JP2001016527A - Television receiver for mobile object and its signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a television receiver for a mobile object capable of eliminating adjustment of an audio detector coil. SOLUTION: Television broadcast received with an antenna 1 is outputted after having been discriminated in a video intermediate frequency signal and audio intermediate frequency signal in a high frequency tuner 2 and a band-pass filter 3. The audio intermediate frequency signal is inputted to a mixer circuit 5 and converted to a second audio intermediate frequency signal (10.7 MHz) being a difference against the local oscillation signal (43.55 MHz) through the circuit 5. After then, an audio detected signal is inputted to a control microcomputer 8 to execute automatic frequency control to a local oscillator circuit 6 so as to optimize the DC level of the audio signal outputted from the circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separate carrier type television receiver mounted on or carried by a mobile object such as an automobile, a bus, or a train.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing the configuration of a conventional separate carrier type mobile television receiver.
In FIG. 2, the mobile television receiver includes an antenna 1 for receiving a television broadcast, and a high-frequency tuner 2 for amplifying a signal received from the antenna 1 at a high frequency and outputting a frequency-converted intermediate frequency signal. ing. A band-pass filter 3 that discriminates the intermediate frequency signal output from the high-frequency tuner 2 into a video intermediate frequency signal (58.75 MHz) and an audio intermediate frequency signal (54.25 MHz) and outputs the signal. A video detection circuit 4 that outputs a video detection signal obtained by detecting the video intermediate frequency signal. In addition, bandpass filter 3
A mixer circuit 5 that outputs a second audio intermediate frequency signal (10.7 MHz) obtained by converting an audio intermediate frequency signal from the digital audio signal into a local oscillation signal, and supplies the local oscillation signal (4
(3.55 MHz), and an audio detection circuit 7 that outputs an audio detection signal obtained by detecting an audio intermediate frequency signal from the band-pass filter 3.

Next, the operation of this conventional example will be described. In this mobile television receiver, a received signal (television broadcast) received by an antenna 1 is input to a high-frequency tuner 2 to amplify it at a high frequency and output an intermediate-frequency signal whose frequency has been converted. The intermediate frequency signal output by the high-frequency tuner 2 is separated into a video intermediate frequency signal and an audio intermediate frequency signal by the band-pass filter 3 and output.
The video intermediate frequency signal is input to the video detection circuit 4 and outputs a detected video detection signal. On the other hand, the audio intermediate frequency signal is input to the mixer circuit 5 and converted into a second audio intermediate frequency signal (10.7 MHz) which is a difference from the local oscillation signal (43.55 MHz). The signal is demodulated by a sound detection circuit 7 into a sound detection signal.

[0004]

However, the above-mentioned conventional mobile television receiver has a drawback that the audio detection circuit 7 needs to adjust the audio detection coil.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in the prior art, and an object of the present invention is to provide a mobile television receiver capable of adjusting a voice detection coil without adjustment.

[0006]

According to a first aspect of the present invention, there is provided a receiving processing means for receiving a television broadcast and outputting a video intermediate frequency signal and a first audio intermediate frequency signal; Video detection means for detecting the video intermediate frequency signal from the reception processing means, and conversion means for converting the first audio intermediate frequency signal from the reception processing means into a second audio intermediate frequency signal converted by a local oscillation signal Variable local oscillation means for outputting the local oscillation signal having a variable frequency to the conversion means, audio detection means for detecting the second audio intermediate frequency signal from the conversion means, and output from the audio detection means The frequency of the variable local oscillation means is automatically controlled in accordance with the level of the voice detection signal to be generated, and the frequency for optimizing the DC level of the voice detection signal output from the voice detection means is optimized. It has a structure obtained by a number control unit. With this configuration, automatic frequency control is performed on the local oscillation circuit so that the DC level of the audio signal is optimized, so that a mobile television receiver in which the audio detection coil is not adjusted can be realized.

According to a second aspect of the present invention, a television broadcast is received via an antenna, and the first broadcast is distinguished and output as a video intermediate frequency signal and a first audio intermediate frequency signal. In the signal processing method for a mobile television receiver, the audio intermediate frequency signal is converted into a local oscillation signal, and then demodulated into a second audio intermediate frequency signal by an audio detector. The frequency of the local oscillation signal is automatically controlled in accordance with the DC level of the detection signal, and the DC level of the audio detection signal output by the audio detection means is set to an optimum value. According to this, since the frequency of the local oscillation signal is automatically controlled so that the DC level of the audio signal is optimized, a mobile television receiver in which the audio detection coil is not adjusted can be realized. .

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a separate-carrier mobile television receiver according to an embodiment of the present invention. In FIG. 1, members corresponding to those in FIG. 2 are denoted by the same reference numerals and described. A mobile television receiver according to an embodiment of the present invention includes an antenna 1 for receiving a television broadcast, and an antenna 1 A high frequency tuner 2 that amplifies a received signal and outputs an intermediate frequency signal obtained by frequency conversion, and a video intermediate frequency signal (58.7) from the intermediate frequency signal output by the high frequency tuner 2.
5MHz) and audio intermediate frequency signal (54.25MHz)
And a band-pass filter 3 for discriminating and outputting the received signal. Further, a video detection circuit 4 as a video detection means for outputting a video detection signal obtained by detecting the video intermediate frequency signal from the band-pass filter 3 and a second audio signal obtained by converting the audio intermediate frequency signal from the band-pass filter 3 into a local oscillation signal 2 audio intermediate frequency signal (10.7MHz)
, A local oscillation circuit 6 as a variable local oscillation means for outputting a local oscillation signal (43.55 MHz) to the mixer circuit 5, and an audio intermediate frequency signal from the band-pass filter 3. Audio detection circuit 7 as an audio detection means for outputting an audio detection signal obtained by detecting the frequency, and frequency control for automatically changing the frequency of the local oscillation circuit 6 so that the DC level of the audio signal of the audio detection circuit 7 is optimized. It has a control microcomputer 8 (hereinafter, referred to as "control microcomputer 8") as a means.

Next, the operation of this embodiment will be described. In this mobile television receiver, a reception signal (television broadcast) received by the antenna 1 is transmitted to the high-frequency tuner 2.
, And amplifies the signal at a high frequency, and outputs an intermediate frequency signal whose frequency has been converted. The intermediate frequency signal output by the high-frequency tuner 2 is separated into a video intermediate frequency signal and an audio intermediate frequency signal by the band-pass filter 3 and output. The video intermediate frequency signal is input to the video detection circuit 4 and outputs a detected video detection signal. On the other hand, the audio intermediate frequency signal is input to the mixer circuit 5 and is converted into a second audio intermediate frequency signal (10.7 MHz) which is a difference from the local oscillation signal (43.55 MHz). Thereafter, the signal is demodulated into a sound detection signal by a sound detection circuit 7. The output of the sound detection signal is input to a control microcomputer 8, and the control microcomputer 8 changes the local oscillation circuit 6 by applying automatic frequency control to the sound signal. So that the DC level is optimal.

That is, the most frequently used audio detection method for TV is the quadrature detection method. This method uses a filter whose phase changes in proportion to a change in frequency, and performs detection by multiplying a signal that has passed through the filter by a signal that does not pass. This filter characteristic is designed so that the phase of the input signal is turned by 90 degrees at the audio intermediate frequency, and the detection output voltage changes according to the amount of phase change with respect to the frequency change. The control microcomputer 8 applies automatic frequency control to the local oscillation circuit 6 so that the detection output voltage of the local oscillation circuit matches the audio intermediate frequency.

Therefore, in the mobile television receiver according to the present embodiment, the local oscillation circuit 6 is subjected to automatic frequency control so that the DC level of the audio signal output from the audio detection circuit 7 is optimized. Therefore, it is possible to eliminate the need for adjusting the voice detection coil.

[0012]

As described above, according to the present invention, the automatic frequency control is performed on the local oscillation circuit so that the DC level of the audio signal output from the audio detection circuit is optimized. It is possible to provide a mobile television receiver in which a coil is not adjusted.

[Brief description of the drawings]

FIG. 1 is a configuration lock diagram of a mobile television receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional mobile television receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 High frequency tuner 3 Band-pass filter 4 Video detection circuit 5 Mixer circuit 6 Local oscillation circuit 7 Audio detection circuit 8 Control microcomputer

Claims (2)

[Claims] 1. A reception processing means for receiving a television broadcast and outputting a video intermediate frequency signal and a first audio intermediate frequency signal; and a video detection means for detecting a video intermediate frequency signal from the reception processing means. Converting means for converting the first audio intermediate frequency signal from the reception processing means into a second audio intermediate frequency signal converted by a local oscillation signal; outputting the local oscillation signal having a variable frequency to the converting means; Variable local oscillator means, a sound detection means for detecting the second audio intermediate frequency signal from the conversion means, and a frequency of the variable local oscillation means according to a level of a sound detection signal output by the sound detection means. Frequency control means for automatically controlling the DC level of the audio detection signal output by the audio detection means to an optimum value. Body TV receiver. 2. A television broadcast is received via an antenna, and said first audio intermediate frequency signal, which is discriminated into a video intermediate frequency signal and a first audio intermediate frequency signal, is output as a local oscillation signal. In the signal processing method for a mobile television receiver, which is converted and then demodulated into a second audio intermediate frequency signal by an audio detection means, the local area is controlled according to the DC level of the audio detection signal output by the audio detection means. Automatically control the frequency of the oscillation signal,
A signal processing method for a mobile television receiver, wherein the DC level of an audio detection signal output by the audio detection means is set to an optimum value.