JPS583603B2 - surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device that has a simple structure, provides good characteristics, and is easy to design.

BACKGROUND ART Recently, surface acoustic wave devices such as filters for telecommunications have been widely used, which utilize the characteristics of so-called surface acoustic waves, which are waves that propagate along the flat surface of an elastic body.

Figure 1 shows an example of this type of surface acoustic wave filter. In the figure, 1 is a piezoelectric substrate, and 2 and 3 are interdigital unit electrode elements with positive and negative electrodes, respectively, provided on the plate surface of this substrate 1. This is a converter.

The transducers 2, 3 are, for example, short on both sides;
A plurality of long unit electrode elements are formed in the center, and these are stacked parallel and alternately as shown in the figure, and the beam width of the surface acoustic wave 4 excited by each unit electrode element 2 on one side is changed to give a weight to the so-called excitation beam width. I try to have it.

Therefore, if the converter 2 side is the input excitation side converter and the converter 3 side is the output receiving side converter, then the input excitation side converter 2
When the surface acoustic wave 4 excited by the wave propagates on the substrate 1 and is received by the output receiving converter 3, an impulse response proportional to the weight of the excitation beam width is obtained, and the input and output responses are
, 3, the frequency characteristics are determined by the shape of the electrodes.

However, in such converters 2 and 3, the input
Since each output has an insertion loss of 3 dB, in recent years, converters using grouped unidirectional electrodes have been considered in order to reduce insertion loss and improve ripple characteristics.

FIG. 2 is a diagram showing an example of the electrode pattern of this type of group type transducer.
positive electrode unit electrode elements 12a1, 12b, each consisting of two electrode elements 12a1, 12b;
1, 12a2, and 12b2 are provided in parallel.

However, λ is the wavelength of the surface acoustic wave on the plate surface of the piezoelectric substrate 11.

And these positive electrode unit electrode elements 12a1, 12b1, 12
Negative electrode unit electrode elements 13a1, 13b1, 13a2, 13 with line width λ/4 parallel to a2, 12b2 and alternately for each set
b2 is provided.

And the positive/negative unit electrode elements 12a1, 12b1.
..., 13a1, 13b1..., ground electrodes 14a, 14b with line widths λ/2 and λ are alternately arranged in parallel between them, and Surface acoustic waves propagating on the surface of the substrate 11 are given directionality.

And a line width λ is parallel to the ground electrodes 14a and 14b.
/4 ground electrode 4c of each set of positive and negative electrode unit electrode element 1
2a1, 12b1..., 13a1, 13b...
・Place it in between.

Note that each of the above positive and negative unit electrodes 12a1..., 13a
1... The earth electrodes 14a... are all arranged so that there is a gap of λ/4 between the electrodes.

In addition, in the filter, two sets of such group type unidirectional electrodes are provided on the piezoelectric substrate 11, one is used on the input side to convert an electric signal into a surface acoustic wave, and the other is used on the output side to convert an electric signal into a surface acoustic wave. It converts waves into electrical signals.

In addition, positive/negative electrode unit electrode elements 12a1...13
A1... A signal is applied in parallel from a signal source 16 via a phase shifter 15 between the earth electrodes 14a, 14b, 14c.
is connected to ground.

However, a filter using such group-type unidirectional electrodes actually has a considerable insertion loss, and this cause becomes noticeable mainly when weighting is applied to one side of the electrode.

Further, due to the electrode structure, such group type unidirectional electrodes have the problem of generating spurious signals at a frequency fs distant from the center frequency f0, deteriorating the characteristics of the converter.

Figures 3, 4, and 5, a and b, respectively show the schematic configuration of group type unidirectional electrodes in which the number N of positive and negative electrode unit electrode elements in each set is N=1, N=2, and N=3. FIG. 3 is a diagram showing frequency characteristics.

That is, the spurious frequency f8 of such a unidirectional electrode can be changed by increasing or decreasing the number N of unit electrode elements in the group.

Therefore, in the past, converters with different numbers of unit electrode elements in each group were used in combination on the input and output sides, and the electrodes on one side were weighted to maximize the guaranteed attenuation and suppress spurious signals. .

However, in this type of device, the combination of the number of unit electrode elements is limited, so the degree of freedom in design is reduced.
Moreover, weighting one electrode increases the insertion loss, and when group-type unidirectional electrodes are used on the excitation side and the reception side, a phase shifter must be provided separately for each side.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a surface acoustic wave device that has small spurious waves, can have a large guaranteed attenuation amount, has low insertion loss, and is easy to design. be.

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG. 6 and FIG. γ.

FIG. 6 is a plan view of the above embodiment, and 101 in the figure is a piezoelectric substrate;
Reference numeral 102 denotes a regular bidirectional electrode made of a combination of interdigital unit electrode elements arranged substantially in the center of the plate surface of the piezoelectric substrate 101.

This regular type bidirectional electrode 102 is, for example, shown in FIG.
As shown in the figure, positive and negative electrode unit electrode elements 102a and 102b
Generally, spurious signals do not occur as shown in the frequency characteristics shown in FIG. 7b.

In FIG. 6, 103 and 104 are unidirectional electrodes arranged on both sides of the bidirectional electrode 1020, each of which is a combination of interdigital unit electrode elements.

Note that these unidirectional electrodes 103 and 104 are each made up of one unit electrode element as one electrode 103.
N = 1, and N = 2, consisting of two unit electrode elements in each set, are used as the other electrode 104, and are connected in parallel via a phase shifter 105.

With such a configuration, even if the frequency characteristics of the unidirectional electrodes 103 and 104 include spurious, the frequency characteristics of the regular bidirectional electrode 102 are sufficiently far from the center frequency f0, so side lobes are extremely low. The overall frequency characteristic combining the excitation side and the reception side is the product of each, and the above spurious is further reduced.

Therefore, by applying a signal to one of the bidirectional electrode 102 and the unidirectional electrodes 103, 104 and extracting the signal from the other, there is no spurious, and the normal bidirectional electrode 102 and the unidirectional electrode 103, 104 can be used. By using these in combination, insertion loss is small and a large guaranteed attenuation amount can be obtained.

Furthermore, the normal type bidirectional electrode 102 can be easily weighted without impairing its characteristics, and has a high degree of freedom in design and is easy to use, and each electrode 102, 103, and 104 can be weighted arbitrarily. can.

Further, since the unidirectional electrodes 103 and 104 are connected in parallel via the phase shifter 105, only one phase shifter 105 is required, and the configuration is simple.

As described in detail above, the present invention has a pair of unidirectional electrodes connected in parallel via a phase shifter on both sides of a bidirectional electrode, so spurious noise is small and a large guaranteed attenuation amount can be achieved. Accordingly, it is possible to provide a surface acoustic wave device that has low insertion loss and is easy to design.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a surface acoustic wave filter, Fig. 2 is a diagram showing an example of an electrode pattern of a group type transducer, and Fig. 3 is a diagram showing an example of an electrode pattern of a group type transducer.
, 4th and 5th figures a and b are diagrams showing the schematic structure and frequency characteristics of the unidirectional electrodes of unit electrode elements of N=1, N=2, and N=3, and FIG. Plan view showing one embodiment, No. 7
Figures a and b are diagrams showing a plan view and frequency characteristics of the normal type electrode of the above embodiment. 101... Piezoelectric substrate, 102... Bidirectional electrode, 103, 104... Unidirectional electrode,
105... Phase shifter.

Claims (1)

[Claims] 1. A piezoelectric substrate, a bidirectional electrode that is a combination of interdigital unit electrode elements arranged on the plate surface of the piezoelectric substrate, and interdigital electrodes that are arranged on the plate surface of the piezoelectric substrate and on both sides of the bidirectional electrode. A surface acoustic wave device comprising a pair of unidirectional electrodes made up of a combination of unit electrode elements, and a phase shifter inserted between the positive and negative unit electrode elements of each of the unidirectional electrodes connected in parallel.