JPH02309880A - Voice filter circuit - Google Patents

Abstract

PURPOSE:To satisfactorily delete or reduce a disturbance signal approximate to 4.5MHz by securing the serial connection between two 4.5MHz band pass filters having different out-band characteristics. CONSTITUTION:The 1st and 2nd 4.5MHz band pass filters 14 and 16 having different out-band characteristics are connected in series in a voice filter circuit 12. Thus the filter characteristics of both filters 14 and 16 connected in series show the multiple effects to satisfactorily delete or reduce a disturbance signal approximate to 4.5MHz. Then the voice S/N is extremely improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a video intermediate frequency amplification circuit and a four ．．
5 MHz audio detection circuit, and removes or reduces the interference signal contained in the audio intermediate frequency signal input from the video intermediate frequency amplification circuit, and then converts the audio intermediate frequency signal inputted from the video intermediate frequency amplification circuit into the audio intermediate frequency signal as described in 4.5 above.
This invention relates to an audio filter circuit that outputs to a MHz audio detection circuit.

(Prior art) In general, in a color television receiver, a composite color video signal and audio signal received by an antenna are amplified by a high frequency amplifier circuit, and then a mixing circuit in the next stage performs hetero gain detection to generate two intermediate frequency signals. signals, and amplify them with a video intermediate frequency amplification circuit. Then, one intermediate frequency signal is input as an audio intermediate frequency signal to a 4.5 MHz audio detection circuit, and from then on, low frequency signals are detected using well-known circuit processing. The signal is played back and output as audio from a speaker.

By the way, the audio intermediate frequency signal given from the video intermediate frequency amplification circuit to the 4.5 MHz audio detection circuit may contain an interference signal, and the 4.5 MHz audio detection circuit is sent with the interference signal still on it. It is known that when an audio intermediate frequency signal is output, the audio S/N deteriorates.

Therefore, conventionally, a video intermediate frequency amplification circuit and a 4°5 M
An audio filter circuit is provided between the Hz audio detection circuit and the interference signal to remove or reduce the interference signal, thereby improving the audio S/N ratio.

(Problems to be Solved by the Invention) As a conventional audio filter circuit 2, as shown in FIG.
．． Bypass filter 4 and 4°5M I-I that have the effect of removing or reducing video signal components of 5Ml4z or less
There is one in which bandpass filters 6 and z bandpass filters are connected in series. 8 is a video intermediate frequency amplification circuit; 10
is a 4.5MHz audio detection circuit.

When an audio intermediate frequency signal as shown in FIG. 4 is input to the audio filter circuit 2 having such a configuration, the signal shown in FIG. An audio intermediate frequency signal having a waveform as shown is output from the audio filter circuit 2.

Referring to Fig. 4, as is clear, this audio intermediate frequency signal uses 4.5M I-1z from amateur radio etc.
In some cases, the interference signal S is included at a frequency of 5.4 MHz, which is close to 4.5 MHz.
As shown in Fig. 5, there is a characteristic in frequency bands other than the predetermined frequency band centered on z that the interference signal S bounces back without being removed. 4.5MHz as is
This will end up being output to the audio detection circuit IO. Of course, there is a problem in that such rebound of the interference signal S deteriorates the audio S/H.

The present invention has been made in view of the above problems, and includes four
．． The purpose is to improve the S/N ratio of audio by sufficiently removing or reducing interference signals near 5 MHz.

(Means for Solving the Problem) In order to achieve such an object, the audio filter circuit of the present invention uses four filters having different out-of-band characteristics.
, 5MHz bandpass filters are connected in series in two stages.

(Function) Two audio filter circuits having different out-of-band characteristics
Since two 4.5 MHz bandpass filters are connected in series, the filter characteristics of both filters act synergistically to sufficiently remove or reduce interference signals near 4.5 MHz.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an audio filter circuit according to an embodiment of the present invention, and parts corresponding to those in FIG. 3 are designated by the same reference numerals, and explanations of the parts having the same reference numerals are omitted.

The characteristic configuration of the audio filter circuit 12 of this embodiment is that two first and second 4.5 MHz band pass filters 14 and 16 having different out-of-band characteristics are connected in series. be.

The first bandpass filter 14 is a ceramic filter manufactured by Murata Manufacturing Co., Ltd. (part name: 5PE4.5M
BJ), and a ceramic filter (part name r5PS4.5MDJ) also manufactured by Murata Manufacturing Co., Ltd. is used as the second bandpass filter I6.

FIG. 2 is a diagram showing the output waveform when the audio intermediate frequency signal having the waveform as shown in FIG. 4 is input to the audio filter circuit I2, and as is clear from FIG. The filter circuit 12 has a sharp peak at 4.5 MHz, and the interference signal S of 5 or 4 MHz caused by amateur radio etc. is sufficiently removed or reduced.

Therefore, in the audio filter circuit I2 of this embodiment, the interference signal S included in the audio intermediate frequency signal can be sufficiently removed or reduced, and as a result, the audio S/N can be significantly improved.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
It is possible to sufficiently remove or reduce interfering signals near 4.5 MHz, thereby improving the S/N of audio.

[Brief explanation of the drawing]

1 and 2 relate to an embodiment of the present invention, and FIG. 1 is a circuit diagram of an audio filter circuit according to the embodiment provided between a video intermediate frequency amplification circuit and a 4.5 MHz audio detection circuit. , FIG. 2 is an output waveform diagram of the same audio filter circuit. 3 to 5 relate to conventional examples, FIG. 3 is a circuit diagram of the audio filter circuit according to the conventional example corresponding to FIG. 1, FIG. 4 is an input waveform diagram of the audio filter circuit, and FIG. The figure is an output waveform diagram of the audio filter circuit. 8...Video intermediate frequency amplification circuit, 10...4.5MH
2 audio detection circuit, 12... audio filter circuit, 14.
...first bandpass filter, 16...second bandpass filter. Figure 1 (Circuit diagram of the embodiment of the present invention) Figure 2 (Output waveform diagram of the embodiment circuit) Figure 3 (Circuit diagram of the conventional example) Figure 4 (Input waveform diagram of the conventional circuit) Figure 5 (Output waveform diagram of conventional circuit)

Claims (1)

[Claims] (1) Provided between a video intermediate frequency amplification circuit and a 4.5 MHz audio detection circuit in a television receiver, etc., to remove interference signals contained in the audio intermediate frequency signal input from the video intermediate frequency amplification circuit. or an audio filter circuit that outputs the 4.5 MHz audio signal to the 4.5 MHz audio detection circuit after reducing the 4.5 MHz audio signal, which has different out-of-band characteristics.
An audio filter circuit comprising two stages of MHz bandpass filters connected in series.