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DKE German Commission for Electrical, Electronic & Information Technologies of DIN and VDE

Overview

This part of IEC 60862 gives practical guidance on the use of SAW filters which are used in telecommunications, measuring equipment, radar systems and consumer products. SAW filters are now widely used in a variety of applications such as TV, satellite communications, optical fibre communications, mobile communications and so on. While these SAW filters have various specifications, many of them can be classified within a few fundamental categories. The scope of this part of IEC 60862 includes various kinds of filter configuration, of which the operating frequency range is from approximately 10 MHz to 3 GHz and the relative bandwidth is about 0,02 % to 50 % of the centre frequency. It is not the aim of this guideline to explain theory, nor to attempt to cover all the eventualities which may arise in practical circumstances. Standard values, given in IEC 60862, and national standards or detail specifications issued by manufacturers, define the available combinations of nominal frequency, pass bandwidth, ripple, shape factor, terminating impedance, etcetera. These specifications were compiled to include a wide range of SAW filters with standardized performances. It cannot be over-emphasized that the user should, wherever possible, select SAW filters from these specifications, when available, even if it may lead to making small modifications to his circuit to enable standard filters to be used. This applies particularly to the selection of the nominal frequency. This standard has been compiled in response to a generally expressed desire on the part of both users and manufacturers for guidance on the use of SAW filters, so that the filters may be used to their best advantage. For this reason, general and fundamental characteristics are explained in this guideline. IEC 60862-1 should be referred to for general information, standard values and test conditions. The features of these SAW filters are their small size, light weight, adjustment-free, high stability and high reliability. SAW filters add new features and applications to the field of crystal filters and ceramic filters. At the beginning, SAW filters meant transversal filters which have two interdigital transducers (IDT). Although SAW transversal filters have a relatively higher minimum insertion attenuation, they have excellent amplitude and phase characteristics. Extensive studies have been made to reduce minimum insertion attenuation, such as resonator filter configurations, unidirectional interdigital transducers (UDT), interdigitated interdigital transducers (IIDT). Nowadays, various kinds of SAW filters with low insertion attenuation are widely used in various applications and SAW filters are available in the gigahertz range. It is of prime interest to a user that the filter characteristics should satisfy a particular specification. The selection of tuning networks and SAW filters to meet that specification should be a matter of agreement between the user and the manufacturer. Filter characteristics are usually expressed in terms of insertion attenuation and group delay as a function of frequency. A standard method for measuring insertion attenuation and group delay is described in IEC 60862-1. In some applications, such characteristics as phase distortion are also important. Insertion attenuation characteristics are further specified by nominal frequency, minimum insertion attenuation or maximum insertion attenuation, pass-band ripple and shape factor. The specification is to be satisfied between the lowest and highest temperatures of the specified operating temperature range and before and after environmental tests. SAW filters are classified roughly into two types: transversal filters and resonator filters. Transversal filters are further classified into five types: bidirectional IDT filter, unidirectional IDT filter, tapered IDT filter, reflector filter and RSPUDT filter. Also resonator filters are further classified into three types, that is, ladder and lattice filters, coupled resonator filter and IIDT resonator filter. The responsible committee is K 642 "Piezoelektrische Bauteile zur Frequenzstabilisierung und -selektion" ("Piezoelectric and dielectric devices for frequency control and selection") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 642 - Piezoelektrische Bauteile zur Frequenzstabilisierung und -selektion