NFC-B (Type B)

NFC-B (Type B)

NFC-B is the NFC communication technology based on ISO 14443 Type B signaling. It uses 10% Amplitude Shift Keying (ASK) modulation — a subtle variation of the carrier rather than the full on/off switching of NFC-A. While less common than NFC-A in consumer NFC applications, NFC-B is the protocol of choice for government-issued identity documents and certain banking smart cards.

Modulation and Encoding

NFC-B's modulation approach differs fundamentally from NFC-A:

Reader to tag (downlink): - 10% ASK modulationASK modulationSignal amplitude variation encodingencodingData writing to NFC tags during manufacturing productionView full → data on 13.56 MHz carrierView full →: The carrier amplitude is reduced by only 10% to represent data transitions. This means the tag receives nearly continuous power during communication, which is advantageous for power-hungry smart card processors. - NRZ-L (Non-Return-to-Zero Level) encoding: The signal level directly represents the bit value. A high level means 1, a low level means 0. Simpler than Modified Miller but requires careful clock recovery.

Tag to reader (uplink): - Load modulationLoad modulationPassive tagPassive tagBatteryless tag powered by reader's electromagnetic fieldView full → response technique varying load impedanceView full → with BPSK subcarrier at 847.5 kHz. The phase of the subcarrier encodes the data — a more noise-resilient approach than the OOK subcarrier used by NFC-A.

Anti-Collision

NFC-B uses a probabilistic slotted ALOHA anti-collisionanti-collisionProtocol for selecting individual tags from multiple in RF fieldView full → algorithm. The reader broadcasts a REQB command specifying a number of time slots (1, 2, 4, 8, or 16). Each tag randomly selects a slot in which to respond. If two tags select the same slot, a collision occurs and the reader retries with more slots. While this approach does not guarantee immediate resolution (unlike NFC-A's deterministic method), it is well-suited to applications where few cards are present simultaneously.

Government and Identity Applications

NFC-B's continuous power delivery (10% ASK preserves 90% of the carrier energy) makes it preferred for power-intensive smart card applications:

• Electronic passports (ePassports): Machine Readable Travel Documents (MRTD) compliant with ICAO Doc 9303 use ISO 14443ISO 14443Standard for contactless smart cards at 13.56 MHz (Types A and B)View full → Type B for biometric data access.
• National identity cards: Many countries implement NFC-B for government-issued eID cards requiring on-card cryptographic operations.
• Banking smart cards: Some EMV implementations use Type B, though Type A dominates.

Practical Considerations

All modern NFC-enabled devices and NFC readers support both NFC-A and NFC-B as part of the NFCIP-2 multi-protocol requirement. The reader's technology detection loop polls for both Type A and Type B tags, so end users never need to know which protocol a tag uses.