mfrc531 NXP Semiconductors, mfrc531 Datasheet - Page 100

• Manufacturer Part Number: mfrc531
• Description: Iso/iec 14443 Reader Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
MFRC531_34
Product data sheet
PUBLIC
15.1.2.3 Receiver circuit
15.1.2.4 Antenna coil
The internal receiver of the MFRC531 makes use of both subcarrier load modulation
side-bands. No external filtering is required.
It is recommended to use the internally generated VMID potential as the input potential for
pin RX. This VMID DC voltage level has to be coupled to pin RX using resistor (R2). To
provide a stable DC reference voltage, capacitor (C4) must be connected between VMID
and ground.
The AC voltage divider of R1 + C3 and R2 has to be designed taking in to account the AC
voltage limits on pin RX. Depending on the antenna coil design and the impedance,
matching the voltage at the antenna coil will differ. Therefore the recommended way to
design the receiver circuit is to use the given values for R1, R2, and C3; refer to
Application note; MIFARE (14443 A) 13.56 MHz RFID Proximity Antennas
voltage on pin RX can be altered by varying R1 within the given limits.
Remark: R2 is AC connected to ground using C4.
The precise calculation of the antenna coil’s inductance is not practicable but the
inductance can be estimated using
that is either circular or rectangular.
The values of the antenna inductance, resistance, and capacitance at 13.56 MHz depend
on various parameters such as:
Therefore, a measurement of these parameters under real life conditions or at least a
rough measurement and a tuning procedure is highly recommended to guarantee a
reasonable performance. Refer to Application notes MICORE reader IC family; Directly
Matched Antenna Design
Antennas
L
•
•
•
•
•
•
•
•
•
•
1
[
nH
l
D
K = antenna shape factor (K = 1.07 for circular antennas and K = 1.47 for square
antennas)
N
ln = natural logarithm function
antenna construction (type of PCB)
thickness of conductor
distance between the windings
shielding layer
metal or ferrite nearby in the environment
1
1
1
= length of one turn of the conductor loop
]
= diameter of the wire or width of the PCB conductor, respectively
= number of turns
=
Ref. 2
2
⋅
I
1
[
cm
for details.
]
⋅
Rev. 3.4 — 26 January 2010
⎛
⎝
ln
〈
Ref. 1
----- -
D
I
1
1
〉
–
056634
K
and MIFARE (14443 A) 13.56 MHz RFID Proximity
⎞ N
⎠
Equation
1
1.8
10. We recommend designing an antenna
ISO/IEC 14443 reader IC
MFRC531
© NXP B.V. 2010. All rights reserved.
Ref.
2. The
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