Product data

MFRC631 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
Product data sheet
COMPANY PUBLIC
Rev. 3.3 — 4 February 2014
227433 107 of 120
NXP Semiconductors
MFRC631
High performance ISO/IEC 14443 A/B reader solution
14.1.4 Antenna coil
The precise calculation of the antenna coils’ inductance is not practicable but the
inductance can be estimated using the following formula. We recommend designing an
antenna either with a circular or rectangular shape.
(4)
• I
1
- Length in cm of one turn of the conductor loop
• D
1
- Diameter of the wire or width of the PCB conductor respectively
• K - Antenna shape factor (K = 1,07 for circular antennas and K = 1,47 for square
antennas)
• L
1
- Inductance in nH
• N
1
- Number of turns
• Ln: Natural logarithm function
The actual values of the antenna inductance, resistance, and capacitance at
13.56 MHz depend on various parameters such as:
• antenna construction (Type of PCB)
• thickness of conductor
• distance between the windings
• shielding layer
• metal or ferrite in the near environment
Therefore a measurement of those parameters under real life conditions, or at least a
rough measurement and a tuning procedure is highly recommended to guarantee a
reasonable performance. For details refer to the above mentioned application notes.
L
1
2= I
1
I
1
D
1
------
ln K–


N
1
18
