SLRC400 datasheet(111/130 Pages) PHILIPS

111 / 130 page

Philips Semiconductors

Product Specification Rev. 2.0 November 2001

•CODE Reader IC

SL RC400

111

Preliminary

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]

C1 [pF]

C2a [pF]

C2b [pF]

0.8

270

330

0.9

270

1.0

220

270

1.1

180 || 22

220

1.2

180

180 || 22

1.3

180

1.4

150

180

1.5

150

1.6

120 || 10

150

1.7

120

150

1.8

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

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