JPH0621754A - Band pass filter - Google Patents

Abstract

PURPOSE:To facilitate various filter characteristics by using capacitors of various capacitance values dispensing with the redesign of a surface acoustic wave resonator. CONSTITUTION:A capacitor 141, surface acoustic wave resonators 151, 152...15n and a capacitor 142 are connected sequentially in series between an input terminal 10 and an output terminal 12. Moreover, capacitors 143, 144,...14n+3 are connected between lines 161, 162,... 16n+1 located between the capacitors 141 and 142 and a line tying an input terminal 11 and an output terminal 13. Through the constitution above, the insertion loss is varied by varying the capacitance of the capacitors 144,145,... 14n+3. Moreover, the suppression ratio is mainly varied and also the band width is varied by varying the capacitance of the capacitors 143,14n+3. Furthermore, the band width and the suppression ratio are mainly varied by varying the capacitance of the capacitors 141, 142. Thus, various filter characteristics are obtained by using capacitors of various capacitance values.

Description

Detailed Description of the Invention

[0001]

The present invention relates to surface acoustic waves (SAW:
surface acoustic wave) relates to a band pass filter configured using a resonator.

[0002]

2. Description of the Related Art Conventionally, as a band-pass filter constructed by using a surface acoustic wave resonator, one having a circuit diagram shown in FIG. 6 is known. In the figure, 1 and 2 are a pair of input terminals, 3 and 4 are a pair of output terminals, 5, 6 and 7 are capacitors, and 8 and 9 are surface acoustic wave resonators.

[0003]

In such a conventional band pass filter, when the filter characteristics such as insertion loss, suppression and bandwidth are changed, the surface acoustic wave resonator 8,
It is necessary to change the characteristics of No. 9, and for this purpose, the surface acoustic wave resonators 8 and 9 have to be redesigned, which causes a problem that it takes much labor.

In view of the above points, the present invention makes it possible to change filter characteristics such as insertion loss, suppression, and bandwidth depending on the capacitance value of a capacitor, and to redesign various types of surface acoustic wave resonators. It is an object of the present invention to provide a bandpass filter in which various filter characteristics can be easily obtained by using a capacitor having a capacitance value.

[0005]

FIG. 1 is a circuit diagram showing the principle of the present invention. In the figure, 10 and 11 are a pair of input terminals,
12 and 13 a pair of output terminals, 14 _{1-14 5,} 1
4 _{n + 2} , 14 _{n + 3} are capacitors, 15 ₁ , 15 ₂ , 15 _n are surface acoustic wave resonators, 16 _{1 to} 16 ₃ , 16 _n , 16 _{n + 1} , 1
7 is a railroad track.

That is, the bandpass filter according to the present invention is
A capacitor 14 is provided between the input terminal 10 and the output terminal 12.
₁ , surface acoustic wave resonators 15 ₁ , 15 ₂ ... 15 _n (however,
n = an integer of 2 or more) and the capacitor 14 ₂ are sequentially connected in series, and the capacitors 14 ₁ and 14 ₂ are connected.
Between the respective lines 16 ₁ , 16 ₂ ... 16 _{n + 1} and the line 17 connecting the input terminal 11 and the output terminal 13 with each other, capacitors 14 ₃ , 14 ₄ ... 14 _{n + 3.} It is to connect and configure.

[0007]

In the present invention, the capacitors 14 ₄ , 14 ₅ ... 1
The insertion loss can be changed by changing the capacitance value of 4 _{n + 2} . Also, suppression can be changed mainly by changing the capacitance values of the capacitors 14 ₃ and 14 _{n + 3} ,
Bandwidth can also be changed. Also, capacitor 1
4 ₁ mainly can change the bandwidth by changing the 14 _second capacitance value, the suppression can also be varied.

[0008]

FIG. 2 is a circuit diagram showing an embodiment of the present invention. In the figure, 18 and 19 are a pair of input terminals, 20 and 21 are a pair of output terminals, 22 to 26 are capacitors, and 27 and 28.
Are surface acoustic wave resonators having the same or substantially the same characteristics, 29 to
32 is a railroad track.

That is, in this embodiment, the capacitor 22 and the surface acoustic wave resonator 2 are provided between the input terminal 18 and the output terminal 20.
7, 28 and the capacitor 23 are sequentially connected in series, and between the lines 29, 30, 31 between the capacitor 22 and the capacitor 23 and the line 32 connecting the input terminal 19 and the output terminal 21, It is configured by connecting capacitors 24, 25 and 26.

FIG. 3 shows the relationship between the capacitance value of the capacitor 25 and the filter characteristic. The broken line 33 indicates a large capacitance value of the capacitor 25, and the solid line 34 indicates a medium capacitance value of the capacitor 25. , The broken line 35 is the capacitor 2
It can be confirmed that when the capacitance value of 5 is small and the capacitance value of the capacitor 25 changes, the insertion loss changes.

FIG. 4 shows the relationship between the capacitance values of the capacitors 24 and 26 and the filter characteristics. A broken line 36 indicates a large capacitance value of the capacitors 24 and 26, and a solid line 37 indicates a capacitance value of the capacitors 24 and 26. Is intermediate, dashed line 3
8 is a case where the capacitance values of the capacitors 24 and 26 are small, and it can be confirmed that when the capacitance values of the capacitors 24 and 26 change, the suppression mainly changes and the bandwidth also changes.

FIG. 5 shows the relationship between the capacitance values of the capacitors 22 and 23 and the filter characteristics. The broken line 39 indicates the capacitance values of the capacitors 22 and 23, and the solid line 40 indicates the capacitance values of the capacitors 22 and 23. Is intermediate, dashed line 4
No. 1 is the case where the capacitance values of the capacitors 22 and 23 are small, and it can be confirmed that when the capacitance values of the capacitors 22 and 23 change, the bandwidth mainly changes and the suppression also changes.

As described above, according to this embodiment, the insertion loss, the suppression, the
Since the filter characteristics such as the bandwidth can be changed, various filter characteristics can be obtained by using capacitors having various capacitance values for the capacitors 22 to 26 without redesigning the surface acoustic wave resonators 27 and 28. Can be easily obtained.

[0014]

As described above, according to the present invention, the filter characteristics such as the insertion loss, the suppression and the bandwidth can be changed by the capacitance value of the capacitor, so that the surface acoustic wave resonator is designed. Without using the above, various filter characteristics can be easily obtained by using capacitors having various capacitance values.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the principle of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a capacitance value of a predetermined capacitor and a filter characteristic.

FIG. 4 is a diagram showing a relationship between a capacitance value of a predetermined capacitor and a filter characteristic.

FIG. 5 is a diagram showing a relationship between a capacitance value of a predetermined capacitor and a filter characteristic.

FIG. 6 is a circuit diagram showing an example of a conventional bandpass filter.

[Explanation of symbols]

14 _{1 to} 14 ₅ , 14 _{n + 2} , 14 _{n + 3} capacitors 15 ₁ , 15 ₂ , 15 _n surface acoustic wave resonator 16 _{1 to} 16 ₃ , 16 _n , 16 _{n + 1} , 17 lines

Claims (2)

[Claims] 1. A first capacitor (14 ₁ ), a first, a second ... An nth (where n = Integer of 2 or more), the surface acoustic wave resonators (15 ₁ , 15 ₂ ... 15 _n ) and the second capacitor (14 ₂ ) are sequentially connected in series, and
Each line (16 ₁ , 16 ₂ ... 16) between the first capacitor (14 ₁ ) and the second capacitor (14 ₂ ).
_{n + 1} ) and the line (17) connecting the second input terminal (11) and the second output terminal (13),
..Nth +3 capacitors (14 ₃ , 14 ₄ ... 14)
_{n + 3} ) are connected to form a bandpass filter. 2. The first, second ... Nth surface acoustic wave resonators (15 ₁ , 15 ₂ ... 15 _n ) are designed to have the same or substantially the same characteristics. The bandpass filter according to claim 1, wherein: