 X 20 mm antenna4T uncompensated/compensated
NFC Forum Reference Polling Devices
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Reference Polling Device - Simplified Schematic
J1
J2
L1
C2
Antenna
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
C1
Device Nominal cap pF
C2 C1
PD-0 103 67
PD-3 208 76
PD-6 485 115
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6
C2
C1
≡
≈C1
C2
R0
Alternative Methods
•Smith Chart
•Analytically
<R0≡
≈ (C1+C2)
Thevenize andR-C transformation
Example:
PD-3 is matched to 50
C1, C2 match 50 to ~ [C1/(C1+C2)]2.50 = 3.6(3.4 by exact calculation)
Therefore, Coil resistance = 3.6 – 1 = 2.6
Reactance at 13.56 MHz = 1/(.(208+76)pF) = 41.3
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 172 X 42 mm4T
LD 347 X 32 mm5T
LD 625 X 20 mm5T
All antennas are uncompensated 8
Reference Listening Device - Simplified Schematic
J5
J2
J1
Used for:
Qualifying Readers
Calibrating specified magnetic field generated by NFC Forum Polling Devices
Detected output
Load modulation
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Setting up Specified Magnetic FieldExample – 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
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RF SigGen
PD-3 LD-1J1
J1
Magnetic Field from Readers
0
2
4
6
8
10
0 5 10 15 20 25 30 35
Distance mm
H A
/m
minimum@14443
PD-3 min
PD-3 nom
Nexus 5
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Example: Tag-talk-first (TTF) Tag Testing
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
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 softwareDetect logic levelManchester decodingCRC check
TTF does not require query command e.g. SENS_REQ
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1.4
1.6
1.8
2
2.2
2.4
2.6
0 50 100 150 200 250 300 350 400
DAS Waveforms
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
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
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Minm activation field for RT using NFC PD-3
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
0 5 10 15 20 25 30 35
Range mm
H A
/m
Tag1
Nom NFC field
Tag2
ISO 14443minm
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
J2
RF Signal Generator J1
PD-X
Oscilloscope
Tag under test
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
I1R1 L1-M
Vi ~C1
M
~1/02.M
~02.M2/R2
(0.M)/R2>>1+j.M -j.M
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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
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
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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
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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
J2
RF Signal Generator J1
PD-X
Oscilloscope
Tag under test
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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