JPH0777444B2 - Filter switching circuit in audio circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION “Industrial application field” The present invention relates to an audio intermediate frequency signal which is set by a band pass filter in response to different frequency intervals of audio signal subcarriers in satellite broadcasting television. The present invention relates to a filter switching circuit in an audio circuit whose bandwidth can be switched.

"Prior Art" Generally, in satellite broadcast television, audio signals of a plurality of different subcarriers are assigned and inserted in the frequency range of one video channel, and further, up to adjacent frequencies of this subcarrier. The intervals often vary from channel to channel.

However, conventionally, in the audio intermediate frequency tuning circuit, in order to prevent interference with an adjacent audio signal, a bandpass filter having a bandwidth based on the subcarrier having the narrowest interval is used.

"Problems to be solved by the invention" As described above, even if the bandpass filter having the narrowest frequency band width avoids interference, in the case of a voice signal having a wide band width, the sideband is cut and the sound quality is deteriorated. Especially, in the case of stereo music, the sound quality tends to deteriorate.

"Means for Solving Problems" The present invention relates to a tuner circuit 2 for receiving a reception signal of satellite television.
After converting to a video intermediate frequency signal with, and detecting and amplifying this,
A subcarrier filter circuit 8 extracts a subcarrier signal for an internal audio signal, an audio intermediate frequency signal is further obtained by a mixing circuit 10, and this signal is reproduced through a bandpass filter and an audio amplifier circuit 16. In the circuit, the band-pass filter includes a narrow band-pass filter 12 having a narrow sub-carrier spacing mainly composed of the ceramic piezoelectric vibrators 18 and 19, and a wide-band band-pass filter 13 having a wide sub-carrier spacing. The bandpass filters 12 and 13 are switched by the switching circuit 34.
According to the filter switching circuit in the audio circuit, the switching diodes 30, 31, 32, 33 coupled to the ceramic voltage oscillators 18, 19 are selectively turned on and off.

"Operation" The tuner circuit 2 selects a predetermined channel from the reception signal of the satellite broadcasting television of 430 to 930 MHz to obtain a 70 MHz video intermediate frequency signal. After this signal is detected and amplified, an audio signal subcarrier filter circuit 8 obtains an audio signal subcarrier signal of 4.8 to 8.2 MHz, and a local oscillation signal is mixed with this to obtain an audio intermediate frequency signal of 10.7 MHz. . When the frequency range to the adjacent subcarrier signal is narrow and there is a risk of interference, the narrowband bandpass filter 12 is selected by the switching circuit 34, and when the frequency range to the adjacent subcarrier signal is wide, In order to improve the sound quality, the switching circuit 34 selects the wideband bandpass filter 13.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

1 is an input terminal of a satellite broadcasting television of 430 to 930 MHz, and this input terminal 1 outputs the signal of the selected channel to 70 MHz.
Tuner circuit 2 for converting into an intermediate frequency signal, intermediate frequency amplifier circuit 3 for amplifying the same, limiter circuit 4 for amplitude limitation, video detection circuit 5 for extracting a composite video signal, and video amplifier circuit 6 for subsequent video. It is coupled to a video output terminal 7 for signal processing. Further, the output of the video amplifier circuit 6 is branched and coupled to a subcarrier filter circuit 8 for extracting a 4.8 to 8.2 MHz subcarrier for an audio signal.
It is coupled to the mixing circuit 10 along with the 8.9 MHz local oscillator circuit 9. This mixing circuit 10 is coupled to a narrow band bandpass filter 12 and a wideband bandpass filter 13 via a coupling capacitor 11, and a voice detection circuit 15, a voice amplification circuit 16 and a voice output terminal via a coupling capacitor 14. Is bound to 17.

The narrow band bandpass filter 12 has a bandwidth of 150 KHz.
The wide band pass filter 13 has a bandwidth of 280KHz.
Then, the narrow band band pass filter 12 and the wide band band pass filter 13 are respectively ceramic piezoelectric vibrators 18, 19, resistors 20, 21, 22, 23, 24, 25, 26, 27, 28,
29, switching diodes 30, 31, 32, 33, switching circuit
It consists of 34. One of the switching circuits 34 is a narrow band contact 35 and the other is a wide band contact 36.
B) is connected.

In the above configuration, the tuner circuit 2 selects a predetermined channel from the satellite broadcasting of 430 to 930 MHz, obtains the video intermediate frequency signal of 70 MHz, and outputs the limiter circuit 4.
The video signal is taken out through the detection circuit 5, further amplified, and sent to the output terminal 7.

4.8 to 8.2MH in subcarrier filter circuit 8 for audio signals
A subcarrier signal for a voice signal between z is extracted, a local oscillation signal in 15.5 to 18.9 MHz is mixed with this, and a signal of 10.7 MHz is extracted from the mixing circuit 10.

Here, when the frequency interval between adjacent subcarriers is narrow, the switching circuit 34 is switched to one narrow band contact 35 side. Then, the switching diodes 30 and 31 are turned on, the narrow-band bandpass filter 12 operates, and a signal having a bandwidth of 150 KHz is sent to the audio output terminal 17 via the audio detection circuit 15 and the audio amplification circuit 16.

When the subcarrier frequency interval is wide, the switching circuit 34
Is switched to the other narrow band contact 35 side, the switching diodes 32 and 33 are turned on, the wide band pass filter 13 is operated, and a signal having a bandwidth of 280 KHz is obtained.

"Advantages of the Invention" (1) The band width of the narrow band band pass filter 12 or the wide band band pass filter 13 can be switched according to the width of the frequency interval between the adjacent audio signal sub-carrier signals, thereby preventing interference. It can be used in a narrow band when, and in a wide band when improving sound quality.

(2) The narrowband bandpass filter 12 and the wideband bandpass filter 13 are three-terminal ceramic piezoelectric vibrators 18,
A ceramic type mainly composed of a ceramic piezoelectric vibrator 19 and a switching diode 3 for switching.
The circuit configuration is simple by using 0, 31, 32, 33,
Moreover, it is possible to obtain a product having excellent characteristics.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a filter switching circuit in a voice circuit according to the present invention.

Claims (1)

[Claims] 1. A satellite broadcast television received signal is converted into a video intermediate frequency signal by a tuner circuit 2, detected and amplified, and a subcarrier filter circuit 8 extracts a subcarrier signal for an internal audio signal. An audio intermediate frequency signal is obtained by the mixing circuit 10, and this signal is reproduced through a bandpass filter and an audio amplifier circuit 16.In the audio circuit, the bandpass filter is mainly composed of ceramic piezoelectric vibrators 18 and 19. A narrow band bandpass filter 12 when the subcarrier spacing is narrow and a wideband bandpass filter 13 when the subcarrier spacing is wide.The switching circuit 34 switches between these bandpass filters 12 and 13. The switching diodes 30, 31, 32 and 33 coupled to the ceramic piezoelectric vibrators 18 and 19 are selectively turned on and off. Filter switching circuit in the speech circuit, characterized in.