RF Amplifier for NXP Contactless Reader IC’s, MFRC500, MFRC530, MFRC531, CLRC632, SLRC400
Receiving Circuit
The receiving path in Fig 8 shows that an oscillator isused to attenuate the 13.56MHz carrier signalin order to decrease the carrier to side-band level ratio. R17 and R18 build a voltage divider to handle the high voltage levels of around 15V(PP) at the antenna (RX_Antenna Pin). Afterwards, a 1:1 buffer amplifier (OA 1) decouples the signal from the band-stop filter by converting a high impedance at the input to low impedance at the output. The series resistorR22 is used to limit the current and the resistor RQ defines the attenuation factor of the band-stop filter. A starting value of approximately 100  for RQ is recommended. CQ is a tuning capacitance on the frequency axis. Due to the fact that the carrier level is decreased, a second amplifier stage (OA 2) can be used to amplify the sideband levels which also have been slightly damped by the band-stop filter.

Mifare 4K Full Colour Printing Cards,125 KHz Contactless Cards,Mifare 4K Card,NXP Mifare 4k Pre-printed cards.

Fig 8. Receiving circuit with Oscillator and Operational Amplifiers

The output signal of the second amplifier stage is added to a DC offset (Vmid of NXP contactless reader IC) of 2.5V and fed into the RX pin of the IC. NOTE: The output signal of the amplifier stage (OA 2) provides the received signal at the RX pin of the reader IC. It must not exceed an determined peak-to-peak value since higher values may cause receiving failures (e.g. 3 Vpp for CLRC632).

Table 3. Components of the Receiving Circuit
Component Value
U1, U2 Dual Operational Amplifier, Analog Devices AD8056 (two AD8055 in one SOIC housing)
R17 Voltage divider, 5.2kΩ, (Small 0402, 0603 or 0805 SMD parts)
R18 Voltage divider, 1kΩ, (Small 0402, 0603 or 0805 SMD parts)
R19,R20, 24, R25 Voltage divider for offset voltage (6V), 10 kΩ, (Small 0402, 0603 or 0805 SMD parts)
R21, R26 33Ω, (Small 0402, 0603 or 0805 SMD parts)
R22 330Ω, (Small 0402, 0603 or 0805 SMD parts)
R23 10kΩ, (Small 0402, 0603 or 0805 SMD parts)
R27 330Ω, (Small 0402, 0603 or 0805 SMD parts)
R28 100Ω, depending on the desired attenuation factor, (Small 0402,

0603 or 0805 SMD parts)

Q 13.56MHz oscillator
CQ Variable capacitor, 5-50pF
C6, C9 Voltage stabilization, 1μF, (Ceramic NP0, tolerance ≤ ± 2%)
C5, C7, C8 DC blocker, 100nF, (Ceramic NP0, tolerance ≤ ± 2%)
RX1 820Ω, (Small 0402, 0603 or 0805 SMD parts)
RX2 560Ω, (Small 0402, 0603 or 0805 SMD parts)
CX1 DC Blocker, 1nF, (Ceramic NP0, tolerance ≤ ± 2%)
CX2 Voltage stabilization, 100nF
VCC 12V Power supply