JPS6048684A - Television signal discriminating system - Google Patents

Abstract

PURPOSE:To attain picture transmission with good quality by providing a discriminating means using a horizontal synchronism or a subcarrier frequency as a reference and a means detecting and discriminating the missing or excess of a horizontal synchronizing signal so as to discriminate the signal based on an OR of both means. CONSTITUTION:Since the horizontal synchronizing signal 1 is inputted at a prescribed period of interval, a monostable multivibrator circuit MS continues the normal operation. If a pulse marked * in the horizontal synchronizing signal is missing because of some cause, the circuit MS is restored, an OR gate G generates an output signal 2, which informs a fault. Further, an oscillator OSC has a frequency smaller than the frequency of the horizontal synchronizing signal and its output resets always a counter circuit COUNTER. A pulse shown in dotted lines in the horizontal synchronizing signal is inserted because of some cause, the OR gate G generates an output signal 3 to inform the fault.

Description

Detailed Description of the Invention (a) 3 Technical Field of the Invention The present invention relates to a television signal determination method, and more particularly to a television signal determination method for determining a control method in an image coding and transmission device. .

(b) Problems with the Prior Art According to the prior art, the television signal determination circuit in the image coding and transmission device creates a clock synchronized with the frequency of the horizontal synchronization signal or subcarrier, which is the input signal.
The control method was determined depending on whether the created clock frequency was within the specified specifications.

FIG. 1 shows an embodiment of a conventional television signal determination circuit.

In the figure, F-DIVI is a 1/2 frequency divider, P-COMP is a phase comparator, LPF is a low-pass filter, VCO is a voltage controlled oscillator, and F-DIV 2 is a 1/n frequency divider. ,F-D
ET is a frequency detection circuit.

In Figure 1, the horizontal synchronizing signal is connected to the 1/2 frequency divider F-DI.
V1, and the phase comparator P-COMP outputs 1/
The phase difference with the output signal of the n frequency divider F-DIV2 is taken, and only the DC component is taken out by the low-pass filter LPF and used as the control voltage of the voltage controlled oscillator VCO. The output frequency of this voltage controlled oscillator VCO is the i/n frequency divider F-DI
The frequency is divided by 1/n by V2, and the phase comparator P-CO
Input to MP.

A well-known phase synchronization circuit like this one generates a clock synchronized with the input horizontal synchronization signal or subcarrier frequency, and this clock frequency is sent to the frequency detection circuit F-DET.
The frequency was counted, and transmission control was changed depending on whether the frequency was within a specified range.

In other words, if the clock is good, the analog signal is A-D converted using this clock, and then transmitted using this clock.
lock type], good images can be transmitted.

However, if this clock does not meet the regulations, the next best option is to use the line clock of the transmission device to A-to-D convert the analog signal and transmit it (non-lock type). Of course, the image quality in this case is good with the lock type, which is worse than when the lock is used, but it is better than when the lock type is used with a clock outside the specified range.

If the control method is changed using such judgment criteria, even if the clock is within the specified frequency range, if one of the horizontal synchronization signal pulses is missing or an abnormal pulse is inserted in the horizontal synchronization signal, the conventional In this method, the clock is generated by a phase synchronization circuit, so the clock fluctuates and is not a highly accurate signal source.For this reason, in the lock type, which is processed assuming high precision when encoding, conversely, it is non-conforming. -The drawback was that the image quality was worse than the lock type.

(C)3 Objects of the Invention An object of the present invention is to provide a television signal determination circuit that eliminates the two drawbacks of the prior art and enables high-quality image transmission.

(d) 8 Structure of the Invention According to the present invention, the above object is to detect the precision of a television signal, and to provide a horizontal 4 based on the frequency of the synchronization signal or subcarrier
This is achieved by providing a television signal determination method characterized in that it comprises a 1J determining means and a determining means for detecting the absence or excess of the horizontal synchronizing signal, and the determination is made by the logical sum of both the determining means.

(e) 0 Embodiment of the Invention In FIG. 2, (al) is a block diagram showing an embodiment of the present invention, and (bl) is a diagram explaining the present invention in detail.

In the figure, MS is a mono stable multi-high break circuit, OSC is an oscillator, C0UNTER is a counting circuit, G is an OR gate, and other symbols and numbers are the same as in FIG.

The present invention will be described in detail with reference to the schematic drawings.

In Figure 2 (bl), ■ indicates the input horizontal synchronization signal.As mentioned above, conventionally, this horizontal synchronization signal is applied to a phase synchronization circuit to generate a clock synchronized with the horizontal synchronization signal. The frequency of that clock is detected by a frequency detection circuit F-
It is inspected by DET, and if the frequency is outside the specified frequency range, an output signal is output and transmission control is changed.

According to the present invention, mono, stable,
The multi-high break circuit MS is activated, and its operating time is set to be somewhat longer than the interval of horizontal synchronizing signal pulses.

This horizontal synchronization signal is always input at regular intervals, so
The mono-stable multi-vibrator circuit MS continues to operate at all times, but if the pulse marked with * is missing for some reason in this horizontal synchronization signal, the mono-stable multi-vibrator circuit MS is activated in the present invention. After recovery, G generates an output signal as shown in ■ to notify the abnormality.

Note that the phase synchronization circuit continues to operate without any abnormality even if the pulse marked with * is missing, and if the frequency of its output clock is within the specified standard, the television signal is determined to be normal.

Also, the oscillator OSC has a frequency slightly lower than the frequency of the horizontal synchronizing signal, approximately 15 KHz, and its output causes the counting circuit C to
0UNTER is constantly reset.

Also, this horizontal synchronizing signal is counted by this counting circuit C0IJNTER. Therefore, when the horizontal synchronizing signal is normally input, the counting circuit C0UNTER is reset by the oscillator oSC, the horizontal synchronizing signal pulse is counted once, and the operation of being reset by the oscillator O3C is repeated.

For this reason, when the pulse shown by the dotted line in ■ is inserted for some reason, the count value of the counting circuit COUNTER becomes 2 or more, and the OR gate G outputs the output signal as shown in ■. Occurs and reports an abnormality.

In this way, not only the output signal of the conventional frequency detection circuit F-DET (mono stable multi-high break circuit MS and counting circuit C0UNTER according to the present invention)
By changing the control mode no matter which of the output signals is output, a more accurate determination can be made.

(f) 1. Effects of the Invention As described in detail above, the present invention has the great effect of realizing a television signal determination circuit that enables high-quality image transmission.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of a conventional television signal determination circuit. In FIG. 2, (al is a diagram showing one embodiment of the present invention, (bl is a diagram explaining the present invention in detail. In the figure, F-D IV 1/2 frequency divider, p- c. MP is a phase comparator, LPF is a low-pass filter, VC○ is a voltage controlled oscillator, F-D I V 2 is a 1/n frequency divider,
F-DET is a frequency detection circuit, MS is a mono/stable/multi-high break circuit, OS C+-, L Q I
hy device, C0UNTER is a counting circuit, G-shimame”-]’
・It is Kate.

Claims (1)

[Claims] Detecting the accuracy of the television signal 1. In an image coding and transmission device that performs different control depending on the detected accuracy, a determination means uses a frequency of a horizontal synchronization signal or a subcarrier as a reference for the accuracy parameter, and detects omission or excess of the horizontal synchronization signal. 1. A television signal determination method, comprising a determination means for determining the re-determination means, and performing determination by a logical sum of the re-determination means.