JPH05199533A - Gamma correction system for image receiving tube, gamma correcting circuit and gamma multiplier - Google Patents

Abstract

PURPOSE:To provide gamma corrected signals without changing white balance for executing optimum gamma correction for each color. CONSTITUTION:First and second gamma correction parts 2 and 5 are respectively provided for each color signal, the respective first gamma correction parts 2 output the gamma corrected signals having the same correcting amount, and the respective second gamma correction parts 5 output the gamma corrected signals having correcting amounts different for each color. A white level reference pulse and a black level reference pulse are inserted into chrominance signals, and arithmetic is executed so that the result of multiplying timing for these reference pulses can be zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction system for performing gamma correction on a video signal supplied to a cathode of a picture tube.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
The gamma correction of the picture tube was performed with the same correction amount for R, G, and B, but the color temperature characteristics of R, G, and B were not the same, and the correct gradation could not be obtained.

Further, in the conventional gamma correction, the zero level is not stable, and there is a possibility that the white balance between the white side and the black side may change.

Furthermore, in recent years, in order to eliminate the adjustment of variations in the picture tube and to stabilize the color temperature, the cathode current of the picture tube is detected to automatically set the cutoff voltage of the video output circuit and drive adjustment. Some have adopted an automatic cut-off system.

FIG. 11 shows an outline of an automatic cutoff servo system in a CRT drive circuit.
Q _D is a video output transistor, and Q _E is a transistor for detecting the cathode current.

The CRT for other electron beams is similar, and is not shown.

Although not shown, the video output circuit of the auto cut-off system described above is based on the first to two horizontal periods in which the vertical blanking period of the video signal input to the video output transistor Q _D ends. The cutoff detection circuit 1 detects the beam current of the CRT when driven by this reference signal by supplying a signal and opening the switch S during this period. Then, by supplying the signal of the cutoff detection circuit 1 to the bias setting circuit 2 of the output transistor Q _D , feedback control is performed so that the cutoff points of the electron guns are aligned, and the white balance is adjusted at low brightness. Is made to be able to do.

However, in this circuit, the switch S
However, there is a problem in that it is necessary to open and close a high voltage, which causes an increase in cost, and by providing this circuit, deterioration of the frequency characteristics of the video signal and deterioration of the pulse characteristics are induced.

Therefore, the switch S shown by the dotted line in the circuit of FIG. 11 is omitted, and the transistor Q for detection is used.
_It suffices that _E always supplies the cathode drive signal, but in this case, the cathode of the CRT is driven by the emitter follower of the detection transistor Q _E , and the output transistor Q _D of the resistance load R _L is connected. The total gamma characteristic of the voltage drive by the emitter follower is γ = 3 or more as shown in FIG. For this reason, there is a problem that the total gamma correction is insufficient as it is, and for example, a dark screen becomes darker and a bright screen becomes brighter and the linearity becomes poor.

Therefore, in the video circuit, a circuit of a diode D, a resistor R and a clamp voltage E _C as shown in FIG. 13 (a) is inserted in the amplification system of the Y signal system to clamp the video signal (Y signal). It is considered that after passing through the circuit 3, gamma correction is applied by a broken line approximation.

That is, as shown in FIG. 13 (b), when the video signal exceeds the clamp voltage E _C , the diode D is turned on so that the video output exhibits a predetermined attenuation as shown by the dotted line. Is.

However, since this correction is a correction of only the Y signal, the color signal is not corrected, and the degree of color saturation and hue shift occur, degrading the image reproducibility.

Further, because of the correction by the resistor and the diode,
It became difficult to give an appropriate correction amount (polygonal line approximation characteristic), and there was still a problem in image reproducibility.

Therefore, it is an object of the present invention to provide a gamma correction system for a picture tube capable of independently and independently performing gamma correction on each color to obtain a correct gradation for each color. Another object of the present invention is to provide a gamma correction circuit for a picture tube whose white balance does not change due to gamma correction. Another object of the present invention is to provide a gamma multiplier capable of obtaining an appropriate gamma correction characteristic by displacing the peak point of the gamma correction waveform.

[0015]

A gamma correction system for a picture tube according to a first aspect of the present invention for achieving the above object has a first gamma correction section and a second gamma correction section for each color signal. Then, each of the first gamma correction units outputs a gamma correction signal of the same correction amount for a color signal, and each of the second gamma correction units outputs a gamma correction signal of a different correction amount independently for each color signal. With this configuration, the gamma correction signals of the first gamma correction unit and the second gamma correction unit are added for each color signal.

The gamma correction circuit for a picture tube according to a second aspect of the present invention inserts a white level reference pulse and a black level reference pulse in a non-signal section of each color signal, and a multiplication result of the signal based on each reference pulse. Is determined to be zero and the zero level of the gamma correction signal is determined.

In the picture tube gamma correction system according to the third aspect of the present invention, a white level reference pulse and a black level reference pulse are inserted in the non-signal section of each color signal, and each color signal into which the reference pulse is inserted is A first gamma correction unit that creates the same amount of gamma correction signal for each color signal and a second gamma correction signal that creates a different amount of gamma correction signal independently for each color signal
A zero level of the gamma correction signal is determined by performing calculation so that the multiplication result of the signal based on each reference pulse becomes zero in the first gamma correction unit and the second gamma correction unit. ..

Further, the gamma correction circuit for a picture tube according to a fourth aspect of the present invention inputs a color signal in which a white level reference pulse, a black level reference pulse, and an intermediate reference pulse of an intermediate level of these are inserted in a no signal section. Variable gain amplifier, first clamp means for clamping the output of the amplifier to zero level at the timing of the black level reference pulse, and gamma multiplier for multiplying the output signal of the amplifier and the color signal to obtain a gamma correction signal. A current / voltage converter for converting the output current of the gamma multiplier into a voltage value, and a second clamp means for clamping the output of the current / voltage converter to a zero level at the timing of a black level reference pulse, Third clamp means for canceling the output signal of the amplifier with the inverted signal of the output of the current / voltage converter at the timing of the white level reference pulse; It is obtained by a differential amplifier for performing gain adjustment of the amplifier to match the output of the current / voltage converter to set the level at the timing of the intermediate reference pulse.

Further, a gamma multiplier of the invention according to claim 5 is the first differential amplifier constituted by a pair of transistors, and the output of the first differential amplifier is a full balance differential differential. Of the pair of transistors that form the first and second differential amplifiers by inputting to the second differential amplifier that is composed of the pair of transistors and received by the second differential amplifier. The output is obtained by making the base region of the other transistor wider than that of the other transistor.

[0020]

According to the first aspect of the invention, the first gamma correction circuit for each color signal makes a rough gamma correction for the common portion, and the second gamma correction circuit for each color signal makes a different gamma correction according to each color. Optimal gamma correction can be performed for each.

According to the second aspect of the present invention, since the calculation power for the timing of the white level reference pulse and the black level reference pulse becomes zero, the white balance does not change even if this gamma correction signal is added to the color signal.

According to a third aspect, the first gamma correction circuit for each color signal performs a rough gamma correction for a common portion, and the second gamma correction circuit for each color signal performs different gamma correction according to each color. In the gamma correction, the timing calculation power of the white level reference pulse and the black level reference pulse becomes zero, so that the gamma correction which is optimal for each color and does not change the white balance can be performed.

According to the present invention, the output of the variable gain amplifier and the input signal are multiplied by the gamma multiplier, and each clamp is adjusted so that the multiplication calculation force becomes zero level at the timing of the white level reference pulse and the black level reference pulse. Since the means operates, the gamma correction waveform that does not change the white balance is obtained, and the feedback control is performed so that the intermediate reference pulse matches the set level of the error amplifier, so that the drift amount can be canceled.

According to claim 5, as the output of the multiplier-
An optimum gamma correction amount can be added to various CRTs by creating a gamma correction curve such that (x−a) ² and changing a.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show a first embodiment of the present invention.

FIG. 1 is a partial circuit block diagram of a picture tube incorporating the gamma correction system of the present invention.
In FIG. 1, R, G, and B color signals (A waveform in FIG. 3)
Are respectively guided to a fixed terminal of the first changeover switch SW _1, the reference pulses are respectively guided to the b fixed terminals of the first changeover switch SW _1. The reference pulse (B waveform in FIG. 3) is synchronized with the color signal, and the white level reference pulse (100IRE) → the black level reference pulse (0IRE)
The pulses are inserted every other horizontal interval in the order of → intermediate reference pulse (50IRE) → black level reference pulse (0IRE). Each of the first change-over switches SW ₁ is switch-controlled by a change-over signal, and outputs a color signal (C waveform in FIG. 3) in which a reference pulse is inserted in a non-signal section.

The output of each first changeover switch SW ₁ is supplied to each contrast / bright control section 1 and each first gamma correction circuit 2, and a color signal adjusted in contrast and brightness by each contrast / bright control section 1 is output. The gamma correction signal (E waveform in FIG. 3) created by each first gamma correction circuit 2 is added by each adder 3. Since each first gamma correction circuit 2 is level-adjusted by the common control signal, it outputs the gamma correction signal with the same correction amount.

The output of each adder 3 is the second changeover switch S.
The second reference switches SW ₂ are respectively led to the a fixed terminals of W ₂ , and the same reference pulse is inserted in the same manner as the first changeover switch SW ₁ .

The output of each second changeover switch SW ₂ is supplied to each drive / bias control section 4 and second gamma correction circuit 5, and the color signal processed by each drive / bias control section 4 and each second gamma are processed. Correction circuit 5
The gamma correction signal created in 1 is added by each adder 6. Each of the second gamma correction circuits 5 has its level adjusted by the R control signal, the G control signal, and the B control signal, and independently outputs the gamma correction signals having different correction amounts.

In the above structure, each first changeover switch S
A reference pulse is inserted into each color signal at W ₁ , and each color signal is guided to each first gamma correction circuit 2. Then, here, a gamma correction signal with the same correction amount is generated for each color signal, and the gamma correction signal is added to each color signal that has passed through each contrast / bright control unit 1 by the adder 3.

A reference pulse is again inserted into each color signal by each second changeover switch SW ₂ , and each color signal is guided to each second gamma correction circuit 5. Then, this time, the gamma correction signals with different correction amounts are created by the individual and independent adjustments for the respective color signals, and the respective gamma correction signals are added to the respective color signals passed through the respective drive / bias control sections 4 by the adder 6
Added in.

The first gamma correction circuit 2 and the second gamma correction circuit 5 have the same circuit configuration, and a concrete circuit diagram thereof is shown in FIG.
Is shown in. In FIG. 2, a variable gain amplifier 10
Has a variable resistor VR and an operational amplifier 11, and a color signal (C waveform in FIG. 3) into which a reference pulse is inserted is guided to the-input terminal of the operational amplifier 11 via the variable resistor VR. The gain of the operational amplifier 11 is changed by the value of the variable resistor VR, and the variable resistor VR is controlled by the error amplifier 21 described below.

The output of the operational amplifier 11 (D waveform in FIG. 3) is fed back to the-input terminal via the first clamp means 12. The first clamp means 12 is the operational amplifier 1
It is composed of 3. This operational amplifier 13 outputs an inverted signal of an input signal during operation, and a black level reference pulse (P
Turn on at the timing of ₁ ). Therefore, the operational amplifier 11
Output is clamped to ground at the timing of P ₁ .

The output signal of the amplifier 10 is introduced into the x ₁ input terminal of the gamma multiplier 14 and the color signal is introduced into the y ₁ input terminal thereof, and both signals are multiplied. Further, the output of the third clamp means 19 described below is introduced to the x ₂ input terminal of the gamma multiplier 14, and the x ₁ input is canceled at the timing of P ₂ . A constant voltage (50 IRE) is supplied to the y ₂ input terminal of the gamma multiplier 14 to generate a correction signal which subtracts the signal of the y ₁ input by a constant value.

The output of the gamma multiplier 14 is supplied to the current / voltage converter 15. The current / voltage conversion unit 15 is composed of an operational amplifier 16, and this voltage output is taken out as a gamma correction signal.

The output of the operational amplifier 16 is fed back to the-input terminal via the second clamp means 17. The second clamp means 17 is composed of an operational amplifier 18. This operational amplifier 18 is the operational amplifier 13 described above.
The same operation is performed and the output of the operational amplifier 16 is clamped to the ground at the timing of P ₁ .

The output of the operational amplifier 16 is supplied to the third clamp means 19. The third clamp means 19 is composed of an operational amplifier 20, which is P
It operates at the timing of ₂ . Therefore, this operational amplifier 2
The intermediate reference pulse is input to the x ₂ input terminal of the gamma multiplier 14 via 0.

Further, the output of the operational amplifier 16 is supplied to the error amplifier 21. The error amplifier 21 is composed of an operational amplifier 22, and the set voltage E _V is supplied to the other input of the operational amplifier 22. The operational amplifier 22 operates at the timing of P ₃ , and outputs the input voltage difference between them to the variable resistor VR. Then, the gain of the amplifier 10 is adjusted so that the level of the intermediate reference pulse matches the set voltage E _V.

In the above configuration, the input color signal and the amplifier 1
The color signal whose level is adjusted to 0 is multiplied by the gamma multiplier 14. The black level of the color signal entering the gamma multiplier 14 is clamped to zero by the first clamp means, the white level is clamped to zero by the third clamp means, and the multiplication calculation force is clamped to the second level at the timing of the white level reference pulse. Since it is clamped to zero by the clamp means, a gamma correction signal which is always zero level can be obtained at the white level and the black level. Therefore,
The white balance is not changed even when added to the color signal.

Further, since the value of the variable resistor VR is adjusted so that the error amplifier 21 operates at the timing of P ₂ and the intermediate reference pulse coincides with the set voltage E _V of the error amplifier 21, the influence of the temperature drift is affected. It can be prevented. When the set voltage E _V is changed, the level of the intermediate reference pulse changes accordingly, so that the output can be adjusted linearly.

A circuit diagram of the gamma multiplier 14 is shown in FIG. 4, the gamma multiplier 14 as a basic system for 4-quadrant multiplier comprising a transistor Q ₁ to Q ₄ of the first differential amplifier, the transistor Q ₅ to Q ₁₀ of the second differential amplifier ing. The base of one transistor Q ₃ of the first side differential pair is connected to the x ₁ input terminal, the base of the other transistor Q ₄ is connected to the x ₂ input terminal, and a color signal is supplied to the transistor Q ₃ . _One of the pair of load transistors Q ₁ and Q ₂ Q ₂ is a multi-emitter (n transistors are connected in parallel). Two outputs e ₁ and e ₂ are output from this first differential amplifier.

The base of one transistor Q ₉ of the second side differential pair is connected to the y ₁ input terminal and the base of the other transistor Q ₁₀ is connected to the y ₂ input terminal, and a color signal is supplied to the transistor Q _9. ing. Then, a pair of transistors Q ₅ to Q transistor Q ₅ constituting each pair of _8, Q ₆ and Q _7, and one side of the base to the output e of Q ₈ for the load
₁ , and the output e ₂ is supplied to the other base. Then are each one Q _6, Q ₇ of the transistor Q _5, Q ₆ and Q _7, Q ₈ is a multi-emitter (parallel connection of n transistors).

In the above structure, the gain G of this circuit is obtained by the following equation.

[0044]

[Equation 1]

Then, by controlling the amplitude of the input signal as shown in FIG. 5A, it is possible to obtain a waveform in which the peak of the gamma correction waveform fluctuates as shown in FIG. 5B.

A second embodiment of the present invention is shown in FIGS.

FIG. 6 is a circuit diagram of a gamma correction system for a picture tube. The same suffix is added to each circuit of each primary color signal R, G, B.

As shown in FIG. 31 (R, G, B), the gamma multiplier 32 (R, G, B) composed of two differential amplifiers is a level adjusting circuit 33R for correction amount, as will be described later.
(R, G, B) is an adder circuit for adding the respective primary color drive signals (R, G, B) and their gamma correction amounts to form a gamma correction drive signal, 34 (R, G, B) is an output transistor, Reference numeral 35 (R, G, B) is a detection transistor for detecting the cathode current flowing in the electron gun of the CRT, and the cathode follower electrodes (K _R , K _G , K _B ) of the CRT are voltage-controlled by the emitter follower output. It is a drive.

Reference numeral 36 (R, G, B) denotes an A / D converter for converting data supplied from a control computer provided in the TV receiver into an analog signal,
The A / D converter 36 (R, G, B) allows the gamma multiplier 31 (R, G, B) and the level adjusting circuit 32.
(R, G, B) can be controlled respectively.

The gamma correction of this circuit is suitable for the NTSC system when the total gamma characteristic is 3 or more as described above.

FIG. 7 is a graph showing the state of gamma correction. A curve A shows the case where the total gamma characteristic is larger than 1, and shows the relationship between the input video signal v _{in of the} CRT and the cathode current I _K.

A correction amount for approximating the curve A to the linear straight line A is shown by a curve B. That is, it is preferable that the amount of gamma correction is a quadratic curve − (x−a) ² where the peak points are shifted so that a large correction is performed at a low level as shown by the curve B.

According to the present invention, a gamma multiplier 31 (R, G, B) for outputting the correction amount is provided, and the correction amount obtained from this circuit is superimposed on the original video signal to drive the voltage of the CRT. Optimal gamma correction is performed by using a signal.

FIG. 8 shows the gamma multiplier 31 (R, G,
This is a basic example of B), and includes transistors Q _{1 to} Q ₄ which are first differential amplifiers and transistors Q _{5 to} Q ₁₀ which are second differential amplifiers. Diode D ₁ ,
A series circuit composed of D ₂ , a resistor R ₁ , and a power supply V ₂ is a load transistor Q ₂ , Q ₃ forming a first differential amplifier,
And a base bias current to the transistor Q _{4 of the} differential pair, and the video signal input v _in is supplied to the transistor Q ₁ .

The transistor Q ₃ is, for example, a multi-emitter (n transistors are connected in parallel),
For example, when n = 2, two transistors are shown.

The first differential amplifier outputs two bipolar outputs e ₁ and e _{2, which} are supplied to the second differential amplifier and become a full-balance type multiplication of e ₁ × e _2. Make up the vessel. However, in this circuit, e ₁ ≈e ₂ and consequently 2
It is a squaring circuit.

Then, the resistor R ₄ converts the current into a voltage and outputs it as a gamma correction amount.

The transistor Q ₉ forming the second differential amplifier is also a multi-emitter type (n = 2).

S ₁ and S ₂ represent constant current sources, which supply currents 2I ₀ and I, respectively. Also, changes in the AC emitter current of each differential amplifier are indicated by i ₁ and i ₂ , and will change depending on the video signal input v _in . Therefore, the currents flowing through the differential amplifiers are ± i and ± i as indicated by the arrows.
_The value changes with ₂ .

Then, the output v of the gamma multiplier
The calculation of _out (correction amount) will be described.

Assuming that the current change of the first differential amplifier is i ₁ when the input video signal v _in is applied, the currents I ₀ + i ₁ and the currents I ₀ + i ₁ are applied to the transistors Q ₁ and Q ₄ , respectively, as shown in FIG. I ₀ −i ₁ flows.

Further, the differential pair of the full-balance type transistors Q ₅ , Q ₇ and Q ₈ , Q ₁₀ forming the second differential amplifier is a: (1-a) depending on the input signal v _in . A current having a ratio flows, and the respective transistors Q ₅ , Q ₇ , Q ₈ , Q
Assuming that the current of ₁₀ is I ₅ , I ₇ , I ₈ , and I ₁₀ , I ₅ = aI ₆ I ₇ = (1-a) I ₆ I ₈ = a · nI ₉ I ₁₀ = (1-a) nI ₉ The relationship of (1) is established.

However, I ₆ is a current flowing in the transistor Q ₆ (IQ ₆ ) I ₉ is a current flowing in the transistor Q ₉ (IQ ₉ ) On the other hand, focusing on the potential V _X at the X point, V _BED3 + V _BEQ5 = V _BED4 + V _BEQ6 (2) Focusing on the potential V _Y at the Y point, V _BEQ2 + V _BEQ6 = V _BEQ3 + V _BEQ9 (3)

However, V _BEQ is the base-emitter voltage of the transistor Q, V _BED is the forward voltage of the diode D, and when the current flowing through the junction of each semiconductor element is I _T and the dark current is I _S , generally, V _BE = V _T · I _n (I _T / I _S ).

Therefore, from the above equation (2),

[0066]

[Equation 2]

Therefore, (I ₀ + I ₁ ) (aI ₆ ) = (I ₀ −i ₁ ) (1-a) I ₆ ∴a = (I ₀ −i ₁ ) / 2I ₀ (5) Expressing equation (3) using current,

[0068]

[Equation 3]

Therefore, (I ₀ + i ₁ ) [(I / 2) −i ₂ ] = [(I ₀ −i ₁ ) / n] [(I / 2) + i ₂ / n] (7) is obtained. Be done.

When i ₂ is obtained from the equation (7),

[0071]

[Equation 4]

The signal v output from this gamma multiplier
_out is v _out = V _CC −R ₄ (I ₅ + I ₁₀ ), where I ₅ = aI ₆ = a {(I / 2) −i ₂ }, the above formulas (5) and (8) With

[0073]

[Equation 5]

Next, I ₁₀ = (1-a) (nI ₉ ) = (1-a)
Since {(I / 2 + i ₂ )}, using the above equations (5) and (8),

[0075]

[Equation 6]

The output V _out of this gamma multiplier is

[0077]

[Equation 7]

The common emitter resistance of the first differential amplifier is R
Then, v _in = i ₁ · R. Therefore, the above equation becomes

[0079]

[Equation 8]

The above equation is generally

[0081]

[Equation 9]

Since it is organized in the form of, it can be expressed by the following equation.

[0083]

[Equation 10]

The above equation (14) shows the tendency of the quadratic equation as shown by the curve B in FIG. 7, and when the coefficient n is changed, the peak point of the gamma correction becomes as shown in FIG. Change.

Further, when the bias voltage V ₂ is changed, FIG.
The level of the output level V _out can be changed as shown in FIG.

As an actual concrete circuit example, when I ₀ = 50 μA I = 50 μA R = 20 KΩ _RL = 10 KΩ v _in = −1 to + V V _CC = 9 V, when n is changed to 1 to 3, The correction amount as shown in FIG. 9 was output.

[0087]

As described above, according to the first aspect of the present invention, since each color signal can be corrected independently, optimum gamma correction can be performed for each color.

According to the second aspect of the present invention, since the timing calculation power of the timing of the white level reference pulse and the black level reference pulse is zero, it is possible to obtain a gamma correction signal that does not change the white balance.

According to the third aspect of the present invention, each color signal can be corrected independently and the multiplication calculation power becomes zero at the timing of the white level reference pulse and the black level reference pulse. Therefore, it is optimal for each color. Moreover, it is possible to obtain a gamma correction signal that does not change the white balance.

According to the fourth aspect of the present invention, the feedback control is performed so that the level of the intermediate reference pulse matches the set level of the error amplifier, so that the drift amount can be canceled.

According to the fifth to seventh aspects of the present invention, a gamma correction circuit is used so that a relatively low level portion of the input video signal is raised and the correction amount is rapidly reduced on the high frequency side. Thus, there is an effect that the CRT drive circuit can be made to be a voltage drive by an emitter follower, and an automatic cutoff system can be easily adopted. Further, since the squaring circuit is formed by two pairs of differential amplifiers, there is an advantage that the correction amount can be easily adjusted in accordance with the characteristics of each CRT.

[Brief description of drawings]

FIG. 1 is a partial circuit block diagram of a picture tube (first embodiment).

FIG. 2 is a circuit diagram of a gamma correction circuit (first embodiment).

FIG. 3 is a waveform diagram of each part (first embodiment).

FIG. 4 is a circuit diagram of a gamma multiplier (first embodiment).

5A is an input waveform diagram of the gamma multiplier, and FIG. 5B is an output waveform diagram thereof (first embodiment).

FIG. 6 is a circuit diagram of a gamma correction system of a picture tube (second embodiment).

FIG. 7 is a graph for explaining gamma correction (second embodiment).

FIG. 8 is a circuit diagram of a gamma multiplier (second embodiment).

FIG. 9 is a data diagram of output correction amounts (second embodiment).

FIG. 10 is an explanatory graph of a gamma correction adjustment level (second embodiment).

FIG. 11 is an explanatory view of an automatic cutoff system for a picture tube (conventional).

FIG. 12 is an explanatory diagram of gamma correction of a voltage drive and a normal resistance amplifier drive (conventional).

13A is a gamma correction circuit diagram, and FIG. 13B is an operation explanatory diagram thereof (conventional).

[Explanation of symbols]

 2 ... 1st gamma correction circuit 5 ... 2nd gamma correction circuit 10 ... Amplifier 12 ... 1st clamp means 14 ... Gamma multiplier 15 ... Current / voltage conversion part 17 ... 2nd clamp means 19 ... 3rd clamp means 21 ... Error amplifier

Claims (7)

[Claims] 1. A first gamma correction unit and a second gamma correction unit are provided for each color signal, and each of the first gamma correction units outputs a gamma correction signal of the same correction amount to the color signal. The second gamma correction unit is configured to output gamma correction signals having different correction amounts independently for each color signal,
A gamma correction system for a picture tube, wherein the gamma correction signals of the first gamma correction unit and the second gamma correction unit are added for each color signal. 2. A zero level of a gamma correction signal is obtained by inserting a white level reference pulse and a black level reference pulse into a non-signal section of each color signal, and calculating so that the multiplication result of the signals based on each reference pulse becomes zero. A gamma correction circuit for a picture tube characterized in that 3. A white level reference pulse and a black level reference pulse are inserted in the non-signal section of each color signal, and each color signal into which this reference pulse is inserted is made into a gamma correction signal of the same correction amount for each color signal. A signal based on each reference pulse is introduced to the 1 gamma correction unit and a second gamma correction unit that creates a gamma correction signal with a different correction amount independently for each color signal, and is based on each reference pulse in the first gamma correction unit and the second gamma correction unit. A gamma correction system for a picture tube characterized in that the zero level of the gamma correction signal is determined by performing a calculation so that the multiplication result of is zero. 4. A variable gain amplifier for inputting a white level reference pulse, a black level reference pulse and a color signal in which an intermediate reference pulse of these intermediate levels is inserted in a no signal section, and the output of this amplifier is a black level reference pulse. A first clamp means for clamping the output signal of the amplifier and the color signal to obtain a gamma correction signal, and an output current of the gamma multiplier to a voltage value. Current /
A voltage converter, second clamp means for clamping the output of the current / voltage converter to a zero level at the timing of the black level reference pulse, and an output signal of the amplifier by an inverted signal of the output of the current / voltage converter. A third clamp means for canceling at the timing of the white level reference pulse; and an error amplifier for adjusting the gain of the amplifier so that the output of the current / voltage conversion unit matches the set level at the timing of the intermediate reference pulse. Gamma correction circuit for a picture tube. 5. A first differential amplifier composed of a pair of transistors, and a second differential amplifier composed of a pair of transistors receiving the output of the first differential amplifier by a full-balance type differential difference. Of the pair of transistors constituting the first and second differential amplifiers, the base region of one of the transistors being the other of the pair of transistors constituting the first and second differential amplifiers. A gamma multiplier characterized in that the output is obtained by widening. 6. A first differential amplifier composed of a pair of transistors, and a second differential amplifier composed of a pair of transistors receiving the output of the first differential amplifier by a full-balance type differential difference. Of the pair of transistors forming the first and second differential amplifiers, the base region of one of the transistors is the other of the pair of transistors. A gamma multiplier for widening the output is provided, the output of this gamma multiplier is added to the color signal, and the cathode of the picture tube is voltage-driven by this added output. Gamma correction system. 7. The gamma multiplier comprises a first differential amplifier composed of a pair of transistors, and a pair of transistors receiving the output of the first differential amplifier by a full-balance type differential difference. It is configured to input to the configured second differential amplifier to perform square multiplication, and one of the pair of transistors forming the first and second differential amplifiers has one transistor for the other. 5. The picture tube gamma correction circuit according to claim 4, wherein the base region of the transistor is widened to obtain an output.