SAW Filters for Automotive Applications

SAW filters for Automotive Applications
The strong influence of insertion loss on system performance requires application of resonant design principles like LCRF (Longitudinal Couples Resonator Filter), IEF (Impedance Element Filter) and balanced bridge filter. VI-Telefilter is using its experience in application and combination of these design principles for the development of low loss filters for automotive applications.
To support the booming market of automotive applications VI-Telefilter has been certified according to TS16949 in 2004.

Design capabilities
For automotive applications the LCRF design principle is used frequently. An LCRF design can be described as combination of two port resonators. The drawing above shows a parallel connection of 4 two port resonators. This allows very low loss reducing resistive losses and avoiding waveguide effects. For filters on quartz the parallel connection is very important to get a reasonable termination impedance for stable production having a short matching path to 50 Ohm source or load. The quartz which is often used due to its high temperature stability has got a low electromechanical coupling coefficient requiring parallel connection.

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Two transducers and three reflectors form a two port resonator per track. The usage of resonant structures allows low loss operation. Parallel connection of several tracks allows the design of medium bandwidth low loss filters on temperature stable quartz substrate keeping a reasonable termination impedance.

VI-Telefilter products for Automotive Applications
There are product lines using quartz and LiTaO3 as substrate materials on the market. Solutions on quartz can offer close-in rejection but are limited in bandwidth to some hundred kHz. Solutions on LiTaO3 can offer a wider bandwidth, 50 Ohm termination impedance and extremely low insertion loss, can however not guarantee close-in rejection. The lack of close-in rejection is caused by the higher temperature coefficient of the material.
VI-Telefilter supports both product lines and the frequencies that are requested in different regions of the world.

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Automotive Applications and VI-Telefilter
All VI-Telefilter plants are TS16949 and ISO14000 certified. Highly-automated and flexible production lines are utilized for high and medium volume products to follow the market needs for low cost solutions.
All design principles needed to adress this market with its special requirements are available. Telefilter invented basic elements (parallel connection on page 2) as early as in 1994.