JP2900663B2 - Weighted electrodes for surface acoustic wave filters - Google Patents

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, and more particularly, to a weighting electrode of a surface acoustic wave filter.

[0002]

2. Description of the Related Art A weighted electrode used in a conventional surface acoustic wave filter is an apodized electrode that changes an intersection width 21 in proportion to a weighting function depending on a location as shown in FIG.
Alternatively, as shown in FIG. 5, a thinning electrode or the like is mainly used in which the cross width 31 is constant and the density of electrode fingers having the cross width is changed in proportion to a weighting function.

[0003]

However, these conventional weighting electrodes have respective disadvantages, and the actual situation is that they are properly used in some cases. That is, although the apodized electrode shown in FIG. 3 can faithfully express the weighting function by the crossover width, an error is generated in a portion where the weighting coefficient is small, that is, a portion where the crossover width is narrow, due to a wave diffraction effect, and the filter characteristics are easily deteriorated. And the energy distribution 25 excited from the electrodes
However, as shown in FIG. 4, there is a drawback in that it is not constant due to the distribution of the weighting function, causing weight loss.

The thinned electrode shown in FIG. 5 has a uniform energy distribution 34 excited (see FIG. 6). However, since the weighting function is expressed by the density depending on the presence or absence of the crossing width, the thinning electrode is compared with the apodized electrode. There is a problem that a quantization error is large and it is difficult to obtain desired characteristics.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a weighting electrode for a surface acoustic wave filter capable of improving the disadvantages of the prior art and reducing the quantization error peculiar to the surface acoustic wave filter. And its purpose.

[0006]

According to the first aspect of the present invention, there is provided a piezoelectric substrate formed on a piezoelectric substrate.
At a predetermined distance from two bus electrodes arranged opposite to each other
Are formed in parallel and on the same line to project toward the other side
A plurality of cross finger electrodes, and
In a state where the tip is stopped at a predetermined interval on the same line
In the set weighted surface acoustic wave filter weighting electrode, the phase of each adjacent cross finger electrode formed in parallel is set.
A pair of floating electrodes , one end of which is connected to each other , are provided between the floating electrodes and the interdigital electrodes.
Set the same interval . And each of the above-mentioned cross finger electrodes and
The intersection width between the floating electrode and the floating electrode is
It is configured to keep it constant .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. The embodiment shown in FIGS. 1 and 2 has a plurality of adjacent electrodes 11 and 14 formed on a piezoelectric substrate and formed by intersecting finger electrodes, and has a space between the plurality of electrodes 11 and 14. And a pair of floating electrodes 17 and 18 connected to each other. This place
In this case, the distance between the adjacent electrodes 11 and 14 is, for example,
For example, it is set to λ / 2. In addition, adjacent electrodes 11,
The spacing between each of 17, 18, and 14 is, for example, λ / 6.
Is set. Here, λ indicates the wavelength of the surface acoustic wave.
You.

A surface acoustic wave generally has two crosses.
Excited by applying a voltage between the electrode fingers of
Its magnitude is proportional to the capacitance of the crossover, and the applied voltage
Proportional. Therefore, the magnitude of the surface acoustic wave excited is
It will be proportional to the amount of charge stored in the fork. This place
In this case, if the floating electrodes 17 and 18 are provided, the freedom of setting the intersection
Since the degree is large, versatility is enhanced. The aforementioned electrode fingers 11 and 13 are connected to the bus electrode 15 and the electrode fingers 12 and 1 respectively.
4 is connected to the bus electrode 16 respectively, and the floating electrodes 17 and 18 are connected to each other. Electrode finger 11
And cross width W ₁ between the floating electrode 17, the sum of the overlap width W ₂ between the electrode fingers 12 and the floating electrode 17 (W ₁ + W _2), and an electrode finger 13 and the overlap width W ₃ of the floating electrode 18 The sum (W ₃ + W ₄ ) of the intersection width W ₄ between the electrode finger 14 and the floating electrode 18 is
They are the same and are constant regardless of location.

With such a configuration, the cross width W
Strength of ₁ and W ₂ and overlap width W ₃ and W ₄ surface acoustic wave excited from is proportional to _{(W 1 -W 3) = (} W 4 -W 2).

For this reason, according to the above embodiment, the sum of the crossing widths between the adjacent floating electrodes 17 and 18 on the bus electrode 15 and 16 side is constant regardless of the location (W ₁ + W ₂ ) = ( W
₃ + W ₄ ), the excitation intensity of the surface acoustic wave is set such that the difference between the cross widths of the bus electrodes 15 and 16 is set equal to (W ₁ −W ₃ ) = (W ₄ −W ₂ ). Since the ratio is set to be proportional, there is an advantage that deterioration due to a diffraction effect, which is a drawback of the conventional apodized electrode, is reduced, and design limitation due to a quantization error unlike a conventional thinned electrode is eliminated.

[0011]

According to the present invention as described in the foregoing, in proportion to the difference between the cross width between the floating electrode excitation intensity constant at and SAW cross width regardless of the location is <br/> adjacent as to
As a result , there is less deterioration due to the diffraction effect, which is a drawback of the conventional apodized electrode, and there is no design limitation due to quantization errors unlike the conventional thinned electrode. Electrodes can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view of a weighting electrode showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the energy distribution of FIG.

FIG. 3 is a plan view showing a conventional apodized electrode.

FIG. 4 is an explanatory diagram showing the energy distribution of FIG.

FIG. 5 is a plan view showing a thinning electrode in another conventional example.

FIG. 6 is an explanatory diagram showing the energy distribution of FIG.

[Explanation of symbols]

 11, 12, 13, 14 Electrode finger 15, 16 Bus electrode 17, 18 Floating electrode 19 Surface acoustic wave energy distribution

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03H 9/145 H03H 9/64

Claims (1)

(57) [Claims] 1. A piezoelectric device formed on a piezoelectric substrate and disposed opposite to the piezoelectric substrate.
In parallel and at the same distance from the two bus electrodes
Plural cross finger electrodes protruding toward the other side on the line
And the tip of each interdigital electrode is aligned on the same line.
In a weighting electrode for a weighted surface acoustic wave filter, which is set to be stopped at a predetermined interval, a distance between adjacent ones of the intersecting finger electrodes formed in parallel with each other.
A pair of floating electrodes having one end connected to each other ,
The distance between the floating electrode and each of the cross finger electrodes is set to
The width of the intersection between each of the interdigital electrodes and the floating electrode is set to be the same,
A weighting electrode for a surface acoustic wave filter, wherein the weighting electrode is constant irrespective of the location of a cross finger electrode.