near field communications (nfc) technology & measurements
DESCRIPTION
Near Field Communications (NFC) is an evolution of contactless data exchange which is being employed in mobile phone applications for data exchange and payment processing, among other applications. This presentation covers the evolution and technical details of this communications protocol along with compliance testing requirements. Learn more: http://wireless-connectivity-test.comTRANSCRIPT
NFC Technology and Conformance Testing
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Agenda
l NFC Basicsl Standard Evolutionl Physical Layer Compliance Tests
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NFC Introduction
l Contactless data exchangel Passive – activel Active – active
l Close proximity ~ 10 cml Data transfer using the “near
field”l Low carrier frequency of 13.56 MHzl Magnetic coupling between
transmitter and receiver similar to transformer principle
l Standard developed jointly by NXP and Sony
l Backward compatible with smart card technologyl ISO/IEC 14443 A/Bl JIS X 6319-4
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NFC Coupling Method
Information is coupled between the polling and listening devices using the near field – equivalent to transformer principle
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Frequency Spectrum of NFC Signal
l Auxiliary carriers transfer information from passive listener (target) to poller (initiator) through load modulation on poller antenna
l Auxiliary carriers are not used in peer to peer communicationl Carrier is used as a power source in active-passive communications
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Modulation Types
l Poller (initiator) uses ASK modulation on 13.56 MHz carrier
l Passive devices communicate on auxiliary carrier via load modulationl ASK for 14443A and PSK for 14443Bl ASK directly on carrier for JIS X
6319-4
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Coding Types Used in NFC
l NRZ-L: logical 1 and 0 coded as high and low level and signal level is maintained throughout a bit period
l Manchester: first half bit is high for a logical 1 and second half is high for logical 0
l Modified Miller: negative going pulse after half a bit interval for a 1 and at the start of a bit interval for a 0. For a 1 followed by a zero, no pulse
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Frequency and Time Representation
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Evolution of NFC Air Interface
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NFC Operating Modes
l Card emulation mode (passive mode): behaves like existing contactless card and conforms to one of the legacy standards
l Peer to Peer mode: both devices are active and exchange datal Reader/Writer mode (active mode): the NFC device is active and
reads or writes a passive legacy RFID tag
Each mode canUse any of 3 technologies
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Poll Mode Resolution
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NFC Standards Overview
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NFC Tag Types
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NFC RF Measurements – Listening Device
l NFC Forum Reference Polling Devicel Sends commands to listening devicel Received response from listening device (load modulation)
l Command generator – modulated 13.56 MHz carrierl Load modulation measuring tool – oscilloscope or signal anlyzer
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NFC RF Measurements – Polling Device
l NFC Forum reference listening devicel Receives polling signal from device under testl Transmits appropriate response via load modulation
l Listening device response generator – arbitrary waveform generator (AWG)
l Measuring waveform tool – analyzes the polling signal and generates a trigger for the response generator
l Measuring Field tool – measures the carrier power from the poller
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NFC Reference Polling and Listening Devices
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RF Tests for NFC Devices in Polling Mode
l Carrier frequency accuracyl Power level measurementl Sufficient power to drive passive devicesl Measured within the specified volume above the coupling device
l Waveform characteristicsl Rise time, fall time, etc.
l Load modulation sensitivityl Correct reception at minimum specified level
l Threshold level testl Polling device must switch off its RF field when exposed to an RF field f
a certain strength
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RF Tests for NFC Devices in Listening Mode
l Load modulation measurementl The signal strength of the load modulation must be within required limits
l Power receptionl The listening device must answer correctly even in bad conditions
l Frame delay timel Response time from the end of the polling command to the start of
transmission from the phone in card emulation model Important in NFC-A mode for anti-collision
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Test Setup for Polling Mode
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Test Setup for Listening Mode
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Carrier Power and Frequency Measurement
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Load Modulation
Polling command
Load modulation
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Automated Measurement Software
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Poller Timing Values
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Poller Signal vs. Time
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Listener Values
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Listener Signal vs. Time
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Summary
l NFC technology is an evolution of contactless data exchangel Addition of peer to peer and read/write to passive smart card model Backward compatible with legacy smart card
l The NFC forum has established both RF and protocol compliance tests l Guarantees interoperability
l RF testing verifies the air interface for polling and listening devicesl Reference poller and listener l Command and response generator (AWG and vector signal generator)l Waveform analysis tool (oscilloscope with NFC trigger and I/Q
demodulation)l Automation software controls acquisition and analyzes waveform data
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