JPS5855692Y2 - surface wave filter - Google Patents

Description

[Detailed description of the invention] The present invention relates to a surface wave filter, and in particular to a surface wave filter that can reduce unnecessary waves as much as possible and propagate surface waves from an input electrode to an output electrode without causing a phase shift. For the purpose of providing.

As shown in FIG. 1, in the surface wave filter, a substrate 2 on which an electrode pattern 3 is formed is adhered to a predetermined position on a stem 1, and the electrode pattern 3 and a part of the stem 1 are implanted or
and is connected by a bonding wire 5.

A shell 6 is welded and attached to the stem 1 to form an envelope.

FIG. 2 shows a substrate on which the electrode pattern is formed.

That is, an input electrode 11 and an output electrode 12 having interdigitated electrodes are provided on a piezoelectric substrate 2, and a sound absorbing layer 13 is formed on each outer substrate.

The envelope of the surface wave filter constructed in this way is kept at zero potential to prevent signals from jumping in due to induction from the input electrode to the output electrode, and one of the human-powered electrodes has a substrate attached to it. An electric signal is applied to this and other input electrodes connected to the stem to generate a surface acoustic wave on the surface of the substrate, which propagates toward the output electrode. It is something.

In a surface wave filter, a capacitor is formed between the input electrode to which an electric signal is applied as described above and the stem surface of the envelope to which the board is attached, which can generate unnecessary waves. become.

When unnecessary waves are generated and propagated in this way, the frequency characteristics of the surface acoustic wave filter deteriorate.

For example, as shown in Figure 3, unnecessary waves a, b, c, d, e, and f appear outside the frequency characteristic band, and ripples appear within the band as g, so such a surface wave filter is For example, when used as a filter for a television set, it causes interference and adversely affects video and audio, which is extremely inconvenient.

The present invention has been made in consideration of this point, and provides a surface wave filter that can propagate desired surface acoustic waves from an input electrode to an output electrode while minimizing unnecessary waves.

In other words, the area of the input electrodes other than the intersection is made as small as possible to suppress the part where unnecessary waves are excited as much as possible.
In addition, a dummy electrode is provided to prevent a phase shift from occurring in the propagating surface waves.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows a part of the input electrode of the surface wave filter of the present invention.

The area A indicated by the dotted line in the figure of the input electrodes formed by interdigitating each other in this way is the intersection, and the width of the electrodes from the bus bar part 21 remains the same as the width of the intersection 23. However, the width of the lead portion 22 leading to the intersection and the lead portion 22A outside the intersection are formed to be narrow.

Furthermore, dummy electrodes 24 and 24A are provided on the substrate on both sides of the lead portion, which is created by narrowing the width of the lead portion 22.

At this time, when the width of the electrode 23 at the intersection is a and the width of the electrode 22 at the lead part is b, the widths C1 and C2 of the dummy electrodes 24 and 24A are a=l)-1-c, -1-c2 It is preferable to provide the following relationship.

In a surface wave filter with input electrodes configured in this way,
Since the area of the lead portion of the electrode is reduced, the unnecessary waves generated by excitation between the input electrode and the stem surface are reduced accordingly.

Furthermore, since the speed at which surface waves propagate is different under the electrode and on the free surface where no electrode is formed, the width of the lead becomes narrower when simultaneously generated surface acoustic waves propagate toward the output electrode. If there is a portion of the substrate where no electrode is formed, a phase difference will occur in the surface waves propagated to the output electrode.

However, in the surface wave filter of the present invention, the formation of the dummy electrode made it possible to prevent the above-mentioned problem of phase difference.

Looking at the frequency characteristics of the surface wave filter of the present invention, it can be seen that the characteristics are improved, with unnecessary waves outside the band shown in FIG. 3 becoming smaller as shown by the dotted line.

As described above, the surface wave filter of the present invention exhibits the excellent effect of lowering the level of unnecessary waves and being able to propagate surface waves from the input electrode to the output electrode without causing a phase shift of the surface waves. It has excellent properties and is industrially useful.

It goes without saying that the electrode structure is not limited to the one illustrated above, and that various modified structures can be obtained according to the gist of the present invention.

[Brief explanation of the drawing]

Figure 1 is a partially cutaway perspective view of a surface wave filter.
Fig. 2 is a plan view of a surface wave filter substrate on which an electrode pattern is formed, Fig. 3 is a frequency characteristic diagram of the surface wave filter, and Fig. 4 is a plan view showing a part of the input electrode of the surface wave filter of the present invention. It is. 1... Stem, 2... Board, 4...
...Lead, 6...Shell, 11...
・Input electrode, 12... Output electrode, A...
・Intersection part, 22...Input electrode lead part, 23
...Intersection of human electrodes, 24, 24A...
...Dummy electrode.

Claims (1)

[Scope of utility model registration request] In a surface wave filter in which an input electrode and an output electrode are formed by interleaving comb-like electrodes alternately on the surface of a piezoelectric substrate, and the two electrodes are coupled via a surface acoustic wave, the intersection of the human-powered electrodes A surface wave filter characterized in that the width of the input electrode is larger than the width of a lead part of an input electrode that supplies power to the intersection part, and a dummy electrode is provided on the side of the lead part.