JPS6157723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass filter consisting of two or more 1/4 wavelength resonators and two or more parallel resonators each consisting of a coil and a capacitor. , an attenuation pole is provided on the high frequency side to provide excellent cutoff characteristics.

A conventional bandpass filter of this type will be explained using a helical filter as an example with reference to the schematic configuration diagram of FIG. In FIG. 1, a shield case 1 made of aluminum or the like has several chambers 3, 3, 3, 3 formed by a plurality of partition walls 2, 2, 2, and each partition wall 2 is provided with a connecting window 4. It is being In each chamber 3 of such a shield case 1, a good conductor such as copper wire is wound around a plastic bobbin, etc., around several tens of turns, one end is open, and the other end is connected to the shield case 1. A wavelength resonator 5 is arranged respectively, and an input winding 6 and an output winding 7 made up of several turns of copper wire are arranged in the chambers 3 and 3 at both ends. One end of the wire 7 is connected to the shield case 1, and the other end is insulated from the shield case 1 and drawn out to the outside of the shield case 1.

The frequency transmission characteristics of this helical filter are as shown by the dotted line in Figure 3, and the cutoff characteristics are gentle on both the low and high frequency sides of the passband, and the disadvantage is that the sharpness is particularly poor near the passband. It was hot.

The present invention seeks to eliminate the above-mentioned drawbacks of the prior art. Embodiments of the present invention will be described below with reference to FIGS. 2 to 4 of the drawings.

First, in the embodiment shown in FIG. 2, 8 is a shield case made of aluminum or the like, and this shield case 8 is provided with three partition walls 9, 10, 9, and the partition walls 9, 10, 9 and the shield case 8. Tsute 4
It constitutes individual chambers 11, 12, 12, 11.

Among these chambers, the chambers 11 and 11 at both ends each have a copper wire wound around several dozen turns around a plastic bobbin, etc., with one end open and the other end connected to the shield case 8. Wavelength resonator 1
3, 13', and an input winding 14 wound with several turns of copper wire, etc., connected to the shield case 8 at one end, insulated from the shield case 8 at the other end, and drawn out to the outside.
and an output winding 15 are arranged.

Chambers 11, 11 at both ends and chambers 12, 12 in the center
A joining window 16 is formed in the partition walls 9, 9 between the
These central chambers 12, 12 are constructed by winding copper wire or the like around a plastic bobbin, etc., from several turns to around 10 turns (considerably less than the windings of the 1/4 wavelength resonators 13, 13'). Coils 17, 17' are arranged.

Further, a capacitor 18 is connected to both ends of the coils 17, 17' to form a parallel resonator 19.

Inside these central chambers 12, 12 are coils 17,
There is an auxiliary winding 20 made by winding several turns of copper wire or the like arranged so as to be inductively coupled to the auxiliary winding 17'.One end of this auxiliary winding 20 is connected to the shield case 8, and the other end is connected to the shield case 8. The adjacent central chamber 1 is pulled out to the outside of the shield case 8.
The auxiliary windings 20 arranged in each of the coils 2 and 12 are connected to each other. Furthermore, the parallel resonator 19
One end is open, and the other end is connected to the side where the auxiliary windings 20 are connected. Also, the point where the auxiliary windings 20 are connected, and the point where the input winding 1
A coil 21 is inserted between the two.

Since the partition wall 10 of the central chambers 12, 12 is usually not provided with a window, the two parallel resonators 19, 19
are electrically separated, but are electromagnetically coupled by the connection between the auxiliary windings 20. Further, the capacitance between the parallel resonators 19, 19 and the shield case 8 forms a capacitively coupled trap circuit, causing an attenuation pole in the cutoff region on the higher frequency side than the passband. Furthermore, a parallel resonant trap circuit is formed by the coupling capacitance between the 1/4 wavelength resonator 13 and the coil 17 and the coil 21, and an attenuation pole is generated in the cutoff region on the lower frequency side than the passband. There is.

As a result, the frequency transmission characteristics of the filter according to the present invention, as shown by the solid line in FIG. 3, can significantly improve the cutoff characteristics on the low frequency side and high frequency side, compared to the conventional helical filter shown by the dotted line in the figure.

Another embodiment is shown in FIG. This is because the auxiliary windings 20 are further connected to each other in the embodiment shown in Fig. 2, and a coil 22 is inserted between the output windings 15 to provide two attenuation poles on the low frequency side and two on the high frequency side of the passband. This is an example in which the cutoff characteristics in the vicinity of the provided passband are significantly improved, and the frequency transmission characteristics are shown by the dashed line in FIG. In the case of the embodiment shown in Fig. 4, by appropriately changing the inductance values of the coils 21 and 22, the cutoff characteristics on the low frequency side of the pass band can be freely changed, and the bounce due to traps can also be controlled. is big.

Next, a case where a window is provided in the shield case 8 that separates the two central parallel resonators 19, 19 will be described. In the embodiments of the present invention described above and other embodiments, the two central parallel resonators 19 are connected to the partition wall 10.
However, if a window is provided in the partition wall 10, the influence of distributed capacitance will be added between the coils 17 and 17', and the cutoff characteristics on the higher frequency side than the passband will become gentler. That is, by changing the size of the windows in the partition wall 10, the high frequency side blocking characteristics can be changed arbitrarily.

As described above, the bandpass filter according to the present invention has cutoff characteristics on both the low frequency side and the high frequency side of the passband.
Due to its superiority, when used as a television receiver video intermediate frequency filter, it facilitates the design of adjacent channel video carrier frequency traps and adjacent channel audio carrier frequency traps.
Moreover, it is possible to provide a device that has a large amount of attenuation in the stopband, has a simple configuration, and can be used as a small-sized video intermediate frequency filter, etc., and is of great practical value.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a conventional bandpass filter;
The figure is a schematic configuration diagram of one embodiment of a bandpass filter according to the present invention, FIG. 3 is a frequency transmission characteristic diagram of the present invention and a conventional bandpass filter, and FIG. 4 is a diagram of another embodiment based on the present invention. It is a schematic configuration diagram. 8... Shield case, 9,9,10... Partition wall, 11, 11, 12, 12... Chamber, 16... Coupling window, 13, 13'... 1/4 wavelength resonator, 14...
Input winding, 15... Output winding, 17, 17'...
Coil, 18, 18... Capacitor, 19, 19
...Parallel resonator, 20,20...Auxiliary winding, 2
1, 22...Coil.

Claims (1)

[Claims] 1 It has two or more 1/4 wavelength resonators and two or more parallel resonators composed of a coil and a capacitor, and at least two parallel resonators are separated by a shielding case, and one end of the parallel resonators is separated by a shield case. are insulated from the shield case and connected to each other, and the other end is open, and an auxiliary winding is provided which is inductively coupled to each of these two parallel resonators, and one end of this auxiliary winding is A band is formed by inserting a coil between the parallel resonator and at least one of the input and output windings connected to the shield case, the other end connected to the parallel resonator, and at least one of the input and output windings inductively coupled to the 1/4 wavelength resonator. filter.