Filter circuit

Translation of description of equivalent WO 2004019491 A2

description

filter circuit

The present invention relates to a filter circuit, particularly to a filter circuit for converting unsymπtetrischen / balanced signals in balanced / unbalanced signals, and in particular to a filter circuit which BAW resonators includes (BAW = Bulk Acoustic afer = bulk acoustic wave). Further, the present invention relates to a filter circuit having a plurality of BAW resonators, which enables transformation of impedance levels between an input port and an output port of the filter circuit.

In resonators based RF filters, such as BAW filters have two basic topologies, which are described in more detail with reference to FIGS. 1 and 2.

The first topology (see FIG. 1) is the so-called "Lad the filter" (ladder filter). The Ladder filter 100 includes an input port 102 to a first input terminal 104 and a second input terminal 106. Further, comprises the filter 100 an output port 108 with a first output terminal 110 and a second output terminal 112. the first input terminal 104 of the input port 102, an input signal a is on, and the first output terminal 110 of the output port 108 is located on an output signal OUT. are in the filter 100 shown in FIG. 1 between the first input terminal 104 and the first output terminal 110 in series two series resonators R_sl and R_s2 connected. Furthermore, two parallel resonators R_pl and R_p2 provided. The first parallel resonator R_pι is parallel to the input port 102 and parallel to the first series resonator R_sl connected. The second parallel resonator R_p2 is parallel to the output port 108 and parallel to the second series resonator R_s2 connected. The second input terminal 106 and the second output terminals circuit 112 are connected to a reference potential 114, z. B. Mass. The parallel resonators R_pl and R_p2 are also connected to the reference potential. In the conventional filter shown in Fig. 1 is a Lad the filter with two stages with a single input and a single output ON OFF for transmitting unbalanced signals.

In FIG. 2 illustrates a known Lattice filter (lattice filter) with a step (two series resonators and two parallel resonators) is explained in more detail. In the description of Fig. 2 are similar or the same components which have already been described with reference to FIG. 1, provided with the same reference numerals.

The lattice filter 120 receives a balanced input signal A at the first input terminal 104 and at the second input terminal 106 of the input port 102. A balanced output terminal OUT is output at the output signal 108 at the terminals 110 and 112th Between the first input terminal 104 and the first output terminal 110 is a series resonator R_sι provided. Similarly, between the second input terminal 106 and the second output terminal 112, a series resonator R_s2 provided. Intermediate see the first input terminal 104 and the second output terminal 112 is a first parallel resonator R_pι connected. Between the second input terminal 106 and the first output terminal 110 is a second parallel resonator R_p2 connected. The filter shown in Fig. 2 120 is fully differential, ie both input ports 102 and 110 are symmetrical (balanced).

Filter with a good selectivity and low insertion loss can be using BAW resonators manufactured which are used to build individual blocks or steps of impedance element filters. This filter ter have two basic topologies, which are explained in more detail with reference to FIGS. 1 and 2.

With regard to the filters described with reference to FIGS. 1 and 2 it should be noted that it preferably is BAW resonators in the series resonators and parallel resonators, wherein the series resonators and the parallel resonators are made in each case with a predetermined Resonanzf FREQUENCY. Preferably the Resonanzf equenzen the paper are rallelresonatoren towards the resonance frequencies of the series resonators out of tune, so as to achieve the desired filtering effect. It should be noted that the series resonators and parallel resonators used in the ladder filter 100 resonators of the series used in the Lattice filter 120 and distinguish parallel resonators, particularly in filter circuits with substantially equal filter tercharakteristika but different topology.

When Ladder filter 100 there is only the possibility of receiving an unbalanced input signal and to output a corresponding unbalanced output. Likewise, the Lattice filter 120 allows only receiving a balanced input signal and outputting a balanced output signal.

However, there are applications where it is necessary to perform a transformation / conversion of an asymmetrical input signal into a balanced output signal, or perform a transformation / conversion of a see symmetric input signal into an unbalanced output signal. Further, there are applications in which an alternative or in addition to the conversion of balanced / unbalanced signals into unbalanced / balanced signals at the inputs and outputs of different gate i impedances exist, which must also be handled. A conventional method to perform an appropriate conversion / transformation, is to provide an additional component which as Symmetrierbauglied (balun) is referred to. The Symmetrierbauglied may be either a magnetic transformer (transformer magnetic), an LC circuit or a strip line structure, said Symmetrierbauglied is arranged on a printed circuit board prior to or after one of the filter circuits shown in Fig. 1 and 2. Although the use of discrete Symmetrierbaugliedern before or after the filters is an option, however, increases the number of required components and the required space on the printed circuit board.

In the surface acoustic wave filters (SAW filters), an acoustic Symmetrierfunktion be implemented without additional components, however, whereby the behavior of the overall filter is considerably deteriorated. Furthermore, these Symmetrierfunktion causes these filters to electrostatic discharges are very sensitive and further the skills in the use of services will be drastically limited, ie transmissible power over such a filter structure are very low. An example of such a SAW filter is described in JP 2000-114917A. A further disadvantage of the coupled SAW filter is that the response of these filters is generally worse than that of impedance element filter, and in particular the so-called roll-off or the selectivity in the vicinity of the pass band.

One approach to conversion of unbalanced signals into balanced signals is described for example in EP 1202454 A, according to the filter structures, similar to those in FIGS. 1 and 2, combined, ie to the output of ladder filter, the lattice filter is connected. However, this approach has significant disadvantages for the practical applications of such a filter, and is particularly ticular disadvantageous that these differential only to floating (floating) loads can be obtained, so no RF leakage current to ground is permitted.

In connection with BAW filters no approach is known which would suggest to the way in which an impedance transformation could be performed.

Starting from this prior art, the present invention seeks to provide an improved filter circuit which allows a simple way, a conversion of balanced / unbalanced in unbalanced / balanced signals, the filter stage and the Symmetrierbauglied is formed on the substrate ,

This object is achieved by a filter circuit according to claim. 1

The present invention provides a filter circuit with a balanced port, an asymmetrical gate a substrate and a series circuit. The series circuit consisting of a filter stage and a Symmetrierbauglied and is arranged between the balanced port and the asymmetrical gate.

Preferably, the filter stage of the series circuit includes a plurality of BAW resonators, and here at least a secondary rien BAW resonator and at least one parallel BAW resonator.

According to a first preferred embodiment, the filter stage is a single-ended filter stage that is connected to the unbalanced gate and the Symmetrierbauglied is connected to the balanced port.

According to a further embodiment, the filter circuit is a symmetrical filter stage, with the balanced port is connected, and the Symmetrierbauglied connected to the asymmetrical gate.

According to still another embodiment, the filter stage, a symmetrical filter stage, which is connected to the balanced port, and further, the serial circuit includes an unbalanced filter stage that is connected to the unbalanced target. In this embodiment, the balun between the balanced filter stage and the single-ended filter stage is connected. All filter stages and the balun are formed also on the same substrate.

In addition, it can be provided to provide adjustment elements in the series circuit which are connected between the filter circuit and the gate unbalanced or balanced port, and are formed together with the elements of the filter stage and the elements of Symmetrierbauglieds on the substrate.

Preferably, in the balun a transducer element, which has at least two coils, which are formed on the substrate.

According to another preferred embodiment of the present invention the coils of the balun are selected such that they have different numbers of turns, so that due to the turns ratio which is established an impedance transformation between the two gates of the filter circuit is effected.

The substrate is preferably a substrate having a high resistance value on which the coils are formed, for example, by metal webs. Alternatively, the coil may be arranged on the substrate in a range in which an acoustic reflector is provided. The present invention thus provides RF filter and in particular RF filters, which are realized using the BAW technology which include additional monolithic passive elements such as transducers (Symmetrierbauglieder), but additionally also coils, capacitors or resistor elements.

The present invention is based on the finding that a combination of the desirable features of impedance danzelementfiltern with the possibility unbalanced / balanced signals into balanced / unbalanced signals convert, can be achieved by a basic manufacturing process of the BAW resonators is modified such that additionally monolithic symbols metrierglieder (balun) to the filter chips (substrates) can be prepared. This also opens up the possibility of an impedance level transformation between the input ports of the filter.

According to the invention it is possible to use impedance element filter, and at the same time transformation of balanced / unbalanced signals into unbalanced / balanced signals and, optionally, a transformation impedance level within the filter chips in monolithic form, so no external components to perform. The symbols are preferably metrierglieder two spiral coils, which are arranged in succession and are magnetically coupled together.

An advantage of the present invention is that a process which is used for manufacturing the baluns, also opens up the possibility of monolithic coil (spiral inductors) to produce with high quality factors (high Q factor), which then as a member of the Symmetriebauglieds or additional can be used as matching elements. Currently, in conventional filter circuits are these matching elements nor as an external element elements outside the filter chip realized, bringing the above-mentioned problems.

A further advantage of the present invention consists in the fact that in addition to the inductors and capacitors in a simple manner may be prepared, also as monolithic elements on the filter chip, as in the preparation of BAW resonators different layers of dielectric material be used. The so the generated capacitors can be used as Anpasskondensatoren or as coupling capacitors.

Compared to conventional BAW manufacturing process only minor modifications are required, which are necessary to the thick metals for the production of

Elements (balun inductor, capacitor) are required, requiring some additional mask layers, but this leads only to a slight increase of additional expenses in the process.

Preferred embodiments of the present invention will be detailed subsequently referring to the appended drawings. Show it:

Figure 1 shows a known Ladder filter with two levels consisting of two series resonators and two parallel resonators.

Figure 2 shows a known lattice filter with one stage and two series resonators and two parallel resonators.

FIG. 3 is a first embodiment of the inventive filter circuit with an unbalanced filter stage to an unbalanced input port and an Symmetrierbauglied to a balanced output; Fig. 4 shows a second embodiment of the inventive filter circuit with a symmetric filter stage to a balanced port and a sym- metrierbauglied on an asymmetrical gate;

Figure 5 shows a third embodiment of the filter circuit according to the invention with a symmetrical filter stage on the balanced port, a single-ended filter stage on the asymmetrical gate and arranged between the two filter stages Symmetrierbauglied.

Figure 6 shows a fourth embodiment of the inventive filter circuit similar to that shown in Figure 4, which additionally comprises matching elements..; and

Fig. 7 is a schematic exemplary representation of a planar Symmetrierbaugliedstruktur.

In the following description of the preferred embodiments of the present invention identical or functionally similar elements have the same reference numerals are provided.

Fig. 3 shows a first embodiment of the inventive filter circuit 200. The filter circuit 200 includes an unbalanced terminal 202 and a balanced terminal 204 with the two symmetrical doors 204a and 204b. Between the unbalanced terminal 202 and the balanced terminal 204, a series circuit consisting of a filter stage 206 and a Symmetrierbauglied (balun) connected 208th In the embodiment shown in FIG. 3, the filter stage 206 is a single-ended filter stage in the form of a ladder filter as has been described by way of example with reference to FIG. 1. converted the filter stage 206 summarizes two series resonators R_si and R_s2 and two parallel resonators R_pι and R_p2,

The unbalanced terminal 202 includes a first node 210 and a second node 212. The second node 212 is connected to a reference potential 214, eg. As ground. The filter stage 206 comprises a series circuit consisting of the two series resonators R_sl and R_s2That are connected between the first node 210 and a third node 216th The first parallel resonator R_pι is between the reference potential 214 and a node 218 between the first series resonator R_sι and the second series resonator R_s2 connected. The second parallel resonator R_p2 is connected between the third node 216 and the reference potential 214th

The Symmetrierbauglied 208 is formed by two coupled coils 220a and 222a, a first terminal 220b of the first coil 220a is connected to the third node 216th A second terminal 220c of the first coil 220a is connected to the reference potential 214th

The first gate 204a of the balance terminal 204 includes a first node 224 and a second node 226, which is connected to the reference potential 214th Also includes the second gate 204b has a first terminal 228 and also the nodes used in conjunction with the first port 204a 226th

the balanced signals are tapped or received between the nodes 224 and 226 or the node 228 and 226th

A first terminal of the second coil 222b, 222a of the symbols metrierbauglieds 208 is connected to the first node 224 of the first balanced gate 204a. A second terminal 222c of the second coil 222a is connected to the first node of the second balanced gate 204b. Fig. 3 thus shows a topology of a ladder filter that with a Symmetrierbauglied (balun) is combined. The filter itself has a ladder structure, and may have more than the two levels shown there, in order to improve the selectivity. The steps may additionally have differently large series and parallel resonators to improve the selectivity even further. In the preferred embodiments of the present invention, at the Symmetrierbaugliedern essentially of two spiral-shaped coils which are magnetically coupled together.

In order to keep the resistive losses and the parasitic capacitance low, it is desirable to produce the metals used for the manufacture of the coil elements with a sufficient thickness using a modified BAW manufacturing process. The thickness of the metal sheets or metal surfaces used should be such that it is in the range of 800nm ​​to lOμm, or compared with the thicknesses of the electrodes used in the BAW resonators denmetalle by a factor of 2 to 20 is larger.

The elements of the filter circuit shown in Fig. 3206 and the elements of Symmetrierbauglieds 208 are formed together on a chip or substrate S, as indicated in Fig. 3 schematically. This requires, as discussed above, only a slight modification of the manufacturing processes for the BAW resonators, which is associated only with slightly higher cost, but has the advantage that external components on a circuit board on which the chip S is placed, is avoided will. This further leads to a relief of the entire manufacturing process.

The substrate S is preferably a substrate with a high resistance value, and the coils are preferably or more separated from the substrate by dielectric layers, a. According to a preferred embodiment of the the present invention this can be realized in a simple manner, since the substrate S, the required acoustic reflector for the BAW resonators is formed, and the extension thereof is selected such that additional borrowed above it the Symmetrierbauglied 208 can be formed.

According to one embodiment, the Symmetrierbauglied has a winding ratio of 1: 1, but the number of turns in the primary and secondary windings are changed to bring about a desired level of impedance transformation between the terminals 202 and 204th

The present invention has the advantage that the integration can be achieved tion of Symmetrierbauglieds 208, and integrating additional coils and capacitors within one based BAW resonators filter structure on the same substrate S, with only a few additional mask steps are required. The combination of balun member and filter stage may have different topologies, which can in principle be chosen if the filtering is to be performed before or after the transformation. In the former case the filter stage would be a ladder filter structure and contained in the latter case, a lattice filter structure. The lattice filter structure is preferred due to the, as compared to ladder-filter structures, improved attenuation outside the pass band.

Hereinafter reference to Figs 4 -... erläutet 6 further embodiments of the present invention in more detail, in which Fig 4 shows a second embodiment in which, instead of the ladder filter structure used in Figure 3 is a lattice filter structure is used, with the balanced input 204 of the filter circuit is connected. The Symmetrierbauglied 208 is connected between the filter stage 206 and the unbalanced input 202nd In the embodiment shown in Fig. 4 in the filter stage 206 is a first series resonator R_si connected between the first port 222b of the second coil 222a of the symbols metrierbauglieds 208 and the terminal 224 of the balanced output 204th A second series resonator R_s2 is connected between the second port 222c of the second coil 222a of the Symmetrierbauglieds 208 and the second terminal 228 of the balanced output 204th A first parallel resonator R_pi is connected between the first port 222b of the second coil 222a and the second node 228 of the balance terminal 204, and a second parallel resonator R_p2 is connected between the second port 222c of the second coil 222a and the first node 224 of the balance terminal 204th

The first node 210 of the unbalanced terminal 202 is connected to the first port 220b of the first coil 220a of the Symmetrierbauglieds 208, and the second node 220c of the first coil 220a is connected to the reference potential 214, as well as the first node 212 of the unbalanced terminal 202nd

Similar to the embodiment shown in FIG. 3 again, the BAW resonators R_sι, R_s2, R_Pι. R_p2 208 formed together with the elements of Symmetrierbauglieds on a common substrate or chip.

Fig. 5 shows another embodiment of the present invention, which differs from the embodiment in shown in Fig. 4 in that between the unbalanced terminal 202 and the Symmetrierbauglied 208 an additional filter stage 230 has been switched, in the illustrated embodiment, a single-ended filter stage in the form of a single-stage ladder filter. The filter stage 230 comprises a series resonator R_sι connected between the first node 210 of the unbalanced terminal 202 and the first Port 220b of the first coil is connected 220a of Symmetrierbauglieds 208th Furthermore, a parallel resonator R_pl is provided which is connected between the first port 220b of the first coil 220a and the reference potential 214th

Also in the embodiment shown in FIG. 5 all BAW resonators and all elements of Symmetrierbauglieds on a common substrate are formed.

Fig. 6 shows another embodiment in which in addition to the embodiment, between the filter stage 206 and the balanced output 204 shown in Fig. 4, a matching block is connected 232nd

The block 232 includes an inductor L and two capacitive elements Ci and C₂, Both the capacitive elements and the inductor are formed in common with the elements of Symmetrierbauglieds 208 and the BAW resonators of the filter stage 206 on the filter chip. Compared with Fig. 4 is the capacitive component C between the first series resonator R_sι connected to the filter stage 206 and the first node 224 of the balanced output 204th The second capacitive component C₂ is between the second series resonator R_s2 the filter stage 206 and the second node 228 of the balance terminal 204 connected. The inductor L is connected in parallel to the balanced output terminal 204, between a node between the first series resonator R_sι and the first capacitive component C and a node between the second resonator R_s2 and the second capacitive component C₂,

An example of an implementation of a planar Symmetrierbaugliedstruktur is explained with reference to Fig. 7. In Fig. 7 a planar structure is shown before wave is formed of a plurality of metallic wires. The coils are integration, which by a plurality of spirally arranged metallic interconnects 300, 302 and 304 det, whereby the strip conductor 302 and 304 are connected together to the reference potential 214 and the electrical connection 306th By the track 302 and 304, which are connected in the manner described above, the second coil 222a of the Symmetrierbauglieds 208 is formed, and in Fig. 7, the terminals are shown 222b or 222c. Through the interconnect 300, the first coil 220a is formed, and their connections 220b and 222c are also shown.

With respect to the above description, it should be noted that, where reference has been made to inputs and outputs, they are generally exchangeable. This means that the direction of the signal flow can be reversed, so that all the structures are suitable for, for. Example, to use a single-ended signal source and a symmetrical load or an unbalanced load and a balanced signal source.

The advantage of the present invention is that this, unlike the prior art, a miniaturized magnetic transformer as an additive element comprises, prepared together with the elements of the filter stage monolithic.

The above description has been made based examples of preferred embodiments, but it is obvious that the present invention is not limited to the embodiments described. In addition to the embodiments described, the filter circuits according to the invention, one or more stages on the input side and / or output include the output side. LIST OF REFERENCE NUMBERS

100 Ladder Filter

102 entrance 104 first input terminal of the input port

106 second input terminal of the input port

108 output port

110 first output terminal of the output port

112 second output terminal of the output port 114 reference potential

120 Lattice Filter

200 filter circuit

202 unbalanced terminal

204 symmetric terminal 204a balanced port

204b balanced port

206 filter stage

208 Symmetrierbauglied

210 212 knots 214 reference potential

216, 218 nodes

220a first coil

220b first terminal of the first coil

220c second terminal of the first coil 222a second coil

222b first terminal of the second coil

222c second terminal of the second coil

224, 226 nodes of the balance terminal 204

228 nodes of the balance terminal 204,230 additional filter stage

232 matching stage

300, 302 metal sheet

304 metal sheet

306 connecting element R_si, R_s2 series resonator

Rpi R_p2 Parallel resonators