The power part, main control interface and clock crystal oscillator can be designed according to the chip manual. This article focuses on the design of NFC antenna.
The antenna design includes antenna part and matching circuit part.
ISO / iec14443 defines six types of antennas. For each NFC equipment, the antenna should be carefully designed to ensure the best performance.
The series equivalent circuit of the antenna part is as follows:
La is the inductance of the coil, RA is the resistance of the coil, and Ca is the equivalent capacitance.
Typical recommended values:
To make the antenna work at 13.56MHz, a capacitor can be connected in parallel or in series outside the antenna. The capacitor and inductor form LC resonant circuit. The size of the series / parallel capacitor can be adjusted to make the resonant frequency 13.56MHz.
The NFC antenna circuit of NXP company is as follows:
Among them, l0 and C0 are low-pass filters to filter out the high-order harmonics of crystal oscillator. C1 and C2 are matching circuits for working frequency and input impedance. RS is a series resistor used to adjust the Q value and bandwidth of the antenna. NFC antenna design tool of NXP is recommended for the specific selection of device value of matching circuit. Just input the antenna parameters and the matching value will be calculated automatically. It is very convenient to use, as shown below: