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 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

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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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