JP2013150214A - Duplexer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate signals of a specific frequency band from signals of frequency bands other than the specific frequency band, and accommodate wideband signals in the frequency bands other than the specific frequency band.SOLUTION: A duplexer circuit comprises: a surface acoustic wave filter for passing received signals of a specific frequency band; a first inductor connected in parallel with the surface acoustic wave filter; and a circuit including a second inductor, a surface acoustic wave resonator and a third inductor connected in series to block the passage of received signals of at least part of the specific frequency band. An output of the surface acoustic wave filter is a first output of the duplexer circuit, and an output of the circuit is a second output of the duplexer circuit.

Description

  The present invention relates to a branching circuit.

  For example, in a mobile phone, a demultiplexing circuit is used to separate a GPS (Global Positioning System) signal received by an antenna from a signal for the mobile phone.

  International Publication No. WO2005 / 053172 includes a band-pass filter that outputs, for example, a GPS signal to an antenna terminal, a parallel resonant circuit, a thin film resonator or an electroacoustic transducer that operates with acoustic volume waves, and A circuit that connects a band stop filter that performs band elimination by anti-resonance is disclosed. However, the band stop filter is not disclosed for a configuration beyond this, and the characteristics required for the band stop filter are also unclear about characteristics other than band elimination. The frequency band used in the field of mobile phones, which are becoming increasingly multiband, is a wide band. However, as described below, it is difficult to deal with the configuration disclosed in this publication.

WO2005 / 053172

  Accordingly, an object of the present invention is, in one aspect, a branching circuit that separates a signal in a specific frequency band and a signal in a frequency band other than the specific frequency band, and the frequency band other than the specific frequency band The present invention is to provide a branching circuit capable of handling a wideband signal.

  The branching circuit according to the present invention includes (A) a surface acoustic wave filter that passes a signal in a specific frequency band for a received signal, and (B) a first surface provided between an input terminal of the surface acoustic wave filter and the ground. And (C) the second signal, the surface acoustic wave resonator, and the third inductor are connected in series. Circuit. Then, the output of the surface acoustic wave filter becomes the first output of the branching circuit, and the output of the circuit becomes the second output of the branching circuit.

  Since the second inductor and the third inductor are provided at both ends of the surface acoustic wave resonator, the stray capacitance generated between the electrode of the device including the surface acoustic wave resonator and the ground is used to specify It is possible to deal with a wideband signal in a frequency band other than the above frequency band.

  In the branching circuit of the present invention, between the connection point between the second inductor and the surface acoustic wave resonator and the ground, and between the connection point between the surface acoustic wave resonator and the third inductor and the ground. You may make it provide a capacitor in at least one of them. Such a capacitor may improve characteristics in a frequency band other than a specific frequency band.

  According to one aspect, when a signal in a specific frequency band and a signal in a frequency band other than the specific frequency band are separated, a wideband signal can be dealt with in a frequency band other than the specific frequency band.

FIG. 1 is a diagram showing a circuit which is a premise of the present embodiment. FIG. 2 is a diagram showing a circuit which is a premise of the present embodiment. FIG. 3 is a diagram illustrating the stray capacitance of the SAW resonator. FIG. 4 is a diagram illustrating a branching circuit in the present embodiment. FIG. 5 is a diagram showing an equivalent circuit of the branching circuit in the present embodiment. FIG. 6 is a diagram showing the frequency characteristics of the branching circuit in the present embodiment. FIG. 7 is a diagram showing the frequency characteristics of the branching circuit in the present embodiment. FIG. 8 is a diagram showing a modification of the branching circuit in the present embodiment. FIG. 9 is a cross-sectional view showing a mounting example of the branching circuit in the present embodiment. FIG. 10 is a diagram for explaining the prior art. FIG. 11 is a diagram showing a frequency band of the prior art. FIG. 12 is a diagram illustrating a frequency band of the conventional technology.

  In the present embodiment, the 1.5 GHz band signal of the GPS signal, and the first frequency band of 800 MHz to 1 GHz and the second frequency band of 1.7 GHz to 2.2 GHz used in the cellular phone are used. A demultiplexing circuit for separation will be described.

  In order to separate a gain signal uniform with respect to a frequency band into signals of three different frequency bands by two attenuation poles, three band pass filters A to C as shown in FIG. 1 may be provided. . As described above, when the signal of the 1.5 GHz band of the GPS signal is separated from the signals of the first frequency band and the second frequency band, the capacitor of the bandpass filter A is connected to, for example, the GPS signal. 2 is obtained, and the capacitor of the bandpass filter B is replaced with a SAW resonator that resonates in the 1.5 GHz band of the GPS signal, whereby a branching circuit as shown in FIG. 2 is obtained. In the example of FIG. 2, a SAW resonator 1001 is introduced. However, a stray capacitance Cs is generated between the electrode of the device including the SAW resonator 1001 and the ground as shown in FIG. 3, and thus a bandpass filter cannot be appropriately configured.

  Therefore, when the circuit shown in FIG. 2 is modified so that the stray capacitance is used as a part of the elements of the filter, a branching circuit according to the present embodiment as shown in FIG. 4 is obtained. The branching circuit of FIG. 4 includes inductors L1 to L3, a GPS SAW filter 11, and a SAW resonator 10 that antiresonates so as to prevent the passage of signals in the GPS frequency band. The SAW filter 11 and the SAW resonator 10 may be configured as one device.

  One end of the inductor L1, one end of the inductor L2, and the input terminal of the GPS SAW filter 11 are connected to the input terminal IN of the branching circuit. The other end of the inductor L1 is grounded. A GPS frequency band signal is output from the output terminal of the GPS SAW filter 11. On the other hand, the other end of the inductor L2 is connected to the input terminal of the SAW resonator 10, and the output terminal of the SAW resonator 10 is connected to one end of the inductor L3. The other end of the inductor L3 is connected to the output terminal OUT of the branching circuit.

  The inductor L1 is used for ESD (electro-static discharge) countermeasures and is also used for matching with the GPS SAW filter 11. Since the output side of the SAW resonator 10 is not connected to the ground by the inductor, the input voltage due to ESD is divided into the stray capacitance connected to the ground. Therefore, ESD countermeasures are strengthened compared to the circuit as shown in FIG. The inductors L2 and L3 form an LC resonance circuit together with the stray capacitance Cs, and improve the characteristics of the first frequency band and the second frequency band.

  When Δ-Y conversion is performed on the stray capacitance portion of the SAW resonator 10 in the branching circuit shown in FIG. 4, the circuit shown in FIG. 5 becomes an equivalent circuit. That is, the inductor L2 and the stray capacitance Cs 'are in series and function as a bandpass filter, and the inductor L3 and the stray capacitance Cs' are in series and function as a bandpass filter. In this way, three band-pass filters are realized together with the GPS SAW filter 11.

  The frequency characteristics of the branching circuit shown in FIG. 4 are shown in FIGS. In each figure, the horizontal axis represents frequency and the vertical axis represents gain. 6 shows frequency characteristics of input return loss (input terminal IN in FIG. 4) and mobile phone output (output terminal OUT in FIG. 4), and FIG. 7 shows frequency characteristics of GPS output (GPS output terminal in FIG. 4). It is shown.

  As shown in FIG. 7, with respect to the GPS output, the loss is reduced only in the 1.5 GHz band for GPS, and an appropriate output is obtained for the GPS output. On the other hand, as shown in FIG. 6, the cellular phone output is matched in a wide band in the first frequency band and the second frequency band other than the 1.5 GHz band for GPS, and the insertion loss is small in the wide band. And appropriate characteristics are realized. As described above, the demultiplexing circuit shown in FIG. 4 has a desired frequency characteristic with a small number of elements.

  If the stray capacitance Cs alone is not sufficient to obtain a desired characteristic, the connection between the inductor L2 and the input terminal of the SAW resonator 10 and the ground is shown in FIG. The capacitor C1 is introduced, and the capacitor C2 is introduced between the connection point between the inductor L3 and the output terminal of the SAW resonator 10 and the ground. In some cases, the capacitor C1 or the capacitor C2 is introduced. Thus, by adding a capacitor, the frequency characteristic can be adjusted, and a frequency characteristic closer to a desired characteristic can be obtained.

  FIG. 9 shows a mounting example (cross-sectional view) of the branching circuit. In the example of FIG. 9, the GPS SAW filter 11 and the SAW oscillator 10 are mounted in the SAW device 21. The SAW device 21 is mounted on the surface of an LTCC (Low Temperature Co-fired Ceramics) substrate 22, and a stray capacitance Cs is generated between the electrode of the SAW device 21 and the ground electrode of the LTCC substrate 22. Since the inductors L1 to L3 are mounted inside the LTCC substrate 22, the overall size is also reduced. Furthermore, the LTCC board 22 is mounted on the printed board 23.

  In the prior art described in the gazette described in the background art section, the inductors L2 and L3 are removed as shown in FIG. Then, in the prior art, frequency characteristics as shown in FIGS. 11 and 12 are obtained. 11 and 12, the horizontal axis represents frequency, and the vertical axis represents gain. 11 shows frequency characteristics of input return loss (input terminal IN in FIG. 10) and mobile phone output (output terminal OUT in FIG. 10), and FIG. 12 shows frequency characteristics of GPS output (GPS output terminal in FIG. 10). It is shown. Comparing FIG. 7 showing the frequency characteristics of the present embodiment with FIG. 12 showing the frequency characteristics of the prior art, the frequency characteristics of the GPS output hardly change. On the other hand, when FIG. 6 showing the frequency characteristics of the present embodiment is compared with FIG. 11 showing the frequency characteristics of the prior art, from the return loss data, in the prior art circuit, the first frequency band other than the 1.5 GHz band and It can be seen that there is no matching in the second frequency band, and that the insertion loss from the mobile phone output has also increased. As described above, the prior art described in the publication described in the Background section cannot cope with a wideband frequency.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, an additional capacitor or inductor may be added to adjust the frequency characteristics.

C Capacitor L Inductor 11 GPS SAW filter 10 SAW resonator

Claims (2)

A demultiplexing circuit,
A surface acoustic wave filter that passes a signal in a specific frequency band with respect to a received signal; and
A first inductor provided between an input terminal of the surface acoustic wave filter and a ground;
A circuit in which the second inductor, the surface acoustic wave resonator, and the third inductor are connected in series to prevent the reception signal from passing signals in at least a part of the specific frequency band;
Have
The output of the surface acoustic wave filter becomes the first output of the branching circuit,
A demultiplexing circuit in which an output of the circuit is a second output of the demultiplexing circuit. A capacitor at least one of a connection point between the second inductor and the surface acoustic wave resonator and the ground and a connection point between the surface acoustic wave resonator and the third inductor and the ground The branching circuit according to claim 1 provided.

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