JPS5925409A - Band pass filter - Google Patents

Abstract

PURPOSE:To eliminate a interference wave with a simple constitution, by having a parallel connection between the 1st and 2nd attenuating pole elements which attenuate the interference wave of specific frequencies contained in the upper and lower bands which are approximate to the pass band of a reference BPF, then providing such electrode elements to one or both of input and output terminals. CONSTITUTION:A reference BPF circuit 4 is connected between an input terminal 2 and an output terminal 3 of a BPF1, and attenuating elements 5a and 5b are connected to either one or both of the terminals 2 and 3. These elements 5a and 5b are formed by having a parallel connection between the 1st attenuating elements 6a and 6b which attenuate the interference wave of specific frequencies contained in the upper band approximate to the pass band of the circuit 4 and the 2nd attenuating elements 7a and 7b which attenuate the interference wave of specific frequencies contained in the lower band. Then the sharp attenuation characteristics are obtained for both upper and lower bands which are approximate to the pass band of the BPF1. Thus it is possible to eliminate assuredly the interference wave contained in both bands.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bandpass filter, and more particularly to a bandpass filter that can steepen the attenuation characteristics in a band close to a passband and increase the amount of attenuation in a stopband.

The drawings showing the embodiments of the present application will be described below.

FIG. 1 is a block circuit diagram of a band-pass filter, where ■ indicates the band-pass filter, 2 indicates its input end, and 3 indicates its output end. 4 is a reference bandpass filter circuit, and a filter circuit having substantially the same passband as that required for the bandpass filter 1 is used. - Shown as an example are inductor elements Ll, L2 . L3. It consists of L4 and capacitor elements CI, C2, C3, and C4, and each inductor element and each capacitor element constitute a parallel resonant circuit, respectively. Also, the inductor element Ll.

L2. L3. A mutual inductance Ml, M2 . M3 is configured. 5a, 5
b is an attenuation element that sharpens the attenuation characteristic in a band close to the pass band to increase the amount of attenuation in the stop band. In the figure, an attenuation element 5a is provided between the reference bandpass filter circuit 4 and the input end 2, and an attenuation element 5b is provided between the reference bandpass filter circuit 4 and the output end 3. Only one of the above may be provided depending on the allowable amount. 6a and 6b are first attenuation pole elements, which are used to greatly attenuate and block interference waves of a specific frequency included in the upper band near the passband, and are made of any well-known notch filter circuit or trap circuit. . The one shown is the intatsuta element L5a ('L5
b),! : A trap circuit is used in which a capacitor element C6a (C6b) is connected in series to a parallel circuit with a capacitor element C5a (C5b). 7a and 7b are the second
This attenuation pole element is used to greatly attenuate and block interference waves of a specific frequency included in the lower band near the pass band, and is composed of any well-known notch filter circuit or trap circuit. The illustrated one is an inductor element L6a, (L
A trap circuit is used in which a capacitor element C3a (C8b) is connected in series to a parallel circuit of a capacitor element C7a (C7b) and a capacitor element C7a (C7b).

In the above configuration, a case will be described in which a desired signal (desired wave) and an interfering wave mixed therewith are input to the input end 2. In this case, the passband of the reference bandpass filter circuit 40 is selected to include the frequency of the desired wave. The desired wave is transmitted through the attenuation element 5a and the reference bandpass filter circuit 4. The light passes through the damping element 5b with almost no attenuation and is output from the output end 3. On the other hand, the interfering wave having a higher frequency than the desired wave is transmitted to the first attenuation pole element 5a, the reference bandpass filter circuit 4. It is attenuated by each of the first attenuation pole elements 6b, and is hardly output from the output end 3. Similarly, the desired wave and the low frequency interference wave are transmitted to the second attenuation pole element 7a, the reference bandpass filter circuit 4. It is attenuated by each of the second attenuation pole elements 7b, and almost no output is output from the output end 3.

Next, assemble the bandpass filter according to the configuration shown in Figure 1,
The measured electrical characteristics are shown in solid lines in FIGS. 2 and 3. FIG. 2 shows the attenuation characteristics of the bandpass filter, and FIG. 3 shows the VSWR characteristics, and the impedance of the measurement system is 75Ω. Note that the circuit constants during assembly were determined as follows.

The inductor elements are Ll, L4... Koinope L2. with a winding diameter of 4 m and a number of turns of 9.5. L3... Winding diameter 6yttys, number of turns 6.5 Koinope L5a, L5b... Winding diameter 6mm, number of turns 5.5
coils, L6a, L6b...winding diameter 6 mm, 5 turns number 5.
It was constructed using five coils. In addition, each coil has a wire diameter of O8
I used my friend's polyurethane coated copper wire.

The capacitor elements are CI, C4... Ceramic capacitor 1.5pF and trimacon 7p
Series circuit of F, C2, C3...Series circuit of ceramic capacitor 2pF and trimmacon 7pF, C5a, C5b...Series circuit of ceramic capacitor 1.5pF and trimmacon 7pF, C7a, C7b... Ceramic capacitor 1.5pF and trimmacon 7pF It was constructed using a series circuit of , .

The mutual inductance is calculated as follows: M1...Ll, L2 has a distance between the axes of each coil of 15 mm, and M2-...L2. The distance between the axes of each coil constituting L3 is 15 mm, and M3, fist, L3. The distance between the axes of each coil constituting L4 was set to 15. In addition, the reference bandpass filter circuit 4
The characteristics of this material are shown by dotted lines in FIGS. 2 and 3, respectively.

From Figure 2, the insertion loss is small (40 to 5.5 dB) in the passband (between 298, 25 and 302.75).
), 307.25 in the upper band close to the passband.
Over 60 dB of attenuation at 293.75 MHz and 70 dB at 293.75 MHz in the lower band.
It can be seen that even more attenuation can be obtained. It can be seen from FIG. 3 that excellent impedance characteristics with a VSWR of 1.29 or less can be obtained in the above pass band.

Next, FIG. 4 shows a block circuit diagram of a modulator using the bandpass filter 1, in which 8 is a modulator used for communal television reception, etc., with a video signal input terminal 9, an audio signal input terminal 10. An output terminal 11 is provided. The video signal input terminal 9 is connected to a television camera, a video signal output terminal of a VTR, or the like. Audio signal input terminal 1
0 is connected to a microphone or an audio signal output terminal of a VTR. A television signal of a predetermined channel is output from the output terminal 11. 12 is a video amplification circuit, and 13 is an audio amplification circuit, each of which is provided as required. 14 is an FM modulation circuit, 4.5MH
It is used to apply FM modulation to the carrier wave of z using the audio signal from the audio amplifier circuit 13. 15
is a local oscillation circuit which oscillates a sine wave having a frequency corresponding to the video carrier frequency of the television signal of the predetermined channel. 16 is a high frequency amplifier circuit, and 7 is a distribution circuit. 18
is an AM modulation circuit, which uses the sine wave sent from the local oscillation circuit 15 via the distribution circuit 17 as a carrier wave and performs AM modulation with the video signal from the video amplifier circuit 12, converting it into a television video signal of a predetermined channel and transmitting it to the subsequent stage. send to.

Reference numeral 19 denotes a frequency conversion circuit, which converts the frequency of the modulated carrier wave from the FM modulation circuit 14 using the sine wave sent from the local oscillation circuit 5 via the distribution circuit 17, and converts it into a television audio signal of a predetermined channel. and send it to the next stage. 20
indicates a mixed circuit.

In the above configuration, the video signal input terminal 9 is connected to V
Assuming that it is connected to the video signal output terminal of the TR, and that the audio signal input terminal 10 is connected to the audio signal output terminal of the VTR, and that the predetermined channel is channel W of the super high band (297 to 303 MHz > The operation of the modulator 8 will be explained. (In TV joint reception, Chi to 62) Other bands such as Nimiso band and super high band are often used. - For example,
(Refer to “Broadcasting Technology” October 1980 issue, p. 137)
. In this case, the output terminal 11 has super high band C.
Assume that a television receiver is connected via a frequency converter that converts hW to a channel in the TV VHF or UHF broadcast wave band (often using a channel that does not have broadcast waves). ○Local oscillation Circuit 15 is ChW
oscillates a sine wave of 298.25 MHz, which is the video carrier frequency of
82 frequency conversion circuit 19. On the other hand, the video signal input from the VTR to the input terminal 9 is transmitted to the video amplifier circuit 1.
2 and input to the AM modulation circuit 18. In the AM modulation circuit 18, modulation is applied using the video signal using the sine wave from the distribution circuit 17 as a carrier wave, and ChW
A video signal is generated and output to the mixing circuit 20.

Furthermore, the audio signal input from the VTR to the input terminal 10 is amplified by the audio amplification circuit 13 and is then amplified by the FM modulation circuit 1.
4 is input. The FM modulation circuit 14 oscillates 4, 5. A MHz carrier wave is modulated using the audio signal, and the signal is further frequency-converted in a frequency conversion circuit 19 to create a ChW audio signal and output to a mixing circuit 20.

In the mixing circuit 20, the ChW video signal and audio signal are mixed and output to the bandpass filter 1. The bandpass filter 1 removes unnecessary frequency components contained in the signal from the mixing circuit 20 so as not to adversely affect television reception of other channels, and outputs the signal. The signal thus transmitted from the output terminal 11 is converted from ChW to, for example, Ch2 by the frequency converter (not shown) and is received by a television receiver. Ch
Since W is a super high band, it goes without saying that ChW cannot be received if a television receiver is connected to the output terminal 11 without using the frequency converter.

Next, FIG. 5 is an explanatory diagram of the operation of the bandpass filter in the modulator, where (A) is a diagram showing the television signal spectrum at point A' in FIG. 4, and (B) is a diagram showing the attenuation characteristic of bandpass filter 1. , (C) is a diagram showing the television signal spectrum at point C' in FIG. At point A', which is the output of the mixing circuit 20, as shown in FIG. A signal is detected in which unnecessary frequency components 24, 25, 26, . . . are mixed in addition to the color subcarrier 22° and the audio carrier 23. This is due to the characteristics of the AM modulation circuit 182 and frequency conversion circuit 19. After this signal also passes through the bandpass filter 1, only the signal in the ChW band remains as shown in the spectrum diagram (C) at point C'. Level of video carrier wave 21 and unnecessary frequency components 24.・
Since the level difference between the two channels can be set to 55 dB or more, there is no risk of interference and beat disturbance even when mixed with signals of other super high band channels.

As mentioned above, even if you use a frequency converter to convert the ChW signal to a TV channel in the broadcast band, for example Ch2, and then mix it with the broadcast wave, for example, the Chi signal, there is no risk of causing beat interference to the broadcast wave. .

As described above, in this application, with a simple configuration, the attenuation characteristics are made steep in both the upper band and the lower band near the pass band, and interference waves of frequencies included in the stop bands on both sides are reliably removed. It has the great advantage of being able to.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram of a bandpass filter, Fig. 2 is a chart showing the attenuation characteristics of the bandpass filter, Fig. 3 is a chart showing the VSWR'lf characteristics of the bandpass filter, and Fig. 4 is a chart showing the bandpass filter I. Block circuit diagram of a modulator using 1, Fig. 5 (A), (BL (C) is an explanatory diagram of the operation of a band pass filter in the modulator. 1. Band pass filter, 2. Input end, 3...
・Output end, 4...Reference band pass filter circuit, 5a
, 5b-Φ・attenuation element, 6a, 6b...first attenuation pole element, 7a,, 7b...second attenuation pole element. Patent applicant Maspro Electric Works Co., Ltd. Representative Takashi Hatayama Figure 1 F Figure 3 Figure 2 Oka*Kan (M)-1z) −

Claims (1)

[Claims] In a bandpass filter in which a reference bandpass filter circuit is interposed between the input end and the output end, the filter is used to attenuate interference waves of a specific frequency included in an upper band close to the pass band of the reference bandpass filter circuit. A first attenuation pole element is connected in parallel with a second attenuation pole element for attenuating interference waves of a specific frequency included in a lower band close to the passband of the reference bandpass filter circuit. A bandpass filter characterized in that an attenuation element is connected to either or both of the input end and the output end.