JPH0326547Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a display device such as a color CRT receiver used as a display terminal of a computer, etc., and particularly relates to a contrast adjustment circuit thereof.

(b) Conventional technology Color display devices such as those mentioned above use TTL (transistor, transistor,
Since digital three primary color signals at logic level are supplied, the contrast adjustment circuit that changes the magnitude of each primary color signal is a transistor for brightness signal amplification, which is used in ordinary television receivers. It is not possible to adopt a method of changing the amount of AC negative feedback of the emitter. This is because, in this method, the display signal, which has a higher frequency than the television video signal, is subjected to phase distortion by the AC negative feedback capacitor. For this reason, conventional display devices of this type include, for example, the color display CMT-141H/L published on page 38 of "All TV Manufacturers Service Book" published by Denshi Gijutsu Publishing Co., Ltd. in September 1984. A contrast adjustment circuit was used.

In other words, Figure 2 shows the above color display.
The contrast adjustment circuit of the CMT-141H/L is partially simplified, and 1 and 1' are a pair of input terminals into which parallel 2-bit red R signals of TTL level from a personal computer, etc. are introduced. One 1 corresponds to the higher-order digit, and the other 1' corresponds to the lower-order digit. 2 is a buffer amplification IC made by Hitachi, Ltd.: HD7407, which is equipped with multistage amplification circuits 3 and 3' that amplify the binary signals of the input terminals 1 and 1', respectively.This IC is a multistage amplification circuit with exactly the same configuration. In addition to the above-mentioned 3 and 3', there are four more.

On the other hand, 4 is a contrast adjustment circuit, and this circuit connects the collectors of the final stage transistors TR ₀ and TR' ₀ of the amplifier circuits 3 and 3', that is, the output terminals 5,
Common connection point A of load resistors R and R' connected to 5'
A first transistor TR ₁ and a resistor R ₂ are connected in series between the and +B ₂ power supply, and the point A is connected to the base of the second buffer transistor TR ₂ , and the above-mentioned first transistor TR ₁ resistance to the base of
The configuration is such that a variable DC voltage for contrast adjustment created by R ₃ , R ₄ and a variable resistor VR ₁ is applied. Then, the output signal from the emitter of the second transistor _TR2 is transmitted to the color drive circuit 6.
The voltage is applied to the red cathode R of the color picture tube 7 through the red signal stage 6R. other G
The same applies to the B signal system.

Therefore, when the base potential of the first transistor TR ₁ is increased by the variable resistor VR ₁ , the impedance between the collector and emitter of this transistor decreases, so that the red signal appearing at point A through the amplifier circuit 3 is reduced. The amplitude of the signal on the higher order digit side will increase. This means that the other amplifier circuit 3'
The same applies to the lower-order digit side signal that appears at point A through the signal. In other words, when the base potential is increased, the amplitude of the composite output of each digit, that is, the R output signal taken out from the emitter of the second transistor _TR2 increases, and conversely, when the base potential is decreased, the amplitude of the output signal The contrast of the color signal is adjusted so that the amplitude of the color signal decreases.

In addition, since the signals of each digit of the R signal are inputted as described above, the A of one of the three amplifier circuits is
_The magnitude of said load resistors R ₁ , R ₁ ' is such that the output signal at point 3' is larger than that at the other point 3'.
It has been selected as _R1 . Therefore, the output signal waveforms for the binary levels "0" and "1" of the input signals S and S' at the terminals 1 and 1' are as shown in FIG.

(c) Problems to be solved by the invention By the way, in the conventional circuit shown in _FIG . Since the collector load currents of TR ₀ and TR' ₀ flow directly, it is necessary to use a large current transistor for the first transistor TR ₁ or to use two transistors connected in Darlington. Furthermore, the output signals of the amplifier circuits 3 and 3' are combined at point A by resistor voltage division using the resistors R ₁ , R ₁ ', R ₂ and the first transistor TR ₁ . There was a problem in that the amplitude change characteristics, ie, the gradation characteristics, were not linear during multicolor display.

Therefore, the present invention was devised with these points in mind, and it is possible to perform multicolor display with good linearity of gradation characteristics without the need to use large current transistors or Darlington connections. The purpose of this invention is to provide a contrast adjustment circuit that can perform the following steps.

(d) Means for solving the problem In the contrast adjustment circuit of the present invention, a plurality of load resistors are connected in series between the collector of the NPN transistor forming the final stage of the display signal amplifier circuit and the power supply. The emitter and collector of a PNP type control transistor having a collector load resistance are connected between the connection midpoint and the reference potential point, and a variable DC voltage for contrast adjustment is applied to the base of this control transistor. did.

(E) Effect According to the above configuration, the magnitude of the current flowing between the collector and emitter of the control transistor can be changed according to the output signal of the amplifier circuit by the variable DC voltage. A contrast-adjusted display signal is obtained from the collector of the transistor.

(f) Embodiment FIG. 1 shows an embodiment of the contrast circuit of the present invention, and the same parts as those of the conventional example shown in FIG. 2 are given the same figure numbers and their explanation will be omitted. The feature of this embodiment is that resistors R ₆ , R ₇ and R' ₆ are connected between the collectors of the final stage transistors TR ₀ and TR ₀ ' of the amplifier circuits 3 and 3' in the IC 2 and the + _B2 power supply. , _R'7 are connected in series _, and a resistor _R8 is used as a common collector load between the midpoints B and C between the two resistors and _the ground point. Each collector and emitter are connected, and a variable DC voltage for contrast adjustment is applied to the bases of both transistors TR ₃ and TR ₄ by resistors R ₃ and R ₄ and variable resistor VR _2. This is what we did.

Now, in this example, the variable resistor
When the base potential of the control transistors TR ₃ and TR ₄ is increased by VR ₂ , the impedance between the collector and emitter of each transistor increases,
The current flowing between each collector and emitter decreases. At that time, each current is turned on or off depending on the potential at the point BC, that is, the outputs of the amplifier circuits 3 and 3', which are "0" and "1", and the combined current of both appears at the point D. The amplitude of the R output signal will be reduced. Conversely, when the base potential is lowered, the contrast is adjusted so that the amplitude of the output signal at point D increases. Also, in this embodiment, for the same reason as the conventional example shown in FIG.
The sizes of R ₆ and R′ ₆ are selected such that R ₁ >R′ ₁ .
Therefore, the output signal waveform at point D in this case also becomes as shown in FIG. 3 depending on the input signal level.

Note that since the above embodiment is for multi-color (64-color) display, each of the three primary color signals is a parallel 2-bit signal, but in the case of 8-color display, of course, it becomes a 1-bit signal at a time. Therefore, only one amplifier circuit and one control transistor are required. Also,
The present invention can of course be applied not only to color display but also to black and white display.

(G) Effects of the invention According to the contrast adjustment circuit of the invention, not all of the collector load current of the final stage transistor of the display signal amplification circuit flows through the control transistor, but only a part of the current flows. There is no need to use a large current control transistor or a Darlington connection for this control transistor, so it can be realized at low cost. In addition, in the case of multi-color display, multiple control transistors to which signals of each digit of the display input are applied can be connected in common, with the collector resistor as a common load. In this case, the collector side of the control transistor The signals of each digit are synthesized, and the load resistances of the final stage transistors connected to the emitter side of the control transistor do not affect each other, thereby improving the linearity of the gradation characteristics. Can be done.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure shows a circuit diagram of a conventional contrast adjustment circuit.
FIG. 3 is a waveform diagram showing the output signal waveform. 3, 3'...Amplification circuit, 4...Contrast adjustment circuit, TR ₀ , TR' ₀ ...Final stage transistor,
TR ₃ , TR ₄ ... control transistors.

Claims (1)

[Scope of utility model registration request] In a display device to which a TTL level display signal is supplied, a plurality of load resistors are connected in series between the collector of the NPN transistor that forms the final stage of the display signal amplification circuit and the power supply, and the connections between the load resistors are The emitter and collector of a PNP type control transistor having a collector load resistance are connected between the midpoint and the reference potential point, and a variable DC voltage for contrast adjustment is applied to the base of this control transistor. A contrast adjustment circuit for a display device that obtains a contrast-adjusted display signal from the collector of the display device.