JP2000295075A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a SAW (surface acoustic wave) filter having several kinds of applications regardless of one kind of a SAW filter. SOLUTION: This SAW filter 100 has SAW filter elements 10 and 20 internally. Input-output terminals 12 and 24 of the elements 10 and 20, output-input terminals 16 and 28 are connected electrically to 1st, 2nd, 3rd and 4th filter terminals 40, 42, 44 and 46 respectively, input-output terminals 14 and 22 are both connected electrically to a 1st common filter terminal 48, and output-input terminals 18 and 26 are both connected electrically to a 2nd common filter terminal 50 respectively. The filter 100 can optionally decide an input side and an output side, and also, whichever is selected as an input side, it can output a signal of a frequency band that passes through the 1st and 2nd SAW filter elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter having two surface acoustic wave filter elements therein, and more particularly, to a surface acoustic wave filter used in a duplexer.

[0002]

2. Description of the Related Art In a cordless telephone, a master unit and a slave unit transmit and receive signals of different frequencies. FIG. 4 shows how signals are transmitted and received in the cordless telephone. For example, a signal having a frequency of f1 is transmitted from the parent device 60 of the cordless telephone to the child device 62. In addition, child unit 6
2 transmits a signal having a frequency different from f1, for example, f2, to the base unit 60. Then, the parent device 60 and the child device 62
Receive signals transmitted from each other. This transmission / reception is performed by antennas 64 and 66 each of which has one master unit 60 and one slave unit 62.

In order to transmit and receive signals of different frequencies using a single antenna, the master unit 60 and the slave unit 62 each have electronic components called antenna duplexers mounted therein. A filter is used for the antenna duplexer. As this filter, two kinds of surface acoustic waves (Surface Acoustics) having different pass bands are used.
Tic Wave (hereinafter, referred to as SAW) A SAW filter having a filter element therein may be used.

FIG. 5 is a block diagram showing a SAW filter used in an antenna duplexer of a base unit of a cordless telephone.

[0005] The SAW filter 70 of the master unit has two SAW filter elements 72 and 74 therein, and has filter terminals 76, 78, 80 and 8 as input / output terminals.
2,84. SAW filter elements 72, 74
Have bandpass filter characteristics that pass only the frequency bands of f1 and f2, respectively. SAW filter element 7
2, 74 are input / output terminals 86, 87, 88, 8 respectively.
9, 90, 91, 92 and 93.

The filter terminal 78 has input / output terminals 87 and 9
1 and SAW filter elements 72 and 74
Is supplied with a ground potential. On the other hand, the filter terminal 76 is electrically connected to the input / output terminals 86 and 90, and f1 or f2
Is input and output.

The filter terminal 82 is connected to the input / output terminal 8.
9 and 92, and is electrically connected to the SAW filter element 7.
2, 74 are supplied with a ground potential. On the other hand, filter terminal 8
0 is electrically connected to the input / output terminal 88 to input / output a signal having a frequency of f1. The filter terminal 84 is electrically connected to the input / output terminal 93 to input / output a signal having a frequency of f2.

When transmitting a signal from the master unit to the slave unit, a signal having a frequency of f1 is input from the filter terminal 80 and output from the filter terminal 76. Conversely, when receiving a signal from the slave unit, the signal of the frequency f2 is
And output from the filter terminal 84.

[0009] The SAW filter of the slave unit transmits a signal of frequency f2 and receives a signal of frequency f1, contrary to the SAW filter of the master unit. Therefore, the SAW filter of the slave unit is different from the SAW filter 70 shown in FIG.
Only the arrangement of the SAW filter elements 72 and 74 is replaced.

[0010]

As described above, the SAW filter of the slave unit has exactly the same SAW filter element as the master unit, but the arrangement of the SAW filter element inside the SAW filter is different. Therefore, the SA of the slave unit
The W filter needs to be manufactured separately from the SAW filter of the master unit. After all, SAW filter for master unit and SA for slave unit
A W filter is required. Therefore, there is a problem that the manufacturing cost is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a SAW filter which is one type of SAW filter but has several uses.

[0012]

According to a first aspect of the present invention, there is provided a surface acoustic wave filter having first and second surface acoustic wave filter elements therein, wherein the first surface acoustic wave filter element comprises: The first surface acoustic wave filter element includes first and second input / output terminals and first and second input / output terminals, and the second surface acoustic wave filter element includes third and fourth input / output terminals and third and fourth input / output terminals. In the surface acoustic wave filter including an input / output terminal, a first filter terminal electrically connected to the first input / output terminal and an electric connection to the fourth input / output terminal are provided on the input / output side. And a first common filter terminal electrically connected to the second input / output terminal and the third input / output terminal. A third filter terminal electrically connected to the first input / output terminal, and a fourth input / output terminal; A fourth filter terminal electrically connected to the terminal; and a second common filter terminal electrically connected to the second input / output terminal and the third input / output terminal. I do.

In the surface acoustic wave filter according to the first invention, when the three terminals of the first and second filter terminals and the first common filter terminal are used as signal input sides, the third and fourth filters are provided. The three terminals of the terminal and the second common filter terminal are signal output sides. Then, a signal in the frequency band passed by the first surface acoustic wave filter element is output from the third filter terminal. Further, a signal in a frequency band passed by the second surface acoustic wave filter element is output from the fourth filter terminal.

On the other hand, the first and second filter terminals and the first
Assuming that the three terminals of the common filter terminal are signal output sides,
The three terminals of the third and fourth filter terminals and the second common filter terminal are on the signal input side. At this time, the signal in the frequency band passed by the first surface acoustic wave filter element is:
Output from the first filter terminal. The signal in the frequency band passed by the second surface acoustic wave filter element is:
Output from the second filter terminal.

Therefore, the three terminal sides of the first and second filter terminals and the first common filter terminal, and the three terminal sides of the third and fourth filter terminals and the second common filter terminal,
Whichever is the input side, the other output side can output a signal in a frequency band to be passed by the first and second surface acoustic wave filter elements. Therefore, in the surface acoustic wave filter of the present invention, which filter terminal is on the input side can be appropriately selected, and one type of surface acoustic wave filter can be used for several types of applications. Therefore, the types of surface acoustic wave filters to be manufactured are reduced, and the manufacturing cost can be reduced.

In the surface acoustic wave filter according to the present invention, when three terminals of the first and second filter terminals and the first common filter terminal are used as signal input sides, A signal in a frequency band passed by the first surface acoustic wave filter element can be output. When this surface acoustic wave filter is rotated by 180 degrees and the three terminals of the third and fourth filter terminals and the second common filter terminal are set to the signal input side, the position of the third filter terminal before rotation is A second filter terminal is provided, and a signal in a frequency band that the second surface acoustic wave filter element allows to pass can be output from the position of the third filter terminal before rotation. Accordingly, a substrate that outputs different frequency bands from the same terminal position can be shared among the substrates to which the surface acoustic wave filter is electrically connected. For example, in an electronic device in which only the transmitting and receiving frequencies are switched, such as a parent device and a child device of a cordless telephone, the substrate can be shared between the parent device and the child device.

According to a second aspect of the present invention, there is provided the surface acoustic wave filter further including first and second matching circuits therein, wherein the first common filter terminal is provided with the first matching circuit. Is electrically connected to the second input / output terminal and the third input / output terminal via the second matching filter circuit, and the second common filter terminal is connected to the second input / output terminal via the second matching circuit. It is characterized by being electrically connected to the third input / output terminal.

Since the surface acoustic wave filter according to the second aspect of the present invention has a matching circuit therein, there is no need to electrically connect a separate matching circuit to the surface acoustic wave filter. Therefore, it is possible to reduce the number of components connected outside the surface acoustic wave filter.

[0019]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 shows a SAW filter according to this embodiment. The SAW filter 100 has SAW filter elements 10 and 20 therein.

The SAW filter element 10 has a comb-shaped electrode 30 and a reflector 32 inside, and has a band-pass filter characteristic for passing only a signal of the frequency f1. The input / output terminals 12, 14 of the SAW filter element 10 and the input / output terminals 16,
18 are electrically connected to the comb-shaped electrodes 30, respectively.
The input / output of signals to the comb-shaped electrode 30 and the supply of the ground potential are performed.

On the other hand, the SAW filter element 20 has a comb-shaped electrode 34 and a reflector 36 inside, and has a bandpass filter characteristic for passing only the signal of the frequency f2. SAW
The input / output terminals 22 and 24 and the input / output terminals 26 and 28 of the filter element 20 are electrically connected to the comb-shaped electrode 34, respectively, and perform input / output of a signal to the comb-shaped electrode 34 and supply of a ground potential.

The SAW filter element is not limited to a SAW filter element comprising a comb-shaped electrode and a reflector, but may use a SAW filter element having various electrode configurations.

The SAW filter 100 of this embodiment includes a first filter terminal 40, a second filter terminal 42, a third filter terminal 44, a fourth filter terminal 46, a first common filter terminal 48, and a second common filter terminal 50. Have.

The first filter terminal 40 is connected to the input / output terminal 12
The second filter terminal 42 is electrically connected to the input / output terminal 24. Further, the third filter terminal 44 is electrically connected to the input / output terminal 16 and
The filter terminal 46 is electrically connected to the input / output terminal 28.

The first common filter terminal 48 is connected to the SA
The input / output terminal 14 of the W filter element 10 and the input / output terminal 22 of the SAW filter element 20 are electrically connected. The second common filter terminal 50 is connected to the input / output terminal 18 of the SAW filter element 10 and the SAW filter element 2.
0 is connected to the input / output terminal 26.

That is, the first filter terminal 40 and the third filter terminal 44 are connected to the first SAW filter element 1 respectively.
0 terminal is electrically connected. In addition, the second filter terminal 42 and the fourth filter terminal 46
It is electrically connected to the terminal of the SAW filter element 20. On the other hand, the first common filter terminal 48 and the second common filter terminal 50 are electrically connected to both terminals of the SAW filter elements 10 and 20.

In the SAW filter 100, the first
Assuming that three terminal sides of the filter terminal 40, the second filter terminal 42, and the first common filter terminal 48 are signal input sides,
The third filter terminal 44, the fourth filter terminal 46, and the second
The common filter terminal 50 is on the signal output side. At this time, the signal of the frequency f1 is output from the third filter terminal 44, and the signal of the frequency f2 is output from the fourth filter terminal 46.

Conversely, if the third filter terminal 44, the fourth filter terminal 46, and the second common filter terminal 50 are the signal input side, the first filter terminal 40, the second filter terminal 42, and the first common filter terminal 48 Are the signal output sides. At this time, the signal of the frequency f1 is output from the first filter terminal 40, and the signal of the frequency f2 is output from the second filter terminal 42.

As described above, in the SAW filter 100 of the present embodiment, it is possible to output signals in both the frequency bands f1 and f2 to the output side, regardless of which terminal side is the signal input side. is there. Therefore, which terminal side is the input side and which terminal side is the output side is
It can be selected as appropriate.

As described above, in the SAW filter 100, which terminal is used for the input side can be appropriately selected, so that the SAW filter 100 can be used for several kinds of applications. Next, the SAW of the present embodiment
Two types of SAWs when a filter is used as a filter of a duplexer in a cordless telephone
The application of the filter will be exemplified. A signal of frequency f1 is transmitted from the base unit of the cordless telephone, and a frequency f1 is transmitted from the slave unit.
2 are transmitted, and each of the master unit and the slave unit receives the signal of the other party.

FIG. 2A is a block diagram showing a case where the SAW filter 100 of the present embodiment is used as a SAW filter of a base station antenna duplexer of a cordless telephone. At this time, the first filter terminal 40, the second filter terminal 42, and the second common filter terminal 50 are grounded, and signals are input / output to the first common filter terminal 48, the third filter terminal 44, and the fourth filter terminal 46. Is done.

When a signal is transmitted from the master unit to the slave unit, a signal of the frequency f1 is input to the third filter terminal 44 and output from the first common filter terminal 48. The first common filter terminal 48 is electrically connected to an antenna (not shown) via a matching circuit (not shown), and a signal of the frequency f1 is transmitted from the antenna.

When the master unit receives the signal of frequency f2 from the slave unit, the signal is input from the antenna to the first common filter terminal 48 via the matching circuit, and the fourth filter terminal 4
6 is output.

On the other hand, by simply rotating the SAW filter 100 shown in FIG. 2A by 180 degrees, the SAW filter 100 can be used as the SAW filter of the slave unit duplexer. FIG. 2B shows FIG.
The block diagram in the case where the SAW filter 100 shown in (a) is rotated by 180 degrees and the SAW filter 100 is used as a SAW filter of an antenna duplexer for a slave unit is shown. At this time, the second common filter terminal 50, the first
Signals are input to and output from the filter terminal 40 and the second filter terminal 42, and the third filter terminal 44 and the fourth filter terminal 4
6 and the first common filter terminal 48 are grounded.

When a signal is transmitted from the slave unit to the master unit, a signal of the frequency f2 is input to the second filter terminal 42 and output from the second common filter terminal 50. Second common filter terminal 50 is electrically connected to an antenna (not shown) via a matching circuit (not shown), and a signal of frequency f2 is transmitted from the antenna to the master unit.

On the other hand, when the slave unit receives the signal of frequency f1 from the master unit, the second unit receives the signal from the antenna via the matching circuit.
The signal is input to the common filter terminal 50, and the signal of f1 is output from the first filter terminal 40.

As described above, the SAW filter according to the present embodiment can be used as a SAW filter for an antenna duplexer for a master unit and a slave unit. Therefore, there is no need to manufacture two types of SAW filters for the master unit and the slave unit,
Since only one type is required, the manufacturing cost can be reduced. Further, the SAW filter of the present embodiment can be rotated only 180 degrees, and the SAW filter of the master and slave antenna duplexer can be used.
Since it can be used as a W filter, SA
The board to which the W filter is connected can be shared between the master unit and the slave unit.

FIG. 3 shows a SAW filter 200 according to another embodiment. The same components as those of the SAW filter 100 shown in FIG. 1 are denoted by the same reference numerals. The SAW filter 200 has a configuration in which matching circuits 52 and 54 for matching impedance with an external device are added to the SAW filter 100 shown in FIG. The matching circuits 52 and 54 are generally used matching circuits each including a spiral inductor and a capacitor. SAW
In the filter 200, the first common filter terminal 48
Is the first SAW filter element 1 via the matching circuit 52.
0 and the input / output terminal 22 of the second SAW filter element 20. The second common filter terminal 50 is connected to the input / output terminal 18 of the first SAW filter element 10 and the input / output terminal 26 of the second SAW filter element 20 via a matching circuit 54.

The SAW filter 200 can be used in two ways, in a manner similar to that shown in FIG. Further, the SAW filter 200 of the present embodiment
Has a matching circuit inside, so that there is no need to connect a matching circuit other than the SAW filter 200. Therefore, the number of components connected to the SAW filter 200 can be reduced.

[0041]

As described above, the SAW filter of the present invention has three filter terminals on the input / output side and three filter terminals on the input / output side. When one of the input / output side and the input / output side is the input side, the other is the output side. Regardless of which side is the input side, output signals in both frequency bands passing through the first and second SAW filter elements. Is possible. Therefore, the SAW filter of the present invention can appropriately select which one is on the input side, and can be used for several types of applications. Therefore, only one type of SAW filter that needs to be manufactured is required, and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a SAW filter according to an embodiment.

FIG. 2 is a block diagram illustrating a method of using the SAW filter according to the present embodiment when the SAW filter is used as a filter of an antenna duplexer for a parent device and a child device of a cordless telephone.

FIG. 3 is a SAW of the present embodiment having a matching circuit inside;
It is a block diagram of a filter.

FIG. 4 is a schematic diagram showing how signals are transmitted and received between a parent device and a child device of the cordless telephone.

FIG. 5 is a block diagram of a conventional SAW filter having two internal SAW filter elements.

[Explanation of symbols]

10, 20 SAW filter elements, 12, 14, 22,
24 input / output terminals, 16, 18, 26, 28 input / output terminals, 40 first filter terminals, 42 second filter terminals, 44 third filter terminals, 46 fourth filter terminals, 48 first common filter terminals, 50 second Common filter terminal, 52, 54 Matching circuit, 100, 200 S
AW filter.

Claims (2)

[Claims] 1. A surface acoustic wave filter having first and second surface acoustic wave filter elements therein, wherein the first and second surface acoustic wave filters are
The surface acoustic wave filter element includes first and second input / output terminals and first and second input / output terminals, and the second surface acoustic wave filter element has third and fourth input / output terminals. In the surface acoustic wave filter including a terminal and third and fourth input / output terminals, on the input / output side, a first filter terminal electrically connected to the first input / output terminal; A second filter terminal electrically connected to the fourth input / output terminal; and a first common filter terminal electrically connected to the second input / output terminal and the third input / output terminal. And a third filter terminal electrically connected to the first input / output terminal; a fourth filter terminal electrically connected to the fourth input / output terminal; A second common filter electrically connected to the second input / output terminal and the third input / output terminal SAW filter characterized by having a child, the. 2. The surface acoustic wave filter according to claim 1, wherein the surface acoustic wave filter further has first and second matching circuits therein, and the first common filter terminal is , The second input / output terminal is electrically connected to the second input / output terminal and the third input / output terminal via the first matching circuit, and the second common filter terminal is connected to the second input / output terminal via the second matching circuit. A second input / output terminal and a third input / output terminal;
A surface acoustic wave filter electrically connected to the input / output terminal of the filter.