7 May 16, 2013
B3725
869.0 MHz
SAW Components
SAW RF filter
Data sheet
Please read
cautions and warnings and
important notes
at the end of this document.
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.
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.
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 “Applications Notes”.
MLC1
Cs1
Lp2
Cs3
to output
matching
Dp1
Lp2
Cs3
Cs1
to output
matching
Lp2
Cs3
Cs1
to output
matching
