JPH0444469A - Horizontal synchronizing signal separator circuit - Google Patents

Abstract

PURPOSE:To always obtain a normal horizontal synchronizing signal independently of the presence of noise invaded in a composite synchronizing signal by detecting noise invaded in the composite synchronizing signal and selecting an internal horizontal synchronizing signal when the noise is in existence. CONSTITUTION:When a composite synchronizing signal is inputted to an input terminal 10, the signal is shaped by a waveform shaping circuit 11, which detects a leading edge of an input signal and outputs a pulse of a prescribed pulse width. An internal horizontal synchronizing signal generator 16 generates a horizontal synchronizing signal always synchronously with an external horizontal synchronizing signal. Then the signal is counted from a trailing edge of the signal for a period and when the count is 1 or over, it is discriminated as presence of noise and when the count is zero, it is discriminated as the absence of noise and the information representing it is inputted to a gate control signal generator 14. The gate control signal generator 14 selects three kinds of control operations based on the information to control the switching of a gate 13 and changeover of a horizontal synchronizing signal switching device 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a horizontal synchronization signal separation circuit that separates a horizontal synchronization signal from a composite synchronization signal of a television signal.

[Summary of the Invention] The present invention provides a gate that passes or blocks a shaped signal with a constant pulse width obtained by detecting the rising edge of an input composite synchronization signal, and an output signal of this gate and an internal horizontal synchronization signal. a horizontal synchronization signal switch that selectively outputs a horizontal synchronization signal switch; a counter that uses the output of the horizontal synchronization signal switch as a trigger to count rising or falling edges of the shaping signal to detect a mixed state of noise; The control signal generator controls the opening/closing of the gate and the switching of the horizontal synchronization signal switch based on the output of the synchronization signal, thereby dealing with the mixing of noise into the composite synchronization signal.

[Prior Art] As a conventional horizontal synchronization signal separation circuit of this type, for example,
As described in Japanese Unexamined Patent Publication No. 1-55775, it is known that a composite synchronizing signal is waveform-shaped by a waveform shaping circuit, outputted as a shaped signal, and the output signal is passed through a gate to obtain a horizontal synchronizing signal.

[Problems to be Solved by the Invention] In such conventional horizontal synchronization signal separation circuits, no countermeasures are taken when noise is mixed into the composite synchronization signal, so if noise is mixed into the composite synchronization signal, the normal synchronization signal is I ¥1! There was a problem.

[Object of the Invention] An object of the present invention is to provide a horizontal synchronization signal separation circuit that can obtain a normal synchronization signal even if noise is mixed into the composite synchronization signal.

[Means for Solving the Problem] In order to achieve such an object, the present invention adds a noise detection means to the horizontal synchronization signal separation circuit, thereby achieving the following:
The feature is that when noise is mixed into the composite synchronization signal, the output of the horizontal synchronization signal separated from the composite synchronization signal is immediately stopped, and the output is switched to the internal horizontal synchronization signal.

[Operation] In the present invention, noise mixed in the composite synchronization signal is detected,
If there is noise, it switches to the internal horizontal sync signal, so regardless of whether noise is mixed into the composite sync signal,
A normal horizontal synchronization signal can always be obtained.

[Example] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a horizontal synchronization signal separation circuit according to the present invention, in which lO is an input terminal for a composite synchronization signal, 11 is a waveform shaping circuit, 12 is a counter circuit, 13 is a gate, and 1
4 is a gate control signal generator, 15 is a horizontal synchronizing signal switch, 16 is an internal horizontal synchronizing signal generator, and 17 is an output terminal for the horizontal synchronizing signal.

FIG. 2 is a signal waveform diagram of each part of FIG. 1.

When the composite synchronization signal shown in FIG. 2(a) is input to the input terminal lO in FIG. 1, the signal is shaped by the waveform shaping circuit 11 into the signal shown in FIG. 2(b) (hereinafter referred to as This signal is called a shaping signal), and this waveform shaping circuit 11 detects the rising edge of the input signal and outputs a pulse with a predetermined pulse width.

Next, this shaped signal is input to the counter circuit 12.

This counter circuit 12 detects whether or not noise is mixed in the composite synchronization signal, and performs counting using the horizontal synchronization signal shown in FIG. 2(e) as a trigger. This is the output of the signal switch 15.

This horizontal synchronization signal switch 15 inputs an external horizontal synchronization signal separated from the composite synchronization signal, that is, a shaped signal passed through the gate 13 and an internal horizontal synchronization signal generated by the internal horizontal synchronization signal generator 16, Select and output one of these signals.

This switching control is performed using the output of the gate control signal generator 14.

Note that the internal horizontal synchronization signal generation 816 generates a horizontal synchronization signal that is always synchronized with the external horizontal synchronization signal. and,
As shown in Fig. 2(e), counting is performed during period t from the falling edge of the signal, and if the count value is 1 or more, there is noise, and if the count value is 0, there is no noise. The signal is input to the gate control signal generator 14. Based on this information, the gate control signal generator 14 operates as shown in FIG. 2(f).

The three types of control shown in (g) and (h) are selected to control the opening and closing of the gate 13 and the switching of the horizontal synchronization signal switch 15.

FIG. 3 is a flowchart showing these control patterns.

(1) When there is no noise (when a noise-free composite synchronization signal is input) As shown in Fig. 2(f), after counting during the period ℃, the gate 13 is closed during the period t. . As a result, an external horizontal synchronization signal is obtained by excluding the vertical synchronization signal component shown by the broken line. Thereafter, the gate 13 is opened for a period t, and an output signal from the horizontal synchronization signal switch 15 is waited for. In this case, an external horizontal synchronization signal is output. Here, period , continues until the next falling edge of the external horizontal sync signal is detected, but this ensures that the horizontal synchronization is always synchronized to the composite sync signal even if the composite sync signal is out of synchronization. I get a signal.

(2) When there is noise (when noise is mixed into the composite sync signal) As shown in FIG. 2(c), when noise is mixed into the composite sync signal, the waveform shaping circuit 11 generates the signal as shown in FIG. 2(d). The waveform is shaped as shown in FIG. 2(g), and an enlarged view of a part of the waveform is shown in FIG. 2(g).

First, counting is performed for a period t, but at this time, since the count value is 1 or more, it is determined that there is noise, and the period is
During this period, the gate 13 is closed and the output of the horizontal synchronization signal switch 15 is switched to the internal horizontal synchronization signal. In this case, period L4
continues until a falling edge of the internal horizontal sync signal is detected.

(3) When noise changes from presence to absence (when noise in the composite synchronization signal disappears) When the state changes from the state with noise to the state without noise, only for the l cycle in which the change occurred, as shown in Figure 2 ( As shown in h), after counting during the period t1, the output of the horizontal synchronizing signal switch 15 is switched to the external horizontal synchronizing signal, and the gate 13 is opened during the period t.

This is to capture the first signal of a normal external horizontal sync signal with no noise, and the gate is opened for a period of time until the falling edge of the first normal external horizontal sync signal is detected. Continue.

Through the above control, a horizontal synchronization signal corresponding to the state of the composite synchronization signal, that is, an external horizontal synchronization signal or an internal horizontal synchronization signal, is obtained from the horizontal synchronization signal switch 15 and output to the horizontal synchronization signal output terminal 17. .

[Effects of the Invention] As described above, according to the present invention, when noise is mixed into the composite synchronization signal, it is possible to immediately switch to the internal horizontal synchronization signal, and normal synchronization separation can always be performed. Since malfunctions do not occur, this is particularly effective in circuits whose circuit operations depend on synchronization signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the horizontal synchronizing signal separation circuit according to the present invention, FIG. 213!7 is a waveform diagram showing signals of each part in FIG. 1, and FIG. 3 is a flow chart showing gate control. 10...Composite synchronization signal input terminal, 11.
......Waveform shaping circuit, 12...
・Counter circuit, 13...Gate, 14
......Gate control signal generation circuit, 15...
......Horizontal synchronization signal switch, 16...
...Internal horizontal synchronization signal generator, 17...
・Horizontal synchronization signal output terminal. Figure 3

Claims (1)

[Claims] A waveform shaping circuit that detects the rising edge of an input composite synchronization signal and outputs a shaped signal with a predetermined pulse width, a gate that passes or blocks the output of the waveform shaping circuit, and a horizontal synchronization circuit that generates an internal horizontal synchronization signal. a signal generator; a horizontal synchronization signal switch that selectively outputs the output signal of the gate and the internal horizontal synchronization signal; and a rising or falling edge of the shaping signal using the output of the horizontal synchronization signal switch as a trigger. 1. A horizontal synchronizing signal separation circuit comprising a counting means for counting, and a control signal generator for controlling opening/closing of the gate and switching of the horizontal synchronizing signal switch based on the output of the counting means.