JPS5829627Y2 - surface acoustic wave device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a surface acoustic wave device, which improves the balance when a comb-shaped electrode pair is used in an electrically balanced state, and improves the characteristics obtained by the surface acoustic wave device. The purpose is to improve the

In general, surface acoustic waves are generated by using a conductor such as A1 for the elastic body portion having a piezoelectric effect, and using comb-shaped electrodes 1 and 2 formed by photolithography, for example.
It is excited by applying an alternating current signal to the comb-shaped electrode pair l including the comb-shaped electrode pair l.

The excited surface acoustic waves propagate along the surface portion of the elastic substrate 5, and after a certain delay time, reach the comb-shaped electrode pair (2) including the comb-shaped electrodes 3 and 4 formed in the same manner as the comb-shaped electrode pair (2). is converted into an electrical signal.

Note that 6 is a surface wave absorber, and 7.8 is a transformer.

Normally, it is used as a filter or delay line obtained as a characteristic of the transducer that is connected to the comb-shaped electrode pair, but as mentioned above, since the surface acoustic waves propagate between the comb-shaped electrode pair I and A certain delay time difference always exists between the input and output of a surface wave device.

The above-mentioned comb-shaped electrode pair ■ and ■ correspond to the stray capacitance C shown in Figure 2.
Since it is directly coupled by 13tc14tC23tC24, the punch-through signal will not have the undesirable delay times caused by this capacitance.

As a result, when the surface acoustic wave device is used in a television receiver or the like, for example, a front ghost signal appears on the screen.

This phenomenon increases as the signal frequency increases.

Therefore, removing the punch-through signal has a great effect on improving the characteristics of the surface acoustic wave device.

This piercing signal is caused by the stray capacitances shown in Figure 2 and the stray capacitances between each comb-shaped electrode and ground shown by C1e, C2e, C3e, and C4e, which are symmetrical depending on the layout of the board and the shape of the comb-shaped electrode. Because of this, even when the input side comb-shaped electrode pair (2) is driven in a balanced manner using a transformer or the like as shown in FIG. 1, the output side comb-shaped electrode pair (2) does not cancel out and is received as an unnecessary signal.

In addition, when it comes to circuits that actually use surface acoustic wave elements,
The elements and their transformers are attached to a printed wiring board, but it is difficult to design the wiring on this printed wiring board so that it is electrically balanced because of positional restrictions on the board.

Furthermore, even with regard to transformers for balanced driving, it is difficult to actually perform balanced driving due to stray capacitance between input and output, unbalanced windings, etc.

By combining these unbalances and canceling out the balance valve, the remaining unbalance component can be expressed as an equivalent stray capacitance between one comb-shaped electrode and the ground.

These capacitances are shown in FIG. 3 as C8 and C81.

Conventionally, as a measure to prevent signals, a conductive band 9 as shown in FIG. 4 is formed between the comb-shaped electrode pair ■ and ■.
By grounding both ends of the conductive band 9, electrical leakage is absorbed by the conductive band 9 to prevent it from affecting the receiving comb-shaped electrode pair (2).

However, since this conductive band 9 must be formed on the same wave propagation surface of the elastic surface, its thickness cannot be increased and it has resistance as a film, and the grounding effect decreases as the frequency increases, so it is difficult to implement. However, this method has the disadvantage that no effective effects can be expected, and that wiring for grounding is required, which increases the number of steps.

Furthermore, when driving the comb-shaped electrodes in a balanced manner, if the aforementioned unbalanced equivalent stray capacitances C and C8/ exist between one comb-shaped electrode and the ground, it is difficult to achieve electrical matching of the comb-shaped electrodes. There was a problem.

The present invention eliminates the above-mentioned conventional drawbacks and provides a surface acoustic wave device having good characteristics by means of easy combing.

FIGS. 5 and 6 show an embodiment of the present invention, in which transformers 7 and 8 are connected in a balanced manner to two comb-shaped electrodes 1°2 constituting one comb-shaped electrode pair. Two comb-shaped electrodes 1
. The comb-shaped electrode pair is balanced against the equivalent stray capacitances C8 and C8/, and the capacitance penetration cancels out the signal, and at the same time, the series capacitance of capacitance 10 and C8, C8/ through the ground is connected to the comb-shaped electrode. This has the effect of making it easier to achieve electrical matching.

Here, C> and C8I are expressed equivalently considering all the capacitances from each of the two comb-shaped electrodes connected to the transformer to the ground, and this is equivalent to the difference between the comb-shaped electrode pair I and It can be expressed similarly in .

Note that the capacitor 10 of the present invention is not only realized by an external capacitor, but also can be formed simultaneously with the comb-shaped electrode by photolithography on an elastic substrate.

FIG. 7 and FIG. 8 show examples of this. In FIG. 7, a ground electrode 11 is formed in the same plane as the comb-shaped electrode 1 with a gap therebetween, and a capacitance is formed between these electrodes 1 and 11. .

Note that it is also possible to fill the gap between the electrodes 1 and 11 with a dielectric.

In FIG. 8, a ground electrode 13 is formed on the surface of the comb-shaped electrode 1 via a dielectric film 12, and a capacitance is formed between these electrodes 1 and 13.

Use of these methods has the advantage that good balance can be obtained in the element itself.

Furthermore, this capacitor 10 is installed on the input side or the output side of the comb-shaped electrode pair, but in order to achieve the function of the surface acoustic wave device, sufficient effects can be expected even if it is installed on the input side and the output side at the same time. be.

9 and 10 show the actual effect of the capacitance 10. FIG.

14 in FIG. 9 shows the filter characteristics of a filter circuit using a surface acoustic wave element without using the capacitance, and 15 in FIG. 10 shows the filter characteristics of a filter circuit using a capacitance according to the present invention. ing.

It can be seen that this has a great effect on the characteristics near the trap of the filter.

As explained above, according to the present invention, the comb-shaped electrode pair can be operated in a balanced state, and the capacitive punching can eliminate unnecessary responses due to signals and improve propagation characteristics. It is also possible to easily match the comb-shaped electrode pair, which is of great industrial benefit.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the configuration of a conventional surface acoustic wave device, Fig. 2 is an equivalent circuit diagram showing the cause of capacitive penetration signals, and Fig. 3 shows unbalanced stray capacitance in a comb-shaped electrode pair. 4 is a perspective view showing a conventional surface acoustic wave device in which capacitive punching constitutes a signal removal means, and FIG. 5 is an equivalent circuit diagram.
Fig. 6 is a perspective view of the main part showing one embodiment of the surface acoustic wave device of the present invention, Figs. 7 and 8 are perspective views of the main part showing other embodiments, and Fig. 9 is a perspective view of the main part showing one embodiment of the surface acoustic wave device of the present invention. FIG. 10 is a diagram showing the characteristics of a circuit using the present invention. 1.2, 3, 4... comb-shaped electrode, 5...
Elastic substrate, 6... Surface wave absorber, 7, 8...
...Transformer, 10... Capacity, 11...
...Ground electrode, 12...Dielectric film, 13...
...Grounding electrode.

Claims (3)

[Scope of utility model registration request] (1) On one surface of the elastic body, a surface acoustic wave transmitting button and a receiving transducer for two comb-shaped electrodes are provided at intervals, and a transformer is balanced between the two comb-shaped electrodes. an elastic surface having an additional capacitance equal to the ground unbalanced equivalent stray capacitance substantially generated between one of the comb-shaped electrodes and the ground, and provided between the other of the comb-shaped electrodes and the ground; wave device. (2) A practical use characterized in that a ground electrode is formed on the same plane as one of the comb-shaped electrodes on the elastic body with a gap therebetween, and an additional capacitance is formed between this ground electrode and one of the comb-shaped electrodes. A surface acoustic wave device according to claim 1 of patent registration. (3) A request for registration of a utility model characterized in that a ground electrode is formed on one surface of a comb-shaped electrode via a dielectric film, and an additional capacitance is formed between this ground electrode and one of the comb-shaped electrodes. The surface acoustic wave device according to item 1.