JPS6081911A - Filter bank - Google Patents

Abstract

PURPOSE:To improve operativity and precision by constituting parallel elements by combining input admittance elements of inputside roll screen type electrodes of surface acoustic wave filters and a capacitor. CONSTITUTION:Parallel elements are constituted by connecting input admittance elements of input-side roll screen type electrodes 2 of surface acoustic wave filters 1 and the capacitor 5 in parallel, so the electrostatic capacity value of each parallel elements is controlled by varying the electrostatic capacity value of the capacitor 5. Therefore, the inductance value of a coil 3 required to obtain a necessary cut off frequency and nominal impedance is varied by varying the number of the filters 1. Consequently, good operativity and high manufacture precision are obtained and the small-sized coil 3 is usable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a filter bank consisting of a plurality of surface acoustic wave filters (1) having different center frequencies.

[Prior art]

Conventional filter banks of this type utilize, for example, the capacitance of the interdigital interdigital electrode (2).

Input side interdigital electrode (2) of surface acoustic wave filter (1)
The input admittance of is made into a parallel element, and the coil (3) is made into a series element, and a plurality of surface acoustic wave filters +ll
& It was constructed by connecting it in a fixed shape. (4) is a terminating resistor.

By the way, when the filter characteristics of each surface acoustic wave filter (1) are defined, the value of the capacitance of the input side interdigital electrode (2) of each surface acoustic wave filter (tl) is determined. Also, in a regular circuit like the one shown in FIG.

As is well known, the required shear fault wave number.

In order to obtain the nominal impedance, the value of the inductance of the coil (3) is determined from the value of the electric capacity. Therefore, in a conventional filter bank of this type,
Once the filter characteristics are defined, the inductance of the coil (3) becomes extremely small.

There were cases where it became larger. In such a case, the coil (3) with the required inductance value
It is necessary to manufacture the coil with good workability and precision, but there are also disadvantages such as the space required for the coil +31 is too large. That is, in the conventional filter bank of this type, each parallel element was composed of only one surface acoustic wave filter + the input admittance of the input-side interdigital electrode (2) of 11. ) is difficult to manufacture or to downsize.

[Summary of the invention]

In this invention, the input admittance of the input-side interdigital electrode (2) of one surface acoustic wave filter (1) is made into a parallel element, and the coil (3) is made into a series element to define a plurality of surface acoustic wave filters fi+. By configuring the above-mentioned parallel element by combining the input admittance of the input-side interdigital electrode (2) of the nine surface acoustic wave filters (1) and the capacitor (5) in a filter bank formed by connecting them in the form of a conventional The shortcomings have been removed and are shown below.

This will be explained in detail using examples.

[Embodiments of the invention]

FIG. 2 shows an embodiment of the filter cylinder according to the present invention.

In the embodiment shown in FIG. 2, the input admittance of the input-side interdigital electrode (2) of a surface acoustic wave filter (1), which is a parallel element of a constant-shaped circuit, and a capacitor (51) are connected in parallel. A regularly shaped series element is constituted by a coil (3).

Now, let's look at the filter structure shown in Figure 2.

As in the conventional case, when the filter characteristics of each surface acoustic wave filter il+ are defined, the electrostatic capacity of the input side interdigital electrode 12) of each surface acoustic wave filter (!) is determined.

However, unlike the conventional method, in the filter bank shown in Fig. 2, each parallel element is configured by connecting in parallel 9 surface acoustic wave filters + 11 input-side interdigital electrodes (2) and a capacitor + 51. Therefore, the capacitance value of each parallel element can be controlled by changing the capacitance value of the capacitor (5). Therefore, by changing the capacitance value of the capacitor (5), the value of the inductance of the coil (3) required to obtain the required new station wave number and nominal i/beadance can be changed. .

Therefore, compared to the conventional method, there are advantages in that one operation is easier, it can be manufactured with higher precision, and a smaller coil (3) can be used.

FIG. 3 shows another embodiment of the filter bank according to the invention. In the embodiment shown in FIG. 3, unlike the embodiment shown in FIG. ) are connected in series. It is clear that in the embodiment shown in Fig. 3, the same advantages as shown in Fig. 2 can be obtained by changing the value of the capacitance of the capacitor (5:) used for each parallel element. Will.

FIG. 4 shows another embodiment of the filter bank according to the invention. In the embodiment shown in FIG. 4, unlike the embodiments shown in FIGS. 2 and 3, the interdigital interdigital electrode (2) on the input side of the surface acoustic wave filter 0) is a parallel element of a fixed circuit.
The input admittance is formed by a combination of a plurality of capacitors +51 connected in series and in parallel. It will be clear that the embodiment shown in FIG. 4 also provides advantages similar to those shown in FIGS. 2 and 3.

Although the above description has been made regarding the embodiments shown in FIGS. 2, 3, and 4, the present invention is not limited to this.
2) in combination with the input admittance.

This may be further combined with a capacitor (5) to form a parallel element.

〔Effect of the invention〕

As mentioned above, in the filter bank according to the present invention, the input side interdigital electrode (2) of one surface acoustic wave filter (1)
) and the capacitor (5) are combined as a parallel element, and the coil (3) is a series element,
By configuring a filter bank by connecting a plurality of surface acoustic wave filters (1) in a fixed shape, there are advantages such as improved workability and accuracy compared to the conventional method.

[Brief explanation of drawings]

Figure 1 is a conventional filter bank configuration diagram, Figures 2 and 3 are
Figure 4 is a diagram showing an embodiment of the filter puncture according to the present invention.7 In the figures, (1) is a surface acoustic wave filter, (2) is an interdigital electrode i3) is a coil, and (4) is a terminal. The resistor (5) is a capacitor. In Figure 9, the same or corresponding parts are indicated by the same reference numerals. Agent Masuo Oiwa 1st Ro1 2nd Quotient 3rd Figure 4121

Claims (1)

[Claims] The input admittance of the input-side interdigital electrode of the surface acoustic wave filter is made into a parallel element, and the coil is made into a series element.
In a filter bank made up of a plurality of surface acoustic wave filters connected in a fixed shape, the parallel element is constructed by combining the input admittance of the interdigital electrode on the input side of the surface acoustic wave filter with a capacitor. filter bank.