JPH02179084A - Automatic channel selection device - Google Patents

Abstract

PURPOSE:To correctly perform an automatic channel selection by discriminating a channel selection state by utilizing the detuning characteristic detecting signal of a video carrier and the level detecting signal of a sound carrier regardless of the presence/absence of a synchronous signal, and controlling a channel selection frequency. CONSTITUTION:The output of a local oscillator 2 and a television carrier signal are mixed by a mixer 1, and a video/audio intermediate frequency carrier signal 16 can be obtained. The signal 16 is inputted to a video carrier detector 5, and a video carrier detuning characteristic detecting signal 17 is inputted to a deciding device 9. Similarly, the signal 16 is inputted to a sound carrier detector 7, and a sound level detecting signal 18 is inputted to the deciding device 9. At the deciding device 9, a selection signal 20 is outputted from a controller 11 when the channel selection state is not set at a tuning state by a channel selection state deciding signal 19 from the deciding device 9 which outputs a deciding signal representing the channel selection state of an oscillator 2 relatively centering tuning time from two signals. When the oscillator 2 is varied sequentially and it is repeated until a time when the signal 19 shows the tuning state and the tuning state is set, the signal 17 is switched to an oscillator 4, then, channel selection is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic channel selection device that can select a television carrier signal regardless of whether or not the video signal is scrambled.

Conventional technology A conventional automatic channel selection device will be explained with reference to FIG.

That is, the conventional automatic channel selection device performs full automatic channel selection of the television carrier wave signal 16 using the video intermediate frequency carrier wave 16 which is PF-converted from the television carrier wave signal in the mixer 1. A video carrier wave detector 6 that detects the detuning characteristic of the video intermediate frequency carrier wave 16, a sync separator 25 that detects synchronization from the demodulated video signal, a detuning characteristic detection signal 17 of the video intermediate frequency carrier wave, and a synchronization detection signal. Determiner 9 that determines the channel selection state by 26
The tuning voltage controller 12 is controlled by the tuning state determination signal 19 from the
It consists of a control device 11 that controls. Then, the control device 11 controls the tuning voltage controller 12 to operate one local oscillator 2 so that the detection level of the carrier wave is the highest and a synchronization signal can be obtained satisfactorily to obtain tuning. This is the so-called voltage phase-lock Druze method (voltage PLL method)
It is.

Problems to be Solved by the Invention In the conventional example described above, it is sufficient that the video signal is not subjected to scrambling processing, but scrambling processing using the so-called sync shift method or sync suppress (synchronous compression) method that shifts the synchronization signal of the video signal is acceptable. If this were done, legal problems would arise.

In other words, conventional automatic tuning devices detect changes in output voltage depending on the presence/absence of the detuning characteristic detection signal of the video carrier wave and the synchronization signal from the synchronization signal separator to determine whether or not the tuning has been performed correctly. The biggest feature is that it is used as a signal.

However, if the video signal has been scrambled and the synchronization of the video signal has been shifted, the synchronization signal separator will no longer be able to discriminate, and as a result, the separator output (synchronization detection signal) will be used as the standard for channel selection. Conventional automatic channel selection devices have the disadvantage of not being able to select channels correctly.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides an automatic channel selection device that can automatically select a channel even with a signal that has been scrambled using a sync shift method or a sync suppress method.

Means for Solving the Problems A video carrier detuning characteristic detection signal from a video carrier detector and a carrier level detection signal from an audio carrier detector are used to obtain tuning using these three signals.

Since a synchronization signal is not used as a reference signal for channel selection, it is not possible to use a synchronization signal by scrambling the video signal.
Correct channel selection can be made regardless of the situation.

Embodiment The automatic device of the present invention is characterized in that it automatically selects a television broadcast carrier signal using an audio intermediate frequency carrier wave and a video intermediate frequency carrier wave.

An automatic channel selection device for a CATV converter according to an embodiment of the present invention will be described below with reference to FIG. The automatic channel selection device of this embodiment is a television channel.

The digital carrier signal is input to mixer 1 and mixer 3 to obtain video and audio intermediate frequency carrier signal 161.

This is supplied to an audio carrier wave detector 7 that detects the carrier level of the audio intermediate frequency carrier wave 16 and a video carrier wave detector 6 that detects the detuning characteristic of the video intermediate frequency carrier wave 16.

The carrier wave level detection signal 18 from the audio carrier wave detector 7 and the detuning characteristic detection signal 17 of the video intermediate frequency carrier wave from the video carrier wave detector 6 are input to the determiner 9 which determines the channel selection state.

The carrier wave level detection signal input to the determiner 9 has a proportional relationship to the input level of the carrier wave, and the detuning characteristic detection signal has a figure-8 characteristic, and a zero level signal is supplied at the tuning point. . Therefore, in the determiner 9.

The tuning/detuning state can be detected by performing calculations based on both of these three signals so as to obtain a mund logic. Video carrier detector 6 as described above. The audio carrier detector 7 and the determiner 9 constitute a determining device 1o. The channel selection state determination signal 19 from the determiner 9 in the determination device 10 is input to the control device 11, and from this control device 11 the channel selection voltage controller 12 and the separation of the video intermediate frequency carrier from the video carrier detector 6 are input. 0N of the loop of the key characteristic detection signal 17 to the second local oscillator 4
It outputs a control signal for controlling the switch 13 that performs 10FF switching.

The operation of the automatic channel selection device configured as described above will be explained below.

First, when a specific channel, channel 10 in this case, is selected, the control device 11 outputs a switching control signal 21 to prevent the video carrier detuning characteristic detection signal 17 of the video carrier detector 6 from being output to the local oscillator 4. switch 13
Turn off.

Next, the control device 11 outputs a channel selection control signal 20 to the channel selection voltage controller 12 in order to select the Shira 0 channel. The output voltage from the tuning voltage controller 12 sets the local oscillator 2 to an oscillation frequency that allows broadcasting signals of 10 channels to be obtained.

The oscillation output of the local oscillator 2 and the television broadcast carrier signal 16 are mixed by the mixer 1 to produce a video image.

An audio intermediate frequency carrier signal 16 is obtained. This video,
The audio intermediate frequency carrier signal 16 is generated by inputting the video intermediate frequency carrier signal selectively to the video carrier detector 6, and outputting the video carrier detuning characteristic detection signal 1 from the video carrier detector 5.
7 is input to the determiner 9. Similarly, the audio intermediate frequency carrier signal is input to the audio carrier detector 7, and the audio carrier level detection signal 18 is input from the audio carrier detector 7 to the determiner 9. In the determiner 9, these two signals are used to determine the tuning status (video and audio intermediate frequency reception status, O/N) at the currently set oscillation frequency of the local oscillator 2
), which outputs a judgment signal relative to the time of tuning.If the tuning state (video, audio intermediate frequency) is not yet in tune, the control device A channel selection control signal 2o is output from 11 to a channel selection voltage controller 12 to sequentially change the oscillation frequency of the local oscillator 2. Thereafter, the same procedure is repeated until the tuning state determination signal 19 from the determiner 9 indicates the tuned state.

When the tuned state is obtained, the tuning voltage setting is maintained by the control device 11, the switch 13' is turned on, and the video carrier detuning characteristic detection signal 17 is applied to the local oscillator 4 to complete the tuning operation. do. In this synchronized state, the KRY signal for descrambling inserted during the vertical blanking period, etc. is extracted, and the descrambling device 14 descrambles the video signal based on the KEY signal, thereby producing a TV set. ◇ As described above, according to this embodiment, the detuning characteristic detection signal obtained based on the video intermediate frequency carrier signal and the audio intermediate frequency carrier signal are obtained by detecting the detuning characteristic detection signal. Based on the two signals of the audio carrier level detection signal indicating the signal level, it is possible to automatically tune into a state in which the detuning characteristic detection signal is at zero level and the audio carrier level detection signal is at the maximum level. It is also possible to automatically tune into a shifted scrambled video (television) signal in which the synchronization signal is suppressed.

Effects of the Invention As described above, according to the present invention, even if the broadcast signal has undergone scramble processing in which the synchronization signal of the video rotor has been shifted or suppressed, the detuning characteristic detection signal of the video carrier wave and the level detection signal of the audio carrier wave can all be detected. By using this to determine the channel selection state and control one channel selection frequency, correct automatic channel selection becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an automatic tuning device according to an embodiment of the present invention. FIG. 2 is a block diagram of a conventional automatic tuning device. 1.3...Mixer, 2,4...Local oscillator, 6...Video carrier wave detector, 7...
- Audio carrier wave detector. 9... Judgment device.

Claims (2)

[Claims] (1) An automatic tuning device that automatically tunes a television carrier signal using an audio intermediate frequency carrier wave and a video intermediate frequency carrier wave, which includes an audio carrier wave detector that detects the carrier level of the audio intermediate frequency carrier wave, and a video intermediate frequency carrier wave. A video carrier wave detector detecting detuning characteristics of a frequency carrier wave, a carrier wave level detection signal indicating the audio carrier level of a received signal from the audio carrier wave detector, and a detuning characteristic detection signal of a video intermediate frequency carrier wave from the video carrier wave detector. What is claimed is: 1. An automatic tuning device comprising: a determiner that determines a tuning state; and a tuning voltage controller that is controlled in a tuning direction based on a tuning state determination signal from the determiner. (2) A CATV converter characterized by incorporating the automatic channel selection device according to claim 1.