SLRC400 Datasheet, PDF (111/130 Pages) NXP Semiconductors – I·CODE Reader IC

Philips Semiconductors
I•CODE Reader IC
Product Specification Rev. 2.0 November 2001
SL RC400
17.3.1 IMPEDANCE MATCHING FOR DIRECTLY MATCHED ANTENNAS
To design a matching circuit for a directly matched antenna we recommend to use the circuit shown in 17.1.
The values for the capacitors C1 and C2a, C2b depend on the antenna’s electrical properties and
environmental influences.
The values for the capacitors shown in the table below are guidelines. In fact, they are used as starting
values for the tuning procedure.
Antenna Coil
Inductance [µH]
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
C1 [pF]
27
27
27
27
27
27
27
27
27
27
27
C2a [pF]
270
270
220
180 || 22
180
180
150
150
120 || 10
120
120
C2b [pF]
330
270
270
220
180 || 22
180
180
150
150
150
120
Table 17-2: Capacitance Values for the Matching Circuit
However, for optimum performance, the accurate values have to be found by the tuning, variation of the
capacitance’s C2x and C1.
The above table assumes a stray capacitance of 15 pF of the antenna coil. The capacitors C1 and C2s
should have a NP0 dielectric with a tolerance of +/-2 %.
The actual values of the antenna inductance and capacitance depend on various parameters like:
• antenna construction (Type of PCB)
• thickness of conductor
• distance between the windings
• shielding layer
• metal or ferrite in the near environment
111
Preliminary