JPS6226913A - Band pass filter circuit - Google Patents

Abstract

PURPOSE:To decrease number of capacitors by one by connecting a zero frequency pole band pass filter and an infinite frequency pole band pass filter between an input terminal and an output terminal and forming a zero frequency pole band pass filter, an infinite frequency pole and pass filter and an attenuation pole between the input and output terminals. CONSTITUTION:A zigzag zero frequency pole band pass filter 16 and a zigzag infinite frequency band pass filter 18 are connected in cascade between the input terminal 12 and the output terminal 14 of a band pass filter circuit 10 via a coupling capacitor C11. The filters 16, 18 are the same as conventional filters. Further, a capacitor C16 is connected between the input and output terminals 12, 14 while bridging over the zero frequency pole and pass filter 16, the infinite frequency pole band pass filter 18 and the coupling capacitor C11. The capacitor C16 is used to form an attenuation pole at both sides of the pass band.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a bandpass filter circuit, and more particularly to a bandpass filter circuit having attenuation poles on both sides of the upper and lower sides of the passband.

(Prior Art) FIG. 7 is a circuit diagram showing an example of a conventional double-sided attenuation pole type bandpass filter which is the background of the present invention.

In this prior art, two capacitors C6 and C1 are added to the bandpass filter shown in FIG. 8 to form attenuation poles on both sides. The bandpass filter shown in FIG. 8 basically consists of a zigzag-shaped zero-frequency pole bandpass filter shown in FIG. 9 and a zigzag-shaped infinite frequency pole bandpass filter shown in FIG. 10 using a coupling capacitor CI. It is connected. In the FIG. 7 circuit, the two added capacitors C6 and C6 form attenuation poles on either side of the passband.

(Problems to be Solved by the Invention) In the conventional circuit described above, two capacitors C4 and C4 are required to form attenuation poles on both sides of the iIN overband. Therefore, the number of parts is large.

Therefore, a primary object of the present invention is to provide a double-sided attenuated pole bandpass filter circuit with a reduced number of components.

(Means for solving the ffI'I problem) This invention has the following features:
Simply put, there is a zero frequency polar band i1 between the input end and the output end! The zero-frequency extreme band-pass filter and the infinite frequency extreme band-pass filter are connected through a coupling capacitor, and the zero-frequency extreme band-pass filter 7 is connected between the input terminal and the output terminal of the infinite frequency extreme band-pass filter and the coupling capacitor. This is a bandpass filter circuit that connects capacitors to form attenuation poles on both sides of the passband.

(Operation) A band-pass filter circuit having a predetermined pass band is obtained by the zero-frequency pole band-pass filter and the infinite-frequency pole band-pass filter. Attenuation poles are formed on both sides of the passband by capacitors connected between the input and output ends.

(Effects of the Invention) According to the present invention, the number of capacitors can be reduced by one compared to the conventional circuit shown in FIG. A filter circuit is obtained.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Embodiment) FIG. 1 is a circuit diagram showing an embodiment of the present invention. Bandpass filter circuit 10 includes an input end 12 and an output end 14 . A zigzag zero frequency pole bandpass filter 16 and a zigzag infinite frequency pole bandpass filter 18 are cascaded between the input end 12 and the output end 14 via a coupling capacitor C0. The zero frequency pole bandpass filter 16 is similar to that shown in FIG. 9 above, and the infinite frequency pole bandpass filter 8 is the same as that shown in FIG.

The bandpass filter circuit 10 further includes a zero frequency pole bandpass filter 16 . between the input terminal 12 and the output terminal 14 .
A capacitor CI 6 is connected across the infinite frequency pole bandpass filter 18 and the coupling capacitor C1□.

As shown in FIG. 2, this capacitor C is iJ! This is for forming an attenuation pole on the overband side.

To explain in more detail, in the circuit of FIG. 1, if the capacitor C16 is not provided, the frequency characteristic will be as shown in FIG. 3. On the other hand, when the capacitors C1, .

The frequencies of the attenuation poles on both sides can be changed as shown in FIG. 4 depending on the capacitance of the added capacitor CI6.

Furthermore, by appropriately adjusting this capacitor C16, the inductor L constituting the LC parallel circuit included in the zero-frequency pole bandpass filter 16, and the capacitor CI3, the pass band can be changed as shown in FIG. Only the frequency of the lower attenuation pole can be changed. Conversely, by appropriately adjusting the inductors L, □ and capacitor C (4) included in the infinite frequency pole bandpass filter I8, only the frequency of the attenuation pole on the upper side of the passband can be adjusted as shown in FIG. It can be changed arbitrarily.

Further, the width of the pass band can be arbitrarily changed by appropriately setting the constants of the capacitor CI6 and other components.

In the above-described embodiment, the zero frequency pole band pass filter 16 was connected to the input end 12 side, and the infinite frequency pole band pass filter 18 was connected to the output end 14 side. However, this may also be connected in reverse, in short, if two such bandpass filters 16 and 18 are connected in cascade between the input end and the output end via the coupling capacitor CII. good.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is just one graph, but does not show an example of the frequency characteristics of the circuit shown in FIG. FIG. 3 is a graph showing the frequency characteristics in the circuit of FIG. 1 without the added capacitor. FIG. 4 is a graph of frequency characteristics showing that the frequencies of the attenuation poles on both sides can be changed. FIG. 5 is a graph of frequency characteristics showing that only the frequency of the lower attenuation pole can be changed. FIG. 6 is a graph of frequency characteristics showing that only the frequency of the upper attenuation pole can be changed. FIG. 7 is a circuit diagram showing an example of a conventional double-sided attenuation pole type band-pass filter circuit, which is the background of the present invention. FIG. 8 is a circuit diagram showing the basic form of the circuit of FIG. 7. FIG. 9 is a circuit diagram showing a zigzag type zero frequency pole bandpass filter. FIG. 10 is a circuit diagram showing a zigzag infinite frequency pole bandpass filter. In the figure, 12 is an input terminal, 14 is an output terminal, 16 is a zero frequency pole bandpass filter, 18 is an infinite frequency pole bandpass filter, CII is a coupling capacitor, and C10 is a capacitor for forming an attenuation pole. Patent applicant Murata Manufacturing Co., Ltd. Agent Patent attorney Yama 1) Yoshito (and 1 other person) Z + KI111 Houmi (Similar 11 Kimun ζ 1 chapter 4-q) Military 1ba 1ela ゛0

Claims (1)

[Claims] A zero frequency pole bandpass filter and an infinite frequency pole bandpass filter are connected in cascade via a coupling capacitor between the input terminal and the output terminal, and between the input terminal and the output terminal. A bandpass filter circuit in which a capacitor is connected across the zero frequency pole bandpass filter, the infinite frequency pole bandpass filter, and the coupling capacitor to form attenuation poles on both sides of the passband.