Filters

Surface acoustic wave (SAW) components, integrated radio frequency modules and microwave ceramic filters are key components of modern information and communications. They select frequencies and have a crucial impact on signal quality in mobile phones as well as in audio and TV equipment, for example. SAW-based applications are steadily catching on in automotive electronics and industrial electronics as well.

Discrete SAW filters

The most important applications of these RF filters include transmit and receive systems of mobile phones, where they allow telephony in various standards such as UMTS and GSM. They also perform additional key functions in mobile phones such as navigation, radio and TV reception as well as Internet access via wireless LANs.

Mobile phones are increasingly becoming multifunctional terminals offering a wide range of new applications while retaining their conveniently compact dimensions. Users of high-end mobile phones expect them to operate without problems everywhere, meaning that they must support several mobile phone standards and thus be multimode and multiband-capable. Despite their increasing number of functions, however, these phones can only retain their compact size if their electronic components and modules become ever smaller or have ever more functions integrated in them.

Multimedia is another application area for discrete SAW filters: they help to determine the picture and sound quality in TV sets, set-top boxes for cable and satellite reception of TV programs as well as DVD and hard disk recorders. But discrete SAW filters and resonators are also used in vehicles, for instance in radio-based remote keyless entry, tire-pressure monitoring, and satellite navigation systems. Discrete SAW filters are also used in industrial electronics applications like wireless machine-to-machine communication or automated wireless electricity meter reading.

Discrete SAW filters are manufactured in various package types depending on their intended purpose. Plastic packages are used for multimedia filters, whereas ceramic packages are ideal for manufacturing filters in automotive electronics systems and equipment. Chip-sized SAW package (CSSP®) technology is used in mobile phone applications, allowing the manufacture of greatly miniaturized products.

Combined filter products

Filter products can be further miniaturized by combining several filter functions in a single component in a space-saving way. They include the 2in1 filters as well as the duplexers used particularly in UMTS mobile phones. Transmit and receive filters are combined in these components, thus allowing simultaneous transmission and reception of radio signals. Bulk-acoustic-wave (BAW) filters are used for the transmit path in addition to SAW filters. BAW-SAW duplexers integrate the benefits of these two filter technologies in a single component.

Modules

The degree of miniaturization is increased still further by integrating discrete filters and duplexers in RF modules. These key components are manufactured customer- and application-specific. Compared to discrete solutions, manufacturers of mobile phones can save up to 90 percent space when placing modules on the circuit board. The use of ceramic multilayer technology as the integration platform, allows dozens of functions to be combined in a single module. Amplifiers and switches can be integrated in addition to several filters. A multilayer low-temperature co-fired ceramic (LTCC) acts as the substrate. The functions of passive electronic components such as capacitors, inductors and varistors are embedded between the layers.