JPH05102788A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To attain miniaturization and improvement of performance of the surface acoustic wave filter. CONSTITUTION:A multi-strip coupler 13 is arranged between a excitation interdigital electrode 11 and a reception interdigital electrode 12 and the aperture length of the multi-strip coupler 13 is selected to the width of a surface acoustic wave excited from the electrode. Thus, high performance and miniaturization of the SAW filter are simultaneously realized in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter, and more particularly to a surface acoustic wave bandpass filter using a multistrip coupler.

[0002]

2. Description of the Related Art In a conventional surface acoustic wave filter using a multi-strip coupler, as shown in FIG. 2, weighted input and output interdigital electrodes 11, 12 are arranged so as not to face each other. , And a multistrip coupler 21 between them. This operation will be described. The surface acoustic waves excited by the input interdigital electrode 11 are coupled by the multi-strip coupler 21, and the output interdigital electrode 1 is coupled.
It is transferred to the propagation path where 2 is arranged and received.

As another conventional surface acoustic wave filter, as shown in FIG. 3, a filter in which a normal type interdigitated electrode 31 and an apodized weighted interdigitated electrode 12 are opposed to each other is also known. There is. Since one of the interdigitated electrodes is a normal type, it is possible to use a structure in which the electrodes are opposed to each other without using a multistrip coupler.

[0004]

A conventional filter of this type uses apodized electrodes for input and output for weighting, and in order to realize the product of the transfer functions of the two,
Although the propagation paths of one electrode are separated and the two propagation paths are connected by a multistrip coupler, at least the length in the cross width direction is input in order to separate the propagation path of the surface acoustic wave propagating through the input / output electrodes. It is necessary to be equal to or more than the sum of the opening lengths of the interdigitating electrodes for power supply and output. Therefore, there is a problem that the chip size of the filter needs an area approximately twice as large. In particular, at relatively low frequencies of 10 MHz to 100 MHz, the feasibility depends on the chip shape, so improvement has been desired.

When an apodized electrode is used for one of the input / output electrodes, a multistrip coupler is not required, but most of the transfer function of the filter needs to be expressed by the apodized electrode on one side. However, there was a problem that it was difficult to improve performance.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore an object of the present invention is to provide a novel surface acoustic wave filter capable of solving the above problems inherent in the conventional art. To do.

[0007]

In order to achieve the above object, in a surface acoustic wave filter according to the present invention, an apodized weighted excitation cross-finger electrode and an apodized weighted reception cross-finger electrode face each other. And a multistrip coupler composed of an electrically open metal strip array is arranged between these electrodes, and the opening length of the multistrip coupler is the same as that of the interdigitated electrode for input and output. It is characterized in that it is arranged so as to include the opening length.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a surface acoustic wave filter according to the present invention.

Referring to FIG. 1, cross-finger electrodes 11 and 12 weighted by the apodized method are arranged to face each other on a piezoelectric substrate, and a multistrip coupler 1 is placed between them.
Place 3. The multi-strip coupler 13 is composed of an electrically open metal strip array, and its opening length is arranged so as to include the opening lengths of the input and output interdigitated electrodes 11 and 12, that is, excited by the electrodes. It is formed to be wider than the width of the surface acoustic wave.

When the number of multistrip couplers 13 is optimized, energy has a property of completely transferring from one propagation path to the other propagation path. In the present invention, however, the propagation paths in which the input and output electrodes face each other are two. Considering the transition from one to the other, due to the superposition theory, the entire propagation paths are combined in the multi-strip coupler, the energy is mixed in the propagation paths, and the propagation wave front becomes uniform.

[0012]

Therefore, according to the present invention, even if the input and output apodized type interdigital electrodes are opposed to each other, not only the product of the transfer functions can be realized by the multistrip coupler therebetween, but Since the configuration in which the propagation paths are displaced can be changed to the opposing type configuration, effects such as a reduction in chip size and cost can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a conventional technique.

FIG. 3 is a configuration diagram showing another example of the conventional technique.

[Explanation of symbols]

 Reference numeral 11 ... Input side apodized weighting type interdigitated electrode 12 ... Output side apodized weighted type interdigitated electrode 13, 21 ... Multi-strip coupler 31 ... Input side regular type interdigitated electrode

Claims (1)

[Claims] 1. A surface acoustic wave filter comprising a plurality of interdigitated electrodes on a piezoelectric substrate, wherein an apodized weighted excitation interdigital electrode and an apodized weighted reception interdigital electrode face each other. A metal strip array that is electrically open to each other is arranged between the excitation cross-finger electrode and the reception cross-finger electrode, and the opening length of the strip array corresponds to the opening length of the cross-finger electrode. A surface acoustic wave filter characterized by containing.