JPH0265312A - Television broadcasting signal deciding circuit - Google Patents

Abstract

PURPOSE:To detect that a broadcast is not executed without fail by detecting that an output level goes to be <= a prescribed value when a tuning frequency is dislocated by the prescribed value even in case that there is or not a synchronizing signal in the video signal of an intermediate frequency in a selected TV channel. CONSTITUTION:A tuner 1 selects the TV channel according to an output signal 50 of a microcomputer 5 for channel selection and the TV channel is converted to the intermediate frequency and inputted to an intermediate frequency processing circuit 2. A video signal 200 is detected and outputted by the intermediate frequency processing circuit 2 and a sound intermediate frequency 100 is outputted. The synchronizing signal in the video signal 200 is detected by a synchronizing signal detecting circuit 4. Then, when the synchronizing signal is not included, it is decided that the broadcast is not executed on the channel. When the video signal is included, the output voltage 50 is changed and the tuning frequency of the tuner 1 is changed by the prescribed value. Then, when it is detected that the output level is lowered to be <=the prescribed value, it is decided that the broadcast is not executed on the channel. Thus, even when the broadcast is executed on the adjacent channel with a strong electric field, the presence or absence of the broadcast on the subject channel is exactly detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a television broadcast signal determination circuit that determines the presence or absence of a television signal.

(Prior Art) In conventional televisions (TVs), when a channel is not being broadcast or a channel that has finished broadcasting is selected, video noise is output on the screen and audio is amplified from the speaker. Some have functions such as muting noise or switching the screen to a blue screen so that viewers do not feel uncomfortable. This function is performed by using a synchronization detection circuit to detect whether or not a horizontal synchronization signal is included in the video detection output of the broadcast signal receiving system, and if not, determining that there is no broadcast.

However, with the conventional television broadcast signal detection circuit that detects the presence or absence of a broadcast signal using only the synchronization detection circuit as described above, even if there is no signal on the selected channel, there is a strong electric field in the adjacent channels above and below. When there is a broadcast, when a carrier that has undergone video modulation of an adjacent channel due to intermodulation inside the tuner enters the band, the synchronization detection circuit detects a synchronization signal, and the broadcast is not performed on that channel. There was an inconvenience in that it was assumed to be broadcast even though it was not.

(Problem to be Solved by the Invention) As mentioned above, in the conventional television broadcast signal determination circuit, the presence or absence of broadcasting is determined by whether or not a synchronization detection circuit detects a synchronization signal in the video signal of the receiving channel. Therefore, even if the selected channel is not broadcasting, if there is a broadcast with a strong electric field on the adjacent channel above or below it,
This has the drawback of causing a malfunction in which a channel that is not broadcast is assumed to be broadcasting. Therefore, the present invention aims to eliminate the above-mentioned drawbacks, and is capable of accurately detecting the presence or absence of broadcasting on a target channel even when broadcasting with a strong electric field is performed on the upper and lower channels adjacent to the target channel whose presence or absence of broadcasting is to be detected. It is an object of the present invention to provide a television broadcast signal determination circuit that can perform the following functions.

[Structure of the Invention] (Means for Solving the Problems) A television broadcast signal determination circuit of the present invention includes a receiving means for receiving a television broadcast signal of a selected channel and converting it into an intermediate frequency signal, video signal detection means for detecting a video signal from a signal; synchronization signal detection means for detecting whether or not a synchronization signal is present in the output of the video signal detection means; AFT detection means outputs a discrimination signal having a voltage level according to the deviation from the television broadcast signal, and detects whether or not the receiving means is tuned to a television broadcast signal; and when the synchronization signal detection means does not detect a synchronization signal. determines that there is no broadcast signal on the selected channel, and the synchronization signal detection means detects a synchronization signal.
The present invention has a configuration comprising determining means for detecting the discrimination signal level of the FT detecting means and determining that there is no broadcast signal on the selected channel when the level is different from a predetermined value.

(Operation) In the television signal determination circuit of the present invention, the receiving means receives the television broadcast signal of the selected channel and converts it into an intermediate frequency signal.

The intermediate frequency signal is detected by a video signal detection means and output as a video signal. The synchronization signal detection means receives the video signal, detects the presence or absence of the synchronization signal, and outputs the result to the determination means. Further, the AFT detection means receives the intermediate frequency signal, outputs a discrimination signal having a level corresponding to the difference between the intermediate frequency and the reference frequency, and detects whether or not the receiving means is tuned to the television broadcast signal based on this output. and outputs the result to the determining means. The determining means determines that there is no broadcast signal of the selected channel when the synchronizing signal is not detected by the synchronizing signal detecting means, and the determining means determines that there is no broadcast signal of the selected channel when the synchronizing signal is detected and the receiving means is tuned to the broadcast signal by the AFT detecting means. If it is detected that there is no broadcast signal, it is determined that there is no broadcast signal.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the television broadcast signal determination circuit of the present invention.

1 is a general tuner that selects the channel of a broadcast signal received by an antenna according to a tuning voltage 50, converts it into an intermediate frequency signal and outputs it; 2 is a tuner that inputs the intermediate frequency signal from the tuner and has a predetermined frequency characteristic. A general intermediate frequency processing circuit including an intermediate frequency amplification stage for amplifying, a video detection stage for detecting and outputting the video signal 200 from the intermediate frequency signal, and an audio output stage for outputting the audio intermediate frequency signal 100; 3 is a receiving means; 8 is a bottom side output circuit that detects whether the tuning frequency matches the carrier frequency of the broadcast signal, that is, whether or not it is tuned by the AFT voltage; 4 is a synchronization circuit that detects the absence of the synchronization signal of the video signal 200; A signal detection circuit 5 outputs a tuning voltage 50 according to the user's channel selection operation means A to the tuner 1, and determines whether the channel selected from the detection results of the AFT detection circuit 3 and the synchronization signal detection circuit 4 is being broadcast. This is a microcomputer for channel selection that includes a determining means for determining whether or not the channel is selected.

Figure @2 is a characteristic diagram of the synchronization signal detection circuit 4, and when there is a broadcast signal with a video carrier frequency f, the video signal 20
A synchronizing signal is detected from 0 and its output is set to low level. On the other hand, FIG. 3 is a characteristic diagram of the AFT detection circuit 3, and when the tuning frequency of the tuner 1 matches the video carrier frequency fp of the received broadcast signal, the AFT voltage is set to a low level.

Next, the operation of this embodiment will be explained. The high frequency broadcast signal received by the antenna enters the tuner 1, where it is received based on the tuning voltage 50 output from the 33M microcomputer 5, and is further mixed with a predetermined local oscillation signal and converted into an intermediate frequency signal. , intermediate frequency! 2!1 Input to logic circuit 2. The intermediate frequency processing circuit 2 amplifies the input intermediate frequency signal with necessary frequency characteristics, detects the video signal 200 with a video signal detection circuit (not shown), outputs it to the next stage (not shown), and further amplifies the audio intermediate frequency signal. Output the signal 100 to the next stage with (η). AFT detection circuit 3
is a general discrimination circuit that inputs a video intermediate frequency signal from the intermediate frequency processing circuit 2, discriminates its frequency, and outputs a discrimination signal having a figure-8 characteristic according to the deviation of the video carrier intermediate frequency from the reference frequency. , includes a shaping circuit that converts the discrimination output into a binary signal, detects whether the tuning circuit of the tuner 1 is accurately tuned to the carrier frequency of the broadcast signal, and sends the result to the tuning microcomputer 5. Output to.

At the same time, the synchronization signal detection circuit 4 is connected to the intermediate frequency processing circuit 2.
It is detected whether or not the same IF) signal is included in the video signal output of , and the result is output to the channel selection microcomputer 5. If the synchronization signal detection circuit 4 does not detect a synchronization signal, the channel selection microcomputer 5 determines that there is no broadcast signal on the selected channel, and outputs this determination signal 300 to the next stage (not shown). . Further, when the synchronization signal detection circuit 4 detects a synchronization signal, the tuning microcomputer 5 first shifts the tuning frequency of the tuner to the carrier frequency f -300KH2 by changing the tuning voltage 50, and then changes the AFT voltage at that time. As shown in FIG. 3, if it is at a low level, it is determined that there is no broadcast signal, and if it is at a high level, the tuning voltage 50 is further changed to set the tuning frequency of the tuner 1 to f,
+300 KH2, and if the AFT voltage at that time is at a high level, it is determined that there is no broadcast signal, and this determination signal 300 is output to the next stage. This judgment signal 300
The next stage that receives the signal mutes the audio signal 100 and video signal @200 output from the intermediate frequency processing circuit 2, or performs processing such as turning the video signal into a blue signal. In addition,
If the detection results of the AFT detection circuit 3 and the synchronization signal detection circuit 4 are other than the above, the channel selection microcomputer 5 sends a determination signal 30 that determines whether there is a broadcast signal on the selected channel.
Outputs 0 to the next stage.

FIG. 4 is a flowchart showing the operation of the channel selection microcomputer 5. First, in step 401, a user's operation of a favorite station is received, and in step 402, a corresponding tuning voltage 50 is output to the tuner 1 to select a channel. Next, in step 403, it is determined whether or not the same signal is detected by the detection output of the synchronization signal detection circuit 4. If the detection output is high level and no synchronization signal is detected, in step 408, there is no broadcast signal. A determination signal 300 is output. If a synchronization signal is detected in step 403, the process proceeds to step 404, where the synchronization frequency of tuner 1 is first shifted to the carrier frequency f, -300, and in step 405, the AFT voltage is not at a high level. ,
If it is determined that the target broadcast signal is not tuned, the process advances to step 40B. Also, in step 405, AF
If the T voltage is at a high level, the tuning frequency of tuner 1 is shifted to fD+300K)-12 in step 406, and if it is determined in step 407 that the AFT voltage is at a high level and not tuned to the target broadcast signal. The process proceeds to step 408. Stellar 1408 outputs a determination signal 300 indicating that there is no broadcast signal on the selected channel JZ.

In addition, if it is determined in step 407 that the AF voltage is synchronized with the O-level, then in step 409 a determination signal 30 is sent indicating that there is a broadcast signal on the selected channel.
Outputs 0.

Figures 5 (A) and (B) show the high frequency spectrum and intermediate frequency spectrum when a strong electric field broadcasting signal with video carrier frequency fp and audio carrier frequency fs exists in the upper adjacent channel of the selected channel. It is a diagram. In this case, the intermediate frequency spectrum includes distortion components ss, :FSp due to tuner intermodulation received in the selected band of tuner 1.
appears, and these distortion components ss and fsp are modulated by f nF - (video intermediate frequency) by the video intermediate frequency signal of the adjacent channel, and are generated at intervals of 4.5M+-12 around f PIF-. do. Therefore, as shown in FIG. 5(C), the synchronizing signal detection circuit 4 malfunctions by detecting a synchronizing signal in the selected band of the tuner, but as shown in FIG. 5(D), the AFTF output circuit 3 In the range of ±300 to +-12 around the center frequency fp, no detection signal indicating tuning is output, indicating that there is no broadcast signal.

According to this embodiment, the synchronization signal detection circuit 4
Even if the AFTF output circuit 3 malfunctions due to the presence of a strong electric field broadcast signal in the upper and lower adjacent channels for the selected channel, the AFTF output circuit 3 will not tune to this if there is no carrier wave of the broadcast signal in the selected channel. Even if the sync signal detection circuit 4 operates due to the distortion component, the frequency is outside the predetermined frequency range, so it can ultimately be accurately determined whether or not there is a broadcast signal on the selected channel of the tuner 1.

[Effects of the Invention] As described above, according to the television broadcast signal determination circuit of the present invention, even when strong electric field broadcasts are performed in the upper and lower channels adjacent to the target channel whose presence or absence of broadcasting is to be detected, This has the effect of detecting whether or not the target channel is being broadcast.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the television signal determination circuit of the present invention, FIG. 2 is a characteristic diagram of the synchronization signal detection circuit shown in FIG. 1, and FIG. Characteristic diagram of the AFTF output circuit. Figure 4 is a flowchart showing the operation of the tuning microcomputer shown in Figure 1. Figure 5 is a high frequency diagram when there is a broadcast signal with a strong electric field in the upper channel of the tuning channel. FIG. 2 is a diagram showing an example of the operation of an intermediate frequency spectrum, a synchronization signal detection circuit, and an AFTF output circuit at that time. 1... Tuner 2... Intermediate frequency processing circuit 3... AFTF output circuit 4... Synchronization signal detection circuit 5... Microcomputer for channel selection Agent Patent attorney Noriyoshi Chika Yudo Hiroshi UjiRF Spect 3rd cause Figure 5

Claims (1)

[Scope of Claims] Receiving means for receiving a television broadcast signal of a selected channel and converting it into an intermediate frequency signal; video signal detection means for detecting a video signal from the intermediate frequency signal; a synchronizing signal detecting means for detecting whether or not a synchronizing signal exists in the output; and a receiving means for discriminating the frequency of the intermediate frequency signal and outputting a discrimination signal having a voltage level corresponding to the deviation from the reference frequency. AFT detection means for detecting whether or not the synchronization signal is tuned to a television broadcast signal; and if the synchronization signal detection means does not detect a synchronization signal, it is determined that there is no broadcast signal on the selected channel, and the synchronization signal detection means determines that there is no broadcast signal on the selected channel; When the means detects a synchronization signal, the tuning frequency of the receiving means is shifted by a predetermined frequency, the discrimination signal level of the AFT detecting means at that time is detected, and when the discrimination signal level differs from a predetermined value, a broadcast signal is sent to the selected channel. A television broadcast signal determining circuit comprising: determining means for determining that there is no such signal.