JPS6113706A - Band pass filter - Google Patents

Abstract

PURPOSE:To simplify the constitution of a band pass filter BPF by providing an LC parallel resonance circuit between a junction of two IC series resonance circuits connected in series to each other and its earth and securing connection between inductances of both LC series resonance circuits together with addition of a trap at a point having a higher frequency than a pass band. CONSTITUTION:An LC series resonance circuit consisting of an inductance L1 and a capacitor C1 is connected in series to an LC series resonance circuit consisting of an inductance L2 and a capacitor C2. Then an LC parallel resonance circuit consisting of an inductance L3 and a capacitor C3 is set between the junction of both LC series resonance circuit and an earth E. The connection is secured between inductances L1 and L2 to produce the mutual inductance, and a trap is added at an optional point having a higher frequency than a pass band. Thus the constitution of a BPF can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a bandpass filter used in various electronic circuits.

Configuration of the conventional example and its problems Conventionally, as shown in FIG. 1, the inductance L1. L2 and two series resonant circuits consisting of capacitors C1 and C2, and inductance L3 between the junction of both series resonant circuits and ground 8.
When adding a trap at any point at a frequency higher than the passband in a bandpass filter consisting of a parallel resonant circuit consisting of a capacitor C3 and a parallel resonant circuit consisting of a capacitor C3, add a capacitor C4 in parallel to one LCC series resonant circuit. It was common to do so. In this bandpass filter, 3
inductances L1 to L3 and four capacitors 01
~C4 is required, and one additional capacitor C4 is required compared to a bandpass filter without a trap.
This resulted in an increase in costs.

Purpose of the Invention The present invention consists of a bandpass filter having a trap in the high range, which was conventionally configured with three inductances and four capacitors, but is configured with three inductances and three capacitors, thereby reducing the cost by one capacitor. The purpose is to lower the

Structure of the Invention In order to achieve the above object, the bandpass filter of the present invention comprises an LC series resonant circuit, another LC series resonant circuit, and an LC parallel resonant circuit between the connection point of the C series resonant circuit and ground. With this configuration, a trap is added at an arbitrary point at a frequency higher than the passband of the bandpass filter, and a trap is added between the interfaces of both of the LC series resonant circuits. can be reduced.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to FIGS. 2 to 4 of the drawings.

In FIG. 2, an LC series resonant circuit of an inductance L1 and a capacitor C1, an LC series resonant circuit of another inductance L2 and a capacitor C2, and both inductances L1. Inductance L3 between the connection point of L2 and earth E
In a bandpass filter constituted by an LCi column resonant circuit of capacitor C3 and capacitor C3, interface L1
and L2 so as to cause mutual induction, and the fourth
As shown in the figure, a trap is added at any point at a frequency higher than the passband.

In the equivalent circuit of Figure 3, inductances L1 and L2
If the mutual inductance obtained by the coupling of is M, then the trap frequency f. is shown by the formula below.

Furthermore, the center frequency 10 of the bandpass filter and tie passband is expressed by the following formula.

By providing a polar coupling between the inductances L1 and L2 as shown in FIG. 2, a mutual inductance M can be obtained, and a trap can be added to the frequency side higher than the passband of the bandpass filter.

Effects of the Invention As described above, the bandpass filter of the present invention has the same characteristics as the trap-equipped bandpass filter, which was constructed with three inductances and four capacitors, by using three inductances and three capacitors. This makes it possible to reduce the number of capacitors by one, thereby reducing costs and downsizing.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram showing the circuit configuration of a conventional band-pass filter, FIG. 2 is an electrical circuit diagram showing an embodiment of the band-pass filter of the present invention, and FIG. The equivalent circuit diagram, FIG. 4, is a frequency characteristic diagram of the same bandpass filter. Ll, L2. L3...-interface, cl, c
2.C3...Capacitor, M...Ll, L
Mutual inductance between the two. Name of agent Patent attorney Toshi Nakao Iokaka Ichimeika 11 Figure 2 Figure 3 Figure 4 ε A □Frequency

Claims (1)

[Claims] It consists of an LC series resonant circuit, another LC series resonant circuit, and an LC parallel resonant circuit between the connection point of both LC series resonant circuits and the ground, and a bandpass circuit is created by coupling between the inductances of both LC series resonant circuits. A bandpass filter that is characterized by adding a trap at any point at a frequency higher than the filter's passband.