JPS6359591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION For example, in a color television receiver using a beam index type color picture tube, the waveform of the drive signal supplied to the color picture tube may be narrowed, or the beam spot diameter may be reduced due to excessive beam current. This increase causes the beam to hit adjacent color phosphor stripes, degrading the color saturation. Such deterioration occurs not only in beam index type color television receivers but also in ordinary color television receivers.

In order to prevent deterioration of color saturation, the beam current may be limited by detecting the maximum level of the video signal and controlling the level of the video signal when this occurs at a reference level.

However, in this case, the level of the white signal, which does not particularly require limiting the beam current, is also limited, so in such a case, there is a drawback that the entire screen becomes dark.

Therefore, the present invention eliminates these drawbacks and makes it possible to limit the beam current only when the color saturation deteriorates.

An example of the present invention, applied to the above-mentioned beam index type color television receiver, will be described below with reference to FIG. 1 and subsequent figures.

First, a beam index type color picture tube, which is the premise of this invention, will be explained. In this method, a single electron beam scans a phosphor surface in which red, green, and blue color phosphor stripes are arranged repeatedly in the horizontal scanning direction.For example, as shown in Figure 1, the phosphor surface is On the inner surface of the screen, index phosphor stripes R, G, and B are arranged in the horizontal scanning direction to form an effective screen area 2, and an electron beam is obtained by scanning the index phosphor stripes R, G, and B. Based on the index signal S _I , the electron beam is directed to the red phosphor stripe R.
When scanning the green phosphor stripe G, use the red primary color signal, and when scanning the green phosphor stripe G, use the green primary color signal.
When scanning the blue color phosphor stripe B, the blue primary color signal is density-modulated.

A black material 4 is formed between the color phosphor stripes R, G and B and around the effective screen area 2, and a metal back 5 is formed over the entire surface. Then, the effective screen section 2 and the horizontal scanning start section 3 on one side thereof.
Across the metal bag 5, index phosphor stripes I are arranged in the horizontal scanning direction to form red, green and blue color phosphor stripes R, G and B.
The pitch is formed by, for example, 2/3 of a set of pitches.

Note that the index phosphor stripe I is red;
Green and blue color phosphor stripes are provided at locations between R, G and B.

FIG. 2 shows an example of a color television receiver according to the present invention using this color picture tube.
The electron beam 6 is the index phosphor stripe I
A photodetector 8 is arranged to detect light 7 emitted when the image is scanned.

Then, the horizontal synchronizing pulse P _H (FIG. 3B) is supplied to the set side of the flip-flop circuit 11,
At the trailing edge of the pulse P _H , the output signal F _X (C in the figure) of the flip-flop circuit 11 rises. Incidentally, the flip-flop circuit 11 is reset at the time when the electron beam scans the boundary position between the horizontal scanning start section 3 and the effective screen section 2. The output signal _F
is turned on, and during this period, the potential obtained from the comparator 13 is supplied to, for example, the first grid 9 of the picture tube 1, a beam current flows, and the electron beam 6 reaches the index phosphor of the above-mentioned horizontal scanning start section 3. The stripe I is now scanned, and an output signal is obtained from the photodetector 8.

The output signal of this photodetector 8 is supplied to a bandpass filter 15 to produce an index signal with a frequency determined by the pitch of the index phosphor stripe I.
S _I (D in the same figure) is taken out. In FIG. 3, only the portion during the horizontal scanning start section 3 is shown. This index signal S _I is supplied to the amplitude detection circuit 16 and amplitude detected, and the detected voltage is
V _D (E in the same figure) is obtained. In FIG. 3, only a portion of the period during the horizontal scanning start portion 3 is shown.

Then, the detection voltage V _D of this amplitude detection circuit 16
is supplied to the sampling hold circuit 17 and sampled and held by the output signal F _X of the flip-flop circuit 11 described above. Therefore,
As the output voltage V _H of the sampling hold circuit 17 (F in the same figure), the detected voltage V _D of the amplitude detection circuit 16 is
A value obtained by holding the value at the end of the period of the horizontal scanning start section 3 is obtained. Then, the output voltage V _H of this sampling hold circuit 17
is supplied to a comparator 13 and compared with a preset reference voltage V ₁ by a variable resistor 19 .

Therefore, the output voltage of the comparator 13, that is, the output voltage of the comparator 13, is adjusted so that a constant beam current flows during the period of the horizontal scanning starting section 3 and an index signal S _I of a constant magnitude is obtained. Voltage applied to the first grid 9 of the picture tube 1
V _M is controlled. This control operation is a negative feedback operation. Note that a relatively large beam current flows during the period of the horizontal scanning start section 3, so that a relatively large index signal S _I can be obtained.

On the other hand, the demodulated red, green and blue primary color signals E _R ,
E _G and E _B are supplied to a black level compensation circuit 20 consisting of, for example, a clip circuit or a clamp circuit, and the output voltage V _M of the above-mentioned comparator 13 is supplied to a level shift circuit 21 so that the voltage is kept at a constant potential lower than the voltage V _M. A lowered voltage V _B is obtained, and this voltage V _B is supplied to the black level compensation circuit 20 so that each primary color signal does not fall below the voltage V _B in the circuit 20.
That is, it is controlled so that the black level becomes the voltage V _B. This voltage V _B is such that, when applied to the first grid 9 of the picture tube 1, a small amount of beam current flows as shown in FIG.

The reason why the picture tube does not cut off and a small amount of beam current flows even at the black level of the video signal is to ensure that an index signal is always obtained regardless of the content of the video signal. Color switching is always performed at the correct timing for the surface, and correct color reproduction is always performed.

The primary color signals of each color whose level has been controlled in the black level compensation circuit 20 are sent to switch circuits 25R and 25G.
and 25B, and the switch circuits 25R, 25G, and 25B are supplied to the switch circuits 25R, 25G, and 25B during the effective screen section 2.
B is turned on sequentially at the position of each color phosphor stripe R, G and B based on the index signal S _I , and a synchronously switched color signal is applied to the first grid 9 of the picture tube 1.

Gate signals G _R , G _G and G _B for switch circuits 25R, 25G and 25B are formed as follows.

First, the output of the PLL circuit 26 is divided by 1/3 by the counter 27 to form red, green, and blue division pulses F _R , F _G , and F _B that differ in phase by 120 degrees from each other. is supplied to the gate circuit 28,
The division pulses F _R , _FG and _FB taken out from the gate circuit 28 during the period of the effective screen portion 2 are used as gate signals G _R , _GG and _GB .

If the cutoff level of the picture tube 1 varies or changes over time, the characteristics between the drive voltage and cathode current, and therefore the characteristics between the drive voltage and the level of the index signal S _I , will change depending on the picture tube's cutoff level. Since the so-called γ value does not change, it changes in parallel as shown by curves 31 and 32 in FIG. Even if the characteristics change in this way, in the above-mentioned receiver, the horizontal scanning start section 3
The output voltage of the comparator 13 is adjusted so that the level of the index signal S _I during the period becomes constant as shown by v _M.
Since V _M is controlled, even if the output voltage V _M of the comparator 13 changes to V _M1 or V _M2 due to a change in this characteristic, the level shift circuit 21 lowers the voltage V _B by a certain level. is V _B1 or
_Therefore , even if the characteristics change, the magnitude of the beam current flowing at the black level does not change, and the level of the index signal S _I obtained at the black level is shown as v _B. becomes constant.

The color saturation deterioration prevention circuit 30 is the main circuit configuration of the present invention, and detects both the maximum value and the minimum value of the demodulated color signal, and when the output of the difference exceeds a predetermined reference level, the color saturation deterioration prevention circuit 30 detects the picture or brightness. By controlling the adjustment circuit to prevent an excessive beam current from flowing, it is possible to prevent the screen from becoming unnaturally dark and to prevent deterioration in color saturation.

In the figure, 40 is a maximum value detection circuit, 50 is a minimum value detection circuit, 70 is an attenuation circuit provided as necessary, 60 is a synthesis circuit, 80 is a detection circuit using a diode Dd that detects the difference detection output, 90 1 is a level comparison circuit, and 100 is an amplifier circuit.

Further, 110 is a picture adjustment circuit controlled by the comparison output, and 120 is a brightness adjustment circuit. 13
0 is a weighting circuit provided as necessary. Picture adjustment refers to adjusting the luminance signal and color signal simultaneously.

FIG. 5 shows a specific example of this color saturation deterioration prevention circuit 30, in which the detection circuits 40 and 50 are each composed of three transistors Q ₁ to Q ₃ and Q ₄ to _{Q 6} connected in parallel. Then, the maximum value of the demodulated color signals E _R to E _B is detected by the transistors _{Q 1 to Q 3 ,} and _the maximum value of _the demodulated color signals E The minimum value among _R to E _B is detected. Each detection output V・MAX,
Since V・MIN is combined as V・MAX−V・MIN=V ₁ to form the difference detection output V _I ,
The synthesis circuit 60 includes a transistor _Q8 for polarity reversal.
has.

Note that the resistor provided in this composite circuit 60
R ₁ and R ₂ are for attenuation and constitute the attenuation circuit 70 shown in FIG. In the figure, the detection output V・MIN is leveled down to 1/2.

The difference detection output V _I is peak-detected by a diode Dd, and then compared with a reference level (voltage) V _S. This comparison circuit 90 is configured as a differential amplifier, and one terminal is supplied with a reference voltage V _S formed by a pair of resistors R _a and R _b , and the other terminal is supplied with a detected output.

Note that when a differential amplifier is used as the comparison circuit 90, the subsequent stage amplifier circuit 100 is not particularly required.

When the detection output, that is, the difference detection output V _I is larger than the reference voltage V _S , the backflow blocking diodes Dp and Db are turned on, so the picture and brightness adjustment circuits 110 and 120 are controlled. The beam current is limited by the comparison output so that it does not become excessive.

Next, the control operation will be explained by taking as an example the case where the demodulated color signals E _R to E _B are inputted when the left half is red and the right half is white as shown in FIG. Even for the same image, the respective signal levels can vary, so the maximum value output and minimum value output change accordingly. FIG. 7 illustrates four cases.

First, when the red signal level and the white signal level are equal, the maximum value output V・MAX and the minimum value output V・
MIN is as shown in A ₁ and A ₂ in the same figure, and considering a 1/2 level down (the output is A ₃ in the same figure),
The difference detection output V _I becomes as shown in _A4 in the same figure, and the control result becomes _A5 in the same figure, which is supplied to the color picture tube 1. In this case, the beam current is controlled based on the red signal E _R with 100% color saturation.
White signal E _W with low color saturation even if the input level is the same
It is not controlled on the basis of

When the white signal level is twice the red signal level, the difference detection output V _I becomes B ₄ in the same figure, so
When the white light level is high enough, the red light
Beam current is controlled by either white signal.

When the white light level is three times the red light level,
Since the difference detection output V _I is as shown in _C4 in the figure, the white signal level is controlled to be the reference level V _S , and the result is as shown in _C5 in the figure. In this way, in the example shown in the figure, the white signal level is controlled to become the reference level V _S only when the white signal level is twice or more than the red signal level, so the input level to be controlled is set higher than the red signal level. It can be made higher. Therefore, the screen will not become dark due to the control operation.

If the white light level is lower than the red light level, the screen will be controlled based on the red light as shown in _D1 to _D5 in the same figure, so the screen will not become dark due to this. .

As explained above, in this invention, the beam current is limited only when the color saturation deteriorates, so when the color saturation is low, such as a white signal, the beam current is not limited, so the entire screen becomes dark. There will be no such thing. This is because the control level is made different when the primary color signal is used and when it is not.

In Figure 8, the detection circuits 40 and 50 are connected to diodes _D1.
〜D ₃ , D ₄ 〜 _{D 6} .

Note that the detection diode Dd may be configured with an NPN transistor, and when a transistor is used, the detection efficiency can be improved more than a diode.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a beam index type color picture tube, Fig. 2 is a system diagram showing an example of a beam index type color television receiver according to the present invention, and Figs. 3 and 4 are explanations of its operation. FIGS. 5 and 8 are connection diagrams showing an example of the color saturation deterioration prevention circuit, and FIGS. 6 and 7 are diagrams illustrating its operation. 1 is a color picture tube, 30 is a color saturation deterioration prevention circuit, 40 is a maximum value detection circuit, 50 is a minimum value detection circuit, 80 is a detection circuit, 90 is a level comparison circuit, 1
10 is a picture adjustment circuit, and 120 is a brightness adjustment circuit.

Claims (1)

[Claims] 1 In a color television receiver in which the maximum beam current must be electronically limited, a first detection circuit detects the maximum value of the three demodulated primary color signals, and a second detection circuit detects the minimum value. a detection circuit, a detection circuit that detects the output of the difference between the first and second detection circuits, and a comparison circuit that compares the detected output with a reference level, and the output of the detection circuit is set to the reference level. A beam index type color television receiver in which the maximum value of the beam current is limited by controlling the amplitude of the video signal supplied to the control electrode of the color picture tube only when the beam current is higher than that of the color picture tube.