JPH06350381A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To obtain desired attenuation characteristic and to minimize a transmission loss between surface acoustic wave filters by arranging 1st and 2nd surface acoustic wave filters on a piezoelectric substrate and connecting them via a common electrode pattern. CONSTITUTION:An electric signal applied to an input terminal 10 of a 1st surface acoustic wave (SAW) filter is shunted to output interdigital electrode pairs 2-5, and a surface acoustic wave is generated. Input interdigital electrode pairs 6-8 connecting to a common electrode pattern B receive the surface acoustic wave generated from the electrode pairs 2-5 and transduce the wave into an electric signal. The electric signal is transduced again into a surface acoustic wave by output side interdigital electrode pairs 13-15 and received by 2nd SAW filter input side interdigital electrode pairs 16-19, in which the surface acoustic wave is transduced into an electric signal and outputted to an output terminal 11. Through the constitution above, since no wire bonding is required, a level jump in the electric signal is prevented and the desired attenuation characteristic is obtained by one piezoelectric substrate.

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 (Surface Acoustic Wave) used in high frequency circuit parts of automobile phones, mobile phones and the like.
Filter, hereinafter SAW filter).

[0002]

2. Description of the Related Art Conventionally, as a microwave band filter used in a wireless communication device or the like, a dielectric filter or an SA is used.
A W filter or the like is used. Along with downsizing of wireless communication devices and the like, devices such as filters used in these devices have been downsized. In particular, the SAW filter is small, stable with respect to changes in temperature and aging, and has a major feature that amplitude characteristics and phase characteristics can be designed almost independently and arbitrarily. It is expected to be used more and more in the future as a filter corresponding to miniaturization. The operating principle of the SAW filter will be described with reference to FIGS. In FIG. 2, an input side comb-shaped electrode pair 21 for converting an electric signal into a surface acoustic wave and an output side comb-shaped electrode pair 22 for converting a surface acoustic wave into an electric signal are arranged on one piezoelectric substrate 20. There is. The input side comb-shaped electrode pair 21 and the output side comb-shaped electrode pair 22 are shown in FIG.
, The E-shaped electrode patterns 26 and 2
7 are arranged to face each other. At this time, the electrode width of the E-shaped electrode patterns 26 and 27 is Vt / (4f
0). Vt is the propagation velocity of the surface acoustic wave propagating on the piezoelectric substrate, and f0 is the center frequency of the filter.

An input terminal 23 is connected to the input side comb-shaped electrode pair 21, and a high frequency voltage Vs is applied to the input side comb-shaped electrode pair 21 via the input terminal 23. Therefore, the high frequency voltage Vs excites a surface acoustic wave by an electric field generated between the electrode fingers of the input-side comb-shaped electrode pair 21, and the surface acoustic wave propagates on the surface of the piezoelectric substrate 20 in a direction perpendicular to the space between the electrode fingers. When the surface acoustic wave reaches the output side comb-shaped electrode pair 22, it is converted into an electric signal again by the output side comb-shaped electrode pair 22.
Then, the electric signal is output from the output terminal 24.
The frequency characteristic of this SAW filter can be expressed by the transfer functions of the following equations (1) and (2).

H (ω) = sin (X) / X (1) X = πn (ω−ω0) / ω0 (2) where ω0: angular frequency of filter center frequency f0 n: logarithm of electrode fingers Side comb-shaped electrode pair 21 and output side comb-shaped electrode pair 22
The maximum output is obtained at the frequency f0 that coincides with the frequency of the surface acoustic wave excited by the comb-shaped electrode pair. Therefore, the frequency characteristic is as shown in FIG. In the SAW filter having the above-mentioned configuration, the attenuation amount of the first side lobe is only 20 dB, and in order to obtain the desired attenuation amount of 20 dB or more, a plurality of SAW filters are connected in series. The connection was performed by wire bonding the output terminal of the first SAW filter and the input terminal of the second SAW filter.

[0005]

In the field of wireless communication to which the present invention belongs, there is a demand for this attenuation amount to be 40 dB or more, and a plurality of SAW filters are connected by the method described above. In this structure, since the SAW filter is very small and the electric signal has a high frequency,
An antenna is formed between the wires connecting the filters, and the electric signal is output without being applied to the SAW filter. Therefore, there is a problem that a desired frequency characteristic cannot be obtained even if a plurality of SAW filters are connected in series. Further, when wire bonding the first SAW filter and the second SAW filter, there is a problem that the frequency characteristic of the filter also changes because the impedance changes. Therefore, the present invention solves the above-mentioned problems, obtains a damping characteristic of 40 dB on one piezoelectric substrate, and at the same time, a first SAW filter and a second SAW filter arranged on one piezoelectric substrate. The purpose is to minimize the propagation loss between them.

[0006]

In order to achieve the above-mentioned object, the present invention provides an E-shaped electrode pattern in a surface acoustic wave filter arranged on one piezoelectric substrate having an input terminal and an output terminal. And at least one first output-side comb-shaped electrode pair for generating a surface acoustic wave by receiving an electric signal from the input terminal, and an E-shaped electrode pattern. At least one first input-side comb-shaped electrode pair that is made to face each other and is alternately inserted, and that receives the surface acoustic wave output from the first output-side comb-shaped electrode pair and converts the surface acoustic wave into an electric signal; ,
A common electrode pattern for propagating an electric signal output from the first input-side comb-shaped electrode pair and an E-shaped electrode pattern are opposed to each other and are alternately inserted, and an electric signal is transmitted from the common electrode pattern. At least one second output-side comb electrode pair for receiving and generating a surface acoustic wave;
At least one first surface-type electrode pattern that receives the surface acoustic waves output from the second output-side comb-shaped electrode pairs, which are alternately inserted while being opposed to each other, is converted into an electric signal, and is output to the output terminal. 2 input-side comb-shaped electrode pairs. Further, the first input side comb-shaped electrode pair and the second output side comb-shaped electrode pair have the same shape.

[0007]

According to the present invention, a plurality of SAW filters are pattern-connected on one piezoelectric substrate. Therefore, the electric signal is applied to the first SAW filter. In the first SAW filter, an electric signal is converted into a surface acoustic wave, a predetermined frequency is attenuated, converted into an electric signal again, and then output. Then, the electric signal output from the first SAW filter is applied to the second SAW filter via the pattern. In the second SAW filter, the electric signal is converted into a surface acoustic wave again, a predetermined frequency is further attenuated, and converted into an electric signal again. Moreover, since the impedances of the first and second SAW filters do not change, the frequency characteristics of the filters do not change.

[0008]

1 is a block diagram of a SAW filter according to the present invention. A first SAW filter and a second SAW filter are connected in series on one piezoelectric substrate 1. Further, the outer circumference of the piezoelectric substrate 1 is grounded. First
The SAW filter is composed of the output side comb-shaped electrode pairs 2 to 5 and the input side comb-shaped electrode pairs 6 to 8 arranged between the output side comb-shaped electrode pairs 2 to 5 and receiving the surface acoustic wave. There is. The output side comb-shaped electrode pairs 2 to 5 are connected in parallel via a connection point A, and the input terminal 10 is connected to the connection point A. Each of the output-side comb-shaped electrode pairs 2 to 5 is configured such that two E-shaped electrode patterns face each other, and the electrodes are fitted to each other by a predetermined length between the opposing electrode fingers. That is, as shown in FIG. 3, the tips of the electrode fingers 30 of the E-shaped electrode pattern are arranged by inserting a predetermined amount between the opposing electrode fingers 28 and 29 of the E-shaped electrode pattern. One of the E-shaped electrode patterns is connected to the input terminal 10, and the other E-shaped electrode pattern is grounded. Also, in the input side comb-shaped electrode pairs 6 to 8, one E-shaped electrode pattern is connected in parallel via the common electrode pattern B, and the other E-shaped electrode pattern is grounded. The second filter is a comb-shaped electrode pair 13 to 1 on the output side.
5 and input side comb-shaped electrode pairs 16 to 19 arranged on both sides of the output side comb-shaped electrode pairs 13 to 15 for receiving surface acoustic waves. Similarly to the first SAW filter, the output side comb-shaped electrode pairs 13 to 15 are also configured such that two E-shaped electrodes face each other. One of the E-shaped electrode patterns is connected to the common electrode pattern B, and the other E-shaped electrode pattern is grounded. The input side comb-shaped electrode pairs 16 to 19 are also configured such that two E-shaped electrode patterns face each other. One of the E-shaped electrode patterns is connected in parallel via the connection point A, and the other E-shaped electrode pattern is grounded. Next, the operation of the SAW filter will be described.
The electric signal is applied from the input terminal 10 and is branched to the output side comb-shaped electrode pairs 2 to 5 via the connection point A. Each of the output-side comb-shaped electrode pairs 2 to 5 to which the electric signal is supplied excites a surface acoustic wave by an electric field generated between the electrode fingers, and generates a surface acoustic wave along the piezoelectric substrate 1. The surface acoustic wave is generated perpendicularly between the electrode fingers of the output-side comb-shaped electrode pairs 2 to 5, that is, in the arrow F and G directions shown in FIG.

The input side comb-shaped electrode pairs 6 to 8 receive the surface acoustic waves generated by the output side comb-shaped electrode pairs 2 to 5 and convert them into electric signals. The converted electric signal is the common electrode pattern B.
Via the output side comb-shaped electrode pair 13 of the second SAW filter
To 16 are output. Specifically, the input-side comb-shaped electrode pair 6 receives the surface acoustic wave generated in the F direction of the output-side comb-shaped electrode pair 2 and the surface acoustic wave generated in the E-direction of the output-side comb-shaped electrode pair 3 to generate an electrical signal. Convert to signal. The output side comb-shaped electrode pairs 13 to 15 input the electric signal output from the first SAW filter and convert it again into a surface acoustic wave. The converted surface acoustic wave is in a direction perpendicular to the electrode fingers of the output side comb-shaped electrode pairs 13 to 15, that is, the output side comb-shaped electrode pair 13 to 15.
Each of 15 occurs in the E direction and the F direction. Then, the input side comb-shaped electrode pairs 16 to 19 receive the surface acoustic waves and convert them into electric signals. The converted electrical signal is
It is output to the output terminal 11 via the connection point C. further,
The number of input side comb-shaped electrode pairs of the first SAW filter and the number of output side comb-shaped electrode pairs of the second SAW filter described above are the same. For example, the input side comb-shaped electrode pair of the first SAW filter and the output side comb-shaped electrode pair of the second SAW filter are symmetrically arranged with the common electrode pattern B as an axis. According to this arrangement, the impedances of the two become equal, the mismatch due to the connection of the SAW filter can be prevented, and the propagation loss can be further reduced. Further, although only the first SAW filter and the second SAW filter are connected here, the present invention can arrange a plurality of SAW filters on one piezoelectric substrate.

[0010]

As described in detail above, according to the present invention, since a plurality of SAW filters are realized by pattern connection on one piezoelectric substrate, it is not necessary to wire-bond a plurality of SAW filters. Therefore, it is possible to prevent jumping of an electric signal generated by wire bonding, and it is possible to realize desired damping characteristics on one piezoelectric substrate, which could not be realized on one piezoelectric substrate.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a SAW filter according to the present invention.

FIG. 2 is a structural diagram of a conventional SAW filter.

FIG. 3 is a detailed view showing the configuration of a comb-shaped electrode pair.

FIG. 4 is a diagram showing frequency characteristics of a conventional SAW filter.

[Explanation of symbols]

1, piezoelectric substrate 2, 3, 4, 5, 13, 14, 15, output side comb-shaped electrode pair 6, 7, 8, 16, 17, 18, 19, input side comb-shaped electrode pair A, C, connection point B, Common electrode pattern 10, input terminal 11, output terminal

Claims (2)

[Claims] 1. A surface acoustic wave filter disposed on one piezoelectric substrate having an input terminal and an output terminal, wherein at least one surface acoustic wave filter receives an electric signal from the input terminal and generates a surface acoustic wave. One output-side comb-shaped electrode pair; at least one first input-side comb-shaped electrode pair that receives the surface acoustic wave output from the first output-side comb-shaped electrode pair and converts the surface acoustic wave into an electric signal; A common electrode pattern that propagates the electric signal output from one input-side comb-shaped electrode pair; and at least one second output-side comb-shaped electrode pair that receives the electric signal from the common electrode pattern and generates a surface acoustic wave. At least one second input-side comb-shaped electrode pair that receives the surface acoustic wave output from the second output-side comb-shaped electrode pair, converts the surface acoustic wave into an electric signal, and outputs the electric signal to the output terminal. Bullet Surface wave filter. 2. The surface acoustic wave filter according to claim 1, wherein a plurality of surface acoustic wave filters are provided on one piezoelectric substrate, wherein the first input side comb-shaped electrode pair and the second output side are arranged. A surface acoustic wave filter characterized in that comb-shaped electrode pairs have the same shape.