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

Overview

This part of IEC 62604 concerns the duplexers, which can separate receiving signal from transmitting signal and are key components for two-way radio communications. They are generally used in mobile phones using CDMA systems such as N-CDMA, W-CDMA/Universal Mobile Telecommunication System (UMTS). Duplexers are necessary for mobile phones to simultaneously receive and transmit signal. Duplexers are 3-port devices which consist of antenna port, transmitter port (TX port) and receiver port (RX port). They have three basic functions. The first function is to transmit transmitting signal from TX port to antenna port. The second function is to transmit receiving signal from antenna port to RX port. The third function is to prevent from leaking transmitting signal from TX port to RX port. The transmitting frequency and the receiving frequency are determined corresponding to each mobile phone system. So far, dielectric duplexers have been mainly used. However, recently SAW duplexers, which are utilized surface acoustic wave (SAW), are becoming popular and replacing the dielectric duplexers year by year in recent mobile phones, because of their advantage of small size, light weight and good electrical performances. In addition to SAW duplexers, BAW duplexers, which are utilized bulk acoustic wave (BAW), are also becoming in the spotlight and popular because of their higher Q property and better performances especially in PCS band. It is neither the aim of these guidelines to explain theory, nor to attempt to cover all the eventualities which may arise in practical circumstances. These guidelines draw attention to some of the more fundamental questions, which should be considered by the user before he places an order for SAW and BAW duplexers for a new application. Such a procedure will be the user's insurance against unsatisfactory performance. Because SAW and BAW duplexers have very similar performance for the usage, it is useful and convenient for users that both duplexers are described in one standard. Standard specifications, such as those of IEC of which these guidelines form a part, and national specifications or detail specifications issued by manufacturers, will define the available combinations of centre frequency, pass bandwidth and insertion attenuation for each of transmitting and receiving filters and isolation level between transmitting and receiving ports, etcetera. This information is compiled to include a wide range of SAW and BAW duplexers with standardized performances. It cannot be over-emphasized that the user should, wherever possible, select his duplexers with standardized characteristics, when available, even if the use of standard duplexers may lead to making small modifications to his circuit. This applies particularly to the selection of the normal frequency. It is of prime interest to a user that the duplexer characteristics satisfy particular specifications. The selection of the front-end circuits in mobile phones and SAW & BAW duplexers to meet such specifications should be a matter of agreement between user and manufacturer. Duplexer characteristics are usually expressed in terms of centre frequency, pass bandwidth and insertion attenuation for each of transmitting and receiving filter parts in the duplexer and isolation level between transmitting and receiving ports. Since the SAW & BAW duplexer is used in RF front-end of the mobile phones, lower insertion attenuation, higher isolation/rejection level, stronger power durability and smaller/thinner package dimension are strictly required. UMTS duplexers, US CDMA duplexers and PCS CDMA duplexers are also explained. As an example of a duplexer for UMTS system, SAW duplexer for UMTS Band I is shown as an example for UMTS band I. The frequency regulation of Band I is provided by 3rd Generation Partnership Project (3GPP). The transmitter and receiver pass bands in the handset are 1 920 MHz to 1 980 MHz and 2 110 MHz to 2 170 MHz, respectively. The sizes of this duplexer is typically 4,9 mm×4,9 mm×1,7 mm. A 41° rotated Y cut X propagated LiNbO₃ crystal is used as substrate. The structure of this filter is a ladder, and the electrodes material is made by Al-Ti alloy for high power durability. Frequency characteristics of this SAW duplexer for UMTS are shown. The typical insertion attenuation from TX port to Antenna port and that from antenna port to RX port are 1,4 dB and 2,3 dB, respectively. The isolation values between transmitter and receiver ports are typically 48 dB for the TX band and 40 dB for the RX band. The frequency characteristics example of US CDMA duplexer is explained. This type of duplexer is also applicable to UMTS Band V. The TX pass-band frequency is 824 MHz to 849 MHz, while RX pass-band frequency is 869 MHz to 894 MHz. The dimensions of this duplexer are typically 3,8 mm×3,8 mm×1,6 mm. Rotated Y cut X propagated LiTaO₃ crystal ,which rotated angle is optimized around 36°, is used as a substrate. The ladder type SAW filters are used for both TX and RX parts. Typical insertion attenuation is 1,8 dB from TX port to antenna port. And 2,5 dB typical insertion attenuation is from antenna port to RX port. The isolation between TX port and RX port is typically 60 dB for the TX band and 47 dB for the RX band. The guard band or a gap distance between transmitting and receiving frequency for UMTS band II or PCS band is relatively narrow, high Q characteristics or sharp transient filter response is required. From this requirement, BAW duplexers which are composed of film bulk acoustic resonators (FBAR) or solid mounted resonators (SMR) are mainly used for PCS CDMA duplexers. The frequency characteristics example of PCS CDMA duplexer using FBAR is shown. The TX pass-band frequency is 1 850 MHz to 1 910 MHz, while RX pass-band frequency is 1 930 MHz to 1 990 MHz. This duplexer can comply the maximum insertion loss of 3,5 dB for TX part and 4,0 dB for RX part, with excellent transient filter responses between TX and RX bands. Also, the maximum isolation values between transmitter and receiver ports are 54 dB for the TX band and 43 dB for the RX band. 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