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Switchable SAW Filter K6257K
Application Notes
Author:
Fröhlich
Updated:
26.08.98
Department: OFW E UE
Abstract:
K6257K is designed for quasi-split-sound, multistandard applications. A BG channel
with reduced group delay predistortion and a double nyquist path with flat group
delay are selectable. In this application note, a switching circuit with a test layout is
proposed and the results are evaluated.
Application note SAW K6257K
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OFW E UE
Switchable SAW Filter K6257K - Application Notes
General
SAW filter OFW K6257K is designed for Multistandard applications (European
standards), except M- and M-related standards. A BG- channel with reduced group
delay and a double nyquist path with flat group delay are selectable. It is optimized
for video-IF signals, used in combination with Quasisplit sound systems. The filter
comes in a flat DIP10K plastic case.
Our testboard will help to inform the user. A proposal for a symmetric SAW driver
output was worked out. The IF driver of a tuner IC, TUA2007 is used here to provide
real conditions on the SAW filter input side. A SAW filters symmetrical output is
terminated usually by the differential amplifier of an IF-IC. Here we choose two
common collector stages as buffer, the symmetric output is combined by
widebandtransformer ( balun) to a practical unsymmetrical output for direct
connection to a network analyzer.
The circuit
Before the introduction of the switchable SAW filter type, one of a set of two
separate SAW filters was switched alternately to the input of the IF amplifier.
Acceptable selectivity of the filter selected requires a circuitry with high attenuation
of the unwanted signal path which has to be shortened and cut off at both output
lines. In addition the circuit is complicated in its layout design. Such a circuit diagra
is shown here:
SAW filter OF K6257K, one type of a new generation, opened up a possibility to
design a norm select with few components occupying a minimum on space.
Application note SAW K6257K
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