JPS6156895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to suppressing triple transit echoes (hereinafter abbreviated as TTE) in surface acoustic wave devices.

In surface acoustic wave devices, the speed of surface acoustic waves is approximately the speed of light.
Because it is small at 1/10 ⁵ and the electrode itself has frequency selection characteristics, it can be used as a small and stable delay line, band
Research is being carried out to apply it to pass filters, etc., but one of the electrical characteristics that poses the greatest obstacle is TTE. This is an interference wave that appears with a delay time three times the delay time of the desired wave, and appears as ripples in the amplitude and phase characteristics of the passband.
In TTE, MEL (Mass
Electrical Loading) and reflections from electrical loads
There are two types of RW (Regenerated Wave), and the former can be easily removed using so-called split electrodes, but the latter cannot be reduced at all, and can be reduced by increasing insertion loss through electrical mismatch. There are many things.

However, split electrodes are disadvantageous in terms of microfabrication because their line width is half that of a normal solid electrode, and if electrical mismatch is made to suppress RW, a large insertion of 5 to 10 dB is usually required. It has the disadvantage of accompanied by loss deterioration.

Figure 1 shows an example of the basic configuration of a conventional surface acoustic wave device. 1 is a piezoelectric substrate, 2 is a transmitting electrode, and 3 is a receiving electrode. Normally, the electrodes are interlocked with each other in a comb shape as shown in the figure. It is called an IDT (Interdigital Transducer), or interdigital electrode or interdigital electrode. 4 is a surface acoustic wave, and 5 is a load resistance. In operation, an alternating current electrical signal applied to the transmitting electrode 2 is first converted into a surface acoustic wave 4, propagates on the piezoelectric substrate 1, reaches the receiving electrode 3, where it is again converted into an electrical signal and transmitted to the load 5. reach

In order to eliminate these drawbacks, the present invention aims to suppress TTE without narrowing the line width of electrode fingers or significantly deteriorating insertion loss, and will be described in detail below. do.

TTE is a major hindrance to putting surface acoustic wave devices into practical use, so it must be sufficiently suppressed.

FIG. 2 shows an embodiment of the present invention, and numerals 1 to 4 are the same parts as in FIG. 1. 6 is a grid-shaped shield electrode, with 6' as the upper part and 6'' as the lower part.A, B, C,
D, E, F and A', B', C', D', E', F' each represent a part of the surface acoustic wave. The shield electrode 6, which is usually placed between the transmitting and receiving electrodes 2 and 3, is used to suppress so-called direct waves that are directly electrically coupled between the transmitting and receiving electrodes 2 and 3. Effective for improvement.
Its shape is usually a simple rod (rectangle).

However, in the present invention, the rectangle is transformed and the second
As shown in figure 6, the upper part 6' and lower part 6'' are λ ₀ /4 (λ:
By installing a grid-shaped shield electrode constricted by the transmission wavelength) between the input and output electrodes, TTE
has been sufficiently suppressed. In Fig. 2, if 2 is the transmitting electrode and 3 is the receiving electrode, then A~
F and A′ to F′ are the reflected waves reflected by the receiving electrode 3.
This is the reflection of the reflected wave RW reflected by the MEL and the load 5 in FIG. Here, E, E' are part of the reflection leakage of F, F', D, D' are E, E', C, C' are D, D', B, B' are C, C', A, A' is B,
A part of the reflection leakage of B′ is reflected. A and A' have a phase difference of 180° and cancel each other out.If the shield electrode 6 is plate-shaped, there will be only two reflections, but if it is grid-shaped, it will be reflected twice as many times as the number of grids. Since it can be made to occur, it can be sufficiently suppressed.
B and B' to F and F' all cancel each other out and disappear. It is the vector sum of MEL and RW. Since TTE repeats the above process three times, it is attenuated by a considerable amount.

On the other hand, a part of the desired wave emitted from the transmitting electrode 2 is similarly reflected by the shield electrode 6, but the components cancel each other out based on the same principle as above, and the desired wave passes through the shield electrode 6. Since the number of times is one, the amount of attenuation is smaller than that of TTE.

In addition, x in Fig. 2 is the pitch of the transmitting and receiving electrodes (=
If it is designed to be larger than λ ₀ /2), a trap phenomenon near the center frequency will not occur and the passband amplitude phase characteristics will not be disturbed. Furthermore, the shield electrode with the above structure has the advantage of being able to suppress RW, which could not be suppressed with conventional split electrodes, in the same way as MEL _. There is an advantage that the manufacturing yield is also good because there is no need to do this. On top of that,
Since there is no need to take any TTE suppression measures for the transmitting and receiving electrodes, this is extremely advantageous in terms of design.

As described above, in the present invention, by providing a lattice-shaped shield electrode constricted by λ ₀ /4 on the surface wave propagation path, TTE can be suppressed to a greater extent than with a plate-shaped shield electrode. Therefore, it is considered to be extremely effective for practical application of surface acoustic wave devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of a conventional surface acoustic wave device and connections between a power source and a load, and FIG. 2 is a diagram showing an embodiment of the present invention. 1... Piezoelectric substrate, 2... Transmitting electrode, 3... Receiving electrode, 4... Surface acoustic wave, 6... Shielding electrode,
A to F and A' to F'...TTE reflection components.

Claims (1)

[Claims] 1. In a surface acoustic wave device in which input and output interdigital electrodes are arranged on a piezoelectric substrate and a surface wave propagates between these input and output electrodes, a grid-like structure is provided between the input and output electrodes. A shield electrode is provided, and the phase of the reflected wave between the input and output electrodes is adjusted by providing a distance difference of λ ₀ /4 (λ ₀ : transmission wavelength) between the upper and lower parts of the shield electrode.
A surface acoustic wave device characterized by attenuating reflected waves by making the waves differ by 180°.