NFC-A (Type A)

NFC-A (Type A)

NFC-A is the NFC communication technology based on ISO 14443 Type A signaling. It uses 100% Amplitude Shift Keying (ASK) modulation for the reader-to-tag direction and load modulationload modulationPassive tagPassive tagBatteryless tag powered by reader's electromagnetic fieldView full → response technique varying load impedanceView full → with a subcarrier for the tag-to-reader response. NFC-A is the most widely deployed NFC protocol in the world, underpinning the entire NTAG product line, MIFARE family, and the majority of NFC ForumNFC ForumIndustry body developing NFC standards, specifications, and certifications since 2004View full → Type 2 and Type 4 tags.

Modulation and Encoding

The NFC-A air interface uses distinct modulation schemes for each communication direction:

Reader to tag (downlink): - 100% ASK modulationASK modulationSignal amplitude variation encodingencodingData writing to NFC tags during manufacturing productionView full → data on 13.56 MHz carrierView full →: The carrier is fully switched on and off to represent data. This produces strong, easily detectable signal edges but momentarily interrupts power delivery to the tag during off periods. - Modified Miller encoding: Bit values are represented by the position of a pause within a bit period. A logic 1 is encoded as a pause in the middle of the bit period; a logic 0 is encoded differently depending on the preceding bit.

Tag to reader (uplink): - Load modulation with subcarrier at 847.5 kHz (fc/16). The tag switches a load across its antenna at the subcarrier frequency, creating sidebands around 13.56 MHz that the reader demodulates. - Manchester encoding with OOK subcarrier modulation.

Data Rates

The base data rate for NFC-A is 106 kbps (fc/128). Higher data rates of 212, 424, and 848 kbps are defined by ISO 14443ISO 14443Standard for contactless smart cards at 13.56 MHz (Types A and B)View full →-4 and supported by more advanced chips like MIFARE DESFire EV3. The negotiation of higher data rates occurs during the protocol activation sequence.

Anti-Collision

NFC-A uses a deterministic bit-level anti-collisionanti-collisionProtocol for selecting individual tags from multiple in RF fieldView full → algorithm. The reader transmits an ANTICOLLISION command, and tags respond with their UID. When collisions occur (multiple tags responding simultaneously), the reader identifies the bit position of the collision and selectively queries tags to isolate each one. This process guarantees that every tag in the field will eventually be identified, unlike the probabilistic approach used by NFC-B.

Chip Compatibility

Virtually all NXP consumer NFC chips use NFC-A: NTAG 213, NTAG 215, NTAG 216, NTAG 424 DNA, MIFARE Ultralight EV1, and the entire MIFARE DESFire family. STMicroelectronics ST25TA also uses NFC-A. This dominance means NFC-A support is mandatory for any NFC reader or NFC-enabled device.