JP2005175638A - Demultiplexer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance suppression characteristics and isolation characteristics in the duplex region of a high frequency side filter in a demultiplexer. <P>SOLUTION: The demultiplexer comprises a common terminal C, a first SAW filter 1 having one input side terminal connected with the common terminal as a signal terminal and two output side terminals connected with a first signal terminal T, and a second SAW filter 2 having two input side terminals connected with the common terminal C and two output side terminals connected with a second signal terminal R. A reference potential electrode T0 connected with one of two output side terminals of the first SAW filter is separated from a reference potential electrode C0 connected with the common terminal and a reference potential electrode R0 connected with the second SAW filter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a duplexer, and more particularly to a duplexer using a surface acoustic wave bandpass filter (hereinafter referred to as a SAW filter).

  Since mobile communication devices such as mobile phones are suitable for miniaturization and high functionality, a duplexer using a SAW filter is frequently used in the transmission / reception unit in recent years.

  FIG. 12 is a circuit diagram showing an example of such a duplexer. As shown in the figure, this duplexer includes two SAW filters 1 and 2 having mutually different band center frequencies, and two terminals on the input side of each of the filters 1 and 2 on the low frequency side and the high frequency side are antennas. The two terminals on the output side are connected to the first signal terminal (transmission side terminal) T and the second signal terminal (reception side terminal) R, respectively.

  Each of the filters 1 and 2 is formed by connecting a series arm resonators 1a and 2a composed of surface acoustic wave resonators and parallel arm resonators 1b and 2b composed of surface acoustic wave resonators in a plurality of stages, and a common terminal. An impedance matching circuit 3 is provided between C and the high frequency filter 2. The matching circuit 3 can be composed of a phase line 3a as shown in FIG. 12, or an inductor 3b and a capacitor 3c as shown in FIG. Both filters 1 and 2 are connected to a common reference potential electrode (common ground pattern) via a common terminal C.

  The following patent document discloses such a duplexer.

Japanese Patent No. 3246906

  By the way, such a duplexer used for communication equipment is desired to further improve the filter characteristics in order to improve the call quality and reduce the power consumption, and has a low loss in the pass band and a high attenuation characteristic in the stop band. It has been demanded.

  Therefore, the present inventor has made various studies and found that the filter characteristics can be further improved by paying attention to the common ground in the duplexer package.

  That is, the conventional duplexer shown in FIG. 12 and FIG. 13 has a parasitic resistance, a parasitic capacitance, and a parasitic inductance between interlayer connection portions such as via holes, wiring patterns themselves, or wiring patterns. In consideration, the circuit configurations are actually as shown in FIGS. 14 and 15, respectively.

  For this reason, the common ground in the duplexer package to which the SAW filters 1 and 2 and the common terminal C are connected is increased in potential by the parasitic resistance 6 and the parasitic inductance 5 and is actually an ideal ground. However, in the conventional duplexer, it is considered that the common ground operates as a signal line in combination with the higher frequency of the communication signal.

  On the other hand, mobile phones tend to be more and more miniaturized, and it is difficult to ensure a sufficient gap between wiring patterns due to the miniaturization of components, and parasitic capacitance components are likely to be generated. For example, as shown in FIGS. 14 and 15, a parasitic capacitance 7 is generated between a conductor line connected from the transmission filter 1 to the common ground and a signal line on the reception side.

  Therefore, the transmission signal that should pass through the low frequency filter 1 through the capacitive coupling due to such parasitic components and the above-described incomplete common ground flows into the filter 2 on the high frequency side (reception side), and these are received on the reception side. This is a cause of deterioration of the suppression characteristic of the filter 2 in the duplex region.

  In particular, the inflow of the transmission signal to the reception side causes noise and deteriorates the call quality. From this point, the transmission signal is prevented from flowing into the reception side, and the isolation characteristics of the reception filter are reduced. It is important to increase.

  Therefore, the problem to be solved by the present invention is that the filter characteristics of the conventional duplexer are not sufficient, particularly the suppression characteristics and isolation characteristics in the duplex region of the high frequency filter are not sufficient. The purpose is to solve this point.

  In order to solve the above-mentioned problem, a duplexer according to the present invention (Claim 1) connects a common terminal and one input terminal to the common terminal as a signal terminal, and two output terminals to the first terminal. A first surface acoustic wave bandpass filter connected to a signal terminal, a second surface acoustic wave band in which two terminals on the input side are connected to the common terminal, and two terminals on the output side are connected to the second signal terminal And a reference potential electrode connected to one of the two terminals on the output side of the first surface acoustic wave bandpass filter, a reference potential electrode connected to the common terminal Separated from a potential electrode and a reference potential electrode connected to the second surface acoustic wave bandpass filter.

  In the conventional duplexer, the first and second SAW filters (surface acoustic wave band-pass filters) and the common reference potential electrode are connected to a common reference potential electrode (common ground pattern). In contrast, in the duplexer of the present invention, the reference potential electrode of the first SAW filter (low frequency side filter) is connected to the common terminal and the reference potential electrode connected to the second SAW filter (high frequency side filter). To separate.

  Accordingly, in the present invention, it becomes possible to prevent the inflow of the high frequency signal from the low frequency side filter to the high frequency side filter through the reference potential electrode, improving the duplex region suppression characteristics and the isolation characteristics of the high frequency side filter. Can be achieved. Even if the reference potential electrode of the low frequency side filter is disconnected in this way, there is almost no adverse effect on the electrical characteristics of the low frequency side filter or the electrical characteristics in the passbands of both the low frequency side and high frequency side filters. It does not occur, and the characteristics of the high frequency filter can be improved.

  In addition, the effect of this invention is demonstrated in detail based on measurement data in description of embodiment of this invention mentioned later.

  In the duplexer of the present invention, both the first and second surface acoustic wave bandpass filters include a series resonator including a surface acoustic wave resonator and a parallel resonator including a surface acoustic wave resonator. An impedance matching circuit may be provided between the common terminal and the second surface acoustic wave band-pass filter.

  Furthermore, another duplexer of the present invention (Claim 3) connects the common terminal and one input terminal to the common terminal as a signal terminal, and connects two output terminals to the first signal terminal. A first surface acoustic wave bandpass filter, a second surface acoustic wave bandpass filter in which two terminals on the input side are connected to the common terminal, and two terminals on the output side are connected to a second signal terminal; The first surface acoustic wave bandpass filter and the second surface acoustic wave bandpass filter are mounted on a multilayer substrate, and a common reference potential electrode is provided on at least one layer of the multilayer substrate. Forming and connecting one terminal on the reference potential side of the common terminal and one terminal on the reference potential side of the second surface acoustic wave bandpass filter to the common reference potential electrode, while the first surface acoustic wave band Each reference voltage on the input side and output side of the pass filter The terminal, which was separated from the common reference potential electrode without connecting to the common reference potential electrode.

  In order to separate the reference potential terminals on the input side and the output side of the first surface acoustic wave bandpass filter from the common reference potential electrode in this way, for example, It can be performed by patterning the conductor film so as to remove a part of the conductor film formed in the layer (for example, by a photoetching method).

  According to the duplexer of the present invention, it is possible to improve the suppression characteristic in the duplex region of the high frequency side filter and improve the isolation characteristic.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as this embodiment) will be described with reference to FIGS. 1 to 11 of the accompanying drawings.

  As shown in FIG. 1, the duplexer according to the present embodiment includes a common terminal C connected to the antenna and two SAW filters 1 and 2 having different band center frequencies. Among them, the low frequency side filter 1 is used as a transmission side filter, and the output side (in this specification, the antenna side of each filter is referred to as “input side” and the transmission / reception terminal side is referred to as “output side”) is the transmission terminal T. The high frequency side filter 2 is used as a reception side filter, and two terminals on the output side thereof are connected to the reception terminal R.

  The common terminal C, the transmission terminal T, and the reception terminal R have one terminal C1, T1, R1 of the two terminals as signal terminals for inputting and outputting signals, and the other terminals C0, T0, R0. Is used as a reference potential terminal connected to ground. The common terminal C and the reference potential terminals C0 and R0 of the reception terminal R (reception side filter) are connected to a common (same) ground pattern. On the other hand, the reference potential terminal T0 of the transmission terminal T (transmission side filter) is not connected to the common ground pattern, and the conductor pattern connected to the reference potential terminal T0 and the common ground pattern are physically separated. Structure. This specific structure will be described later with reference to FIGS.

  The configurations of the SAW filters 1 and 2 on the transmission side and the reception side are not particularly limited, but in this embodiment, the serial arm resonators 1a and 2a each made of a surface acoustic wave resonator and a parallel structure made of a surface acoustic wave resonator are used. It is assumed that the arm resonators 1b and 2b are connected in two stages in a so-called ladder type. Note that the number of connection stages of the series arm and parallel arm resonator in these SAW filters is not limited to two, and three or more stages may be connected.

  Two terminals on the input side of the reception filter 2 are connected to the common terminal C. At this time, the impedance matching circuit 3 is provided between the signal terminal of the reception-side filter 2 and the signal terminal C1 of the common terminal C. This is because the receiving filter 2 has a high impedance in the attenuation band on the low frequency side to prevent crosstalk. As shown in FIG. 1, as the impedance circuit 3, a phase rotation line 3a may be inserted in series between the signal terminal of the reception filter 2 and the signal terminal C1 of the common terminal, as shown in FIG. As described above, the impedance matching circuit 3 can be formed by the inductor 3b and the capacitor 3c.

  In the present embodiment, in addition to the impedance matching circuit 3, the input side terminal of the transmission side (low frequency side) filter 1 is not connected to the reference potential terminal C0 (common ground pattern) of the common terminal C, and the transmission side filter is further connected. A reference potential terminal on one output side (transmission terminal) is separated from a common ground pattern to which the reception-side filter 2 and the common terminal C are connected. The signal is prevented from flowing from the transmission side to the reception side through the common ground pattern, the suppression characteristic in the attenuation region on the low frequency side of the reception side filter 2 is further improved, and the isolation characteristic between the reception side and the transmission side is enhanced. Because. This point will be described in more detail.

  FIG. 2 shows an equivalent circuit of the duplexer according to the present embodiment shown in FIG. 1 in consideration of the parasitic capacitance 7, the parasitic resistance 6, and the parasitic inductance 5, like the conventional duplexer (FIG. 14). It is. Referring to FIG. 14, in the duplexer of the present embodiment, unlike the conventional duplexer, a route (indicated by reference numeral 10 in FIG. 14) is a route through which a signal flows to the reception side (reception side filter 2) via the parasitic capacitance 7. ) Is cut off, which makes it possible to prevent a signal from flowing from the transmission side to the reception side.

  FIG. 4 is a diagram showing the bandpass characteristics of the reception-side filter in the duplexer of the present embodiment in comparison with a conventional duplexer. A thin line (1) indicates a conventional duplexer, and a thick line (2) indicates a duplexer according to this embodiment. As is apparent from this figure, according to the present invention, a larger attenuation amount can be obtained in the attenuation region 21 on the low frequency side of the reception side filter, and the suppression characteristic can be improved.

  FIG. 5 is a diagram showing the band pass characteristics of the transmission filter in comparison with a conventional duplexer. As in FIG. 4, the thin line (1) indicates the conventional duplexer, and the thick line (2) indicates the duplexer according to the present embodiment. As for the transmission side filter, both the pass band 21 and the attenuation band 22 have substantially the same pass / attenuation characteristics as the conventional duplexer, and even if the reference potential terminal of the transmission side filter is separated from the common ground pattern. It can be seen that there is no inconvenience that degrades the filter characteristics.

  Further, FIG. 6 is a diagram showing the isolation characteristics between the transmission side and the reception side in comparison with a conventional duplexer. As shown in FIG. 6, this embodiment (thick line (2)) is shown. ), It is possible to improve the isolation characteristics between the transmission side and the reception side in the transmission frequency band 21 as compared with the conventional case (thin line (1)).

  In order to separate the reference potential terminal of the transmission side filter (the reference potential electrode connected to the transmission side filter) from the common ground pattern, for example, as shown in FIGS.

  7 to 11 are diagrams illustrating the duplexer according to the present embodiment (each diagram (b)) in comparison with a conventional duplexer having the same structure (each diagram (a)). 9 and FIG. 9 show the case where the SAW filter is mounted by wire bonding, and FIGS. 8 and 10 show the case where the SAW filter is mounted on a flip chip.

  As shown in these drawings, the duplexer according to the present embodiment mounts SAW filters (transmission-side filter 1 and reception-side filter 2) on the multilayer substrate 11, and each wiring pattern on the front surface, back surface, or inside of the substrate 11. And terminal electrodes (the common terminal C, the transmission terminal T, the reception terminal R, etc.) are formed, and both the filters 1 and 2 are hermetically sealed by the case 12. In each figure, reference numeral 15 denotes a common ground pattern, 3a denotes a phase rotation line constituting an impedance matching circuit, 16 denotes an interlayer connection via hole, and 17 denotes a terminal electrode. In each figure, detailed wiring patterns and the like in the substrate are omitted.

  In the conventional duplexer (each figure (a)), the common terminal, each reference potential terminal of the transmission side filter 1 and the reception side filter 2 are all formed in the substrate via a conductor pattern or via hole, Alternatively, although connected to the common ground 15 on the back surface of the substrate, in the duplexer of the present embodiment (each figure (b)), the conductor pattern connected to the reference potential terminal of the transmission-side filter 1 is connected to the common ground 15. Patterning is performed so as to be separated (the separated portion is indicated by S).

  FIG. 11 is a diagram showing a back surface structure of the duplexer shown in FIGS. 9 and 10 having a common ground 15 (conductor film) on substantially the entire back surface of the substrate. In FIG. The signal terminal of the terminal, T1 indicates the signal terminal of the transmission terminal, and R1 indicates the signal terminal of the reception terminal. In the conventional duplexer (FIG. 1A), the common terminal 15 and the reference potential terminals C0, T0, R0 of the filters on the transmission side and the reception side are connected to the common ground 15 through conductor patterns and via holes. It was. On the other hand, in this embodiment, as shown in FIG. 5B, the portion S from which the conductor film is removed is formed to separate the reference potential terminal T0 of the transmission terminal from the common ground 15 on the back surface of the substrate.

  As described above, according to the present embodiment, the duplexer can be simply operated by patterning so that a part of the conductor pattern is separated without significantly changing the package structure / substrate structure of the conventional duplexer. The characteristics can be improved. Further, there is no increase in the number of parts (elements) or an increase in manufacturing cost.

  The embodiments of the present invention have been described with reference to the drawings. However, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the claims. Is obvious.

  For example, the duplexer of the present invention is suitable for use in a transmission / reception unit of a mobile phone, but is not limited to this, and is not limited to this, but a PDA having a PHS or a communication function, a wireless LAN card, and the like. It is possible to apply to an electronic device having a proper communication function. In the above embodiment, when the frequency on the transmission side is lower than the frequency on the reception side, the low frequency side filter is the transmission side filter and the high frequency side filter is the reception side filter. The duplexer of the present invention can also be configured in the same manner when the frequency on the receiving side is lower than the frequency on the transmitting side, the low frequency side filter is on the receiving side, and the high frequency side filter is on the transmitting side. In the embodiment, the reference potential terminal of the common terminal and the reference potential terminal of the second SAW filter (reception-side filter) are connected to a common ground. In addition to being separated from the reference potential terminal, it may also be possible.

It is a circuit diagram showing a duplexer concerning an embodiment of the present invention. It is a figure which shows the equivalent circuit of the splitter which concerns on the said embodiment. It is a circuit diagram which shows the modification of the splitter which concerns on the said embodiment. The bandpass characteristic (attenuation ratio from the common terminal side to the reception terminal side) of the high frequency side (reception side) SAW filter included in the duplexer of the above embodiment is shown as the bandpass characteristic of the high frequency side SAW filter in the conventional duplexer. FIG. The band pass characteristic (attenuation ratio from the transmission terminal side to the common terminal side) of the low frequency side (transmission side) SAW filter included in the duplexer of the above embodiment is shown as the band of the low frequency side SAW filter in the conventional duplexer. It is a diagram shown in comparison with pass characteristics. The isolation characteristic (attenuation ratio from the transmission terminal side to the reception terminal side) between the transmission-side SAW filter and the reception-side SAW filter included in the duplexer of the embodiment is shown in comparison with a conventional duplexer. FIG. It is a figure which compares and shows the 1st example of the cross-section of the splitter which concerns on this invention with the conventional cross-section. In the figure, (a) is a conventional structure, and (b) is a structure according to the present invention. It is a figure which compares and shows the 2nd example of the cross-section of the splitter which concerns on this invention with the conventional cross-section. In the figure, (a) is a conventional structure, and (b) is a structure according to the present invention. It is a figure which compares and shows the 3rd example of the cross-section of the splitter which concerns on this invention with the conventional cross-section. In the figure, (a) is a conventional structure, and (b) is a structure according to the present invention. It is a figure which shows the 4th example of the cross-section of the duplexer concerning this invention compared with the conventional cross-section. In the figure, (a) is a conventional structure, and (b) is a structure according to the present invention. It is a figure which shows the back surface structure of the duplexer of FIG. 9 and FIG. In the figure, (a) is a conventional back surface structure, and (b) is a back surface structure according to the present invention. It is a circuit diagram which shows an example (conventional example 1) of the conventional splitter. It is a circuit diagram which shows another example (conventional example 2) of the conventional splitter. It is a figure which shows the equivalent circuit of an example (conventional example 1) of the said conventional splitter. It is a figure which shows the equivalent circuit of another example (conventional example 2) of the said conventional splitter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Low frequency side SAW filter 2 High frequency side SAW filter 3 Impedance matching circuit 11 Multilayer substrate 15 Common ground pattern 16 Via hole for interlayer connection C Common terminal T Transmission terminal R Reception terminal

Claims (4)

A common terminal,
A first surface acoustic wave bandpass filter in which one terminal on the input side is connected as a signal terminal to the common terminal, and two terminals on the output side are connected to the first signal terminal;
A second surface acoustic wave bandpass filter in which two terminals on the input side are connected to the common terminal, and two terminals on the output side are connected to a second signal terminal;
A duplexer having
The reference potential electrode connected to one of the two terminals on the output side of the first surface acoustic wave bandpass filter is changed to a reference potential electrode connected to the common terminal and the second surface acoustic wave bandpass. A duplexer characterized by being separated from a reference potential electrode connected to a filter. Both the first and second surface acoustic wave bandpass filters are formed by connecting a series resonator composed of a surface acoustic wave resonator and a parallel resonator composed of a surface acoustic wave resonator in a plurality of stages,
The duplexer according to claim 1, further comprising an impedance matching circuit between the common terminal and the second surface acoustic wave bandpass filter. A common terminal,
A first surface acoustic wave bandpass filter in which one terminal on the input side is connected as a signal terminal to the common terminal, and two terminals on the output side are connected to the first signal terminal;
A second surface acoustic wave bandpass filter in which two terminals on the input side are connected to the common terminal, and two terminals on the output side are connected to a second signal terminal;
A duplexer having
Mounting the first surface acoustic wave bandpass filter and the second surface acoustic wave bandpass filter on a laminated substrate;
Forming a common reference potential electrode on at least one layer of the laminated substrate;
While connecting the common reference potential electrode to one terminal on the reference potential side of the common terminal and one terminal on the reference potential side of the second surface acoustic wave bandpass filter,
Each of the reference potential terminals on the input side and the output side of the first surface acoustic wave bandpass filter is separated from the common reference potential electrode without being connected to the common reference potential electrode. The reference potentials on the input side and the output side of the first surface acoustic wave bandpass filter are patterned by patterning the conductor film so as to remove a part of the conductor film formed on any layer of the multilayer substrate. The duplexer according to claim 3, wherein a terminal is separated from the common reference potential electrode.