JPH02224388A - Surface acoustic wave filter mounting circuit board - Google Patents

Abstract

PURPOSE:To cancel induction between wiring patterns enough so as to obtain a filter of an excellent filter property that signals of frequencies outside the pass band is sufficiently attenuated by a method wherein a floating electrode is provided between a pair of output wiring patterns and an earth pattern, where the electrodes is not connected to these patterns. CONSTITUTION:A space is provided between a pair of output wiring patterns 31c and 31d and an earth pattern 31b, and a floating electrode 32 is provided to the above space so as not to be connected with any pattern. By this setup, a capacitance is induced between the earth pattern 31b and the floating electrode 32, the floating electrode 32 and the output wiring pattern 31c, and the floating electrode 32 and the output wiring pattern 31d respectively, so that an output signal flows to the ground through the intermediary of the capacitance. By this setup, the induction between wiring patterns can be canceled enough to obtain an excellent filter property that signals of frequencies outside the pass band is sufficiently attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave filter mounting circuit board on which a surface acoustic wave filter is mounted.

[Prior Art] FIG. 7 is a diagram schematically showing an example of a surface acoustic wave filter.

That is, this surface acoustic wave filter 2 has an input electrode 4 and an output electrode 5 of an ink digital type formed on the surface of a piezoelectric substrate 3 separated from each other, housed in a metal stem 6, for example, and connected to the input electrode 4. The connected signal input terminal 7a and the ground terminal 7b, as well as a pair of signal output terminals 7C and 7d connected to the output electrode 5, are respectively drawn out to the back side. Each terminal is, for example, a pin terminal.

Such a surface acoustic wave filter 2 is, for example, an eighth filter.
It is mounted on a circuit board on which a differential input amplifier 10 and the like as shown in the figure are formed.

FIG. 9 shows an example of a conventional conventional circuit board.

That is, this circuit board (printed board) 20 has an input wiring pattern 21a connected to the signal input terminal 7a of the surface acoustic wave filter 2, a ground pattern 21b connected to the ground terminal 7b, and each signal output terminal 7c and A pair of output wiring patterns 21c and 21d connected to 7d
It has

The earth pattern 21b is similar to other patterns 21a121c
and 21d, and is formed on almost the entire surface with a gap between them. The output wiring patterns 21c and 21d are connected to the input terminals 11a and llb of the differential input amplifier 10 via a capacitor (not shown) or the like.

However, when the surface acoustic wave filter 2 is mounted on such a circuit board 20, since the input wiring pattern 21a and the output wiring patterns 21c and 21d are relatively symmetrical, it is easily induced, and therefore the filter characteristics are not good. Specifically, there is a problem in that the amount of attenuation outside the passband (the so-called bottom) in the amplitude characteristics is small.

Therefore, as a way to improve these points,
3-121308 proposes a circuit board as shown in FIG.

That is, this circuit board (printed board) 20a is obtained by bending the input wiring pattern 21a as described above laterally, and extending an extension part 22 from the bent part toward the midpoint between the output wiring patterns 21c and 21d. According to the above-mentioned publication, the effect of canceling the induction between wiring patterns can be obtained.

[Problem to be solved by the invention]

However, as described in the above publication, the gains of the two inputs of the semiconductor that constitute the differential input amplifier 10 may differ, and furthermore, due to variations between manufacturing lofts, the two input gains of the semiconductor may differ. Since differences also vary between people, there is a problem in that even if a circuit board 20a as shown in FIG. 10 is used, the amount of attenuation outside the passband in the amplitude characteristic cannot be increased very much.

Therefore, the present invention provides a circuit board for mounting a surface acoustic wave filter that can sufficiently cancel the induction between wiring patterns and realize good filter characteristics with a large amount of attenuation outside the passband in the amplitude characteristics. The main purpose is to

[Means to solve the problem]

In order to achieve the above object, the circuit board of the present invention is characterized in that a floating electrode, which is not connected to either of these patterns, is provided between the pair of output wiring patterns and the ground pattern as described above. shall be.

[Effect]

According to the above configuration, capacitance is generated at three locations between the ground pattern and the floating electrode, between the floating electrode and one output wiring pattern, and between the floating electrode and the other output wiring pattern, and the capacitance is generated at three locations. The output signal will now flow to ground.

Depending on the amount of signal flowing to this ground, the balance of the output signals flowing through the two output wiring patterns can be set to a level ratio that matches the differential input amplifier, thereby sufficiently canceling the induction between the wiring patterns. You will be able to do this.

〔Example〕

FIG. 1 is a plan view partially showing a circuit board according to an embodiment of the present invention. In the following, differences from the conventional example will be mainly explained.

For example, as shown in FIG. 5, the circuit board 30 of this embodiment mounts a surface acoustic wave filter 2a in which a signal input terminal 7a, a ground terminal 7b, and a pair of signal output terminals 7c and 7d are drawn out in a straight line. This is an example of a case.

That is, this circuit board 30 is made of, for example, a printed circuit board, and includes an input wiring pattern 31a connected to the signal input terminal 7a of the surface acoustic wave filter 2a, a ground pattern 31b connected to the ground terminal 7b, and each signal output terminal. 7
The output wiring patterns 31c and 31d have a pair of end portions connected to the output wiring patterns 31c and 7d that are bent laterally, respectively.

The ground pattern 31b is similar to other patterns 31a131c
and 31d, and in the example of parentheses, the output wiring patterns 31c and 31d and the signal output terminal 7c.
It is formed almost over the entire surface, excluding the vicinity of the connecting portion with 7d and 7d. Output wiring patterns 31c and 31d
are connected, for example, to the input terminals 11a and Ilb of the differential input amplifier 10 as described above via a capacitor (not shown).

Then, gaps are provided between the output wiring patterns 31c and 31d and the earth pattern 31b so that they are located in the excluded portion 33 excluding the earth pattern 31b as described above, that is, between the output wiring patterns 31c and 31d and the earth pattern 31b. A floating electrode 32 is provided which is not connected to any of these patterns.

In this way, the earth pattern 31b and the floating electrode 3
2, capacitance is generated at three locations between the floating electrode 32 and one output wiring pattern 31c, and between the floating electrode 32 and the other output wiring pattern 31d, and the output signal is grounded via this capacitance. It becomes flowing.

Depending on the amount of signal flowing to the ground, it is possible to set the balance of the output signals flowing through the two output wiring patterns 31c and 31d to a level ratio that matches the differential input amplifier, thereby ensuring sufficient induction between the wiring patterns. You will be able to cancel. the result,
It becomes possible to realize good filter characteristics in which the amplitude characteristics have a large amount of attenuation outside the passband.

FIG. 6 shows measurement results of amplitude characteristics when using the circuit board 30 as shown in FIG. 1, together with a comparative example.

A shown by a solid line is the case when the circuit board 30 described above is used, and B shown by a broken line is the case when a normal circuit board without the floating electrode 32 or excluded portion 33 as described above is used. As can be seen from this figure, when the above circuit board 30 is used, the amount of attenuation in the portion 40 outside the passband is 5 to 1.
0dB is also larger.

In addition, the floating electrode 32 and the ground pattern 31b as described above
A dielectric film may be provided at least between the two output wiring patterns 31c and 31d so as to span therebetween. An example of doing so is shown in FIG. 34 is a dielectric film.

In this way, when the manufacturing loft of semiconductors changes, for example, and the balance between the inputs of a differential input amplifier changes, the copper foil pattern on the circuit board 30 remains the same, and the dielectric film 34 separates the individual electrostatic charges. Since the capacitance can be adjusted, it becomes possible to easily realize a circuit board 30 that is optimal for the loft of the semiconductor.

Further, the number of floating electrodes 32 as described above does not necessarily have to be one, and a plurality of floating electrodes 32 may be provided close to each other as necessary. FIG. 3 shows an example in which two floating electrodes 32 are provided.

Further, it is possible to provide a plurality of floating electrodes 32 and to provide a dielectric film 3.
4 may be used in combination.

Further, means such as those in each of the above embodiments include the signal input terminal 7a.
, the ground terminal 7b and the signal output terminal 7C17d are not drawn out in a straight line, and the surface acoustic wave filter 2 shown in FIG. 7 is of course applicable. An example of such a case is shown in FIG. 4, which corresponds to the example of FIG.

〔Effect of the invention〕

As described above, according to the present invention, by providing the floating electrode as described above, induction between wiring patterns can be sufficiently canceled. As a result, it becomes possible to realize good filter characteristics in which the amplitude characteristics have a large amount of attenuation outside the passband.

[Brief explanation of the drawing]

1 to 4 are plan views partially showing circuit boards according to embodiments of the present invention. Figure 5 shows
FIG. 2 is a diagram schematically showing an example of a surface acoustic wave filter. 6th
The figure is a diagram showing an example of measurement results of the amplitude characteristics of a surface acoustic wave filter using the circuit board of FIG. 1, together with a comparative example. FIG. 7 is a diagram schematically showing an example of a surface acoustic wave filter. FIG. 8 is a circuit diagram showing an example of a differential input amplifier. 9 and 10 are plan views partially showing examples of conventional circuit boards, respectively. 2.2a...Surface acoustic wave filter, 7a...Signal input terminal, 7b...Ground terminal, 7c, 7d. - Signal output terminal, 30...Circuit board according to the embodiment, 3
1a... Input wiring pattern, 31b1.・Earth pattern, 31c, 31d... Output wiring pattern, 32・
...Floating electrode, 34...Dielectric film. Figure 1b Figure 6 Frequency (MHz) Figure and 1d 1C Figure 1d 2+c

Claims (1)

[Claims] (1) A board on which a surface acoustic wave filter having at least a signal input terminal, a ground terminal, and a pair of signal output terminals is mounted, wherein an input wiring pattern connected to the signal input terminal and a pair of signal output terminals are connected to the ground terminal. and a pair of output wiring patterns connected to each of the signal output terminals, the pair of output wiring patterns and the earth pattern are connected to any of these patterns. A circuit board for mounting a surface acoustic wave filter, characterized in that a floating electrode is provided.