B39182B4328P810 Datasheet, PDF (5/8 Pages) TDK Electronics – SAW Components SAW RX filter

SAW Components
SAW RX filter
Data sheet
B4328
1842.5 MHz
ESD protection of SAW filters
SAW filters are Electro Static Discharge sensitive devices. To reduce the probability of damages
caused by ESD, special matching topologies have to be applied. In general, “ESD matching” has to
be ensured at that filter port, where electrostatic discharge is expected.
Electrostatic discharges predominantly appear at the antenna input of RF receivers. Therefore only
the input matching of the SAW filter has to be designed to short circuit or to block the ESD pulse.
Below three figures show recommended “ESD matching” topologies.
For wideband filters the high-pass ESD matching structure needs to be at least of 3^rd order to
ensure a proper matching for any impedance value of antenna and SAW filter input. The required
component values have to be determined from case to case.
Cs1
Cs3
Cs1
Cs3
Lp2
to output
Lp2
to output
matching
matching
Fig. 1 MLC varistor plus ESD matching
Fig. 2 Suppressor diode plus ESD matching
In cases where minor ESD occur, following simplified “ESD matching” topologies can be used
alternatively.
Cs1
Cs3
Lp2
to output
matching
Fig. 3 3^rd order high-pass structure for basic ESD protection
In all three figures the shunt inductor Lp2 could be replaced by a shorted microstrip with proper
length and width. If this configuration is possible depends on the operating frequency and available
pcb space.
Effectiveness of the applied ESD protection has to be checked according to relevant industry
standards or customer specific requirements.
For further information, please refer to EPCOS Application report:“ESD protection for SAW filters”.
This report can be found under www.epcos.com/rke. Click on “Application Notes”.
Please read cautions and warnings and
important notes at the end of this document.
5 July 04, 2013