Product data

Product data sheet

COMPANY PUBLIC

Rev. 3.3 — 4 February 2014

227433 106 of 120

NXP Semiconductors

MFRC631

High performance ISO/IEC 14443 A/B reader solution

but will also emit power at higher harmonics. The international EMC regulations define the

amplitude of the emitted power in a broad frequency range. Thus, an appropriate filtering

of the output signal is necessary to fulfil these regulations.

Remark: The PCB layout has a major influence on the overall performance of the filter.

14.1.2 Antenna matching

Due to the impedance transformation of the given low pass filter, the antenna coil has to

be matched to a certain impedance. The matching elements C1 and C2 can be estimated

and have to be fine tuned depending on the design of the antenna coil.

The correct impedance matching is important to provide the optimum performance. The

overall quality factor has to be considered to guarantee a proper ISO/IEC 14443

communication scheme. Environmental influences have to be considered as well as

common EMC design rules.

For details refer to the NXP application notes.

14.1.3 Receiving circuit

The internal receiving concept of the MFRC631 makes use both side-bands of the

sub-carrier load modulation of the card response via a differential receiving concept (RXP,

RXN). No external filtering is required.

It is recommended to use the internally generated VMID potential as the input potential of

pin RX. This DC voltage level of VMID has to be coupled to the Rx-pins via R2 and R4. To

provide a stable DC reference voltage capacitances C4, C6 has to be connected between

VMID and ground. Refer to Figure 33

Considering the (AC) voltage limits at the Rx-pins the AC voltage divider of R1 + C3 and

R2 as well as R3 + C5 and R4 has to be designed. Depending on the antenna coil design

and the impedance matching the voltage at the antenna coil varies from antenna design to

antenna design. Therefore the recommended way to design the receiving circuit is to use

the given values for R1(= R3), R2 (= R4), and C3 (= C5) from the above mentioned

application note, and adjust the voltage at the RX-pins by varying R1(= R3) within the

given limits.

Remark: R2 and R4 are AC-wise connected to ground (via C4 and C6).