JPS6024012Y2 - High pass filter - Google Patents

Description

[Detailed description of the invention] The present invention is a π-type high-pass filter, and provides a high-pass filter that has the same number of elements as a conventional high-pass filter but also has a trap function. .

FIG. 1 shows a conventional high-pass filter.

This high-pass filter is a filter used in combination with the intermediate frequency trap circuit of a television.

In FIG. 1, 1 and 2 are a capacitor and an inductance, respectively, and the capacitor 1 and inductance 2 constitute a parallel resonant trap circuit.

Similarly, a capacitor 3 and an inductance 4 constitute a parallel resonant trap circuit.

5 is a capacitor, and an inductance 6.7 is connected to both ends of the capacitor 5 to form a π-type high-pass filter.

The characteristics of the filter shown in Fig. 1 are shown by the broken line a in Fig. 8, and the two parallel resonant trap circuits trap the intermediate frequency band ω2 to ω3 of the television to prevent intermediate frequency interference. It is.

However, in the above conventional filter, the intermediate frequency W
It is not possible to ensure a large amount of attenuation in the vicinity of the frequency band ω1 below the frequency band ω1.

In the above conventional filter, the interference around ω□, especially the interference frequency located around half of the intermediate frequency, can be detected after the tuner because the twice the harmonics generated by the television tuner exactly match the intermediate frequency. Impossible to separate or remove.

Particularly recently, CB communication has become popular in various countries, and this CB communication uses a frequency band below the IP band of the television, which causes interference.

Therefore, it is required to secure more attenuation in the frequency band below the IF band than in the past.

The present invention has been made in view of the above points, and will be explained below.

FIG. 2 shows an equivalent circuit obtained by converting the π-type circuit shown in FIG. 1, consisting of the capacitor 5 and the inductance 6.7, into a T-type circuit.

FIG. 3 shows the actance characteristic between A-8 in FIG.

The actance 2AB between A-8 is expressed by the following equation.

ZAB””5・°L・ (ω(L6+L?)-Sat) ωC5 ω in Figure 3.

Below, ZAB becomes capacitive.

Therefore, in this invention, as shown in Figure 4, the reactance Z
By adding inductance M in series with AB,
This constitutes a series trap.

FIG. 5 shows an equal number circuit according to an embodiment of the present invention, where π
In this configuration, one end of an inductance 6.7 constituting a type filter is grounded via an inductance M.

FIG. 6 shows an embodiment of the present invention, in which the inductance M in FIG. 5 is obtained by inductively coupling an inductance 6.7.

FIG. 7 shows a state in which the filter of this embodiment is provided on a printed circuit board.

In FIG. 7, 8 is a printed circuit board, 9, 9', 9'' are conductor patterns of the printed circuit board 8, 5 is a capacitor, 6,
7 is an inductance, and when the winding direction of the inductance 6.7 arranged in parallel is reversed, the above inductances become harmonically connected to each other, and the interlinkage magnetic flux can be increased without bringing the inductance 6.7 closer together. .

b in FIG. 8 shows the characteristics of the embodiment of the present invention, and ω1
It is possible to increase the amount of attenuation in the vicinity.

As described above, the present invention has the advantage of being able to add a trap function even though it has the same number of elements as a conventional high-pass filter.

[Brief explanation of drawings]

Figure 1 is an electrical circuit diagram of a conventional high-pass filter;
Figure 3 is an equivalent circuit diagram of the same filter, Figure 3 is an A-B actance characteristic diagram in Figure 2, Figure 4 is a basic configuration diagram of the high-pass filter of the present invention, and Figure 5 is the same filter. 6 is an electrical circuit diagram of a high-pass filter according to an embodiment of the present invention, FIG. 7 is a top view showing the filter configured on a printed circuit board, and FIG. 8 is a conventional example. and a frequency characteristic diagram of the filter of the present invention. 1.3,5... Capacitor, 2,4,6,7.
...Inductance.

Claims (1)

[Scope of utility model registration request] By connecting inductances between both ends of the capacitor and the ground to form a π-type circuit, connecting parallel trap circuits to the input and output sides of the π-type circuit, and inductively connecting the two inductances, the above can be achieved. A high-pass filter that includes a trap circuit that reduces the parallel trap frequency.