NFC use cases and working principles

As the chip price falls and the global market expands, NFC applications grow rapidly. The falling price of passive tags makes it popular to use NFC for inventory management, payment, and other applications. This article describes how NFC works, how NFC is used, and where it is used.

 

 

Introduction

This article translated from inside NFC: usages and working principles

Near-Field Communication (NFC) is the technical standard for short-distance wireless communication. NFC is designed for simple and intuitive communication between different devices. NFC is based on radio frequency authentication (RFID) technology. Use wireless electromagnetic fields instead of traditional direct radio transmission technologies such as Bluetooth. NFC requires physical contact or very close proximity to work, thereby obtaining security. NFC can do a lot of useful work on mobile phones, such as making payments with e-wallets and establishing connections between bluetooth devices.

NFC device use case

NFC has many functions and is developing rapidly. The figure below demonstrates multiple ways to use NFC technology. There are three main usage methods.

Simulate card mode

In this mode, mobile phones with NFC functions are like traditional contactless smart cards read by external card readers. For example, some confidential data on the Visa card is written in the mobile phone's security unit. The data is read by the external card reader and sent to further operate. This allows you to use NFC mobile phones for non-contact payment and ticketing services without changing the existing facilities. Mobile Payment and ticket access control are examples of this usage.

Point-to-Point Mode

In this mode, two devices with NFC functions can exchange data with each other. Both devices are involved in communication. Such as exchanging business cards. Business cards can be exchanged when we contact two devices. Another example is that Bluetooth headsets can be paired through contact. The third example is the NFC chat application. The two mobile phones communicate with each other in the NFC Forum data exchange format.

Read/write mode

In this mode, NFC devices (such as mobile phones) can read and write NFC tags (see the following section for details ). NFC smart poster is an example. The NFC tag is embedded in the poster, and more information about the poster content is written. The device can read the information in the tag for further operations. In another example, the device in the dead caseCode.

Many experts believe that 96-bit Electronic Product Code (EPC), as shown in, will be the next generation of Universal Product Code (UPC). The transaction identification code that everyone is familiar with now is a bar code.

How NFC works

The radio frequency (RF) sine wave generated by the reader (mobile phone) transmits energy to the tag and then reads data from the tag. After NFC is started, the signal center frequency of the sine wave is 13.56 MHz. If there is a tag within the range of the magnetic field disturbance produced by the sine wave, the tag obtains the energy from the magnetic field disturbance, and generates the original sine wave back frequency or the wave that changes the frequency attribute. The mobile phone detects this change to know that there are tags nearby. RFID is usually called a near-pairing system for communication at a very close distance. The range of near-pairing systems is usually 0 to 1 cm. This means that the tag is appended to the reader or pressed to the reader. The advantage of this close distance is that the label battery plant can produce a lot of energy. This energy is sufficient to support tag communication without the need for Built-in power. Near-matching is also conducive to highly confidential occasions. Demonstrates some simple relationships between NFC applications and NFC hardware.
 

Reader

It is usually based on a microcontroller (such as a mobile phone with NFC function), with an integrated circuit that can generate a 13.56mhz radio frequency, with encoder, decoder, antenna, comparator, there are also hardware that transmits energy to tags and reads modulation information from reverse scattering. The reader continuously generates RF signals, observes the received RF signals, reads the information, and demonstrates how the mobile phone generates RF signals and how the tag antenna obtains energy.

 

Tag

An RFID device contains a silicon-based memory connected to an external antenna. Label without power supply. Passive tags obtain energy in the electromagnetic field generated by the reader, and then start to send modulation information. Data modulation (modulation of 0, 1) is completed by direct modulation or PSK or phase modulation. Demonstrate the hardware inside the NFC tag, where we can see the memory logic circuit and so on.

The most common is the "passive" label (as shown above) because it does not have a power supply. Passive tags are powered by the reader's RF carrier. The following is the tag type: 1) ndef NFC-tag Data Exchange Format 2) Mifare 1 K tag

Modulation and Data Transmission

Modulation refers to the process of modifying Signal Features and calling a carrier to transmit information. The NFC carrier frequency is 13.56 MHz. Features of the signal to be modified include amplitude, frequency, and phase. Data ExchangeIt is completed through the modulation process of the RF carrier. In this process, a data pulse (1 and 0) is added to (mixed to) the carrier. The clock frequency of the data stream is much slower than that of the carrier. The properties (amplitude and/or frequency and/or phase) are changed after the data is added to the carrier. The mobile phone detects the change, decodes the data, and sends it to the next step.
The carrier generates a small AC in the antenna ). The Rectifier on the Integrated Circuit Chip converts the AC to the DC power and then uses it to provide power to the chip. Then the chip is "activated ". The clock splitter separates the carrier Clock Pulse and uses this pulse to synchronize the logic, memory and modulation units of the label IC circuit and the reader circuit. The logical unit is separated from 0, 1 in the carrier.ProgramTo determine how to respond (if necessary ). If the logical unit verifies that the data flow is valid, the chip unique authentication data of the memory unit and other user data in the memory are accessed. The logical unit uses the pulse of the clock splitter to decode the data. Decodes the data stream input to the modulation unit. The modulation unit blends the data stream with the carrier, and adjusts the reflectivity of the antenna in the data stream rate through electronics. The RF of the electronically adjusted antenna feature reflection is received. This modulated the RF carrier amplitude. The reader detects changes in the modulation carrier and finds data. It shows that the carrier is loaded with binary data by simple amplitude modulation.
 
It provides a simple carrier signal modulation for RFID tags. 1 indicates a higher carrier, and 0 indicates a lower carrier. The reader decrypts the signal to find the data. Note that the data is encoded. The reader uses an appropriate decoder to decode the data, sends it to the mobile phone for the next step on the NFC stack, and finally submits it to our application.

Data transmission Summary

1. The reader continuously generates RF load sine wave signals and always observes the modulation. The discovery of electromagnetic field modulation means the discovery of a tag.

2. The tag enters the RF field generated by the reader. Once the tag gets enough energy, it processes the carrier and loads the data clock into an output transistor, typically input through a coil.

3. The output Transistor Shunt coil of the tag outputs the memory sequence according to the data clock.

4. Shunt coils make the carrier instantaneous fluctuations (back-to-tide), so that the carrier amplitude has a significant change.

5. The peak value of the reader detects the amplitude modulation data and inputs the read bit stream to the decoding or modulation method.

Reference

1. http://www.eetimes.com/design/microwave-rf-design/4018928/Radio-Basics-for-RFID-Modulation-and-Multiplexing/
2. http://www.rfid-handbook.de/rfid/types_of_rfid.html
3. http://www.tutorialsweb.com/rfid/operation-of-rfid-systems.htm
4. nfc_forum_mobile_nfc_ecosystem_white_paper.pdf
5. Basic concepts of rfid.pdf
6. eeol_2009jul17_rfd_dt_ta_01.pdf
7. http://www.developer.nokia.com/info/sw.nokia.com/id/bdaa4a0f-fcf3-4a4b-b800-c664387d6894/Introduction_to_NFC.html
8. QT Development
9. QT mobility Development