Near Field Communication Transmitter Using Amplitude and Phase Modulation

摘要

In a short range (~5cm) Near Field Communication (NFC) transmitter 10, a quadrature modulator 12 provides both amplitude modulation of the signal (fig. 2) and phase modulation (fig. 3) via a delay 20. A single 13 MHz tone is generated at a Direct Digital Synthesiser (DDS) 18 and fed to a first mixer 14 for mixing with data signal 11 to produce an In-Phase (I) signal, and also phase shifted by 90o and mixed with a delayed version of the data signal 20 to give a Quadrature (Q) signal. The I and Q signals are then combined 24, digitised 26 and transmitted via antenna 30 which couples magnetically to another nearby antenna. The use of amplitude and phase modulation facilitates demodulation when the receiver must compress the signal (figs. 4 & 5) for energy harvesting purposes.