JPH02282291A - Driving circuit for color display - Google Patents

Abstract

PURPOSE:To allow the free switching of the blue on a CRT display to blue or light blue by selectively operating one-directional conducting elements. CONSTITUTION:Respective circuits of R, B, G operate independently when switches SW1, SW2 are off. Transistors Q1, Q3 turn on and diodes D1, D4 prevent the backflow of a B signal to clamp circuits 1, 3 when only the B signal is inputted while the SW1, SW>=2 are on. Video amplifiers 4 to 6 operate through an emitter follower consisting of Q1 to Q3 and R6 to R8. the outputs thereof are made into the output signals of R, B, G via cut off adjusting circuits 7 to 9. As a result, the red and green phosphors emit light slightly in addition to the blue phosphor on the CRT, thus forming a light blue. The D2, D3 turn off and the operations similar to the case in which the SW1, SW2 are off take place when the B signal and the signals exclusive of the B signal are inputted. The white of the same color tone as the color tone of the white when the SW1, SW2 are off is then displayed on the CRT.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to a color camera having three video amplifiers that amplify R (red), G (green) and B (blue) video signals on each side. The present invention relates to a display driving circuit.

[Prior Art] Generally, a CRT color display drive circuit is configured to include three video amplifier systems that independently amplify the three colors of RGB. As one of these video amplifier systems, a circuit as shown in Fig. 4 has been known for some time (Transistor Technology Vol. 22, No. 253, p. 40).
(see 7). This circuit is constructed by cascading a preamplifier 31, a gain adjustment circuit 32, a clamp circuit 33, a main amplifier 34, a DC component cutting capacitor C, and a cutoff adjustment circuit 35. RlG or B video signal I
After N is amplified three to four times by the preamplifier 31, the gain between R, G, and 8 is adjusted by the gain adjustment circuit 32. Next, the black level is made constant by the clamp circuit 33, amplified approximately ten times by the main amplifier 34, and then the DC component is cut by the capacitor C. After the cutoff is adjusted by the cutoff adjustment circuit 35, the signal is supplied to the cathode of the CRT color display.

[Problems to be Solved by the Invention] By the way, among the three primary colors of CRT color displays, red, green, and blue, blue phosphors usually have low visibility to the human eye, making it difficult to see characters displayed in blue. There are drawbacks. For this reason, instead of the usual blue phosphor, we used light blue phosphor, which is a mixture of blue, red and green.
RT color displays have also been developed.

However, when light blue phosphors are used in CRT color displays, the problem is that the color reproduction range becomes narrower than when blue phosphors are used, as is clear from the CIE chromaticity table shown in Figure 5. was there. For this reason, two types of CRTs must be prepared: one that uses blue phosphor and one that uses light blue phosphor, depending on whether you place emphasis on color reproducibility or legibility of characters. There wasn't.

In addition, in CRTs using light blue phosphor, 9300'K+27MP, which is generally said to be white.
CD (x = 0.281 in CIE chromaticity table
sy=θ, 311 ), there was a problem in that the thickness of the line displayed on the CRT would be significantly different for red, green, and blue because the current value flowing through each electron gun was different.

The present invention has been made in view of such problems, and includes:
The color display drive circuit allows you to select either blue or light blue as the emitting color depending on the display purpose, and even when displaying white, the line thickness does not differ between red, green, and blue. The purpose is to provide.

[Means for Solving the Problems] A color display drive circuit according to the present invention includes first, second, and third video amplifiers that amplify red, blue, and green video signals, respectively, and the first video amplifier. a first video amplifier connected between the input side of the amplifier and the input side of the second video amplifier and selectively passing a current from the input side of the second video amplifier to the input side of the first video amplifier; a unidirectional conducting element connected between an input side of the second video amplifier and an input side of the third video amplifier;
and a second unidirectional conduction element that allows current to flow from the input side of the video amplifier to the input side of the third video amplifier.

[Operation] In the present invention, when the first and second unidirectional conduction elements are selected, that is, when these elements are in an operable state, a blue signal is input alone to the second video amplifier. Then, a part of the blue signal flows into the first and third video amplifiers for red and line via the first and second unidirectional conduction elements, so that not only the blue phosphor but also the blue signal flows into the first and third video amplifiers for red and line. , the red and green phosphors also emit a slight amount of light, making the CRT
It will be displayed in light blue above.

Further, when all the red, green, and blue signals are input to the first to third video amplifiers, no current flows through the first and second unidirectional conductive elements, so that the red, green, and blue signals are input to the first to third video amplifiers. Balanced current values for green and blue enable white display with equal thickness of these three primary colors.

Furthermore, when the first and second unidirectional conductive elements are set to a non-selected state, the display using the three primary colors of red, green, and blue is performed in the same manner as before, so the color reproduction range is wide. Color display becomes possible.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing a color display driving circuit according to a first embodiment of the present invention. The red, green, and blue video signals INR, INB, and ING are respectively input to a clamp circuit L2.3 for making the black level of each signal constant. The output of the red clamp circuit 1 is input to the base of the transistor Q1 via a resistor R□ and a diode D1. The output of the clamp circuit 2 is input to the base of the transistor Q2 via a resistor R2.

Furthermore, the output of the clamp circuit 3 is input to the base of the transistor Q3 via a resistor R3 and a diode D4. These transistors Q11Q21Q3 are emitter follower circuits whose emitters are grounded through resistors R, , R7, and R, respectively, and their outputs are input to video amplifiers 4 and 5.8, respectively. Video amplifier 4, 5. The output of Ei is sent to the cut-off adjustment circuit 7 via DC cut capacitors C+, C2, and C3, respectively.
．． 8.9 is entered.

These cutoff adjustment circuits 7.8.9 adjust the cutoff of each color video signal and output an output signal 0UTR10UTB10UTG for driving the cathode of the CRT display.

In this circuit, the video amplifier is 4°5.6
The transistor Q0. Q2. The following circuit is connected between each base of Q3. That is, a resistor R4, a diode D2, and a switch S are connected between the base of the transistor Q2 for blue and the base of the transistor Q1 for red.
W 1 are connected in series. Furthermore, between the base of the blue transistor Q2 and the base of the green transistor Q3, a resistor R1, a diode D3, and a diode SW2 are connected.
are connected in series. The switches sw, , and sw2 are switches for switching between blue light emission and light blue light emission, and when in the on state, light blue light emission is possible. Further, the diodes D2 and D3 are connected in the direction in which current flows from the blue signal system to the red and green signal systems.

Next, the operation of the circuit of this embodiment will be explained.

When the switches S W s and SW2 are both off, the R, G, and H circuits operate independently as in the conventional case. That is, as shown on the left side of FIG. 2(a), o,'yvp
The black level of each signal of approximately p+7+lNR1INB and ING is kept constant by clamp circuits 1, 2.3, and is amplified by video amplifiers 4 to 6 through emitter followers composed of transistors Q1 to Q3 and resistors R6 to R8. And DC component cutting capacitors C1 to C3
After the DC component is cut off, the cutoff adjustment circuits 7 to 9 perform cutoff adjustment and output as output signals 0UTR10UTB and 0UTG amplified to about 40Vpp.

Therefore, when the switches sw, , sw2 are off, the second
As shown on the right side of Figure (a), the blue displayed on the CRT will be expressed using ordinary blue phosphor.

Next, the operation when the switches SW, SW2 are on will be explained. First, when the B signal is not input, the switches SW+ and SW2 operate in the same way as when they are off. That is, if we assume that the base of the transistor Q for the R signal is the point ■, the base of the transistor Q2 for the B signal is the point ■, and the base of the transistor Q3 for the G signal is the point ■, then, for example, only the R signal is input. In this case, the potential at point (2) is higher than that at point (2), so diode D2 is turned on and no current flows from point (2) to point (2). Therefore, as a result, the switch SW1 operates in the same way as when it is turned off. The same applies when only the G signal is input and when the R signal and the G signal are input.

Next, a case where only the B signal is input will be described. In this case, transistor Q2 is turned on, but the second
As shown on the right side of the figure (b), the potential at point ■ exceeds the potential at points ■ and ■, so current flows from point ■ to points ■ and ■.
Transistors Ql and Q3 are also turned on. At this time, the diode D1. D4 prevents the B signal from flowing back into the clamp circuits 1 and 3. In this way, by turning on the transistor QzQ3 as well as the transistor Q2, the video amplifiers 4 to 6 operate through the emitter follower made up of the transistors Q1 to Q3 and the resistors R6 to R8, and the outputs are converted to DC by the DC cut capacitors C1 to C3. After being cut off, the R, B, and G output signals 0UTR are output via the cutoff adjustment circuits 7 to 9.

Output as 0UTB and 0UTG. In this case, since the B signal is actually the main signal, the output signals 0UTR and 0UTG are the output signal 0UT, as shown on the right side of FIG. 2(b).
smaller than B. As a result, in addition to the blue phosphor on the CRT, the red and green phosphors also slightly emit light, resulting in a light blue color.

Next, a case where a B signal and a signal other than the B signal are input will be described.

For example, as shown on the left side of Fig. 2(b), if all signals of R1G and H are input, points ■, ■, ■
All potentials are the same. Therefore, diode D2,
Both D3 are turned off, and the entire circuit is switched sw,
, sw2 are off.

As a result, what is displayed on the CRT is the switch SWI.
, the white is the same tone as the white when SW2 is off.

FIG. 3 is a circuit diagram showing a color display driving circuit according to a second embodiment of the present invention.

This circuit is designed to switch the blue color displayed on the CRT between normal blue and light blue depending on whether or not the INY signal is input.

In this circuit, clamp circuits 11, 12, 13, resistors R111R121R13, diodes D1. .

Dl. , transistor Q1□+QI21 Q13N resistor R16°R171R18, video amplifier 14, 15 .
1B, capacitors C8I, C□2+C1] and cutoff adjustment circuits 17, 18, and 19 are the same as those described in the first embodiment. In this circuit, a resistor R14 and an NPN transistor Q□4 are connected in series between the base of the transistor Q11 for the B signal and the base of the transistor Q1□ for the G signal, and the transistor Q□□ for the B signal is connected in series. A resistor Rte and an NPN transistor Q1 are connected between the base of the R signal transistor Q1G and the base of the R signal transistor Q1G.
5 are connected in series. And transistor Q
The aforementioned signal INY is input to each base of 141 Qs5.

Next, the operation of this circuit will be explained.

First, when the INY signal is at the "'0°" level, none of the transistors Q141 to Q15 turn on, and the RI
Each of the G and B circuits operates independently. Therefore, in the first embodiment, it functions in the same way as when the switches SW□ and SW2 are off.

Next, when ■NY signal is at 1'1'' level and only B signal is input, current flows from point ■ toward point @ and [phase], so transistor Q
11, transistors Q12 and Q13 are also turned on. Therefore, the blue displayed on the CRT becomes light blue.

Further, when the B signal and a signal other than the B signal are input at the same time, the following operation is performed. For example, if all R, G, and B signals are input, transistors QI4 and Q15
are not turned on, and the white displayed on CRTJ: is r.
The white color is the same tone as when the NY signal is not input.

Therefore, when the INY signal is not input, the result is the same as when the switches SW t and SW2 are off in the first embodiment, and when the INY signal is input, the switch SW t and SW2 are turned off in the first embodiment. , , the same result as when SW is turned on.

[Effects of the Invention] As explained above, according to the present invention, by selectively enabling unidirectional conduction elements such as diodes and transistors, the blue color on a CRT display can be freely changed to blue or light blue. You can switch to Therefore, the blue fluorescent color can be made to have high visibility, and the color reproduction range is not narrowed unlike a CRT using a light blue phosphor. Further, even if light blue is selected, when white light is emitted at +27 MPCD at 9300°, the function is the same as when using a conventional blue phosphor, so there is no large difference in line thickness between red, green, and blue.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a color display drive circuit according to a first embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the circuit of FIG. 1, and FIG. FIG. 4 is a circuit diagram showing the configuration of a conventional video amplifier circuit, and FIG. 5 is a schematic diagram showing the color gamut of a CRT. 1 to 3, 11 to 13, 33; Clamp circuit, 4 to 6, 14 to 16; Video amplifier, 34; Main amplifier, 7 to 9, 17 to 19, 35; Cutoff adjustment circuit, C1 to CG1C11 to C131C; DC component cutting capacitors, R1 to RetR+ to R18; resistors, R1 to Rs x R1s to R18; resistors NQI to Q3+ Q 1s to Q15; transistors, D□ to D4 Dl. D□2; Diode

Claims (1)

[Claims] (1) A first amplifying the red, blue and green video signals, respectively;
second and third video amplifiers connected between the input side of the first video amplifier and the input side of the second video amplifier, selectively connecting the input side of the second video amplifier to the input side of the second video amplifier; a first unidirectional conducting element that allows current to flow to the input side of the first video amplifier; and a first unidirectional conductive element that is selectively connected between the input side of the second video amplifier and the input side of the third video amplifier; A color display drive circuit comprising: a second unidirectional conduction element that allows current to flow from the input side of the second video amplifier to the input side of the third video amplifier.