JPS61274415A - Unidirectional idt excitation type filter - Google Patents

Abstract

PURPOSE:To simplify manufacturing process, and also to reduce insertion loss by dividing a bus bar for integration-connecting an IDT, providing a conductor for grounding a meander line through a divided gap, and also connecting the divided bus bar so as to step over said conductor. CONSTITUTION:Bus bars 7 and 8 for integration-connecting IDT electrode fingers 2, 2,... and 3, 3,... respectively are divided at a suitable part, ground use conductor patterns 9 and 10 are drawn out to the outside periphery of a piezoelectric substrate 1 on the way of a meander line 5 through its divided gap, and the meander line is grounded through conductor patterns 11 and 12 for integration- connecting them. Also, the divided bus bars 7 and 8 are connected by jumper wires 13 and 14, respectively. In such a way, the meander line 5 can be grounded in each part on its production, therefore the ohmic loss can be decreased, and also the width of the bus bar 7 and 8 can be designed freely, therefore, the jumper wire can be attached easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an IDT excitation type filter such as a surface acoustic wave (SAW) filter, and particularly to a group type unidirectional IDT excitation type filter.

(Prior art) SAW filters have become widely used compared to LC filters, etc. because they are smaller, lighter, less sensitive to vibration and shock without adjustment, and are easier to mass produce. However, they have a relatively large insertion loss. There was a flaw in that. Especially common SAW
Various unidirectional transducers such as three-phase type and reflector type have been proposed to reduce the bidirectional loss in the filter by 6 dBi, but among these, a group type unidirectional transducer using a 90 degree phase shifter is proposed. The filter used has been praised for its relatively low loss.

However, even in a filter using a group type unidirectional transducer as described above, there is a problem that the meander line, which is a grounding line, has a considerable ohmic loss, so the insertion loss is large, and the filter characteristics are not satisfactory.

In order to solve this problem, the inventor of the present application has already developed the above-mentioned IDT.
[It has been proposed to reduce the ohmic loss of the meander line by insulating a part of the surface of the bus bar that connects the pole fingers and straddling this and grounding the meander line from the middle. However, it has become clear that there is a problem in that it requires a considerable amount of man-hours to actually implement this method.

(Object of the Invention) The present invention has been made in order to eliminate the problems of the conventional IDT excitation type filter using a unidirectional transducer as described above without causing significant complication of the manufacturing process. An object of the present invention is to provide a unidirectional IDT excitation filter with significantly reduced insertion loss.

(Summary of the invention) In order to achieve the above-mentioned object, in the present invention, IDT=i
The buspar to be integrated and connected is divided at a suitable place, and a conductor pattern is provided to ground the meander line through the division gap, and the divided buspar is connected by a jumper wire across the conductor pattern. be.

(Embodiments of the Invention) The present invention will be described in detail below using nine embodiments shown in the drawings.

Before explaining the embodiments, an 8AW filter including a unidirectional transducer will be briefly explained in order to make the present invention easier to understand.

Figure @2 is a conceptual diagram showing the general configuration of a SAW filter using a conventional group type unidirectional transducer, in which zero-phase IDTs 2, 2 .・・・・・・
and the 90-degree phase IDT3.3.・・・・・・
In general, a phase shifter 4 provides a phase difference between the IDTs 2, 2. ...and 3.3. ...
A meander line 5t is arranged between the electrode fingers of . . . and grounded to form a unidirectional input transducer. The meander line 5 has a total line width of 1/2λ (λ is the excited SA
(wavelength of W), and in the part where the phase changes from 90 degrees to zero phase, λ
By doing so, the SAW is configured to propagate only in one direction.

Generally, a transducer similar to the input quadrature transducer is placed on the output side with a shield electrode 6 interposed therebetween.

As is clear from the above explanation, both of the meander lines 15 and 5' are wired over a considerable distance between the input and output quadrangle juicers, and upper grounding is performed only at the ends of each of the input and output quadrangle juicers. As mentioned above, the ohmic loss becomes considerably large, which becomes the insertion loss of the filter and deteriorates the filter characteristics. Moreover, it goes without saying that this loss becomes more significant as the frequency of the excited SAW becomes higher.

In order to solve this problem, the present invention adopts the following configuration.

That is, as shown in FIG. 1, Tt electrode fingers, 2.・・・
...and 3,3. . . . Buspars 7 and 8, which are integrally connected to Conductor patterns 11 and 12 drawn out to the outer periphery and integrally connected
The meander line is grounded through the ground.

Further, the divided buspars 7 and 8 are connected to the Japan/Pa line 1, respectively.
3 and 14 are connected.

By doing so, the meander line 5 can be grounded at various points on its extension line, so the total ohmic loss can be greatly reduced, and the widths of the buspars 7 and 8 can be designed relatively freely, making it easy to use with wire bonders. It will be understood that it is possible to install jumpers throughout the village without any particular difficulty.

Although only the most common group type unidirectional SAW filter has been described above, the present invention is not intended to be applied only to this filter. It will be obvious that the transducer may be applied to a type of filter in which the transducer is bidirectional and has unidirectional output transducers on either side.

Furthermore, the present invention need not be limited to filters that use SAW'i (it is equally applicable to filters that utilize any wave that can be excited by an IDT).

Finally, as a result of applying the present invention to a filter with 10 pairs of unidirectional input/output IDTs, a center frequency of 600 MHz, and a bandwidth of 40 MHz, it was found that a conventional filter that was grounded only at both ends of the meander line had an insertion loss of 8 dB. It was confirmed that the insertion loss was reduced to 3 dB by simply grounding the meander line at two additional locations, which was a significant effect.

(Effects of the Invention) Since the present invention is configured as described above, the group type unidirectional surface acoustic wave filter, which has conventionally been considered optimal for realizing a low-loss IDT excitation type filter, particularly a surface acoustic wave filter, can be used. The disadvantages of this method can be removed by adding only a very small number of steps, and it exhibits a remarkable effect in realizing a filter with even lower loss.

[Brief explanation of drawings]

FIG. 1 is a partial plan view showing an embodiment of a unidirectional IDT excitation filter according to the present invention, and FIG. 2 is a general configuration diagram of a conventional unidirectional SAW filter to which the present invention is applied. . 1...Piezoelectric substrate, 2, 3...River...IDT electrode 5...Meander line. 7.8... Bus bar, 9.10.
...... Conductor butter: y, 13.14.
・・・・・・Jumper wire.

Claims (1)

[Claims] An input/output interdigital transducer (IDT) electrode is provided on the surface of the piezoelectric substrate, one of the pairs of electrode fingers of the IDT electrode is set to zero phase, the other is set to 90 degree phase, and one of the input/output IDT is In a filter in which a meander line is arranged between both IDT electrode fingers and grounded, the busper that integrally connects the IDT electrode fingers is divided at a proper place, and the meander line is grounded through the dividing gap. 1. A unidirectional IDT excitation type filter, characterized in that a conductor pattern is provided, and the divided buspars are connected by jumper wires across the conductor pattern.