Integration Manual

GTM353W Integration Manual
Author:
R
. Claessens
Version:
4.0 Draft 2
Creation Date:
September 20, 2006
Page:
21 of 52
Option Confidential:
This document is Option Confidential - it may not be duplicated, neither distributed externally without prior and written permission of
Option NV.
3.3.4 Electrical interface
The (U)SIM card holder is connected with the module by means of long wires. The (U)SIM
card holder and wires are radiated on with different types of noisy signals, e.g. the radiation
signals of the module antenna. The SIM interface signals conduct this noise into the module
and radiate these signals into the module, with potential disasterous results.
This phenomenon can be significantly reduced by following design rules for EMC
interference minimisation:
1. Place noise suppression capacitors on the SIM card holder.
2. Route the SIM card holder signals carefully in relation to other signalling lines and
potential noise generation sources.
3. Limit the line length: a maximum length of 200mm is advised.
3.3.4.1 Noise suppression capacitors
On the module suppression capacitor are placed on the signals RTS, CLK and I/O. The value
of these suppression capacitors equals 17pF each.
Although the module foresees suppression capacitors it is important to place suppression on
the contacts of the SIM card holder. The value of these suppression capacitors must be equal
to 10pF. It is important to place the capacitors as short as possible to the SIM card reader.
Every mm PCB track (or FFC signalling line) counts. The size of the capacitor also matters. It
is advisable to use 0402 type capacitors.
Figure 9 shows the impedance graph of a 10pF capacitor.
Figure 9: Impedance of 10pF capacitor