JPS5941666Y2 - blanking circuit - Google Patents

Description

[Detailed explanation of the idea] Related to blanking circuits for color television receivers, etc.

In color television receivers and other deflection systems that enlarge the image (hereinafter referred to as zoom) by changing the amplitude and scanning period of the deflection current, the normal image receiving state (
When switching from zoom (hereinafter referred to as "normal") or from zoom to normal, a method may be adopted in which the power is temporarily turned off to protect the deflection system circuit.

Also, if you do not turn off the power when switching, the screen will become blurred and very ugly, so the picture tube (
A good method is to set the CRT (hereinafter referred to as CRT) in a cutoff or close to cutoff state, and after switching, do not display an image until the circuit operation of the deflection system is stabilized.

However, in both of the above-mentioned methods of temporarily turning off the power at the time of switching, and methods of putting the CRT in a cutoff or near-cutoff state, a blanking pulse is generated by the switching circuit at the time of switching, and the DC voltage I for the first grid of the CRT is A conventional blanking circuit that superimposes this by capacitive coupling has the disadvantage that the screen becomes abnormally bright immediately after switching, making it very unsightly.

First, a conventional example will be explained based on FIG. 1 and FIGS. 3A and 3B.

Figure 1 is a diagram showing a conventional example of a blanking circuit, Figure 3A
, B are waveform diagrams showing signal waveforms of each part.

In Fig. 1, 1 is a blanking pulse signal input terminal, 2 is a power supply terminal, 3, 4.5 are DC voltage input terminals for the first grid, 6, 7.8 are output terminals for the first grid, 1
1 is a transistor, 13゜14.15 is a capacitor, 1
2.16, 17°18 is the resistance.

The blanking pulse signal applied to the blanking pulse signal input terminal 1 is amplified by the transistor 11, and the obtained blanking pulse is transferred to the first grid DC voltage input terminals 3, 4, 5 by the capacitors 13, 14, 15. are capacitively coupled to and superimposed on the first grid DC voltage applied to the output terminal 6°7.8 to the first grid via the resistor 16°17.18, respectively, and the output terminals 6, 7
8. The required first grid voltage waveforms are obtained respectively.

If we adopt a method of temporarily turning off the power when switching, the third
A waveform shown in FIG. A is obtained on the collector side of transistor 11.

Also, in order to bring the CRT as close as possible to the cutoff at the time of switching, a blanking pulse as shown in FIG. 3A may be applied to the first grid.

Here, the difference in the average value of the blanking pulse during normal and zooming due to the difference in pulse width is calculated using terminals 3 and 4.5.
If we assume that the DC voltage for the first grid, which is applied from In order to lower the screen and make the screen monochrome, resistors 16, 1γ, 18 and capacitors 13, 1, respectively.
The time constant of 4.15 cannot be too large.

Therefore, signal waveforms as shown in Figure 3B are generated at terminals 6, 7, and 8, and immediately after switching, the first grid voltage of the CRT rises abnormally, and the brightness rises abnormally, causing the person looking at the screen to It makes people feel uncomfortable.

The present invention provides a blanking circuit that prevents an abnormal increase in CRT brightness immediately after switching and eliminates the discomfort caused by the screen immediately after switching.

An embodiment of the present invention is shown below in FIGS. 2 and 3 C2D.

The explanation will be based on E.

Further, in FIG. 2, the same numbers as in FIG. 1 indicate the same parts.

Figure 2 is a diagram showing the blanking circuit of the present invention, Figure 3C
2D and 2E are waveform diagrams showing signal waveforms at each part.

In FIG. 2, 20 is a self-clamp circuit, which is composed of a capacitor 21, a diode 22, and a resistor 23.

9 is a clamp voltage supply terminal, and the clamp voltage b1 is an arbitrary voltage that is still lower than the sum of the voltage difference v1 between the peak value and the average value of the blanking pulse and the lowest voltage among the DC voltages for the first grid. It is a value.

Here, the difference in the average value due to the difference in pulse width of the blanking pulse during normal and zooming is absorbed by changing the DC voltage for the first grid applied from terminals 3 and 4.5 using a relay, etc. To simplify the explanation, the same pulse waveform will be explained intermittently.

Now, the output impedance of the blanking pulse amplification circuit consisting of the transistor 11 and the resistor 12 is sufficiently low compared to the resistor 23 or the resistors 16, 17, and 18, and the collector side of the transistor 11 has an amplified circuit as shown in FIG. 3C. Assume that a blanking pulse appears.

Also, here, the switching period of the blanking pulse (FIG. 3C) is assumed to be t5.

The blanking pulse obtained on the collector side of this transistor 11 is connected to a capacitor 21, a diode 22, and a resistor 2.
In addition to the self-clamp circuit 20 consisting of 3, the positive period of the blanking pulse is normally clamped to the clamp voltage b1 applied from the terminal 9.

Therefore, if all the DC voltages for the first grid applied from the terminals 3, 4.5 are now constant and this is b2, then the capacitive coupling capacitors 13, 14, . 15 are voltage values (b2b
1+vl).

First, during the switching period t5, no blanking pulse is applied to the self-clamp circuit 20, and the diode 22 is in a non-conducting state.

Here, if the time constant consisting of the capacitors 21, 13, 14, 15 and the respective resistors 23° 16, 17, 18 is selected to be sufficiently shorter than the switching period t, the signal waveform at the output point χ of the self-clamp circuit 20 is as shown in the third diagram, and the capacitor 21 is discharged until it reaches the clamp voltage b1.

At the same time, the voltage value (
b2-bl).

The switching is then completed and a blanking pulse is applied to the self-clamping circuit 20, causing the diode 22 to conduct during the positive period of the blanking pulse.

Therefore, the positive period of the blanking pulse is clamped to the clamp voltage b1 again, and the DC potential at the output point χ of the self-clamp circuit 20 drops to (btVl), and the capacitor 13. 'The charging of f4 and 15 is the resistance 16 and 17, respectively.
Until completion via 18, the DC potential at the terminals 6, 7.8 remains below the DC voltage b2 for the first grid.

Therefore, the voltage of the first grid does not rise abnormally immediately after switching, and the brightness of the CRT does not rise abnormally.

However, in reality, at the output point χ of the self-clamp circuit 20, the DC potential does not immediately drop to the (t)I Vl) potential when the blanking pulse is input, and the output of the amplifier circuit consisting of the transistor 11 and the resistor 12 Due to the impedance and capacitor 21, it approaches the DC potential (bl vt) with a certain time constant.

At this time, the amplitude of the flanking pulse also changes, and a signal waveform as shown in FIG. 3E is obtained at the output terminals 6, 7.8 to the first grid, and the abnormal luminance phenomenon on the picture tube screen disappears.

As explained above, according to the present invention, when enlarging an image on the receiver side, the blanking pulse is temporarily turned off by temporarily turning off the power to protect the deflection system and disrupt the picture tube screen at that time. Even if the system is stopped, there is no abnormal increase in brightness on the picture tube screen immediately after switching, and this can be realized with a relatively inexpensive circuit configuration, so its industrial value is extremely large.

[Brief Description of the Drawings] Figure 1 is a circuit diagram showing an example of a conventional blanking circuit.
FIG. 2 is a circuit diagram showing one embodiment of the blanking circuit of the present invention, and FIGS. 3A, B, and CE are signal waveform diagrams of various parts of FIGS. 1 and 2, respectively. 1...Blanking pulse signal input terminal, 3,4゜5
...DC voltage input terminal for the first grid, 6,7°8.
... Output terminal to the first grid, 9... Clamp voltage supply terminal, 13, 14.15... Capacitive coupling capacitor 7, 16, 17, 18... Resistor, 20... Self-clamp circuit .

Claims (1)

[Scope of utility model registration request] In a television receiver, the positive period of the blanking pulse obtained from the pulse circuit output is self-clamped to a voltage lower than the sum of the voltage difference between the peak value and the average value of the blanking pulse and the DC voltage for biasing the picture tube. and a blanking circuit configured to be superimposed via a capacitor on the picture tube bias DC voltage applied via a resistor.