JPS6226914A - Band pass filter circuit - Google Patents

Abstract

PURPOSE:To decrease the capacitance of a capacitor forming an attenuation pole by using the 1st and 2nd capacitors connected between an input terminal and the post-stage of the coupling capacitor and between the output terminal and the pre-stage of the coupling capacitor respectively so as to form the attenuation pole at both sides of the pass band. CONSTITUTION:A zero frequency pole band pass filter 16 and an infinite frequency pole 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. The 1st capacitor C16 is connected between the input terminal 12 and a connecting point 18 between the coupling capacitor C11 and the infinite frequency pole band pass filter 18. Further, the 2nd capacitor C17 is connected between a connecting point 16a of the coupling capacitor C11 and the zero frequency pole band pass filter 16 and the output terminal 14. The attenuation pole is formed by the 1st and 2nd capacitors C16, C17 at both sides of the pass band.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application to Industry) 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. 4 is a circuit diagram showing an example of a conventional double-sided attenuating rod-shaped bandpass filter that is the background of the present invention.

This conventional circuit is constructed by adding two capacitors C6 and C7 to the bandpass filter shown in FIG. 5 to form attenuation poles on both sides. The bandpass filter shown in FIG. 5 basically consists of a zigzag-shaped zero-frequency pole bandpass filter shown in FIG. 6 and a zigzag-shaped infinite frequency pole bandpass filter shown in FIG. 7 using a coupling capacitor C1. It is connected.

In the FIG. 4 circuit, added capacitors c6 and C7 form attenuation poles on either side of the passband.

(Problems to be Solved by the Invention) In the conventional circuit shown in FIG.
7 to form attenuation poles on both sides of the pass band, these capacitors C4 and C7 need to have large capacitance values.

Therefore, the main object of the invention is to provide a bandpass filter circuit in which attenuation poles can be formed on both sides of the passband using smaller capacitance capacitors.

(Means for Solving the Problems) Simply put, the present invention consists of a zero frequency pole bandpass filter and an infinite frequency pole bandpass filter connected in cascade via a coupling capacitor between an input end and an output end. a first capacitor connected in parallel between the input end and the rear stage of the coupling capacitor, and a second capacitor connected in parallel between the front stage of the coupling capacitor and the output end; It is a pass filter circuit.

(Function) The first capacitor forms attenuation poles on the −L side and the lower side of the passband, and the second capacitor forms the other attenuation pole.

(Effects of the Invention) According to the present invention, the input terminal and the rear stage of the coupling capacitor 1!
- and between the front stage of the coupling capacitor and the output terminal, respectively, to form attenuation poles on both sides of the ifη overband. Compared to the circuit, the capacitance of the capacitor for forming this attenuation pole can be made smaller.

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 zero frequency pole band pass filter 16 and an infinite frequency pole band J, tlli i1m pass filter 18 are connected in cascade between the input terminal 12 and the output terminal 14 via a coupling capacitor Cr +. The zero-frequency pole bandpass filter 16 is similar to the zigzag-shaped one shown in FIG. 6, and has an infinite frequency pole band il! The overfilter 18 is similar to that shown in FIG. 7 and has a zigzag shape.

A first capacitor CIb is connected between the input terminal 12 and the connection point 18a of the coupling capacitor C++ and the infinite frequency pole bandpass filter 18.

Further, a second capacitor CI7 is connected between the connection point 16a of the coupling capacitor CII and the zero-frequency pole bandpass filter 16, and the output end 14.

These first and second capacitors C36 and C87
However, as shown in FIG. 2, attenuation poles are formed on both sides of the passband.

To explain in more detail, if these first and second capacitors C16 and C1 are not present, a zero frequency pole bandpass filter as shown in FIG. 6 and an infinite frequency pole bandpass filter as shown in FIG. When simply connected in cascade, the frequency characteristics shown in FIG. 3 are exhibited.

On the other hand, the first and second capacitors C16 and C1? When connected, sharp attenuation poles are formed at the lower and upper sides of the passband, as shown in FIG.

In the circuit of FIG. 1, in order to change the frequency of the attenuation pole, the first capacitor C1 and/or the second
The capacitance of the capacitor CI7 may be adjusted appropriately.

Further, in the above embodiment, the zero frequency pole bandpass filter 16 is connected to the coupling capacitor C1 before the coupling capacitor C1.
After 11, infinite frequency pole bandpass filters 18 were respectively connected. However, the order of connection of these two filters 16 and 18 may be reversed. In short, it is sufficient that the zero frequency horizontal band i1m pass filter 1G and the infinite frequency pole band pass filter 18 are connected in cascade between the input end 12 and the output end 14 via a coupling capacitor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is a graph showing an example of the frequency characteristics of the embodiment shown in FIG. FIG. 3 is a graph showing frequency characteristics when there are no two capacitors to be connected in the circuit of FIG. 1. FIG. 4 is a circuit diagram showing an example of a conventional bandpass filter circuit, which is the background of the present invention. FIG. 5 is a circuit diagram showing the basic form of the circuit of FIG. 4. FIG. 6 is a circuit diagram showing a zero frequency pole bandpass filter. FIG. 7 is a circuit diagram showing an infinite frequency pole bandpass filter. In the figure, ]2 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, CI1 is a coupling capacitor, and C10 is a first
C10 indicates the second capacitor. Patent applicant Murata Manufacturing Co., Ltd. Representative Patent attorney Yama 1) Yoshito (and 1 other person)

Claims (1)

[Claims] A zero-frequency pole bandpass filter and an infinite frequency pole bandpass filter are cascade-connected between an input end and an output end via a coupling capacitor, and a stage subsequent to the input end and the coupling capacitor is included. A bandpass filter circuit, comprising: a first capacitor connected between the coupling capacitor and the output end;