JPS5826688B2 - Dansei Hiyoumenhasouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device that takes measures against induced noise.

A surface acoustic wave device is basically constructed by disposing two ink digital electrodes on a dielectric substrate.

One electrode is for input to convert an electric signal into an acoustic signal, and the other electrode is for output to convert the surface acoustic wave propagated on the substrate surface, that is, an acoustic signal, into an electric signal again.

Such a surface acoustic wave device is useful as a filter having frequency characteristics depending on the electrode pattern and the like.

By the way, in such a surface acoustic wave device, an electric signal is not completely converted into an acoustic signal by the input electrode, but a portion is radiated into space as a radio wave.

When this radio wave propagates through space and is received by the output electrode, it becomes noise.

As a method for removing this induced noise, the present inventors have already proposed that two output electrodes be provided to cancel out the noise.

That is, two output type poles are arranged so that the difference in distance from the input electrode is (N+) λ, and the signals from the two output electrodes are processed by a differential amplifier. .

Here, N is a positive integer, and λ is the wavelength of the surface acoustic wave.

In this way, surface wave signals received in opposite phases are added together.

On the other hand, since the noise signal that directly propagates in space has a fast speed, the phase difference when received by the two output electrodes can be ignored, and the signal is canceled out as an in-phase signal.

On the other hand, as is well known, ink digital electrodes have dielectric films arranged close to each other, and therefore have a considerably large capacitance, which causes a reduction in the conversion efficiency of the surface acoustic wave device.

As a means to compensate for this, it is known to connect an inductance in parallel to the electrodes.

This invention not only takes the above-mentioned induction countermeasures, but also realizes compensation for efficiency reduction due to capacitance with a minimum number of parts.
The present invention also provides a surface acoustic wave device with improved operating characteristics.

Now, by simply combining the individual techniques of countermeasures against induction and compensation for efficiency reduction due to capacitance described above, a surface acoustic wave device as shown in FIG. 1 can be constructed.

That is, 1 is a dielectric substrate, and an input ink digital electrode 2 that performs electro-acoustic conversion is disposed at the center of the surface of the substrate, and the input electrode 2 is located at a distance of tl and t2, respectively. A pair of output ink digital electrodes 30, 3□ for performing acoustic-to-electrical conversion is provided.

Here, the difference between 21, and / is 1. ff1
−4−(N1 +))λ.

Then, the signals obtained at the output electrodes 30, 3□ are guided to the respective input terminals of the differential amplifier 4.

Inductance elements 5□, 5□ are connected in parallel to the pair of output electrodes 34, 3□ to cancel the influence of capacitance, respectively.
is connected.

In this case, when the output electrodes 30 and 32 are directly connected to each input terminal of the differential amplifier 4, each input terminal is connected to an inductance element 5□,
It will be DC grounded through 5□.

Therefore, in order to prevent this, a capacitor 6 is connected to each input terminal of the differential amplifier 4.

6□ must be entered.

In this way, when conventionally known individual techniques are simply combined, two inductance elements and two capacitors are required in addition to the differential amplifier in the periphery.

This invention not only achieves similar effects by reducing the number of peripheral parts, but also aims to further improve the operating characteristics, an example of which is shown in FIG.

Components corresponding to those in FIG. 1 are given the same reference numerals as in FIG. 1, and detailed description thereof will be omitted.

As is clear from the figure, in this invention, the output electrode 30
, 32 are directly connected to each input terminal of the differential amplifier 4.

In place of the inductance elements 50, 5□ which were connected in parallel to the output electrodes 31, 3□ in FIG. Inductance elements 7 are provided.

In this case, if the optimum value of the inductance elements 50 and 52 in FIG. 1 is L, the value of the inductance element 7 in FIG. 2 may be 2L.

Of course, with the above configuration, induced noise can be canceled out.

In addition, the inductance element 7 also provides output electrodes 30,
The reduction in conversion efficiency due to the capacitance of 32 can be compensated for.

Since the capacitors 6 □ and 6 □ for holding the DC potential at the input terminal of the differential amplifier 4 shown in FIG.
The same effects as before can be obtained with the minimum number of parts.

Further, although it is desirable that the DC potentials at the two input terminals of the differential amplifier be essentially equal in order to maintain balance, they are generally not equal.

However, in the present invention, since the inductance element 7 short-circuits the two input terminals of the differential amplifier 4 in a direct current manner, perfect balance is achieved and the operating characteristics are improved.

Note that this invention is not limited to the above embodiments.

For example, in the embodiment, the output electrodes are arranged on both sides so as to sandwich the input electrodes, but various modifications may be made, such as arranging a pair of output electrodes in one surface wave propagation direction from the input electrodes. be.

[Brief explanation of drawings]

Fig. 1 shows an example of a surface acoustic wave device constructed by simply combining prior art techniques to take measures against induction and compensate for efficiency reduction due to electrode capacitance, and Fig. 2 shows a surface acoustic wave device according to the present invention. FIG. 1 is a diagram showing the configuration of an example of a device. 1... Dielectric substrate, 2... Ink digital electrode for input, 3□, 32... Ink digital electrode for output,
4... Differential amplifier, 7... Inductance element.

Claims (1)

[Claims] 1. The difference in distance between the dielectric substrate, the input ink digital electrode that performs electro-acoustic conversion arranged on the surface of this substrate, and the input ink digital electrode is (N+-!-
) λ (where N is a positive integer and λ is the wavelength of the surface acoustic wave); It is characterized by comprising a differential amplifier arranged to input two signals obtained from the electrodes into respective input terminals, and an inductance element connected between the two input terminals of the differential amplifier. Surface acoustic wave device.