Near Field Communication (NFC) read and write capabilities are now fully supported in both Android and iOS 13 mobile devices, opening up a host of new Bluetooth Low Energy (BLE) use cases.
One of the most useful and convenient uses leverages NFC to enhance Bluetooth pairing with the highest level of security and ease of use through Out of Band (OOB) pairing. With NFC, security credentials and device capabilities can be exchanged privately with just a simple tap—no user input is required. At the recent ST Developers Conference, ST’s Keith Walters provided an overview of NFC technology and capabilities, and described the range of NFC tags and readers available from ST.
As we explained in more details when we announced receiving our Tag Certification, NFC is a short-range RFID wireless technology that operates at 13.56 MHz, and is based on high-frequency RFID standards ISO 14443 A and B, ISO 15693, and FeliCa which is a standard defined by Sony that is primarily used in Japan. NFC typically operates by using an active reader and a passive memory tag: the NFC tag is essentially a wireless EPROM that harvests operating power from the energy field generated by the NFC reader, which triggers the tag and reader to communicate. NFC is designed for use at a very short range, with a typical read-range of six inches maximum. It operates by bringing the reader (such as a smartphone or credit-card reader) near to the tag or tapping it.
NFC adoption is growing quickly, bringing electronics to devices that new products. In 2018 NFC was a standard feature in two out of every three smartphones shipped. Moreover, NFC is the basis of smartphone-based payment systems as well as contactless chip-enhanced credit cards.
NFC for Bluetooth Pairing
There are several ways to pair two BLE devices, including entering a PIN or performing a numeric comparison, but this requires a user interface –a keypad and/or a display–which adds cost, complexity, size, and power consumption. For many NFC applications, such as a pair of Bluetooth wireless earbuds, there’s simply no space for a keypad or display.
NFC OOB provides an alternative way of pairing BLE devices, as it doesn’t require a UI and actually layers in additional security features. QR codes and NFC are two examples of OOB pairing mechanisms. However, NFC is superior to QR codes for device pairing since NFC does not require line-of-sight to operate. Also, QR codes are static (read only) and can be rendered unreadable if the ink pattern is damaged or covered by dirt or contaminants.
Major benefits of NFC-enabled BLE pairing are speed and simplicity. There’s no need to scan for radios or set your device in “Discovery Mode” or enter a PIN and confirm it. It’s just a simple tap-and-pair action.
NFC offers lower costs because it eliminates the UI required by other pairing methods, helping to realize a smaller and less expensive solution. Finally, NFC is also power efficient. Battery-powered NFC devices can remain in a deep sleep mode until the unit wakes up with a tap from a reader.
ST NFC Tags and Readers for Bluetooth Pairing
ST offers a full range of NFC tags to implement Bluetooth pairing. Our most flexible solutions are ST’s Dynamic I2C tags: ST25DV and M24SR. These dynamic tags are based on a dual-port EEPROM where one port is an I2C bus, and the other port is NFC. Since the contents of ST’s dynamic tags can be updated on the fly by the host, it offers many of the same capabilities of an active NFC transceiver, including the ability to:
- Update security keys and authentication credentials after each pairing.
- Selectively advertise capabilities depending on the application and available power.
- Employ a field-detect pin to wake the host from a deep sleep or power-down mode without the need for a physical button.
- Stream data such as a firmware update from the phone to the Bluetooth device by leveraging the on-chip RAM buffer in the ST25DV.
Standalone NFC tags are ST’s lowest cost option. The ST25TA and ST25TV can only store static pairing information such as the Bluetooth MAC ID and device role, without the ability to dynamically authenticate data for secure pairing. These tags can be used in low cost applications where security is not crucial, such as environmental sensors, and can be added “after-the-fact” to existing devices with no wiring to the radio required.
ST also offers a variety of NFC readers. The ST25R Reader family spans a range from Entry Level all the way to the Ultimate NFC Front End. The ST25R95 is the low price leader, typically found in high volume industrial and consumer applications.
The ST25R3911B was the first reader on the market to introduce the concept of automatic antenna tuning. When the antenna is either capacitively loaded (such as with an NFC smartphone) or inductively loaded (as with an NFC tag or card) the reader can automatically sense its loading and retune the antenna circuit. This allows the antennae to maintain optimal output power under all circumstances.
The ST25R3916 builds upon the success of its predecessor by adding 2-dimensional automatic antenna tuning, which can adjust both parallel and series capacitance. It also includes an integrated noise suppression receiver, which can compensate for interference from nearby switching power supply or an LCD backlight driver. Finally, it introduced active waveform shaping to optimize data transfers in sub-optimal environments. This makes the ST25R3916 ideal for access control and contactless payment applications.