nfc forum measurements
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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
5
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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13
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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