Duplexer with improved transmission/receiving band separation

CA 02392833 2002-05-28

DUPLEXER WITH IMPROVED TRANSMISSION/RECEPTION BAND SEPARATION

In wireless communication systems,, particularly in mobile radiotelephone systems that do not allow TDD (time domain duplexing), two difTercnl frequency bands are usually provided that serve as transmission band and reception band from the point of view of the communication participant. Λ common antenna is used for the transmission and reception of signals on the communication transmission device, particularly in the mobile radiotelephone device (cell phone). A duplexer is therefore generally needed for the separation of transmission and reception signals, this being 1 o connected between antenna and transmission and reception path. Such a duplexer is essentially composed of two interconnected filters, namely a RX filter between 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 device must be able to simultaneously

5 transmit and receive, each of the two filters must be able to suppress a signal lying in.

the other frequency band well. Typical values that are required in such wireless communication systems, for example for the suppression of the Tx band by the Rx filter, lie in the range around 50 dB and above. At the same time, tlie respective signals dare experience only minimum losses when passing through the filter in the

0 respective frequency band. A typical value for a maximally tolerable attenuation of the Tx band in the Tx filter is 2 dB or better,

Known duplexers that meet these high demands made of the band separation (stop band suppression) and the insertion attenuation are constructed, for example, of microwave ceramic filters. Given an adequate band spacing of TX and Rx band,

5 surface-active wave filters (SAW filters) can also be employed. When, however, TX and Rx bands lie extremely close to one another, it is very difficult or even impossible to simultaneously meet all demands with SAW filters by themselves. One example of such a system is the American CDMA/TDMA-1900 (according to IS- 95 or, respectively, IS-136) wherein transmission and reception band are respectively 60

0 MHz wide and wherein a duplex spacing (constant spacing between transmission and

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CA 02392833 2002-05-28 reception signals) of X(.) MHz is provided. Given said bandwidth, a spacing of only 20 MHz thereby remains between the two hands, this corresponding to approximately 10000 PPM given said frequency band. Within only 20 MHz. rhe respective filter must thereby switch ΰυπι the pass band with, for example, 2 dB attenuation into the stop band where, for example, said 50 dB attenuation is required. This requires a transmission behavior that exhibits steep signal edges in the pass band. Since a temperature-dependent frequency drift of the filter as well as manufacturing tolerances must also be additionally taken into consideration, it was hitherto not possible to construct. such a duplexer only on the basis of SAW filter technique. This required SAW filters Thar comprise a pass band with extremely steep signal edges.

It is therefore an object of the present invention to specify a duplexer for such communication systems that enables the employment of SAW filter technique and, thus, allows for a miniaturization of duplexers,

This object is achieved with a duplexer according to claim 1, Advantageous developments of the invention can be derived from the subclainw.

The invention is based on the idea of composing at least one of the filters between antenna and RX path (reception filter) and between antenna and DX path (transmission filter) of at least two sub-filters whose pass bands lie in mutually neighboring frequency sub-ranges of the requir ed tiauamissiou or, rcspootivoly, reception band and thereby cover the entire band. These sub-filters fashioned as surface-active wave filters can then be correspondingly narrower-bond than the filters previously employed. Each of the two sub-filters, for example, then need only cover half the bandwidth of the corresponding transmission or, respectively, reception band. The required overall width of the corresponding transmission or, respectively, reception band derives from the addition of the two frequency sub-ranges.

A better optimization, is possible for a narrow-Uaud SAW filler, this particularly enabling the formation of steeper signal edges in the pass band. A better separation of the bands is already possible with only one signal edge improved in steepness, insofar as this delimits the corresponding transmission or reception band from the neighboring reception or, respectively, transmission band, The split filter can thus be fashioned as SAW filter, which was hitherto not possible because of rhe

CA 02392833 2002-05-28 signal edges That could not he set steeply enough and because of the slight band spacing. With the steeper signal edges of the sub-filters, the invention also enables a belter suppression of the respectively other band (transmission or, respectively, reception baud) of 50 dB anil more. Over and above this, the matching required for setting the frequency position given traditional duplexers of microwave ceramic (MWK) is eliminated given the employment of SAW filters.

Preferably, both input filters as well as output filters are fashioned as split surface wave fi Iters. The inventive duplexers thus completely composed of SAW filters, so that the advantages of SAW filters compared to traditional MWK filters or, o respectively, duplexers can be completely exploited. In particular, a fhnher miniaturization is passible with a duplexer composed only of SAW filters, this enabling a further miniaturization of the corresponding terminal devices wherein the inventive duplexer ia to bo employed. Since sub-filters for frequency sub-ranges that are narrower then the overall band are provided in the transmission and in the reception band, a suppression of the respectively other band or, respectively, frequency sub-range is possible in a simpler way, When, tor example, input and output filters having a bandwidth of 60 MHz were employed for the American CDMA-1900 system, then a maximum spacing of 20 MHz remained given a duplex spacing of 80 MHz between the two bands (frequency ranges). Inventively, a spacing

0 of 50 MHz is now possible with input and output filters split into at least two sub- filters. Even given non-optimum signal edges of the corresponding pace bands, a better suppression of the respectively other band can thus be achieved, Due to the structuring only with SAW filters, a one-chip solution for all filters of the duplexer also becomes possible.

In the inventive duplexer, moreover, switches can be provided for switching between the sub - filters and, thus, for switching between the frequency sub-ranges, Due to tho provision of a switch, respectively only one of the sub-filters of the split SAW filter is always connected to the antenna, SO that the other sub-filter or subfilters do not disturb the properties of the active” sub-filter. It is thus also possible to

0 optimize the sub-filters independently of one another to a suitable frequency position and a suitable edge steepness. When input and output filters are fashioned as split

CA 02392833 2002-05-28

SAW filters, then a sub-filter of the output filter is al located tn each sub-filter of the input filter, these together foiming a sub-filter pair. With the assistance of a shared switch or two individual switches, a switch can then be synchronously undertaken from an active to a previously passive, further sub-filler pair, The sub-filter pairs are thereby allocated such to the frequency sub-ranges that the duplexer spacing is adhered to. Usually, the frequency positions of tho sub-filters in the input filter and in the output filter are thereby respectively shifted by the same amount. This shift always ensues in pairs.

In another advantageous development, the duplexer is fashioned for transmission and reception wilhin at least two different communication systems that use different frequency bauds. This is achieved in a simple way in that the plurality input and output filters and the appertaining switches are correspondingly multiplied. A separate set of input and output filters and the appertaining switches is therefore provided for each communication system for which the Inventive duplexer is

Ί 5 designed. For example, terminal devices that are provided tor utilization in two different communication systems (dual band cell phones) are already known and employing separate duplexers for each of the systems is already known. Inventively, it is also possible tu design one duplexer for more than two communication systems.

In a further development of the invention, one switch can switch both between

0 sub-filter pairs within a communication system as well as between sub-filter pairs that belong to two different communication systems. The duplex spacing can thereby also vary and, thus, so can the spacing between the frequency sub-ranges of the sub-filter pairs. When the two communication systems are present parallel tn one another and exhibits different degrees of coverage, a better network coverage is then possible far a

5 coiinnunicaliun terminal device using the inventive duplexer. When different communication systems are used in different countries, then a correspondingly equipped communication terminal device can be used in both systems in cross-border fashion. A common advantage is thereby always that only one duplexer is required far the different communication system. A splitting of the input and/or output filters o into two or even more sub-filters can thereby be undertaken in both communication system systems. However, it si also possible that one communication system exhibits

CA 02392833 2002-05-28 an adequately high duplex spacing that can be realized with the assistance of respectively one SAW filter for input and output filter, in combination with a communication system that comprises split input and/or output filters, a switching possibility between at least three pairs of filters, whereof at least two sub-filter pairs 5 arc on an SAW base, thus derives for an inventive duplexer.

Preferably, all input and output filters of the duplexer and, potentially, the switches in addition thereto are arranged in a common housing or at least on a οπτητηηη module. This is easier to handle for the manufacturer of the terminal device and can be more simply optimized for terms of its properties.

o Preferably, an inventive duplexer is constructed only of surface wave filters for the leceptiou Laud and the transmission band, all of these being integrated on a shared piezoelectric substrate or being arranged on two substrates. Due to the high integration density that is thereby possible, the highest degree of miniaturization for the duplexer can thus be achieved with the first-cited embodiment. On a shared

IS substrate, further, the shared employment of other circuit and network components is also possible for the different filters, this yielding a finther enhancement of’the integration density. Further, a simplified adaptation of the filters to one another and lu a network is also passible on the common, substrate.

It is also possible to integrate all filters and sub-filters together with &

o potentially required matching network of passive components and the switches on a shared module. This also simplifies the manipulation and simplifies the employment since the manufacturers of the terminal devices need process only one module.

Lithium tantalate red y having a section angle of 35 through 46° (I .T35-46) is preferred for the surface wave filter and SAW sub-filters. This material has an

5 especially good temperature response with which a transmission behavior having narrow band widths and steep signal edges can be set.

Since, due to the higher sparing between the frequency sub-ranges, signal edges that are not as steep also lead to the desired decoupling between transmission and reception hand given the inventive duplexer, the employment of lithium niobate o red y having a section angle of 60-70^a (LN60-70) and, in particular, close to 64° (LTÙ4) is fundamentally also possible. Even lower insertion atténuations can thus be

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CA 02392Θ33 2002-05-2Θ achieved compared to lithium tantalate. This can be particularly advantageous given tlie employment of lithium niohate for the output filters, since a high transmission power is desired particularly given a communication terminal device, a low insertion attenuation being internally required for (his. Given an unchanging transmission 0 power, a lower insertion attenuation results in a lower power consumption.

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

in order tn achieve the good filter properties, the electrode material is o preferably correspondingly power-resistant. Electrodes that comprise the following layers of material or, respectively, a sandwich structure having the following combinations of material layers arc therefore well-suited: aluminum and copper layers, aluminum and magnesium layers or aluminum/copper and copper or magnesium layers.

An approved power compatibility is also achieved when the layer comprising titanium is provided between electrode material and substrate, particularly a. titanium layer.

The surface wave filters of the inventive duplexer are preferably fashioned as reactance filters, with which the required, high insertion attenuation can bo easily

0 achieved, particularly at the output filter.

The invention is explained in greater detail below on the basis of exemplary embodiments and the appertaining seven figures.

<td> Figure 1</td><td> shows the position and arrangement of transmission and reception band.</td>

<td> 23 Figures</td><td> shows a real filter curve.</td>

<td> Figure 3</td><td> shows the arrangement and position of frequency sub-ranges according to the invention.</td>

<td> Figures 4 through 6</td><td> show various integration units of a duplexer together with periphery.</td>

<td> 3 0 Figure 7</td><td> shows an exemplary interconnection of one-pon resonators to form a reactance filter.</td>

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CA 02392833 2002-05-28

In a schematic illustration, Higurel shows the arrangement and position of transmission band TX and reception band RX of the American Cl )M A-l 900 system. The transmission band TX extends from 1850 through 1910 MHz and is thus 60 MHz wide. The reception band RX extends from 1930 through 1990 MHz wul thus likewise has a width of 60 MHz. A communication connection - as viewed proceeding from the communication terminal device - uses, for example, a transmission frequency &amp;T that lies in the transmission band TX and, simultaneously therewith, uses a reception frequency 1tR. in the reception band RX. The spacing between sxT and sxR is what is referred to as the duplex spacing d A and amounts to 10 80 MHz for said CDMA ay stem. Fur a communication connection within this system, all frequency pairs having the duplex spacing SO MHz arc Buitable. The spacing BA between transmission. TX and reception band RX amounts to 20 MHz.

In a schematic illustration, Figure 2 shows a possible pass curve of a filter with required bandwidth entered therebelow. Here the transmission band TX. What h is decisive for the filter quality is, in particular, the insertion attenuation ED. Within the corresponding band, that is the greatest spacing from the broken-line zero line for zero attenuation relative to the pass curve. Usually, the pass range Is also Wider then the required frequency range of die respective band, since the signal edges of a filter cannot bo vertically set in the pass band. Given the pass curve shown in the figure for 20 a transmission filter, the right-hand edge F_re is critical, this limiting the passband relative to the neighboring frequency range of the reoeption band RX. This edge must be steep enough so that the input filter here exhibits an adequately low sensitivity or, respectively, an adequately high stop hand suppression SU in the region of the reception band RX. For a corresponding input filter, the left-hand edge F_u of the

5 passband will be critical, this limiting the reception band RX relative to the transmission band TX.

Figure 3 shows how the transmission and reception ranges TX, RX arc inventively split into respectively two frequency sub-ranges having what is here an identical bandwidth. A frequency sub-range RX1, RX2 of the reception band is

0 respectively thereby allocated such to a frequency sub-range TX1, TX2 of the transmission band that the duplex spacing DA can be adhered to. For example, a

CA 02392833 2002-05-28 transmission frequency iXT has a reception frequency ficR allocated to it in the required duplex spacing DA of, for example, ΚΠ MHz. Whereas the spacing BA between transmission and reception band in known duplexers corresponds to the spacing flR - DT, it amounts to HR-£2T=12R - 1ST ~ 50 MHz (fbr said CDMA system) given the inventively split transmission or, respectively, reception bands or, respectively, appertaining filters. The filters belonging to the corresponding frequency sub-ranges exhibit a passband in the corresponding frequency sub ranges. Due to the higher band spacing BA, however, filters having less steep edges can be selected for this purpose, these nonetheless achieving the required stop band suppression SU of, typically, 50 dB.

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

In a schematic illustration, Figure 4 shows a duplexa: composed of four subfi Iters EK 1, EK 2, F 1’1, ΚΓ2 together with the interconnection thereof to an antenna A and the appertaining transmission path PA and reception path LNA. Both the input filter as well as the output filter arc fashioned as split surface wave fillers each having two sub-filters. The input filter comprises the sub-filters FR1 and FR2, whereas the output filter comprises the sub-filters FT1 and FT2. A switch S that can switch between two sub filter pairs FT1/FR1 and FT2/FR2 is arranged between the antenna A and the duplexer composed of the four Bub-filtere. A sub-filter pair thereby respectively comprises a filter composed of input and output filter, for example the pairFRl/FTl or FR1/FT2. Further switches S' S connect, for example, the oumponents of ihc reception path LNA Lo the input filter, whereby the switch S' switches between the sub-filters of the input filter. Correspondingly, the switch S switches between the various output filters FT1, and FT2 that are optionally connected to the components of the transmission path PA· The broken illustrates a module Ml on which the four sub-filters are integrated. The matching network composed, for example, of passive components such as resistors, capacitors and

CA 02392833 2002-05-28 inductances or striplines (not shown in the Figure) is realized outside the module, just Eke the switches S.

Figure 5 shows a corresponding arrangement wherein, however, the matching network is also additionally integrated un an enlarged module M2 in addition to the sub-filters.

An even more highly integrated module M3 is shown in Figure 6. This module M3 also comprises the matching network and the switches S in addition to comprising the sn Milters.

In a schematic illustration, Figure 7 shows a circuit arrangement tor a o reactance filter composed of surface wave one-port resonators. An SAW one-port resonator is constructed on a piezo-electric substrate 1 and comprises an inrerdigltal transducer IDT provided with two terminals that is arranged between two reflectors Ref. For a simple reactance filter, at least two such one-port resonators arc then interconnected such that at least one of the reconaters is serially arranged between input HS and output AS and at least one of the resonators is connected to the ground in a parallel branch. Together with a neighboring, parallel resonator RIP, a serial resonator, for example R1S, forms a basic element of a reactance filter. A reactance filter, however, is preferably composed of a plurality of series-connected basic elements, for example of three basic elements as shown in die Figure. In the

0 exemplary embodiment, the resonators R2S and RIP as well as R2S and R2P form two further basic elements. Within a basic element, the resonant frequencies of parallel and serial resonator are shifted such relative to one another that the anti resonant frequency of the serial resonator comes to lie exactly on the resonant frequency of the parallel resonator. The filter thereby exhibits a pass behavior with a

5 pass bund that exhibits an especially low insertion attenuation of, for example, 2 dB and less.

The exemplary embodiments only stand by way of example for possible embodiments of the invention. The invention, however, is not limited to die exemplary embodiment® and can comprise further variations that are not shown.

CA 02392833 2002-05-28

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List of Reference Characters Tx transmission band Rx reception band su stop baud Suppression 5 ED insertion attenuation fxT transmission frequency fkR reoeption frequency F,· F •^Ίι * re left and right edge of the pass band Txl, Tx2 frequency sub-ranges of the transmission band 10 Rxl,Rx2 frequency sub-ranges of the reception band FR1.FR2 sub-filters of the Split input filter FT1.FT2 sub-filters nfthe split output filter A antenna S.S'.S” switches 13 LNA low noise amplifier of the Rx path PA power amplifiei' of the Tx path Ml, M2, M3 modules RIS.R2S one port resonators in the serial branch RIP, R2P one-port resonators in the parallel branch 20 ES serial branch input AS serial branch output Ref reflector IDT interdigital transducer