Testing the effect of tuning, coupling and phase shift between a NFC reader and a NFC device when using the NFC active modulation.

NFC communication is based on ISO14443 standard which is today mainly used in payment systems, transportation and access control. NFC (Near Field Communication) is becoming the new buzz word to replace the existing names such as contactless smart card, RFID, ... Conventional contactless smart cards or transport tickets are packaged in plastic/paper housing including a chip + an antenna and are collecting power from the NFC reader to power themself, listen the reader command and respond. However, NFC is also integrated in mobile phones, watches or other connected devices which are made of several metallic elements (e.g. Main PCB Board, Aluminium housing, Shielding, Components, ...) which are affecting the RF antenna performance as a metallic element is a short circuited coil). In order to not lose and even improve performances, the NFC device, which could be powered by its own batteries, could manage the NFC active modulation.

Thanks to this simulation circuit available on Multisim we can play with several parameters to influence the communication between a NFC reader and a NFC device in order to observe the effect on the signals on both devices antennas.

The parameters we can play with are : The components values to change the antenna tuning, the reader phase to change the active modulation phase, the coupling factor of the transformer to change the communication distance, ... After having changed these parameters, we can run the simulation and observe the effect of the NFC active modulation on the NFC reader antenna.

Thanks to this simulation we can see that due to phase, coupling or component modification, the reader can receive a positive (constructive) modulation or negative (destructive) modulation which is detected by the NFC reader (in fact an ISO14443 compatible reader) to decode the modulated subcarrier. The same signals can be observed on the reader with a conventional contactless smart card

Bruno participated in the definition and specification of the ISO 14443, ISO 10373, ISO 15693 and NFC Forum since 1996. He designed several readers and chips from very short range (antenna on die) to longer range (RFID gate) communications.