JP2000022494A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide press-band by grounding through a dielectric element a multi-strip coupler, which is composed of plural strips while connecting the strips with almost the same phase of surface acoustic wave(SAW) to one strip terminal at least, and the strip terminal connected to that coupler. SOLUTION: A multi-strip coupler 4 is arranged on the right side of first and second IDT and formed over a first SAW track 2 and a second SAW track 3 of a piezoelectric substrate. At the upper and lower terminals of strips of the multi-strip coupler 1, the strips with almost the same phase of SAW to be propagated are mutually connected by a common connecting bar 6. The strip connected at the upper terminal and the strip connected at the lower terminal are connected by an inductor element 5 of 100 nH. Inside the first SAW track, a reflector 7 is arranged outside both the first IDT and the multi- strip coupler 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element structure for improving a pass band characteristic of a surface acoustic wave device.

[0002]

2. Description of the Related Art A surface acoustic wave device is a circuit element that performs signal processing by converting an electric signal into a surface wave, and is used for a filter, a resonator, a delay line, and the like. Usually, by providing a metal electrode called an IDT (interdigital transducer, comb-shaped electrode, IDT) on an elastic substrate having a piezoelectric effect (piezoelectric substrate), conversion / reverse conversion (excitation, Reception, reflection, propagation)
It is carried out.

As a conventional surface acoustic wave device, an input / output ID
A surface acoustic wave device in which a multistrip coupler is provided between T is known. A surface acoustic wave device in which strips having substantially the same phase of a propagating surface acoustic wave are connected at one strip end of the multistrip coupler. A wave device is proposed in Japanese Patent Publication No. 58-34038. Also,
The surface acoustic wave device in which the strips in which the surface acoustic waves propagating at both strip ends have substantially the same phase are connected,
It has been proposed in Japanese Patent Application Laid-Open No. 9-18282.

The above-described surface acoustic wave device has a feature that the amount of attenuation outside the pass band, particularly on the low frequency side, can be improved as compared with a multi-strip coupler in which the strip ends are not short-circuited. FIG. 3 shows a conventional surface acoustic wave device.

[0005] Two IDTs are provided on a piezoelectric substrate. The IDT of the first surface acoustic wave track and the IDT of the second surface acoustic wave track are arranged so that the respective surface acoustic wave tracks are shifted. A multistrip coupler is arranged between the IDT of the first surface acoustic wave track and the IDT of the second surface acoustic wave track so as to straddle the two surface acoustic wave tracks. The surface acoustic wave input from the IDT of the first surface acoustic wave track propagates through the first surface acoustic wave track.

[0006] The surface acoustic wave propagating in the first surface acoustic wave track is propagated to the second surface acoustic wave track by the multistrip coupler.
Output as DT. In this way, the multistrip coupler is used as a signal transmitting means between two surface acoustic wave tracks.

[0007]

However, in the case of a conventional surface acoustic wave device using a connected multi-strip coupler, at least at one end of the strip, the surface acoustic waves that propagate are almost in phase. However, there is a problem that the pass bandwidth cannot be sufficiently secured. An object of the present invention is to provide a surface acoustic wave device using a multistrip coupler that can secure a wide pass band. In this specification, a signal transmitting means between the surface acoustic wave tracks is also referred to as a multi-strip coupler for convenience.

[0008]

The object of the present invention is to provide at least two surface acoustic wave tracks formed on a piezoelectric substrate,
Formed on a piezoelectric substrate, straddling different surface acoustic wave tracks, and at least one strip end,
A multi-strip coupler composed of a plurality of strips in which strips having propagating surface acoustic waves having substantially the same phase are connected, and a strip end to which the multi-strip coupler is connected are grounded via an inductive element. This is achieved by a surface acoustic wave device.

[0009] Further, at least two surface acoustic wave tracks formed on the piezoelectric substrate, and formed on the piezoelectric substrate,
Strips formed across different surface acoustic wave tracks and having the same phase of propagating surface acoustic waves at both strip ends connected to each other. This is achieved by a surface acoustic wave device characterized in that the formed strip ends are connected via an inductive element.

[0010]

The inventor of the present application has found that a strip connected at one strip end and a strip not connected at the other strip end or between strips connected at the other strip end becomes capacitive. It has been found that when the tracks are connected by a multistrip coupler using the method, sufficient bandwidth cannot be secured due to impedance mismatch with the inside of the multistrip coupler. Therefore, the inventor of the present application intends to cancel the state in which the strip connected at one strip end and the strip not connected at the other strip end or the strip connected at the other strip end becomes capacitive. The strips were connected by inductive elements.

[0011]

FIG. 1 is a plan view of an electrode structure showing a surface acoustic wave device according to the present embodiment. As shown in FIG. 1, about 230 on a piezoelectric substrate 1 using an ST cut quartz plate.
The IDT, the multi-strip coupler 4 and the reflector 7 are formed by an aluminum film having a thickness of nm. The upper and lower ends of the multistrip coupler 4 are alternately connected to a common connection bar
Connected with. The number of multistrip couplers 4 is 2
There are 49.

The first IDT is provided on the first surface acoustic wave track 2. The logarithm of the first IDT is 134.
For five pairs, the intersection length is 15λ. One electrode finger of the first IDT is connected to the input terminal, and the other electrode finger is grounded. The second IDT is provided on the second surface acoustic wave track 3. The logarithm of the second IDT is 134.5 pairs, the cross length is 7λ, and the arrangement period of the strips is 11.56.
6 μm. One electrode finger of the first IDT is connected to the input terminal, and the other electrode finger is grounded.

The multistrip coupler 4 has a first IDT
And the right side of the second IDT, and is formed over the first surface acoustic wave track 2 and the second surface acoustic wave track 3 of the piezoelectric substrate. At the upper and lower ends of the strip, the multi-strip coupler 4 has a common connection bar 6 at which strips whose surface acoustic waves propagated are substantially in phase.
Connected by The strip connected at the upper end of the multistrip coupler 4 and the strip connected at the lower end are connected by an inductive element 5 of 110 nH.

In the first surface acoustic wave track, the first I
Reflectors 7 are arranged on both outer sides of the DT and the multistrip coupler 4. The number of the reflectors 7 is 200 on both the left and right sides, and the pitch of the reflectors 7 is slightly wider than the pitch of the IDT. The first ID in the second surface acoustic wave track
Reflectors 7 are arranged on both outer sides of the T and the multistrip coupler 4. The number of the reflectors 7 is 200 on both the left and right sides, and the pitch of the reflectors 7 is slightly wider than the pitch of the IDT.

The arrangement pitch of the multistrip couplers 4 in the first surface acoustic wave track 2 and the second surface acoustic wave track 3 is 5.783 μm. FIG. 2 is a graph comparing the frequency response characteristics of the surface acoustic wave device of the present embodiment and the conventional surface acoustic wave device. The minimum insertion loss of the surface acoustic wave device according to the present embodiment is 2.2 to 3 dB, and the bandwidth is 285 kHz. The surface acoustic wave device using the multistrip coupler 4 shown in FIG. 3 has a configuration in which the inductive element 5 is removed from the surface acoustic wave device according to the present embodiment shown in FIG.

The minimum loss of the conventional surface acoustic wave device shown in FIG. 2 is 4 dB to 3 dB, and the bandwidth is 225 kHz. As is apparent from FIG. 2, the pass band width of the surface acoustic wave device according to the present invention is 2 times smaller than that of the conventional surface acoustic wave device.
The spread was 5%, and the minimum loss was improved by 1.8 dB.

The present invention is not limited to the above embodiment, and various modifications are possible. The gist of the present invention is between strips having one strip end connected by the common connection bar 6 and strips not connected at the other strip end, or between strips having the other strip end connected by the common connection bar 6. The inductive element 5
To connect the strips (common connection bar 6). Therefore, one of the upper end and the lower end of the multistrip coupler 4 does not need to be connected alternately, and one terminal of the inductive element 5 may be grounded (not shown). Note that a material other than quartz, such as a lithium tetraborate substrate, a lithium tantalate substrate, or a lithium niobate substrate, may be used as the piezoelectric substrate.

[0018]

According to the present invention, the pass band characteristics of a surface acoustic wave device having a multi-strip coupler having a plurality of strips over a first surface acoustic wave track and a second surface acoustic wave track are improved. Since the band can be improved and the band can be widened, a higher performance surface acoustic wave can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a surface acoustic wave device using a multistrip coupler according to an embodiment of the present invention.

FIG. 2 is a graph showing a frequency response characteristic of the surface acoustic wave device according to the embodiment.

FIG. 3 is a plan view of a conventional surface acoustic wave device using a multistrip coupler.

[Explanation of symbols]

 Reference Signs List 1 piezoelectric substrate 2 first surface acoustic wave track 3 second surface acoustic wave track 4 multistrip coupler 5 inductive element

Claims (3)

[Claims] A piezoelectric substrate formed of a piezoelectric material;
A first surface acoustic wave transducer that excites, receives, reflects, and propagates a surface acoustic wave of a first surface acoustic wave track on the piezoelectric substrate, and excites, receives, and reflects a surface acoustic wave of a second surface acoustic wave track. A second surface acoustic wave transducer that propagates, and at both strip ends of a plurality of strips formed over the first surface acoustic wave track and the second surface acoustic wave track on the surface of the piezoelectric substrate. A surface acoustic wave device having signal transmission means between surface acoustic wave tracks in which strips whose propagating surface acoustic waves have substantially the same phase are electrically connected in a floating state. A surface acoustic wave device characterized in that the strip ends connected to a signal transmission means between them are connected via an inductive element. 2. The surface acoustic wave device according to claim 1, wherein a portion connected to the strip via an inductive element is grounded. 3. A surface acoustic wave device according to claim 1, wherein a signal transmission means between the surface acoustic wave tracks comprises a multistrip coupler having both strip ends connected in common.