JPH01318418A - Multi-frequency band pass filter - Google Patents

Abstract

PURPOSE:To control the change of characteristics caused when the working frequency is switched by arranging in parallel the filters having the band pass characteristics at different center frequencies respectively and at the same time sharing both input and output terminals of each filter. CONSTITUTION:For the electric characteristics secured between the inputs and outputs of band pass filters 3a and 3b, the approximately equal transmission characteristics, i.e., the amplitude frequency characteristics 12a and 12b and the group delay time frequency characteristics 13a and 13b are secured with the working center frequencies 11a and 11b respectively. Therefore the multiple frequencies can be transmitted with the coaction of both filters 3a and 3b. At the same time, these filters have the characteristics independent of each other and therefore the approximately equal transmission characteristics can be secured between both filters. Thus it is possible to avoid such a case where the characteristics of a transmission line are changed by the switch of frequencies and the signal quantity is deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high frequency filter for communication equipment, and particularly to a multifrequency bandpass filter suitable for multifrequency switching.

[Conventional technology].

Conventionally, as shown in FIG. 3, this type of bandpass filter has been equipped with a wideband filter 3A having a band capable of passing multiple frequencies between an input terminal 1 and an output terminal 2. FIG. 4 shows an example of filter characteristics when switching between two frequencies. In FIG. 4, 11. a,,,, 1
lb is the center frequency used, 12 is the amplitude frequency characteristic, 13
is the group delay time frequency characteristic.

(Problems to be Solved by the Invention) - In the conventional filter described above, the slopes of the amplitude frequency characteristics and the second group delay time frequency characteristics are opposite at the two used frequencies 11a and llb, and the transmission path characteristics are changed by frequency switching. Therefore, 1. To equalize this, it is necessary to switch the equalizer at the same time as switching the frequency, which poses a problem that the configuration becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-frequency band-pass filter that eliminates the above-mentioned problems and suppresses characteristic changes that occur when switching frequencies.

[Means for Solving the Problems] The multi-frequency band-pass filter of the present invention has a configuration in which filters having band-pass characteristics at different center frequencies are arranged in parallel, and the input terminal and output terminal of each filter are shared. It is said that

[Effect]

The above-described configuration allows multiple frequencies to pass through, has substantially the same transmission characteristics, and eliminates the need for a switch when switching frequencies.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a circuit diagram of an embodiment of a multifrequency bandpass filter according to the present invention. In the figure, the multi-frequency band-pass filter has two band-pass filters 3a and 3b having different passbands arranged in parallel, and an input terminal 1.
The structure is such that the output terminal 2 and output terminal 2 are used in common.

The electrical characteristics between the input and output of the bandpass filters 3a and 3b are as shown in FIG.
Almost the same transmission characteristics for lb, that is, amplitude frequency characteristics 12a
, 12b, and group delay time frequency characteristics 13a, 13b.

Therefore, in this configuration, two bandpass filters 3
The cooperation of a and 3b allows multiple frequencies to pass through, and since each bandpass filter has independent characteristics, its transmission characteristics can be made almost the same, and the characteristics of the transmission path change by switching the frequency. Therefore, it is possible to avoid a situation where the signal quality deteriorates. Further, when changing the frequency, there is no need to change the flower vase with a switch, and the structure can be simplified.

In the above embodiment, the minimum two-frequency band-pass filter is used, but a filter with three or more frequencies can be constructed in the same manner.

〔Effect of the invention〕

As explained above, the present invention arranges bandpass filters with different passbands in parallel and shares the input and output terminals, so it is possible to pass multiple frequencies and at the same time have almost the same transmission characteristics. This has the effect of preventing signal quality deterioration, eliminating the need for a switch for frequency switching, and lowering the cost of a communication device with a frequency switching function.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of the multi-frequency band-pass filter according to the present invention, FIG. 2 is an electrical characteristic diagram of the multi-frequency band-pass filter according to the present invention, and FIG. 3 is a diagram of the conventional band-pass filter. The block circuit diagram, FIG. 4, is an electrical characteristic diagram of the bandpass filter of FIG. 3. 1...Input terminal, 2...Output terminal, 3a, 3b, 3
A... Band pass filter, lia, llb... Center frequency used, 12.12a, 1'2b... Amplitude frequency characteristic, 13.13a, 13b,... Group delay time frequency characteristic. Figure 1 Figure 2° Frequency

Claims (1)

[Claims] 1. A multi-frequency band-pass filter characterized in that a plurality of filters having band-pass characteristics at mutually different center frequencies are arranged in parallel, and these filters are configured to share one input terminal and one output terminal.