EP1238464A2

EP1238464A2 - Duplexer with improved transmission/receiving band separation

Info

Publication number: EP1238464A2
Application number: EP00993470A
Authority: EP
Inventors: Jürgen MACHUI
Original assignee: Epcos AG
Current assignee: TDK Electronics AG
Priority date: 1999-12-14
Filing date: 2000-12-06
Publication date: 2002-09-11
Also published as: US20030076194A1; US6861924B2; WO2001045273A3; CA2392833A1; JP2003517239A; WO2001045273A2; CN1411632A; DE19960299A1; KR20020059762A

Abstract

The invention relates to a duplexer for a wireless communication system with a transmission band and a receiving band. According to the invention, a split surface wave filter consisting of at least two partial filters which cover adjacent partial frequency ranges of the corresponding band and which together form an entire band, is provided as an input and/or output filter. At least two pairs of partial filters are provided, each pair comprising a filter in the input and output filter respectively. A switch is used to switch between the at least two pairs. If the duplexer interval remains the same, a greater band interval is created between the transmission and receiving bands or between the corresponding partial frequency ranges, said band interval being produced with surface wave filters.

Description

description

Duplexer with improved transmission / reception band separation

In wireless communication systems, in particular in mobile radio systems that do not allow TDD (Time Domain Duplexmg), two different frequency bands are usually provided, which from the point of view of the communication subscriber serve as the transmission and reception band. In the communication transmitter, in particular in the mobile radio (cell phone), the

Sending and receiving signals uses a common antenna. To separate transmission and reception signals, a duplexer is therefore generally necessary, which is connected between the antenna and the transmission and reception path. Such is essentially composed of two interconnected filters, namely an RX filter between the antenna and Rx path (LNA = Low Noise Amplifier) for received signals and a Tx filter between Tx path (PA = Power Amplifier) and antenna for signals to be sent.

Since the communication terminal must be able to send and receive at the same time, each of the two filters must be able to well suppress a signal located in the other frequency band. Typical values which are used in such drameless communication systems, for example for the suppression of the Tx band by the

Rx filters are required, are in the range of 50 dB and more. At the same time, the respective signals may only experience minimal losses when passing through the filter in the respective frequency band. A typical value for a maximum tolerable damping of the Tx band in the Tx filter is 2 dB or better.

Known duplexers that meet these normal requirements for strip separation (blanking area blanking) and emfuge vaporization are constructed, for example, from microwave ceramic filters. If there is a sufficient band gap between the TX and Rx bands, surface wave filters (SAW filters) can also be used become. However, if the TX and Rx bands are very close to one another, all requirements can only be met with great difficulty or not at all with SAW filters. An example of such a system is the American CDMA / TDMA-1900 (according to IS-95 and IS-136), in which the transmit and receive bands are 60 MHz wide each, and in which a duplex distance (= constant distance between transmit and Received signals) of 80 MHz is provided. At the bandwidth mentioned, there is only a distance of 20 MHz between the two bands, which corresponds to approximately 10,000 PPM for the frequency band mentioned. Within only 20 MHz, the respective filter must pass from the pass band with, for example, 2 dB attenuation to the stop band, where, for example, the 50 dB attenuation mentioned is required. This requires a transmission behavior that has steep flanks in the passband. Since a temperature-dependent frequency drift of the filter and manufacturing tolerances must also be taken into account, it was previously impossible to build such a duplexer only on the basis of SAW filter technology. This would require SAW filters that have a pass band with extremely steep flanks.

The object of the present invention is therefore to provide a duplexer for such communication systems, which enables the use of SAW filter technology and thus permits further miniaturization of duplexers.

This object is achieved with a duplexer according to claim 1. Advantageous embodiments of the invention can be found in the subclaims.

The invention is based on the idea of assembling at least one of the filters between the antenna and RX path (receive filter) and between the antenna and TX path (transmit filter) from at least two sub-filters, the passbands of which lie in adjacent frequency subregions of the required transmit or receive band and doing the whole Cover the tape. These partial filters designed as surface wave filters can then be correspondingly narrower in bandwidth than the filters previously used. Each of the two sub-filters, for example, then only has to cover half the bandwidth of the corresponding transmission or reception band. The required total width of the corresponding transmission or reception band results from the addition of the two frequency subregions.

A better optimization is possible for a narrow-band SAW filter, which in particular enables the formation of steeper flanks in the pass band. A better separation of the bands is possible even with only one flank improved in the slope, provided that this delimits the corresponding transmission or reception band from the neighboring reception or transmission band. The split filter can thus be designed as an SAW filter, which was not possible until now because of the edges that cannot be set steeply enough and the small bandgap. With the steeper flanks of the partial filters, the invention also enables a better suppression of the other band (transmission or reception band) of 50 dB and more. In addition, when using SAW filters, the adjustment required in conventional microwave ceramic duplexers to set the frequency position is omitted.

Both input and output filters are preferably designed as split surface wave filters. The duplexer according to the invention thus consists entirely of SAW filters, so that the advantages of SAW filters over conventional MWK filters or duplexers can be fully exploited. In particular, a further miniaturization is possible with a duplexer consisting only of SAW filters, which also means a further miniaturization of the corresponding terminal devices, namely the duplexer according to the invention

Should be used. Since sub-filters are now provided for frequency sub-ranges in the transmit and receive bands which are narrower than the entire band, suppression of the other band or frequency subrange becomes easier. For example, if input and output filters with a bandwidth of 60 MHz were used for the American CDMA-1900 system, a maximum distance of 20 MHz remained at a duplex spacing of 80 MHz between the two bands (frequency ranges). According to the invention, a distance of 50 MHz is now possible with input and output filters split into at least two sub-filters. This allows better suppression of the other band to be achieved even if the corresponding pass bands are not optimal. The construction of exclusively SAW filters also enables a single-chip solution for all filters of the duplexer.

In the duplexer according to the invention, switches for switching between the sub-filters and thus for switching between the frequency sub-ranges can also be provided. By providing a switch, only one of the sub-filters of the split SAW filter is connected to the antenna at a time, so that the other sub-filter (s) do not interfere with the properties of the "active" sub-filter. It is therefore also possible for the sub-filters to be independent of one another If the input and output filters are designed as split SAW filters, then each sub-filter of the input filter is assigned a sub-filter of the output filter, which together form a pair of sub-filters switch or two separate switches may then synchronously. from an active further on a previously passive part pair of filters are switched. the partial filter pairs are allocated to frequency sub-ranges so that the Duplexerabstand is maintained. Übli ^¬ cherweise are thereby the frequency locations of the sub-filters in input and in Output filter u m shifted the same amount. This shift always takes place in pairs. In a further advantageous embodiment, the duplexer is designed for sending and receiving within at least two different communication systems that use different frequency bands. This is achieved in a simple manner by multiplying the number of input and output filters and the associated switches accordingly. A separate set of input and output filters and the associated switches are therefore provided for each communication system for which the duplexer according to the invention is designed. So far, for example, terminal devices are provided which are intended for use in two different communication systems (dual-band mobile phone) and which use a separate duplexer for each of these systems. According to the invention, it is also possible to design a duplexer for more than two communication systems.

In a further embodiment of the invention, a switch can switch between partial filter pairs within a communication system as well as between partial filter pairs that belong to two different communication systems.

The duplex spacing can also change, and with it the spacing between the frequency sub-ranges of the sub-filter pairs. If the two communication systems are parallel to one another and have different degrees of coverage, then better network coverage is possible for a communication terminal using the duplexer according to the invention. If different communication systems are used in different countries, a correspondingly equipped communication terminal can be used across borders in both systems. Common advantage of ISC is that only one duplexer is required for the different communication systems. In both communication systems, the input and / or output filters can be split up into two or more sub-filters. However, it is also possible for a communication system to have a sufficiently high duplex spacing, which is achieved using an SAW filter for input and output filters is feasible. In combination with a communication system that has split input and / or output filters, a duplexer according to the invention thus has the option of switching between at least three pairs of filters, of which at least two partial titer pairs are SAW-based.

All of the input and output filters of the duplexer and, if appropriate, the switches, are preferably arranged in a common housing or at least on a common module. Such a device is easier to handle by the end device manufacturer and is easier to optimize in terms of its properties.

A duplexer according to the invention is preferably constructed exclusively from surface wave filters for the receiving and transmitting bands, all of which are integrated on a common piezoelectric substrate or arranged on two substrates. Due to the possible high integration density, the highest degree of miniaturization for the duplexer can be achieved with the first-mentioned embodiment. The common use of other switching and network components for the different filters is also possible on a common substrate, which results in a further increase in the integration density. A simplified adaptation of the filters to one another and to a network is also possible on the common substrate.

In addition, it is possible to integrate all filters and sub-filters together with any necessary adaptation network of passive components and the switches on a common module. This also simplifies handling and simplifies use, since the end device manufacturer only has to process one module.

For the surface acoustic wave filter and SAW partial filter is as

Substrate material lithium tantalate red y with a cutting angle of 35 to 46 ° (LT35-46) preferred. This material has a particularly good temperature response, with which a transmission behavior with narrow bandwidths and steep flanks can be set.

Since with the duplexer according to the invention, due to the greater distance between the frequency sub-regions, less steep edges also lead to the desired decoupling between the transmission and reception bands, the use of lithium niobate rot y with an intersection angle of 60-70 ° (LN60-70) and in particular is also in principle near 64 ° (LT64) possible. In this way, even lower insertion losses can be achieved compared to lithium tantalate. This can be particularly advantageous when using lithium niobate for the output filters, since the communication terminal in particular strives for a high transmission power, which in turn requires low insertion loss. With the transmission power remaining the same, lower insertion loss results in lower power consumption.

It is also possible to provide SAW filters for input and output filters which are constructed on different substrate materials. The combination of lithium niobate for the outlet filter and lithium tantalate for the inlet filter is preferred.

To achieve the good filter properties, the electrode material is preferably correspondingly stable. Electrodes that have the following material layers or a sandwich structure with the following material layer combinations are therefore particularly suitable: aluminum and copper layers, aluminum and magnesium layers or aluminum / copper and copper or magnesium layers.

An improved performance compatibility is also achieved if a layer comprising titanium, in particular a titanium layer, is provided between the electrode material and the substrate. The surface wave filters of the duplexer according to the invention are preferably designed as reactance filters, with which the required high insertion vaporization can be achieved particularly well with the output filter

The invention is explained in more detail below on the basis of exemplary embodiments and the associated seven figures

Figure 1 shows the location and arrangement of the transmission and reception band.

Figure 2 shows a real filter curve

FIG. 3 shows the arrangement and position of partial frequency ranges according to the invention

Figures 4 to 6 own different levels of integration of a

Duplexers including peripherals.

FIG. 7 shows an exemplary interconnection of

Single gate resonators to a reactance filter

FIG. 1 shows a schematic representation of the arrangement and position of the transmission band TX and reception band RX of the American CDMA 1900 system. The transmission band TX extends from 1850 to 1910 MHz and is thus 60 MHz wide. The reception band RX extends from 1930 to 1990 MHz and thus also has a width of 60 MHz. From the point of view of the communications device, a communication connection uses, for example, a transmission frequency fxT which lies in the transmission band TX and at the same time a reception frequency fxR in the reception band RX. The distance between fxT and fxR is the so-called duplex distance DA and is 80 MHz for the CDMA system mentioned. All frequency pairs with a duplex distance of 80 MHz are suitable for a communication connection within this system. The distance BA between transmit band TX and receive band RX is 20 MHz FIG. 2 shows a schematic representation of a possible transmission curve of a filter with the required bandwidth shown below, here of the transmission band TX. EDF vaporization is particularly important for filter quality. This is the greatest distance from the dashed zero line for zero attenuation to the transmission curve within the corresponding band. Usually, the pass band is also wider than the required frequency band of the respective band, because the edges of a filter are in the pass band

(Passband) cannot be set vertically. The right flank F _re , which delimits the pass band hm from the adjacent frequency range of the reception band RX, is decisive in the transmission curve m shown in the figure for a transmission filter. This flank must be steep enough for the

Input filter in the area of the reception band RX has a sufficiently low sensitivity or a sufficiently high blocking area suppression SU. The left flank F _{1 of} the pass band, which delimits the reception band RX hm from the transmission band TX, would be decisive for a corresponding input filter.

FIG. 3 shows how, according to the invention, the transmission and reception ranges TX, RX e are split into two frequency subregions of here bandwidth. A frequency sub-area RX1, RX2 of the receive band is assigned to a frequency sub-area TX1, TX2 of the transmission band in such a way that the duplex distance DA can be maintained. For example, a transmission frequency fXT with the required duplex spacing DA of 80 MHz, for example, is assigned a reception frequency fxR. While the distance BA between the transmission and reception bands in known duplexers corresponds to the distance flR - f3T, it is flR - f2T = f2R - f3T = 50 MHz in the case of transmission and reception bands or associated filters split according to the invention (for the CDMA system mentioned). The filters belonging to the corresponding frequency sub-ranges have the corresponding frequency sub-ranges Passband on. Due to the higher band gap BA, however, filters with less steep flanks can be selected, which nevertheless achieve the required blocking area suppression SU of typically 50 dB.

In addition to the division of the transmission and reception bands shown here, m two frequency sub-areas Txl, Tx2; Rxl, Rx2, it is of course also possible to divide the corresponding bands into three or more frequency sub-ranges, with a separate sub-filter being provided for each frequency sub-range

FIG. 4 shows a schematic representation of a duplexer consisting of four partial filters FR1, FR2, FT1, FT2 together with its connection to an antenna A and the associated transmission path PA and the receiving deposit LNA. Both the input filter and the output filter are designed as split surface wave filters with two sub-filters. The input filter comprises the sub-filters FR1 and FR2, while the output filter comprises the sub-filters FT1 and FT2. A switch S is arranged between the antenna A and the duplexer consisting of the four partial filters and can switch between two partial filter pairs FT1 / FR1 and FT2 / FR2. A sub-titer pair each comprises a filter of input and output filters, for example the pair FRl / FTl or FR2 / FT2. Further switches S ^λ S ^{, v} - connect, for example, the components of the reception path LNA to the input filter, with switch S between the sub-filters of the input filter switches. Accordingly, the switch S switches between the various output filters FT1 and FT2, which are optionally connected to the components of the transmission path PA. With a dashed line, a module Ml is shown, on which the four sub-filters are integrated. The matching network, consisting for example of passive components such as resistors, capacitors and inductors or strip lines (not shown in the figure), is implemented outside the module, as are the switches S. FIG. 5 shows a corresponding arrangement, in which, however, the adaptation network is additionally integrated in addition to the partial filters on an enlarged module M2.

A module M3 which is integrated even higher is shown in FIG. 6. In addition to the sub-filters, this module M3 also includes the adaptation network and the switches S.

FIG. 7 shows a schematic representation of a circuit arrangement for a reactance filter constructed from surface wave single-gate resonators. Em SAW-Emtorresonator is built on a piezoelectric substrate 1 and comprises an interdital transducer IDT provided with two connections, which is arranged between two reflectors Ref. For a simple reactance filter, at least two such resonator resonators are now connected in such a way that at least one of the resonators is arranged in series between input ES and output AS and at least one of the resonators is connected to ground in a parallel branch. A serial resonator, for example RIS, forms an element of a reactance filter together with an adjacent parallel resonator R1P. However, a reactance filter preferably consists of a plurality of basic elements connected in series, for example three basic elements as shown in the figure. In the exemplary embodiment, the resonators R2S and R1P and R2S and R2P form two further basic elements. Within a basic element, the resonance frequencies of the parallel and serial resonator are shifted relative to one another in such a way that the anti-resonance frequency of the serial resonator comes to lie exactly on the resonance frequency of the parallel resonator. The

Filter em pass-through behavior with a pass band, which has a particularly low emfu vaporization of, for example, 2 dB and less.

The exemplary embodiments are only examples of possible configurations of the invention. However, the invention is not limited to the exemplary embodiments and may include further variations, not shown.

Claims

claims

1. Duplexer for a wireless, a transmission and a reception band (Tx, Rx) having communication system, - in which different filters are provided as input and output filters for the transmission and reception band or for transmission and reception signal, in which at least one of the input and output filters is designed as a split surface wave filter with at least two partial filters (FR1, FR2; FT1, FT2) covering adjacent frequency subregions of the transmission or reception band.

2. Duplexer according to claim 1, in which the input and output filters are designed as split surface acoustic wave filters (FR1, FR2; FT1, FT2).

3. duplexer according to claim 1 or 2, wherein a switch (S) for switching between the

Sub-filters (FR1, FR2; FT1, FT2) and thus between the frequency sub-ranges (Rxl, Rx2; Txl, Tx2) is provided.

4. duplexer according to one of claims 1-3, designed to transmit and receive in at least two different frequency bands using communication systems, in which for the at least two frequency bands (Rx, Tx)

Split surface wave filters (FR1, FR2; FT1, FT2) serving as input and / or output filters are provided.

5. duplexer according to one of claims 1-4, the input and output filters are designed as split surface wave filters, each with at least two adjacent frequency subregions (Rxl, Rx2; Txl, Tx2) of the sub-filters (FRl, FR2, FT1, FT2) covering the transmission or reception band (Rx, Tx), in which a first sub-filter (FT1) of the input filter is assigned a first sub-filter (FR1) of the output filter and a second sub-filter (FT2) of the input filter is assigned a second sub-filter (FR2) of the output filter such that the frequency sub-ranges for each second sub-filter are shifted in the same direction against the corresponding frequency sub-ranges of the first sub-filters, and are provided in the switch (S) for switching between sub-filter pairs (FR1, FT1; FR2, FT2) assigned to one another.

6. Duplexer according to one of claims 1-5, in which the input and / or output filters formed as split surface wave filters (FRl, FR2; FT1, FT2) comprise more than two sub-filters.

7. Duplexer according to one of claims 1-6 in which all input and output filters and the switch or switches (S) are arranged in a common housing.

8. Duplexer according to claim 7, in which all input and output filters are formed on a common piezoelectric substrate.

9. duplexer according to claim 7 or 8, wherein a matching network and all existing Filters or sub-filters are integrated on a common module (M).

10. Duplexer according to one of claims 7-9, wherein the switches (S) are arranged on a common substrate with the filters.

11. duplexer according to any one of claims 1-10, wherein the substrate material comprises at least one of Em and output filter lithium tantalate red y with a cutting angle of 35 to 44 ° - LT35-44 -.

12. Duplexer according to one of claims 1-10, wherein the substrate material at least one of Em- and output filter lithium niobate rot y with a cutting angle of 60 to 70 ° -LN60-70- and in particular with a cutting angle close to 64 ° -LN64 - is.

13. A duplexer according to claims 11 and 12, wherein the substrate material for the input filter LN64 and the substrate material for the output filter LT35-44 comprises.

14. Duplexer according to one of claims 1-13, wherein the surface acoustic wave filters have electrode structures which consist of a material selected from aluminum and copper, aluminum and magnesium, aluminum / copper and magnesium

15. A duplexer according to claim 14, wherein the electrode structures comprise a titanium layer.

16. Duplexer according to one of claims 1-15, in which the surface wave filter or filters are designed as a reactance filter.

17.Use of the duplexer according to one of the preceding claims in a transceiver.