JPS5840702Y2 - television signal detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting whether or not a television signal is being received in a television receiver, and provides a device that performs accurate detection.

When using a television receiver late at night, if you go to sleep even after the broadcast ends and the television signal disappears, the television receiver may continue to operate for a long time, heating up or using unnecessary power. Since the TV signal is no longer present due to the end of broadcasting, a device that detects this and automatically turns off the power is being considered. What is desired is something that can be detected.

Furthermore, as a channel selection means for a television receiver, a device that performs frequency sweep using an automatic sweep type oscillation circuit and automatically stops when a television signal is received has been considered.

In that case as well, it is necessary to accurately detect the presence or absence of a television signal.

Television signal detection devices conventionally used for such purposes include those that detect the presence or absence of a video carrier or audio carrier or both carriers of a television signal, and those that detect the presence or absence of a horizontal synchronization signal, a vertical synchronization signal, or both synchronization signals. Detectors and the like are used.

However, with these conventional devices, stable detection can be performed in areas where the electric field strength of television signals is sufficiently strong, but in areas where the electric field is weak, the detection operation becomes unstable and there are many erroneous controls. There was a drawback.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a device that can overcome these conventional drawbacks and accurately detect the presence or absence of a television signal even in the case of a weak electric field.

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

First, Fig. 1 shows an example applied to automatic power cut-off.
Here, 1 is a tuner, 2 is a VIP circuit, 3 is a video detection circuit, 4 is a video amplification circuit, 5 is a color reproduction circuit, 6 is a synchronization separation circuit, 7 is a horizontal oscillation circuit, 8 is a vertical oscillation circuit, and 9 is a deflection circuit. The circuit 10 is a cathode ray tube, which is similar to those in a conventional television receiver.

11 is a detection circuit which is a feature of this device, and here,
First, the oscillation outputs are taken out from the horizontal oscillation circuit 7 and the vertical oscillation circuit 8, which oscillate in synchronization with the synchronization signal separated from the television signal, and the waveform shaping circuit 12
Shape into a pulse waveform with H, 12V.

Next, the frequency of the horizontal oscillation pulse is divided by 1/525 by the frequency dividing circuit 13H, and the frequency of the vertical oscillation pulse is divided by 1/2 by the frequency dividing circuit 13V.

The frequency-divided outputs are added to the counters 14H and 14V, respectively, and are counted for the same amount of time by timing pulses from the timing pulse generation circuit 15.

As is well known, there is 2 f between the horizontal frequency fH and vertical frequency fv of television signals in Japan.
Since there is a relationship such that H=525 f v, if a television signal is being received and the horizontal oscillation circuit 7 and vertical oscillation circuit 8 are operating correctly in synchronization with the synchronization signal, the above-mentioned The signal obtained by dividing the horizontal oscillation pulse by 1/525 and the signal obtained by dividing the vertical oscillation pulse by 1/2 both have the same frequency of 30.

Therefore, if these are counted by the counters 14H and 14V for the same period of time, for example, 10 seconds, the counting outputs will be equal.

Conversely, when the television signal ceases to exist due to the end of broadcasting, the synchronization between the horizontal oscillation circuit 7 and the vertical oscillation circuit 8 is lost, and the frequencies of their respective oscillation outputs deviate from the above relationship. Their counting outputs when counting by time are different.

Therefore, the count outputs of these counters 14H and 14V are compared in the comparator circuit 16, and when the two stitch count outputs are equal, a comparison output is generated to warn that a television signal exists, and when the two stitch count outputs are not equal, a comparison output is generated. Generates a comparison output indicating that no television signal is present.

Then, the detection output of the comparison circuit 16 is applied to the processing circuit 17, and when the comparison output indicating the absence of a television signal is continuously generated from the comparison circuit 16 for a certain period of time, for example, 5 minutes or more, A detection output is generated and the power supply control circuit 18 is cut off to automatically cut off the power of the television receiver.

In such a processing circuit 17 and 2, a resistor and a capacitor are connected in series, and the charge stored in the capacitor is periodically discharged by the comparison output from the comparison circuit 16 when a television signal is present. It is possible to use a device in which the switching transistor is switched by the voltage across the capacitor when the charge in the capacitor increases due to the presence of the capacitor and no discharge occurs.

The counters 14H, 15V and the comparison circuit 16 are periodically reset and operated by timing pulses from the timing pulse generation circuit 15.

In addition to the ratio of the frequency division ratio in the frequency dividing circuits 13H and 13V being set to 1/525 and 1/2 as described above,
It goes without saying that any ratio of 525:2 may be selected.

Next, FIG. 2 shows an embodiment in which the present invention is applied to an automatic sweep type selection device.

Note that the same parts as in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

In this device, first, a control voltage generation circuit 19 is provided which generates a tuning control voltage having a sawtooth waveform in order to sweep the tuning frequency of the tuner 1 by changing it over time.

On the other hand, since it is necessary to increase the operating speed in such a device, a multiplier circuit 20H920V is provided in place of the frequency divider circuits 13H and 13V as shown in Fig. 1, and the ratio of the respective multiplication factors is set to 2:525. Multiply the horizontal oscillation pulse and the vertical oscillation pulse.

For example, the horizontal oscillation pulse is multiplied by 20, and the vertical oscillation pulse is multiplied by 5250.

When multiplied in this way, if a television signal exists and is oscillating in proper synchronization with it, the frequency of the multiplied signal will both be as high as 315 KHz,
Even if the counters 14H and 14V count each time for a short period of time, for example, 0.01 seconds, it is possible to detect whether or not the synchronization is properly performed.

Therefore, it is sufficient to repeat such a short-time counting operation in a short period, for example, at a period of 2/100 seconds, and if the processing circuit 17 is also made to have a small time constant, it will respond sufficiently quickly. When a television signal is present, it is possible to stop the sweep operation of the control voltage generation circuit 19 so as to properly tune to the television signal.

Note that if the device shown in FIG. 1 requires high-speed operation, a multiplier circuit as shown in FIG. 2 may be used, and if the device shown in FIG. 2 does not require high-speed operation, the It goes without saying that a frequency dividing circuit as shown in the figure may also be used.

Alternatively, the horizontal oscillation pulse may be frequency-divided and the vertical oscillation pulse may be multiplied to have the same frequency.

In either case, the frequency may be divided or multiplied at a ratio that will result in the same frequency when the oscillation output of the horizontal oscillation circuit and the oscillation output of the vertical oscillation circuit are accurately synchronized.

In this way, in the present invention, the oscillation output of the horizontal oscillation circuit and the oscillation output of the vertical oscillation circuit are frequency-divided or multiplied, and the counter counts the same amount of time, and when both needle count outputs are equal, a television signal is present. , and when they are different, it is detected as if the television signal does not exist. Therefore, accurate detection can be performed without being affected by the electric field strength of the received television signal.

In particular, even if the television signal exists in a weak electric field, it is impossible to see the correct screen in a state where the horizontal oscillation circuit and vertical oscillation circuit cannot be properly synchronized, so this device is designed to handle such conditions. Also, by detecting the absence of a television signal and eliminating half-finished intermediate states, a reliable detection state can be obtained.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a television signal detection device according to an embodiment of the present invention. 7... Horizontal oscillation circuit, 8... Vertical oscillation circuit, 11... Detection circuit, 12 H, 12V.
・・・・・・Waveform shaping circuit, 13H, 13■・・・・・・
Frequency dividing circuit, 14H, 14V...Counter, 15
...Timing pulse generation circuit, 16...
... Comparison circuit, 17 ... Processing circuit, 18 ...
...Power supply control circuit, 19... Control voltage generation circuit, 20H, 20V... Multiplier circuit.

Claims (1)

[Scope of utility model registration request] It is equipped with a horizontal oscillation circuit and a vertical oscillation circuit that oscillate in synchronization with a synchronization signal separated from the television signal, and accurately synchronizes the oscillation output of the horizontal synchronous oscillation circuit and the oscillation output of the vertical oscillation circuit. Divide or multiply the frequency by a ratio that makes the frequency the same if the two pulses are the same, count the resulting two pulses with a counter for the same time, compare the counting outputs with a comparator circuit, and find out if the two counting outputs are different. A television signal detection device that generates an output that detects the absence of a television signal in a state where the television signal is present.