AN1949 STMicroelectronics, AN1949 Datasheet - Page 6

• Manufacturer Part Number: AN1949
• Description: RFID Reader using STMicroelectronics PSD MCU and CRX14 Coupler to Implement a China National ID Card Reader
• Manufacturer: STMicroelectronics

AN1949 - APPLICATION NOTE
Figure 4. Circuit for the Antenna System on the Board
Since the difference will not be large, the adjustment to the antenna matching circuit is fairly simple, using
an oscilloscope. Using two variable capacitors, substitute these for the C26+C27 and the C28+C31. Their
adjustable range shall be around the original value of C26+C27 and C28+C31 (27pF and 125pF). Then
carefully adjust the capacitors. When the voltage on the antenna loops reaches its maximum value, the
correct value for the capacitor has been found.
For more details, see AN1806: Antenna (and Associated Components) Matching-Circuit Calculation for
the CRX14 Coupler.
Check the Filter and Amplifier. The signal after the operational amplifier (point 3, on the schematic di-
agram) should be about 3.5V (peak-to-peak) as shown in
4.6V (peak-to-peak), as shown in
6/22
Z a
Figure
6..
C 1
C 2
Figure
R a
R p
L a
5.. The signal on the RF
IN
pin should be
AI09745