JPH10313229A - Multi-terminal pair saw filter and its using method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain miniaturization for a 1-input 2-output SAW filter and a SAW transmitter-receiver and to reduce the loss. SOLUTION: Two SAW filters F1, F2 are connected in parallel at one-side terminals and an inductor Lp is provided to a common terminal 4a connecting to the connecting point of the terminals as a matching circuit. A resonator and especially an electrode finger pair number and a cross width of IDT being components of the SAW filters F1, F2 toward the common terminal 4a are selected so that the impedance of the SAW filter F2 single body when viewing the common terminal 4a is in parallel resonance with the inductance of the inductor Lp at a pass frequency band of the SAW filter F1 and the impedance of the SAW filter F1 single body when viewing the common terminal 4a is in parallel resonance with the inductance of the inductor Lp at a pass frequency band of the SAW filter F2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-port SAW filter having two SAW filters and having one of the input / output terminal pairs shared, and a method of using the same.

[0002]

2. Description of the Related Art Two SAWs whose pass bands are different from each other
A multiport SAW filter having a configuration in which filters are connected in parallel at one end is used as a SAW duplexer. For example, "Double Mode SAW Filter for Domestic Digital Mobile Phones" (Watanabe et al., 1996 IEICE Basic and Boundary Society Conference, A-198)
The first and second SAW filters are connected in parallel via a matching circuit, and a specific frequency component of a received signal supplied to a pair of terminals connected in parallel (hereinafter, “shared terminal pair”) is a first frequency component.
From the remaining pair of terminals of the SAW filter, and other specific frequency components from the remaining pair of terminals of the second SAW filter, etc. (“demultiplex”) SA
A W splitter is disclosed. Also, in "Study of SAW resonator type duplexer" (Igata et al., 1992 IEICE Spring Conference, A-397), the first and second SAW filters are connected in parallel via a matching circuit. A specific frequency component of the received signal supplied to the terminal pair related to the parallel connection, that is, the shared terminal pair, is output from the remaining terminal pair of the first SAW filter, and the remaining terminal pair of the second SAW filter is output. A SAW duplexer that outputs another specific frequency component of the transmission signal supplied to the common terminal pair from the shared terminal pair is disclosed.
The one in which the input terminal pairs of the two SAW filters are shared as in the former can be called a one-input two-output SAW filter, and the direction of the signal flow in one SAW filter is one-input and two-output as in the latter. The opposite of a SAW filter can be called a SAW duplexer. The term SAW duplexer is used in a broad sense to include both a one-input two-output SAW filter and a SAW duplexer, and is used in a narrow sense to encompass only a SAW duplexer. In this application, this term is used in a broad sense.

[0003] Each of the SAW duplexers disclosed in these prior art documents has a configuration in which a matching circuit is provided for a shared terminal pair. Specifically, in the former, one S
An IDT capacitor connected in series to an AW filter and an inductor connected in parallel between a pair of common terminals. In the latter case, a delay line connected in series to one SAW filter on a printed circuit board and an inductor connected in parallel between a pair of common terminals. Realizes a matching circuit to be provided for the shared terminal pair.
Generally, the input impedance of the SAW filter becomes capacitive outside the pass band. Therefore, parallel resonance can be caused by connecting an inductor in parallel between the shared terminal pair. That is, for a signal having a frequency belonging to the pass band of one SAW filter, a state can be created in which the input impedance of the other SAW filter is almost open impedance. Thereby, a frequency component belonging to the pass band of one SAW filter among the reception signals supplied to the common terminal pair also passes through the other SAW filter (one-input two-output filter) or a SAW filter for transmitting the transmission signal. The problem that the output of (1) passes through a SAW filter for passing a received signal (transmitter / receiver) can generally be solved.

An IDT capacitor (the former) or a delay line (the latter) is provided in order to apparently cancel out the difference in input impedance characteristics between two SAW filters connected in parallel. For example, these two SAWs
It is assumed that, in the pass band of the first SAW filter among the filters, the impedance of the second SAW filter alone as viewed from the shared terminal pair side is set to exactly resonate with the inductance of the inductor described above. But,
With this setting, in the pass band of the second SAW filter, the first SAW filter viewed from the shared terminal pair side is used.
The impedance of the filter alone does not resonate in parallel with the inductance of the inductor described above. This is these two
This is because the frequency characteristics of the SAW filters must be different for the purpose of demultiplexing. The provision of the IDT type capacitor and the delay line between the second filter and the common terminal pair, for example, is intended to compensate for this difference, that is, the first filter is provided.
In the pass band of the SAW filter, the apparent impedance of the second SAW filter as viewed from the shared terminal pair side, and in the pass band of the second SAW filter, the first SAW filter as viewed from the shared terminal pair side. Is to cause the impedance of the inductor to resonate in parallel with the inductance of the inductor described above. In other words, the first and second
In order to prevent the SAW filters from affecting each other.

[0005]

However, in the above-mentioned prior art, since it is necessary to provide an IDT capacitor and a delay line, the configuration of the device becomes large and insertion loss occurs.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to realize a device which is smaller in size and lower in loss than a conventional device.

[0007]

According to the present invention, there is provided a multi-port SAW filter according to the present invention, comprising: a common terminal pair for inputting and outputting a signal; a first terminal pair and a second terminal pair; A first SAW filter having a pair as an input / output terminal and a passband in a first frequency band;
A second SAW filter having a pass band in a frequency band; and an inductor connected between the common terminal pair. In the first frequency band, an impedance of the second SAW filter as viewed from the common terminal pair is the impedance of the inductor. In order to satisfy the inductor sharing condition that impedance resonates in parallel with the inductance and in the second frequency band, the impedance when the first SAW filter side is viewed from the shared terminal pair resonates in parallel with the inductance of the inductor.
The electrode structure of the first and second SAW filters is defined.

In the multi-port SAW filter according to the present invention, at least one of the first and second SAW filters is a first SAW resonator belonging to a series arm connected to the common terminal pair and the series arm. And the product of the number of electrode finger pairs and the electrode cross width of the first SAW resonator is multiplied by the product of the number of electrode finger pairs and the electrode cross width of the second SAW resonator. The value is determined so as to satisfy the inductor sharing condition.

In the multi-port SAW filter according to the present invention, at least one of the first and second SAW filters has a SAW resonator belonging to a parallel arm connected to the shared terminal pair. The product of the number of electrode finger pairs and the electrode intersection width of the SAW resonator is determined so as to satisfy the inductor sharing condition.

[0010] In the method of using a multi-port SAW filter according to the present invention, the shared terminal pair may be an input terminal of the first SAW filter and an input terminal of the second SAW filter.
By using the first terminal pair as an output terminal of the first SAW filter and the second terminal pair as an output terminal of the second SAW filter, a duplexer is configured with the multi-port SAW filter according to the present invention. Things.

A method of using a multiport SAW filter according to the present invention relates to a receiving circuit capable of receiving signals at a plurality of frequencies, a receiving antenna shared by the plurality of frequencies, and a method of using the SAW filter according to the present invention. A multi-terminal SAW filter, wherein the shared terminal pair is connected to a receiving antenna, and the first and second terminal pairs are connected to the receiving circuit.

[0012] In the method of using a multi-port SAW filter according to the present invention, the shared port pair may be an input terminal of the first SAW filter and an output terminal of the second SAW filter.
By using the first terminal pair as an output terminal of the first SAW filter and the second terminal pair as an input terminal of the second SAW filter, a duplexer is configured with the multi-terminal pair SAW filter according to the present invention. Things.

[0013] A method for using a multi-port SAW filter according to the present invention includes a pair of receiving circuit and transmitting circuit, a transmitting and receiving antenna shared by the receiving circuit and transmitting circuit, and
A multi-port SAW filter according to the present invention, wherein the shared terminal pair is connected to a transmitting / receiving antenna, the first terminal pair is connected to the receiving circuit, and the second terminal pair is connected to the transmitting circuit.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. Note that members common to the embodiments are denoted by the same reference numerals, and description thereof is omitted.

Embodiment 1 FIG. 1 shows an example of a usage pattern of the device according to the first embodiment of the present invention. In the figure, reference numeral 1
Is a receiving circuit 2 for receiving signals at frequencies f1 and f2;
Receiving antenna 3 and receiving antenna 3 shared by
1 and 2 output SAW filter 4 according to this embodiment, which is provided between the SAW filter 4 and the receiving circuit 2. The one-input / two-output SAW filter 4 includes a shared terminal pair 4a for connection to the reception antenna 3, and a first terminal pair 4b and a second terminal pair 4c for connection to the reception circuit 2. First terminal pair 4
b is used for receiving the frequency f1, and the second terminal pair 4c is used for receiving the frequency f2.

As shown in FIG. 2, the one-input two-output SAW filter 4 has a SAW filter F1 including a frequency f1 in its pass band and a SAW filter F2 including a frequency f2 in its pass band. One end of each of the SAW filters F1 and F2 is connected to the common terminal pair 4a.
The other terminal pair of the W filter F1 is connected to the first terminal pair 4b, and the other terminal pair of the SAW filter F2 is connected to the second terminal pair 4c.
, Respectively. The inductor Lp is connected to the common terminal pair 4a. Note that each terminal pair 4
a, 4b and 4c, the SAW filters F1 and F2, and the inductor Lp all share the ground G.

FIG. 3 shows the configuration of the SAW filters F1 and F2 in this embodiment in more detail. In the figure, symbols Rs11, Rp11, Rs12, Rp12, Rs2
1, Rp21, Rs22 and Rp22 are SAW resonators, respectively. Of these, R
s11, Rs12, Rs21 and Rs22 are connected to the serial arm,
Rp11, Rp12, Rp21 and Rp22 are provided on the parallel arms, respectively. Each of the SAW filters F1 and F2 has a configuration in which they are ladder-connected. In interpreting the present invention, it is not necessary to limit the number of resonators forming the ladder connection to four.

In this embodiment, for example, a resonator having the electrode arrangement shown in FIG. 4 is used as the SAW resonator Rs11 and the like. In the figure, reference numeral 5 denotes an ID.
T (inter digital transducer), and reflectors 6 disposed on the left and right of the T. However, it is also possible to configure the resonator only with the IDT 5 without using the reflector 6. Also, the IDT 5 has a configuration in which a plurality of electrode fingers extended from one terminal and an electrode finger drawn from the other terminal are engaged with each other just as if the fingers intersect, and the interval between the electrode fingers corresponds to a desired resonance frequency. It is set to be the interval. In the figure, N represents the number of pairs of electrode fingers constituting the IDT 5, and W represents the number of electrode fingers extracted from one terminal and the number of electrode fingers extracted from the other terminal. The width at which the finger intersects.

When the configuration shown in FIGS. 3 and 4 is used, when the SAW filter F1 alone is viewed from the shared terminal pair 4a side, the input impedance is the SAW resonator Rs11.
Side coupling capacitance generated in the IDT 5 of FIG.
-1 of the product of p11 and the side coupling capacitance generated in IDT5
/ 2 power. The side coupling capacitance generated in the IDT 5 is proportional to the product of the electrode finger pair N and the intersection width W. Accordingly, the input impedance of the SAW filter V1 alone viewed from the shared terminal pair 4a is equal to the SAW resonators Rs11 and Rp11.
11 Number of electrode finger pairs N and intersection width W in each IDT 5
Can be determined by Similarly, the input impedance of the SAW filter F2 alone viewed from the shared terminal pair 4a is the ID of each of the SAW resonators Rs21 and Rp21.
It can be determined by the number N of electrode fingers and the intersection width W at T5. In this embodiment, the shared terminal pair 4a
The impedance of the SAW filter F2 alone viewed from
At least the SAW filter is designed to resonate in parallel with the inductance of the inductor Lp in the pass band of the AW filter F1, and to resonate in parallel with the inductance of the inductor Lp in the pass band of the SAW filter F2 when viewed from the shared terminal pair 4a. Resonator R
The number N of electrode fingers and the intersection width W in IDT5 of s11, Rp11, Rs21, and Rp21 are set.

FIGS. 5 and 6 show the principle and effect of such setting. First, the SAW filter generally has the configuration shown in FIG.
Has a characteristic as shown by a curve on the Smith chart. In the figure, the symbol P indicates the characteristic in the vicinity of the pass band, and the symbols L and H indicate the characteristic on the low band side and the high band side when viewed from the pass band, respectively. In the Smith chart, the upper half of the circle generally represents the inductive impedance, the lower half of the circle represents the capacitive impedance, and the center of the circle represents the matching state. From the characteristics described above, it can be understood that the impedance outside the pass band of the SAW filter is substantially capacitive.

In the embodiment shown in FIGS. 1 to 4, the general characteristics of the SAW filter as shown in FIG.
It realizes a duplexer that does not require the use of capacitors and delay lines as part of a matching circuit. That is, as shown in FIG. 6, the characteristics of the SAW filter F1 are represented by a curve L1-P1-H.
1 and the characteristic of the SAW filter F2 is set to a characteristic such as L2-P2-H2, and the pass band (P
In 1), if the SAW filter F2 operates near L2 and the SAW filter F1 operates near H1 in the pass band (P2) of the SAW filter F2, a single inductor Lp is used as a matching circuit. With only this, it is possible to achieve the effect of preventing the target demultiplexing, that is, the effect of preventing one of the SAW filters F1 and F2 from affecting the other. Note that the frequency f1 is lower than the frequency f2. According to this embodiment, therefore, it is possible to obtain a small-sized device having a smaller number of circuit elements than the conventional device. In addition, since the insertion loss is reduced because the capacitor and the delay line are not interposed, the loss can be reduced as a whole of the mobile communication terminal device 1, and the power saving of the mobile communication terminal device is more excellent. It can contribute to the realization of the device.

Embodiment 2 FIG. 7 and 8 show a configuration of an apparatus according to Embodiment 2 of the present invention. First, the mobile communication terminal device 1A shown in FIG. 7 includes a receiving circuit 2 for receiving a signal of frequency f1, a transmitting circuit 7 for transmitting a signal of frequency f2, and transmission / reception shared by the receiving circuit 2 and the transmitting circuit 7. Signals received by the antenna 3A and the transmission / reception antenna 3A are input from the common terminal pair 4a and supplied to the receiving circuit 2 via the first terminal pair 4d, and input from the transmission circuit 7 via the second terminal pair 4e. Shared signal pair 4
transmission / reception duplexer 4A provided to transmission / reception antenna 3A via a
It is composed of As shown in FIG. 8, the duplexer 4A includes a SAW filter F including a frequency f1 in its pass band.
SAW filter F including R and frequency f2 in its passband
T has a configuration provided in place of the SAW filters F1 and F2 shown in FIG. However, the frequency f1 and the frequency f
2 is a different value. Thus, the present invention
Not only the one-input two-output SAW filter shown in FIG. 2 but also a SAW duplexer can be realized.

Embodiment 3 FIG. FIG. 9 shows an example of the internal configuration of a SAW filter used in Embodiment 3 of the present invention. This embodiment is obtained by modifying the connection state of the resonator inside SAW filter F1, F2, FR or FT in any one of the first and second embodiments. That is, in FIG. 3 described above, the serial arm is provided near the shared terminal pair 4a, but in this embodiment, a parallel arm is provided instead of the serial arm. In the figure, R
p1 and Rp2 are SAW resonators belonging to the parallel arm, and R1
s1 and Rs2 are SAW resonators belonging to the series arm.
Even when such a configuration is adopted, the same operation and effect as those of the first or second embodiment can be obtained. In the case of the configuration shown in FIG. 9, S as viewed from the shared terminal pair 4a
Since the impedance of the AW filter alone is generally determined by the number N of electrode fingers in the IDT 5 of the SAW resonator Rp1 and the cross width W thereof, the characteristic design shown in FIG. 6 is based on the electrode structure of the IDT 5 of the SAW resonator Rp1. Do.

[0024]

According to the multi-port SAW filter of the present invention, the second SA from the shared port in the first frequency band.
The first and second impedances are viewed so that the impedance when viewed from the W filter side and the impedance when viewed from the shared terminal pair to the first SAW filter side in the second frequency band resonate in parallel with the inductance of the inductor connected between the shared terminal pair. 2S
Since the electrode structure of the AW filter is determined, the first and second S
There is no need to provide a capacitor or a delay line for compensating for the difference in characteristics of the AW filter, and a device having a smaller size and a smaller insertion loss than the conventional device can be obtained.

According to the multi-port SAW filter according to the present invention, at least one of the first and second SAW filters is replaced with the first SAW resonator belonging to the series arm connected to the shared terminal pair and the series arm. And the product of the number of electrode fingers and the electrode cross width of the first SAW resonator is multiplied by the product of the number of electrode fingers and the electrode cross width of the second SAW resonator. By setting the multiplied value, the conditions for sharing the inductor and eliminating the capacitor and the delay line can be satisfied.

According to the multi-port SAW filter according to the present invention, at least one of the first and second SAW filters has a SAW resonator belonging to a parallel arm connected to the shared terminal pair. Thus, by setting the product of the number of electrode fingers and the electrode cross width of the SAW resonator, the conditions for sharing the inductor and eliminating the capacitor and the delay line can be satisfied.

According to the method of using the multi-port SAW filter according to the present invention, the shared terminal pair is used as the input terminal of the first SAW filter and the input terminal of the second SAW filter, and the first terminal pair is used as the output terminal of the first SAW filter. By using the second terminal pair as the output terminal of the second SAW filter, a duplexer can be configured with the multi-terminal pair SAW filter according to the present invention.

According to the method of using a multiport SAW filter according to the present invention, a receiving circuit capable of receiving signals at a plurality of frequencies, a receiving antenna shared by the plurality of frequencies, And the first and second pairs of terminals are connected to a receiving circuit, respectively, so that the efficiency of receiving signals at a plurality of frequencies can be improved. And, in particular, a device suitable for a mobile communication terminal can be realized.

According to the method of using the multi-port SAW filter according to the present invention, the shared terminal pair is used as the input terminal of the first SAW filter and the output terminal of the second SAW filter, and the first terminal pair is used as the output terminal of the first SAW filter. By using the second terminal pair as the input terminal of the second SAW filter, a duplexer can be configured with the multi-terminal pair SAW filter according to the present invention.

According to the method of using the multi-port SAW filter according to the present invention, a pair of receiving circuit and transmitting circuit;
A transmission / reception antenna shared by the reception circuit and the transmission circuit and the multi-port SAW filter according to the present invention are provided, and the shared terminal pair is used as the transmission / reception antenna, the first terminal pair is used as the reception circuit, and the second terminal pair is used as the reception terminal. By connecting to a transmission circuit, efficiency can be improved when transmission and reception are shared by a single antenna, and a device particularly suitable for a mobile communication terminal can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a mobile communication terminal device that can use the device according to Embodiment 1 of the present invention.

FIG. 2 shows a multi-terminal pair SA according to the first embodiment of the present invention.
FIG. 3 is a circuit diagram illustrating a configuration of a W filter.

FIG. 3 is a circuit diagram showing an example of an internal configuration of the SAW filter according to the first embodiment of the present invention.

FIG. 4 is a plan view showing an example of the configuration of a resonator, particularly an electrode arrangement, according to Embodiment 1 of the present invention.

FIG. 5 is a Smith chart showing a typical characteristic example of a SAW filter.

FIG. 6 is a Smith chart showing a characteristic setting example of a SAW filter according to the first embodiment of the present invention.

FIG. 7 shows a multi-terminal pair SA according to Embodiment 2 of the present invention.
It is a block diagram which shows the structure of the mobile communication terminal device which can use a W filter.

FIG. 8 shows a multi-terminal pair SA according to Embodiment 2 of the present invention.
FIG. 3 is a circuit diagram illustrating a configuration of a W filter.

FIG. 9 shows a multi-terminal pair SA according to Embodiment 3 of the present invention.
FIG. 3 is a circuit diagram illustrating an example of an internal configuration of a SAW filter in a W filter.

[Explanation of symbols]

1, 1A mobile communication terminal device, 2 receiving circuit, 3
Receiving antenna, 3A transmitting / receiving antenna, 41-input 2-output SAW filter, 4A duplexer, 4a shared terminal pair,
4b, 4d first terminal pair, 4c, 4e second terminal pair, 5
IDT, 6 reflector, 7 transmission circuit, F1, F2, F
R, FT SAW filter, Lp inductor, Rs1
1, Rp11, Rs12, Rp12, Rs21, Rp2
1, Rs22, Rp22, Rp1, Rs1, Rp2, R
s2 SAW resonator, f1, f2 frequency.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshiko Tera 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Inside Mitsubishi Electric Corporation

Claims (7)

[Claims] 1. A shared terminal pair for signal input / output, a first terminal pair and a second terminal pair, the shared terminal pair and the first terminal pair being input / output terminals, and a first frequency band being a pass band. First
A SAW filter, a second SAW filter using the shared terminal pair and the second terminal pair as input / output terminals and a passband in a second frequency band different from the first frequency band, and a SAW filter connected between the shared terminal pair; An impedance when viewed from the shared terminal pair side to the second SAW filter side in the first frequency band and resonates in parallel with an inductance of the inductor; and in the second frequency band, from the shared terminal pair to the first SAW filter. A multi-port SAW filter, characterized in that the electrode structure of the first and second SAW filters is determined so that an inductor sharing condition that impedance viewed from the side resonates in parallel with inductance of the inductor is satisfied. 2. At least one of the first and second SAW filters is a first SAW resonator belonging to a series arm connected to the shared terminal pair and a second SAW resonator belonging to a parallel arm connected to the series arm. A value obtained by multiplying the product of the number of electrode fingers and the electrode cross width of the first SAW resonator by the product of the number of electrode fingers and the electrode cross width of the second SAW resonator is defined as the inductor sharing condition. 2. The multiport SAW filter according to claim 1, wherein the filter is set to satisfy the condition. 3. The SAW filter according to claim 1, wherein at least one of said first and second SAW filters has a SAW resonator belonging to a parallel arm connected to said common terminal pair.
3. The multi-port SAW filter according to claim 1, wherein a product of the number of electrode finger pairs and the electrode cross width of the AW resonator satisfies the inductor sharing condition. 4. The first terminal pair as the output terminal of the first SAW filter, the shared terminal pair as the input terminal of the first SAW filter and the input terminal of the second SAW filter, and the second terminal pair as the second terminal. Claims 1 to 3 are respectively used as output terminals of a 2SAW filter.
A method of using a multiport SAW filter, comprising configuring a duplexer with the multiport SAW filter according to any one of the above. 5. A receiving circuit capable of receiving signals at a plurality of frequencies, a receiving antenna shared by the plurality of frequencies, and a multi-port SAW filter according to claim 1; 5. The method according to claim 4, wherein the shared terminal pair is connected to a receiving antenna, and the first and second terminal pairs are connected to the receiving circuit, respectively. 6. The pair of shared terminals serves as an input terminal of the first SAW filter and the output terminal of the second SAW filter, the first terminal pair serves as an output terminal of the first SAW filter, and the second terminal pair serves as a terminal of the first SAW filter. Claims 1 through 3 are used as input terminals of a 2SAW filter.
A method of using a multiport SAW filter, comprising configuring a duplexer with the multiport SAW filter according to any one of the above. 7. A shared terminal pair comprising: a pair of a receiving circuit and a transmitting circuit; a transmitting / receiving antenna shared by the receiving circuit and the transmitting circuit; and the multi-port SAW filter according to claim 1; 7. The method of using a multi-port SAW filter according to claim 6, wherein the first terminal pair is connected to the receiving circuit, and the second terminal pair is connected to the transmitting circuit.