JPH06101801B2 - Horizontal oscillation circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal oscillator circuit in a television receiver, and more particularly to driving the oscillator circuit with a first pulse based on a horizontal synchronizing signal, and Second based on output
The present invention relates to a direct drive type horizontal oscillation circuit that controls an oscillation phase by a phase comparison output of a phase control circuit that compares the phase of a pulse with the phase of the first pulse.

2. Description of the Related Art A conventional example of such a direct drive type horizontal oscillation circuit will be described with reference to FIG. That is, (1) in the figure is an input terminal to which a horizontal sync pulse (see FIG. 3 (a)) based on the horizontal sync signal separated by the sync separation circuit is input, and (2) is the rising edge of this horizontal sync pulse. A first monostable multivibrator (3) that outputs a pulse of the pulse td (see FIG. 3 (b)) has a pulse width tw at the trailing edge of the pulse output from the first monostable multivibrator (2). In the second monostable multivibrator that outputs a pulse (see FIG. 3 (c)), the pulse output from the second monostable multivibrator (3) is sent to the horizontal drive circuit as a horizontal oscillation pulse. The output of the horizontal drive circuit is sent to the base of the horizontal output transistor that constitutes the horizontal output circuit. Here, the base waveform of the horizontal output transistor is as shown in FIG. 3 (d). (4) is the phase of the flyback pulse (hereinafter referred to as FB pulse) as shown in Fig. 3 (e) obtained from the flyback transformer in the horizontal output circuit and the phase of the horizontal synchronizing pulse input to the input terminal (1). According to the comparison output, the first
A phase control circuit that performs oscillation phase control by changing the time constant of the monostable multivibrator (2) to eliminate the phase difference. The phase control circuit (4) shapes the FB pulse waveform as shown in FIG. 3 (f). A waveform shaping circuit (5), a phase comparator (6) for phase-comparing the waveform-shaped FB pulse and the horizontal synchronizing pulse, and its output state is controlled by a phase comparison output from the phase comparator (6). And a low-pass filter (hereinafter, LPF) for controlling the pulse width td by varying the time constant of the first monostable multivibrator (2) by receiving the output of the charge pump (7). (8).

Specifically, the phase comparator (6) detects the falling edges of the waveform-shaped FB pulse and the horizontal synchronization pulse, and
When the horizontal sync pulse is delayed with respect to the FB pulse, the H level is output from the first output end (6a) by the phase difference, and when it is advanced in the opposite direction, the second output end (6a) is output by the phase difference. 6b) outputs the H level. The charge pump circuit (7) outputs the LPF when the first output terminal (6a) of the phase comparator (6) is at H level.
The charge / discharge capacitor constituting (8) is discharged (that is,
It is composed of a switching element that lowers the output voltage) and a switching element that charges the charging / discharging capacitor (that is, raises the output voltage) when the second output terminal (6b) is at the H level. When both ends (6a) and (6b) are at the L level, a high impedance state is set so as not to affect the charging state of the charging / discharging capacitor. Then, the LPF (8) suppresses a high frequency signal component generated by switching of the switching element by the charging / discharging capacitor charged and discharged as described above, and the resistance (9), Capacitor (1
The time constant of the first monostable multivibrator (2), which is determined together with (0), is made variable. Therefore, for example, the waveform was shaped as shown in the portion A of FIG.
When the horizontal sync pulse (see FIG. 4 (b)) is delayed with respect to the FB pulse (see FIG. 4 (a)), the phase difference is caused by the first output terminal (6a) of the phase comparator (6). However, the charge pump circuit (7) discharges the charge / discharge capacitor of the LPF (8), so that the output voltage of the LPF (8) decreases. Then, the time constant of the first monostable multivibrator (2) is changed. Therefore, the period of the pulse (horizontal oscillation pulse) output from the second monostable multivibrator (3) is delayed, the phase of the FB pulse synchronized with this pulse is delayed, and the phase difference from the horizontal synchronization pulse is eliminated. Operate.

The pulse width tw of the second monostable multivibrator (3) is determined by the time constant determined by the output of the operational amplifier (13) together with the resistor (11) and the capacitor (12).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in such a conventional horizontal oscillation circuit, when noise is superposed on the horizontal synchronizing pulse, for example, noise before the horizontal synchronizing pulse as shown in part B of FIG. When S _N (see Fig. 4 (b)) is superimposed, it is actually FB
Although the phase of the horizontal synchronizing pulse is slightly behind that of the pulse, the noise S _N becomes a pseudo horizontal synchronizing pulse, and the phase of the horizontal synchronizing pulse is advanced in reverse. Therefore, it is necessary to shift the phase that is almost in agreement by about one horizontal period (hereinafter referred to as 1H), and therefore the second output end (6b) of the phase comparator (6) is continuously in the H level state. (See FIG. 4 (d)), but the output voltage of the charge pump circuit (7) and LPF (8) becomes high, but the pulse width td of the first monostable multivibrator (2) cannot be zero. Therefore, there has been a problem that the phases of the FB pulse and the horizontal synchronizing pulse are displaced for a long period of time (that is, the raster position is displaced for a long period of time).

The present invention has been made in view of the above circumstances, and an object thereof is to provide a horizontal oscillation circuit capable of correcting erroneous oscillation phase control that occurs when noise is superimposed on a horizontal synchronization pulse. .

Means for Solving the Problems In order to achieve the above object, in the present invention, an oscillating circuit is driven by a first pulse based on a horizontal synchronizing signal, and a second pulse and a first pulse based on the output of the oscillating circuit are driven. In a direct drive type horizontal oscillation circuit for controlling oscillation phase by a phase comparison output of a phase control circuit for comparing phases, when the output of the phase control circuit exceeds a predetermined value, the phase comparator in the phase control circuit is set to 1 The control means is provided in a reset state for a predetermined period longer than the horizontal period.

With such a configuration, for example, when noise is superimposed on the horizontal synchronizing pulse and the phase control circuit malfunctions,
When it is detected that the output of the phase control circuit exceeds a predetermined value, the control means resets the phase comparator for a predetermined period of one horizontal period or more.

Embodiment Hereinafter, one embodiment of the present invention will be described with reference to the drawings.
The same parts as those of the conventional one are designated by the same reference numerals and the description thereof will be omitted.

That is, according to the present embodiment, when the output of the phase control circuit (4) exceeds a predetermined value as shown in FIG. 1, the phase comparator (6) in the phase control circuit (4) is set to one horizontal level. A control circuit (14) which is in a reset state for a predetermined period longer than the period is provided. In this case, for example, noise is superimposed on the horizontal synchronizing pulse to cause the phase control circuit (4) to malfunction, and its output Can be prevented from falling into a so-called locked state in which is fixed in a state where it exceeds a predetermined value.

Specifically, the control circuit (14) compares the output voltage of the LPF (8) with a reference voltage determined by the variable resistor (15), and when the output voltage of the LPF (8) becomes higher than the reference voltage, The voltage comparator (16) whose output becomes H level, and the pulse width (1H min. Or more) determined by the time constant of the resistor (17) and the capacitor (18) at the rise of the output of this voltage comparator (16). And a third monostable multivibrator (19) for outputting the pulse of the third monostable multivibrator (19) and the horizontal synchronization pulse is bypassed during the pulse output period of the third monostable multivibrator (19) to reset the phase comparator (6). Switch circuit (20)
And a buffer (21).

Therefore, as shown in part B of FIG. 4, noise S _N (see FIG. 4 (b)) is superposed before the horizontal synchronizing pulse and the phase shifts by about 1H, whereby the phase comparator When the second output terminal (6b) of (6) is continuously in the H level state and the output voltage of the LPF (8) becomes higher than the reference voltage, the output of the voltage comparator (16) rises. A pulse is output from the third monostable multivibrator (19) for a predetermined period. Then, during this pulse output period, the horizontal synchronizing pulse input to the phase comparator (6) is bypassed by the switch circuit (20), and the phase comparator (6) outputs H of the second output terminal (6b). It will be released from the level state.

Incidentally, as the switch circuit of this embodiment, specifically, a switching transistor, a relay switch, or the like is used.

EFFECTS OF THE INVENTION As described above, the horizontal oscillation circuit of the present invention can immediately correct even if the oscillation phase control is erroneous due to the influence of noise or the like, so that the oscillation phase control falls into a so-called locked state. The so-called inconvenience does not occur if the raster position shifts for a long period of time.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional example, FIG. 3 is a signal waveform diagram for explaining the operation thereof, and FIG. 4 is an operation explanation at the time of noise superposition. It is a signal waveform diagram used for. (2) …… First monostable multivibrator, (4) …… Phase control circuit, (6) …… Phase comparator, (14) …… Control circuit, (19) …… Third monostable multivibrator.

Claims (1)

[Claims] 1. An oscillation circuit is driven by a first pulse based on a horizontal synchronizing signal, and is oscillated by a phase comparison output of a phase control circuit that compares the phases of a second pulse and the first pulse based on the output of the oscillation circuit. In a direct drive type horizontal oscillation circuit for performing phase control, when the output of the phase control circuit exceeds a predetermined value, the phase comparator in the phase control circuit is in a reset state for a predetermined period of one horizontal period or more. A horizontal oscillation circuit characterized by being provided.