JPH0951450A - Gamma correction circuit - Google Patents

Abstract

(57) Abstract: An excessive increase in brightness of a CRT screen is prevented regardless of the resistance value of the resistor R1 arranged (inserted) between the collector of an output amplification transistor and the cathode of a CRT. To provide a gamma correction circuit capable of preventing the deterioration of the characteristics of the high frequency component of the output signal of the output amplification transistor and effectively operating the gamma correction performed on the image transmitting side. SOLUTION: The cathode of the CRT 9 is formed by setting the capacitance of a capacitor C1 forming a parallel circuit composed of a resistor R1 and a capacitor C1 to be larger than the cathode capacitance of the CRT 9.
It is possible to bypass the high frequency component of the voltage applied to the capacitor C1 arranged in parallel with the resistor R1 and to pass it.
By setting the collector of the output amplification transistor Q2 of the amplification circuit 31 to have a low impedance, the influence of the electrostatic capacitance C _CB generated between the collector and the base of the output amplification transistor Q2 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction circuit, and more particularly to a display device using a cathode ray tube such as a television receiver.

[0002]

2. Description of the Related Art Picture tube (also called CRT or cathode ray tube)
The R, G, and B three-color phosphors do not emit light in proportion to the voltage of the input video signal. Therefore, the sender (broadcasting station, etc.)
Then, the characteristics of the R, G, B signals are corrected (gamma correction) and transmitted. Along with this, when a high-saturation image (image with a deep color) is received on the receiver side, a phenomenon occurs that the resolution is lowered. This is because the output of the image pickup tube is proportional to the brightness of the subject, but after passing through the non-linear circuit called gamma correction, it is converted into a luminance signal and a color signal by a matrix circuit, etc. The brightness information of the subject is transmitted. This is due to the fact that the transmission of luminance details is reduced because the band is limited for this color signal.

FIG. 4 is a graph showing the detail reproduction characteristics of the three primary color images.

As described above, in the current television broadcasting, the gamma characteristic of the cathode ray tube is corrected on the transmitting side (broadcasting station, etc.). R for which the sending side has performed gamma correction
When a G / B signal is converted into a luminance signal and a color signal and transmitted, the principle of constant luminance, that is, the principle that information indicating brightness is transmitted only in the channel of the luminance signal and not in the channel of the color signal is established. Will not do. Therefore, as described above, if gamma correction is performed on the transmission side and the band of the color signal is narrowed to 1/3 to 1/4 or less of the band of the luminance signal and transmitted, the higher the saturation becomes, the more As shown in FIG. 4, the transmission characteristic of the luminance signal in the frequency band higher than the transmission band of the color signal deteriorates.

FIG. 5 is a graph showing the characteristics when γ <1, γ> 1 and γ = 1.

Γ generally represents a linear relationship between input and output. In television, it is a numerical value used to indicate the degree to which the brightness of a screen (video) is stretched or compressed. For example, in FIG.
6 is a graph showing the visual response of the eye showing the characteristic in the case of <1, and FIG. 5B is a graph showing the characteristic of the cathode current with respect to the cathode voltage of the CRT showing the characteristic in the case of γ> 1. FIG. 5C is a graph showing the characteristics of the amplifier showing the characteristics when γ = 1. In the figure, the characteristics are on a linear scale, respectively. If both vertical and horizontal coordinate axes are expressed in a logarithmic scale, the characteristics are approximated by a straight line, and the inclination value is gamma (γ). In order to reproduce a faithful color on a color television, it is necessary to set the total gamma including image transmission and image reception to 1.

By the way, as described above, FIG.
CRT cathode current I with respect to T cathode voltage Vk
It is the graph which showed the characteristic of k, and the characteristic is represented by the following formulas. That is, Ik = g (Vk) ^ γ ... Equation 1 rk = Vk / (γIk) ... Equation 2 The symbols in the equation are as follows. Also, “(Vk)
^ Γ ”represents Vk to the power of γ.

Vk: CRT cathode voltage (referenced to cutoff voltage) Ik: CRT cathode current rk: Equivalent resistance of CRT cathode γ: Gamma constant (2 <γ <3) g: CRT photoelectric conversion characteristic Constants related to sensitivity Figure 6
FIG. 3 is a diagram showing gamma of a transmission / reception system.

In FIG. 6, first, amplifiers 32 and 34 are provided.
The gamma value of γ ₂ , γ _4, is generally 1 when operated in the linear region. The gamma value of the image pickup tube, that is, γ ₁ is the inclination value of the photoelectric conversion characteristic, and
At 31, γ ₁ ≈1. Further, the gamma value of the picture tube 35 is an inclination value of the electro-optical conversion characteristic, and if this is γ ₅ , each color (three primary colors) is γ ₅ ≈2.2. This means that the light emission output is not directly proportional to the signal voltage, and unless corrected in any way, the gamma value will be the same as that of a cathode ray tube (CRT).
Even if the input terminal of 35 is 1, the hue and the saturation change (see FIG. 4) due to the change in the brightness of the video signal (in particular, the increase in the brightness). That is, the gamma characteristic of the picture tube causes a change in the mixing ratio of the three primary colors of R, G, and B, which makes it impossible to faithfully reproduce the colors.

Therefore, in the current television system,
A gamma correction circuit 33 is provided on the image transmission side to set the total gamma value of the transmission / reception system to be 1 and to suppress the screen from becoming too bright (excessive increase in screen brightness). There is. For example, the image pickup tube 31, since the gamma value gamma ₃ of the gamma correction circuit 33 in the case of using the Puranbikon is _{γ = γ 1 · γ 2 ·} γ 3 · γ 4 · γ 5 = 1, γ 3 = 1 / (γ _{1 ·} γ _{2 ·} γ _{4 ·} γ ₅ )
Can be obtained by Where γ ₁ = γ ₂ =
γ ₄ = 1 Also, since γ ₅ = 2.2, γ ₃ = 1
/ (Γ _{1 ·} γ _{2 ·} γ _{4 ·} γ ₅ ) = 1 / 2.2 = 0.45. Here, FIG. 7 is a graph showing the characteristics of the gamma correction circuit 33, and FIG. 8 is a graph showing the electro-optical conversion characteristics of the picture tube (CRT) 35.

FIG. 7 (b) shows the E ₀ -E _i characteristics of the video signal corrected by the gamma correction circuit 33 with a gamma value of 0.45 for the video signal input from the Plumbicon (image pickup tube) 31. 7 is a graph represented by a linear scale, and FIG.
7A is a graph in which both vertical and horizontal coordinate axes of the graph of FIG. 7B are represented on a logarithmic scale (logarithmic scale). Thus, by representing both the vertical and horizontal coordinate axes of the graph on a logarithmic scale, the characteristic of the gamma correction circuit 33 is represented by a straight line, and the inclination tan θ _{1 of} the straight line is the gamma value (γ ₃ = 0.45) is represented.

FIG. 8B shows the picture tube (CR).
T) 35 is a graph showing the EL characteristics of the video signal input to the video signal 35 on a linear scale, and FIG. 8A is a graph in which both the vertical and horizontal coordinate axes of the graph of FIG. It is a graph represented by (scale). In this way, by displaying both the vertical and horizontal coordinate axes of the graph on a logarithmic scale, the picture tube (CRT) 3
The electro-optical conversion characteristic of 5 is represented by a straight line, and the slope ta of the straight line is ta.
nθ ₂ represents the gamma value (γ ₅ = 2.2) of the picture tube 35.

Ideally, by setting the gamma constant γ ₃ of the gamma correction circuit 33 on the image sending side as described above,
The total gamma value of the transmission / reception system can be set to 1 (γ ₃ × γ ₅ ≈1), and the hue and the saturation can be changed by the change in the brightness of the video signal input to the picture tube 35 (in particular, the increase in brightness). Figure 4
(See) can be prevented.

However, as described above, the image transmitting side (broadcasting station)
Considers the gamma value of the picture tube 35 on the image receiving side as γ ₅ = 2.2,
The video signal is transmitted after being subjected to signal processing with the image sending side gamma constant γ ₃ , but in reality, depending on the type of the television receiver, the electro-optical conversion characteristics of the picture tube (CRT) 35,
That is, the value of the gamma constant varies to some extent (2 <γ <
3).

FIG. 9 is an example of a circuit diagram showing one system of a conventional cathode ray tube (CRT) drive circuit.

In FIG. 9, the color difference signal v ₁ input from the input terminal 41 is input to the base of the transistor Q1 which constitutes the video signal amplifier circuit 31, and the emitter of the transistor Q1 is the resistor R _{E and} the cathode of the CRT2. It is connected to the reference potential point GND and the input terminal 42 for the luminance signal Y via the first cutoff voltage adjusting resistor Rc. Further, the collector of the transistor Q1 is connected to the emitter of the transistor Q2, the base of the transistor Q2 is connected to the plus side of the constant voltage source E3, and the collector of the transistor Q2 has a typical value of about 3.3.
A cathode ray tube (CRT) having a resistance value of kΩ and having a function of suppressing an excessive increase in screen brightness, a CRT is provided through a resistor R1.
It is connected to the cathode 1 of No. 2 and is also connected to the positive side of the constant voltage source E2 and the capacitor C4 via the resistor R0. Also, the collector of the transistor Q2 and the resistor R1
A voltage vi is generated in between, and the negative side of the constant voltage source E2, the negative side of the constant voltage source E3, and the electrode of the capacitor C4 opposite to the resistor R0 are connected to the reference potential point GND, respectively.

Further, the heater 4 is a heater voltage source e _H
, The screen grid 5 is connected to the positive side of the screen voltage source E _S , the focus grid 6 is connected to the positive side of the focus voltage source E _F , and the anode 3 of the CRT 2 is connected to the high voltage anode voltage. Source H
It is connected to the positive side of V. One end of the heater voltage source e _H and the minus side of the constant voltage sources E _S , E _F , and HV3 are connected to the reference potential point GND, respectively. Also, the resistor R0, the collector-emitter path of the transistor Q2, the collector-emitter path of the transistor Q1,
A current ic is flowing in the series circuit composed of the resistor R _E and the cutoff adjustment resistor Rc, and the CRT2 of the resistor R ₁
Impedance rk (equivalent resistance of cathode 1) exists equivalently on the side, and impedance r in FIG.
Typical values for k are 25 kΩ to 140 kΩ.

The conventional cathode ray tube (C
In the (RT) drive circuit, as described above, the image transmitting side (broadcasting station) transmits the gamma-corrected color signal (video signal) with the gamma characteristic of the image receiving side CRT 2 set to γ ₅ = 2.2. On the other hand, in reality, there are variations in the electro-optical conversion characteristics of the CRT2, that is, the value of the gamma constant depending on the type of television receiver (the gamma value that most CRTs have is larger than 2.2). Tends to be too bright, and this causes a phenomenon (inconvenience) that the hue and the saturation change (see FIG. 4) particularly with an increase in luminance.

The resistor R1 in the structure of the conventional cathode ray tube (CRT) drive circuit is for suppressing it. That is, the collector of the output amplification transistor Q2 and CR
By inserting the resistor R1 between the cathodes 1 of T2, the resistor R1 enters in series with the equivalent resistance rk of the cathode 1, and the cathode current Ik increases (increases the screen brightness) and the cathode current Ik increases. It works to reduce the increase rate of the AC component ik, and acts to suppress the tendency that the screen of the CRT 2 becomes too bright. As a result, an excessive increase in the screen brightness of the CRT 2 can be suppressed, and the gamma correction performed on the image sending side can effectively function (as described above).

FIG. 10 is a diagram for explaining the effect of the resistor R1.

FIG. 10A is an equivalent circuit of FIG. The collector of the output amplification transistor Q2 and the resistor R0
The input voltage vi, which is supplied to the cathode 1 of the CRT 2 and flows through the resistor R1 as an alternating current component ik of the current of the cathode 1, and an equivalent resistance r of the cathode 1 of the CRT 2 is generated.
can be represented as being supplied to k.

The input voltage vi is expressed by the following equation. _{That, vi = (R0 · v 1} ) / (R E + Rc) ......... formula 3 Note that the equivalent circuit of FIG. 10 (a) and satisfies R1 <rk.

FIG. 10 (b) is an ik-Ik characteristic curve showing the effect of the resistor R1. By inserting the resistor R1, the CRT2 having the characteristic shown by the dotted line m before insertion is as follows. It has been conventionally known that the characteristics change as shown by the solid line n, and it has been used to suppress an excessive increase in the screen brightness of the CRT 2.

Now, television receivers in recent years have been increasingly used as a display for receiving a television broadcast, receiving a character broadcast, and reproducing a signal such as a video disc. For this reason, as in the one circuit example shown in the above-mentioned conventional example, the video amplifier circuit and the color signal output circuit of the television receiver are made to have a higher band so that the signal can be reproduced more faithfully. Particularly, in the color signal output circuit, it is necessary to apply a voltage having a high signal frequency and a large amplitude to the picture tube.

FIG. 9 shows a circuit for extracting the primary color signal from the collector by adding the color difference signal v1 to the base of the transistor Q1 and the luminance signal to the emitter. Further, the transistor Q2 is simply operated by the DC voltage E3,
The primary color signal is supplied to the CRT 2. This is the CR
This is because it is amplified and supplied to a high voltage in a wide band necessary for driving T2.

By the way, in general, a transistor has a capacitance C _CB between its base and collector. FIG. 11 is a diagram showing an equivalent circuit of an amplifier circuit including the transistor Q2.

As shown in FIG. 11A, a capacitance C _CB exists between the base and collector of the transistor Q2. Then, as shown in FIG. 11B, the input signal e ₁ applied to the base is amplified and appears in the collector, and a current im passing through the electrostatic capacitance C _CB flows. This effect is equivalent to the base being (1 + G) as shown in FIG.
Since it is grounded by a capacitor having a double capacity, it is difficult to amplify up to a high frequency. Incidentally, G represents the voltage gain of the output signal e ₂ .

This phenomenon is called the mirror effect, and a phenomenon occurs in which the high frequency component of the signal is cut. For example, in the case of the conventional example shown in FIG. 9, the resistance R1 is 3.3 kΩ, the electrostatic capacitance C _CB of the output amplification transistor Q2 is approximately 4 pF, and the cathode capacitance of the CRT2 is approximately 4 pF, and the cutoff frequency is obtained as follows. . That is, (cut-off frequency) = 1 / (2π × 3.3 × (4 + 4)) = 6 (MHz) ・ ・ ・ Equation 4 As a result, the high frequency component (6 MHz or more) in the output signal of the output amplification transistor Q2 is cut. I understand that it will end up.

By the way, in order to reduce the influence of the capacitance C _CB , the collector may be fixed at a low impedance all the time. Therefore, a method of reducing the resistance value of the resistor R1 can be considered in order to obtain the f characteristic (frequency characteristic) regarding the high frequency component. However, according to this method, the increase rate of the alternating current component ik of the cathode current is reduced with respect to the increase of the cathode current Ik (increase of the screen brightness), and the excessive increase of the screen brightness of the CRT 2 is suppressed. This causes a problem (defect) that the power consumption increases and the gamma correction performed on the image sending side does not function effectively.

[0030]

As described above, according to the conventional cathode ray tube (CRT) drive circuit, in order to suppress an excessive rise in the screen brightness of the CRT, the collector of the output amplification transistor and the cathode of the CRT are suppressed. If the resistor R1 is inserted between them, there is a problem (fault) that the characteristics of the high frequency component of the output signal of the output amplification transistor deteriorate.

When the resistance value of the resistor R1 is decreased, the screen brightness of the CRT is excessively increased, and
There is a problem (deficiency) that the gamma correction performed on the image transmission side does not function effectively.

Therefore, in order to solve such a problem, the present invention solves the above problem by collecting the output amplification transistor and the CRT.
Irrespective of the magnitude of the resistance value of the resistor R1 arranged (inserted) between the cathodes of the CRT screen, an excessive increase in the brightness of the CRT screen is prevented, and a deterioration of the frequency characteristic of the high frequency component of the output signal of the output amplification transistor is prevented. Another object of the present invention is to provide a gamma correction circuit that allows the gamma correction performed on the image sending side to effectively function.

[0033]

A gamma correction circuit according to a first aspect of the present invention is a gamma correction circuit which constitutes a cathode ray tube drive circuit, and which is supplied to a cathode ray tube and a cathode of the cathode ray tube. A video signal amplifying circuit for amplifying a signal; and a CR parallel circuit, which is inserted and connected between the output end of the video signal amplifying circuit and the cathode of the cathode ray tube and is composed of a capacitor and a resistor. And

A gamma correction circuit according to a second aspect of the present invention is a gamma correction circuit which constitutes a cathode ray tube drive circuit. The gamma correction circuit comprises an RGB color display tube and three RGB color display tubes for amplifying a video signal. 3 RGB primary color signals are supplied to each cathode
System video signal amplification circuits, and three systems composed of capacitors and resistors inserted and connected between the output terminals of the three system video signal amplification circuits and the three system cathodes of the RGB color display tube. And a CR parallel circuit of.

According to the gamma correction circuit of the first or second aspect, the CR parallel circuit composed of a capacitor and a resistor is provided between the output end of the video signal amplification circuit and the cathode of the cathode ray tube. Since the above is provided, it is possible to prevent the deterioration of the high frequency characteristic, and it is possible to effectively function the gamma correction performed on the image transmitting side. Further, since the resistance value of the resistor can be set to a large value, it is possible to have an effect of preventing an excessive increase in the screen brightness of the CRT. A gamma correction circuit according to a third aspect of the present invention is the gamma correction circuit according to the first or second aspect, wherein the capacity of the capacitor forming the CR parallel circuit is larger than the cathode capacity of the cathode ray tube. And

According to the gamma correction circuit of the third aspect, in addition to the function of the gamma correction circuit of the first or second aspect, the resistance value of the resistor can be set large. Since it is possible, the gain on the black side can be increased with respect to the white side, and the image quality can be further improved.

A gamma correction circuit according to a fourth aspect of the present invention is the gamma correction circuit according to the first, second or third aspect, wherein the video signal amplification circuit is a voltage source output type amplifier. .

According to the gamma correction circuit of the fourth aspect, since the voltage source output type amplifier (opamp) is used as the video signal amplification circuit, the IC
It is possible to configure a circuit that is suitable for high efficiency and has excellent noise resistance.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram and a frequency characteristic diagram showing an embodiment of a cathode ray tube (CRT) drive circuit when a gamma correction circuit according to the present invention is applied to a black and white picture tube.

In FIG. 1 (a), one end of a signal source (input voltage) vi connected to the positive side of a cut-off cathode DC constant voltage source V _K0 (180V) has a resistor R1 and a capacitor C1 at the other end. Is connected to one end of the parallel circuit, and the other end of the parallel circuit is connected to the cathode 1 of the CRT 9. The heater 4 is connected to the heater voltage source e _H , the screen grid 5 is connected to the plus side of the screen voltage source E _S , and the focus grid 6 is connected to the plus side of the focus voltage source E _F. Thus, the anode 3 of the CRT 9 is connected to the positive side of the high voltage anode voltage source HV. One end of the heater voltage source e _H and the minus side of the constant voltage sources E _S , E _F , HV, and V _K0 are connected to the reference potential point GND, respectively. At this time, the capacitance of the capacitor C1 that constitutes the parallel circuit including the resistor R1 and the capacitor C1 is set to a value sufficiently larger than the cathode capacitance (≈4 pF) of the CRT 9. The signal source vi and the DC constant voltage source V _K0 are equivalent to a video signal amplifier circuit 31 which constitutes a conventional cathode ray tube (CRT) drive circuit, and the input voltage vi constitutes the video signal amplifier circuit 31. Is the same as the voltage (signal) induced in the collector of the output amplification transistor Q2. A typical set value of the resistor R1 and the capacitor C1 is, for example, R1.
= 6.8 kΩ and C1 = 120 pF.

According to the cathode ray tube (CRT) drive circuit including the gamma correction circuit of the present invention configured as described above, the capacitance of the capacitor C1 forming the parallel circuit composed of the resistor R1 and the capacitor C1 is reduced. , The CRT9
By setting the value to be sufficiently larger than the cathode capacitance (≈4 pF) of, the high frequency component of the cathode voltage applied to the cathode 1 of the CRT 9 is bypassed through the capacitor C1 arranged in parallel with the resistor R1. It becomes possible. Further, since the collector side of the output amplification transistor Q2 can have a low impedance, the influence of the electrostatic capacitance C _CB generated between the collector and the base of the output amplification transistor Q2 can be reduced. This makes it possible to prevent an excessive increase in the brightness of the CRT screen, prevent the deterioration of the characteristics of the high frequency component of the output signal of the output amplification transistor, and effectively make the gamma correction performed on the image transmitting side effective.

On the other hand, FIGS. 1B and 1C show the input voltage v
9 shows the input / output characteristics of the cathode voltage vk with respect to i, (b) shows the input / output characteristics of the low frequency signal component, and (c) shows the input / output characteristics of the high frequency signal component. As can be seen from (b) and (c), according to the present invention, the resistance value of the resistor R1 can be set large, so that for the low-frequency signal component, the gain on the black side is increased relative to the white side. As for the high frequency signal component, the gains on the white side and the black side can be made equal by preventing the deterioration of the high frequency signal component. This makes it possible to improve the image quality.

The embodiment of the gamma correction circuit in which the present invention is applied to a black and white picture tube has been described above, but it is of course possible to apply the present invention to a color picture tube, which will be described below. .

FIG. 2 shows an RG of the gamma correction circuit according to the present invention.
FIG. 11 is a circuit diagram showing another embodiment of a cathode ray tube (CRT) drive circuit when applied to a B color display tube.

In FIG. 2, one end of the input voltage v _R of the primary color signal source Red whose one end is connected to the reference potential point GND is connected to one end of a parallel circuit composed of a resistor R _1R and a capacitor C _1R. The other end of the CR parallel circuit is connected to one end of a parallel circuit composed of a resistor R _2R and a coil L _1R . The other end of the LR parallel circuit, which is connected to one end of the resistor R _3R, the other end of the resistor R _3R is connected to the cathode 1R of CRT 8.

The other end of the input voltage v _G of the primary color signal source Green, one end of which is connected to the reference potential GND, is connected to one end of a parallel circuit composed of a resistor R _1G and a capacitor C _1G . The other end of the CR parallel circuit is connected to one end of a parallel circuit composed of a resistor R _2G and a coil L _1G .
The other end of the LR parallel circuit, which is connected to one end of the resistor R _3G, the other end of the resistor R _3G is connected to the cathode 1G of CRT 8.

Further, the other end of the input voltage v _B of the primary color signal source Blue, one end of which is connected to the reference potential point GND, has the resistor R _1B.
And a capacitor C _1B are connected to one end of the parallel circuit, and the other end of the CR parallel circuit is connected to a resistor R _2B and a coil L.
_It is connected to one end of a parallel circuit consisting of _1B . Also,
The other end of the LR parallel circuit, the resistor R _3B be connected to one end of the cathode 1B and the other end of CRT8 of the resistor R _3B
It is connected to the.

The heaters 4R, 4G and 4B are connected in parallel to the heater voltage source e _H , respectively, and the screen grids 5R, 5G and 5B are connected to the plus side of the screen voltage source E _S for focusing. grid 6R, 6G, 6B are connected to the positive side of the focus voltage source E _F. Further, the anode 3 of the CRT 8 is connected to the positive side of the high voltage anode voltage source HV. Further, one end of the heater voltage source e _H and the minus side of the constant voltage sources E _S , E _F , and HV are respectively at a reference potential point G.
It is connected to ND.

Here, the parallel circuit composed of the resistor R _2R and the coil L _1R , the parallel circuit composed of the resistor R _2G and the coil L _1G, and the parallel circuit composed of the resistor R _2B and the coil L _1B are respectively: It is a cathode peaking circuit for improving the f characteristic. The resistors R _3R , R _3G , and R _3B are current limiting resistors for protecting the circuit on the amplifier side from the discharge of the CRT 8.

The color cathode ray tube (CPT) drive circuit including the gamma correction circuit according to the present invention, which is configured as described above, is provided in each of three signal routes of the primary color signals R, G, B. The invention is a CR parallel circuit (three systems), that is, an R signal parallel circuit including a resistor R _1R and a capacitor C _1R, and a _{G including} a resistor R _1G and a capacitor C _1G.
An example of an embodiment of the gamma correction circuit in which the present invention is applied to a black and white picture tube by each circuit of the signal parallel circuit and the B signal parallel circuit including the resistor R _1B and the capacitor C _1B is described. The same effect can be obtained with each of the primary color signals R, G, B.
It can be realized by the CR parallel circuit of the present invention provided in the signal route of.

Next, a case where a voltage source output type amplifier is used in a cathode ray tube (CRT) drive circuit including the gamma correction circuit according to the present invention will be described.

FIG. 3 shows a cathode ray tube (CR) using a voltage source output type amplifier in a video signal amplifier circuit 31 of a cathode ray tube (CRT) drive circuit including a gamma correction circuit according to the present invention.
T) is a circuit diagram showing a drive circuit.

In FIG. 3, the signal source (input voltage) v ₁ of which one end is connected to the reference potential point GND, which constitutes the voltage source output type amplifier 7, has the other end via the resistor R _E , the resistor R 0 and the capacitor. It is connected to one end of a parallel circuit composed of Cf and is also connected to the (−) input terminal of the operational amplifier 45. Further, the (+) input terminal of the operational amplifier 45 is connected to the plus side of the DC voltage source E1, the other end of the CR parallel circuit is connected to the output terminal of the operational amplifier 45, and the resistor R1 and the capacitor C1 are connected. Is connected to one end of the parallel circuit, and the other end of the CR parallel circuit is CR
It is connected to the cathode 1 of T2. Also, heater 4
Is connected to the heater voltage source e _H , the screen grid 5 is connected to the plus side of the screen voltage source E _S , and the focus grid 6 is connected to the focus voltage source E _F.
The positive electrode 3 of the CRT 2 is connected to the positive side of the high voltage anode voltage source HV.
The one end of the heater voltage source e _H and the minus side of the constant voltage sources E _S , E _F , and HV are respectively at a reference potential point G.
It is connected to ND.

At this time, the resistor R1 and the capacitor C
And a capacitor C constituting the CR parallel circuit composed of 1 and
The capacity of 1 is the same as that of the above-described embodiment of the invention.
Is set to a value sufficiently larger than the cathode capacity of (4pF). The capacitor Cf is a period capacity for preventing oscillation of the voltage source output type amplifier 7. As typical values of the resistor R1 and the capacitor C1, for example, the resistance value of the resistor R1 is 6.8 kΩ and the capacitance of the capacitor C1 is 120 pF.

In the circuit according to the embodiment of the present invention, the transistors Q1 and Q2 shown in FIG. 9 are replaced with an operational amplifier form. In this case, the output is made from the output terminal of the operational amplifier 45 shown in FIG. vi is (-R0 /
It is represented by R _E ) × v ₁ . This corresponds to the signal source (input voltage) vi of FIG. Then, the signal source (input voltage) v output from the output terminal of the operational amplifier 45 in FIG.
i is C composed of the resistor R1 and the capacitor C1
By passing through the R parallel circuit and being supplied to the cathode 1 of the CRT 2, the same operation and effect as described above, that is, the prevention of an excessive rise in the brightness of the CRT screen, the signal supplied from the signal source (input voltage) vi Thus, it is possible to prevent the deterioration of the f characteristic related to the high frequency component, and effectively operate the gamma correction and the like performed on the image transmitting side. It is needless to say that the circuit according to the embodiment of the present invention can be applied to both a black and white picture tube and an RGB color display tube.

[0056]

As described above, according to the present invention, the capacitance of the capacitor C1 forming the CR parallel circuit composed of the resistor R1 and the capacitor C1 is sufficiently larger than the cathode capacitance of the CRT (≈4 pF). By doing so, it is possible to prevent the deterioration of the high frequency characteristics, and it is possible to effectively function the gamma correction performed on the image transmitting side.

At the same time as the above effect, the resistance value of the resistor R1 can be set to a large value.
It is also possible to obtain the effect of preventing an excessive increase in the screen brightness of.

Further, when the level of all the amplitudes is constant, the gain on the black side can be increased with respect to the gain on the white side, so that clear image quality can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram and a frequency characteristic diagram showing an embodiment of a cathode ray tube (CRT) drive circuit when a gamma correction circuit according to the present invention is applied to a black and white picture tube.

FIG. 2 is a schematic diagram of a cathode ray tube (C) in which the gamma correction circuit according to the present invention is applied to an RGB color display tube.
FIG. 11 is a circuit diagram showing another embodiment of the (RT) drive circuit.

FIG. 3 is a circuit diagram showing a cathode ray tube (CRT) drive circuit using a voltage source output type amplifier in a video signal amplification circuit of a cathode ray tube (CRT) drive circuit including a gamma correction circuit according to the present invention.

FIG. 4 is a graph showing detail reproduction characteristics of a three-primary-color image.

FIG. 5 is a graph showing characteristics in the case of γ <1, γ> 1, γ = 1.

FIG. 6 is a diagram showing gamma of a transmission / reception system.

FIG. 7 is a graph showing characteristics of a gamma correction circuit.

FIG. 8 is a graph showing an electro-optical conversion characteristic of a picture tube (CRT).

FIG. 9 is an example of a circuit diagram showing one system of a conventional cathode ray tube (CRT) drive circuit.

FIG. 10 is a diagram for explaining the effect of the resistor R1.

FIG. 11 is a diagram showing an equivalent circuit of an amplifier circuit including a transistor Q2.

[Explanation of symbols]

1 ... Cathode 3 ... Anode 4 ... Heater 5 ... Screen grid 6 ... Focus grid 9 ... Cathode ray tube (CRT) C1 ... Capacitor R1 ... Resistor vi ... Signal source (input voltage) vk ... Cathode voltage V _KO ... Cut-off cathode voltage e _H … Heater voltage source HV… High voltage anode voltage source E _S … Screen voltage source E _F … Focus voltage source

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[Procedure amendment]

[Submission date] August 28, 1995

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG. 4

[Figure 5]

FIG.

[Fig. 2]

FIG. 6

FIG. 7

[Figure 3]

[Figure 8]

[Figure 9]

[Figure 10]

FIG. 11

Claims (4)

[Claims] 1. A gamma correction circuit constituting a cathode ray tube drive circuit, comprising: a cathode ray tube; a video signal amplifier circuit for amplifying a video signal supplied to a cathode of the cathode ray tube; and an output of the video signal amplifier circuit. A gamma correction circuit comprising a CR parallel circuit composed of a capacitor and a resistor inserted and connected between an end and a cathode of the cathode ray tube. 2. A gamma correction circuit constituting a cathode ray tube drive circuit, which comprises: an RGB color display tube; an image signal is amplified; and three primary color signals of RGB are supplied to each of the three cathodes of the RGB color display tube. 3 video signal amplifying circuits, and capacitors 3 and 3 inserted and connected between the output terminals of the 3 video signal amplifying circuits and the 3 cathodes of the RGB color display tube.
A gamma correction circuit comprising a system CR parallel circuit. 3. The gamma correction circuit according to claim 1, wherein the capacitance of the capacitor forming the CR parallel circuit is larger than the cathode capacitance of the cathode ray tube. 4. The gamma correction circuit according to claim 1, wherein the video signal amplification circuit is a voltage source output type amplifier.