JPH0247669Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a beam index type color television receiver.

(b) Prior art In a beam index type color television receiver, an index signal obtained from an index element repeatedly arranged in a certain relationship with three primary color phosphors on the inner surface of the face plate of a picture tube is extracted to the outside, Since the position of the electron beam is controlled using the index signal, it is necessary to emit the electron beam to obtain the index signal even when reproducing a black image.

The conventional example for realizing such a configuration is the first one.
As shown in the figure, the pedestal-clamped video signal applied from the input terminal 1 is guided from the first emitter follower transistor TR ₁ through the drive second transistor TR ₂ to the output terminal 2. In the video output circuit for applying voltage to the cathode electrode of the picture tube, a switching diode _D1 is connected to the base of the first transistor _TR1 .
A level setting circuit 3 is connected through the level setting circuit 3 to clip the portion of the video signal S below the level _E1 as shown in FIG. It is limited to what can be obtained. The level setting circuit 3 includes a variable resistor 4 whose one end is connected to a DC power supply (+Vc ₁ ) and the other end is grounded, a third transistor TR ₃ of emitter follower connection type whose base is given the output of the variable resistor 4, and the above-mentioned switching diode
It consists of D ₁ .

However, this conventional example has the disadvantage that if the level manually adjusted by the variable resistor 4 encounters an unfavorable condition during operation of the television receiver, it cannot be automatically corrected.
For example, if a dropout of the index signal occurs due to fluctuations in the power supply voltage, etc., the synchronization of the color signal by the index signal is disrupted, and a normal color image cannot be reproduced. However, it is common practice to take measures to compensate for such loss of the index signal. However, even if such compensation is performed, if there are many missing index pulses, it will be difficult to compensate completely, so the lower limit level must be raised to prevent missing index pulses. However, such automatic adjustment is not possible, and it is difficult to search for a preferable adjustment point that prevents the level from being raised too much (as this would worsen the contrast) with manual adjustment. In FIG. 1, TR ₄ is a blanking transistor that is turned on by a retrace pulse 6 applied from a terminal 5 and cuts off the second transistor TR ₂ during the retrace pulse period.

(c) Purpose of the invention The present invention is a beam index type color television receiver that is designed to automatically prevent the loss of index pulses and to adjust the level of the prevention to a suitable state. The purpose is to provide

(d) Structure of the invention The present invention solves the problem of missing index pulses in a beam index type color television receiver that has a level setting circuit that sets a level that defines the lower limit of the amount of electron beam for a pedestal clamped video signal. means for detecting the number of missing index pulses and outputting a pulse according to the number of missing index pulses, and the output of the means is applied through an integrating circuit to control the level of the level setting circuit. be.

(E) Embodiment In FIG. 3, where the same parts as in FIG. 1 are given the same reference numerals, the differences from FIG. ₁ are as follows: The point is that the pulse is applied from the terminal 7 through the integrating circuit 8. Incidentally, the integrating circuit 8 consists of a resistor _R1 and a capacitor _C1 .

FIG. 4 shows a block circuit diagram of an index signal processing circuit including _the circuit portion shown in _FIG . This is a video drive circuit. Reference numeral 12 denotes a differentiating circuit that forms a pulse C synchronized with the rising edge of the index pulse L applied to the terminal 11; 13 a detection circuit that essentially detects the omission of the index pulse;
4 is a pulse oscillation circuit that is turned on during the output pulse period of the detection circuit 13 and emits a pulse having the same frequency as the index pulse during this period; 15 is a ternary count of the output of the pulse oscillation circuit 14 and an output pulse; , first counting circuit that generates 16
17 is a second counting circuit that counts the index pulse low inputted from the terminal 11 in ternary form to generate outputs ``nu'', ``ru,''; 17 is a triplet frequency ( A decoder 18 outputs a pulse train of 0°, 120°, and 240° with a frequency whose period is the repetition pitch of the three primary color phosphor stripes. This is a switching circuit that outputs an output of a constant phase (in the illustrated case, a phase that matches the position of the G phosphor stripe) from the outputs W, F, and Y. This output signal is led from an output terminal 19 to a mixing circuit (not shown), where it undergoes phase modulation by the color signal, and is further added to the output of the video drive circuit 10 in an adder to feed the picture tube. guided by grid electrodes.

In FIG. 4, the output pulse 2 of the detection circuit 13 is applied to the integration circuit 8;
4 may be added to the output pulse.

A specific example of the circuit shown in FIG. 4 is shown in FIG. The waveforms of each part in FIGS. 4 and 5 are shown in FIG. 6.

To briefly explain the operation with reference to the waveforms in FIG. 6, consider the case where a reset pulse wave is applied to the terminal 20. Since the index pulse low is also applied to the terminal 11 in advance during the high level period of the reset pulse, the index pulse becomes as shown in FIG. 6b. This index pulse low is differentiated by a differentiating circuit 12, and only a pulse synchronized with its rising edge is output. Detection circuit 13
is a retriggerable monostable multivibrator 21
Moreover, the time constant τ is selected to be Ti < τ < 2 Ti with respect to the period Ti of the index pulse, so the output is at a low level during normal operation without missing index pulses. When a drop occurs in the index pulse pulse, it becomes high level, and remains high level until the next index pulse is input. Therefore, the output pulse has a width corresponding to the number of missing index pulses P, as shown in FIG. 6D. Pulse oscillation circuit 1
4 is turned on only during the high level period given by the detection circuit 13, and outputs a pulse equal to the index pulse. The number of these pulses matches the number of missing index pulses. This pulse is counted by the first counter 15, while the index pulse pulse is counted by the first counter 15.
The output of the second counter 16, which counts the digits, is passed through the decoder 17 to the switching circuit 18 in the form of wa, ka, y. The output pulse shown in FIG. 6 is generated at the output, but at this time, despite the index pulse zero dropout P, the phases of the output pulser before and after the period a in which the dropout occurs are the same. In this way, by compensating for the missing index pulse, the output terminal 1
The phase of the pulse obtained in 9 remains unchanged, but if the number of missing index pulses is large,
The circumstances are different, and we will not be able to provide sufficient compensation. This is because the phase of the pulse generated from the pulse oscillator 14 is not necessarily the same as the phase of the index pulse (in particular, the phase of the index pulse usually differs depending on the electron beam scanning speed at the top and bottom edges and the center of the screen). This is because a malfunction occurs in which the phase of the pulse train obtained at the output terminal 19 differs by 120° or 240° before and after the missing period. Pulses corresponding to the number of missing index pulses are added to the level setting circuit 3 and act to raise the lower limit level of the electron beam amount, so the minimum amount of electron beam increases and index pulses are more likely to occur. Missing Tux pulses are prevented. Moreover, since the pulse is applied through the integrating circuit 8, the base potential of the third transistor TR3 of the level setting circuit ₃ gradually rises and stops at an appropriate level, as shown in FIG. After that, it gradually declines. Stopping at an appropriate level means that if the index pulse continues to be missing, the base potential rises, and when the index pulse is no longer missing, the base potential stops rising. is the very level that does not cause index pulse dropouts. Therefore, there is an advantage that the contrast is not deteriorated compared to the case where the output pulse 2 is simply added.

(f) Effects of the invention As described above, the invention has the effect of automatically preventing index pulse omission.
In addition, to achieve this, pulses corresponding to the number of missing index pulses are added to the level setting circuit through an integrating circuit, which has the effect of automatically adjusting to a suitable position, making this invention extremely effective. It is.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a part of a conventional beam index type color television receiver, and FIG. 2 is an explanatory diagram thereof. Fig. 3 is a circuit diagram of a part of a beam index type color television receiver in which the present invention is implemented, and Fig. 4 is a block diagram of the main part of the beam index type color television receiver in which the present invention is implemented. 5 is a circuit diagram showing the specific configuration of FIG. 4, and FIG. 6 is a circuit diagram showing the specific configuration of FIG. 4.
FIG. 6 is a waveform chart of each part in FIG. S...Video signal, 3...Level setting circuit, Lo...
...Index pulse, 8...Integrator circuit, 13...
...Detection circuit, 14...Pulse oscillation circuit.

Claims (1)

[Scope of utility model registration request] In a beam index type color television receiver, which has a level setting circuit that provides a level that defines the lower limit of the amount of electron beam to a pedestal-clamped video signal, the missing index pulse is detected and detected. 1. A beam index type color television receiver, characterized in that means is provided for outputting pulses according to the number of pulses, and the output of this means is applied through an integrating circuit so as to control the level of the level setting circuit.