JPH04196770A - Gamma correction circuit - Google Patents

Abstract

PURPOSE:To relax a limit of an operating point and an input amplitude and to realize a circuit with simple constitution by adjusting a voltage level of a variable bias power supply and a resistance of an emitter resistor. CONSTITUTION:Since a voltage V2 is a fixed level after initial setting of a bias, an input signal Vin(=V1-V2) is increased as the level of the V1 and an output voltage at an output terminal 13 is increased. Since the operating curve is set nonlinear, since the slope of the curve is decreased as the input signal V1 gets larger, the output voltage is suppressed toward a larger signal input and not almost suppressed toward a smaller signal input. That is, the output signal is linear when the input signal is small by setting the operating range and the output signal is suppressed when the input signal is larger and close to a white level peak. Thus, the limit in the dynamic range is relaxed and the amplitude of the input signal is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a gamma correction circuit that effectively suppresses doming, blooming, etc. that appear when a white peak signal screen is received in a color television receiver.

BACKGROUND ART In video circuits, a circuit as shown in FIG. 2 has conventionally been used as a gamma correction circuit to prevent blooming and the like.

In this circuit, the beam current of the color cathode ray tube 3o is
resistor 29 and PNP) shunt to the collector of transistor 24. In other words, current flows into the resistor 29 and the collector of the NPN transistor 21 until the base-e-emitter voltage of the PNP transistor 24 becomes active. When the collector potential is high, the white portion is suppressed.

Problems to be Solved by the Invention However, when such a circuit is used, the signal amplification section located at the front stage is generally used within a linear operation range. Therefore, there was a drawback that the operating point and the human force amplitude were limited.

It is an object of the present invention to provide a circuit with a simple configuration that alleviates restrictions on operating points and input amplitudes by combining signal amplification and gamma correction functions that prevent blooming and the like.

Means for Solving the Problems The present invention solves the above problems by adjusting the voltage level of the variable bias power supply and adjusting the resistance value of the emitter resistor, thereby utilizing the nonlinear characteristic region of the differential amplifier to achieve signal amplification. Gamma correction is performed at the same time.

Effects According to the present invention, as described above, since the functions of signal amplification and gamma correction are combined, the circuit configuration is simple, and since the nonlinear characteristic region is used, the operating point, unlike when using the linear characteristic region, is Restrictions on operating range are relaxed.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention.

In FIG. 1, 1 is an input terminal, 2 is a capacitor, 3.
4 is an NPN) transistor, 6, 6 is a variable resistor, 7.8 is a load resistance, 9 is a variable bias power supply, 1o is a current source, 11
．． 12 is a resistor, and 13 is an output terminal.

The video signal applied to input terminal 1 has its DC component removed by capacitor 2, and then is passed through resistor 11. It is biased with a voltage determined by a resistor 12 and is input to the base of the NPN transistor 3. The emitter and collector of the NPN 1-ranging nut 3 are each equipped with a variable resistor 5. A resistor 7 is connected. A variable resistor 6 is connected to the other end of the variable resistor 5 connected to the emitter of the NPN transistor 3, and the emitter of an NPN transistor 4 is connected to the other end of the variable resistor 6. N
A resistor 8 is connected to the collector of the PN transistor 4, a variable bias power supply 9 is connected to the base, and the connection point between the variable resistors 5 and 6 is grounded through a current source 10. NPN) transistor 3 and NPN) transistor 4 constitute a differential amplifier.

Next, we will explain the operating range of the differential amplifier.

Generally, a differential amplifier is used within an operating range centered on the operating point t shown in FIG. This is to operate the differential amplifier linearly, and therefore the amplitude of the input signal must be kept below the creative range, and the dynamic range, which is usually several tens of mV or less, is greatly limited.

FIG. 4 shows an enlarged view of the upper right portion of the characteristic curve in FIG. 3. Here, it is assumed that the operating point is shifted from t in FIG. 3 to t' in FIG. 4 by adjusting the variable bias power supply 9, and the operating range h', which is a nonlinear characteristic region, is used.

In Figure 1, v2 is a fixed value after the initial setting of the DC bias, so the input signal vin=■1-V2 is 71
The output voltage of the output terminal 13 increases as the amount of human power increases, and in this operation, the output voltage of the output terminal 13 also increases. However, since the operating curve is set nonlinearly, the input signal v1
As the curve becomes larger, the slope of the curve becomes smaller. Therefore, the output voltage is suppressed as the signal becomes larger, and is hardly suppressed as the signal becomes smaller. In other words, by setting the operating range as shown in the characteristic diagram in Figure 4, when the input signal is a small signal, the output signal operates linearly, and when the input signal becomes a large signal and approaches the blank peak, the output signal operates linearly. Make movements that are suppressed.

As can be seen from the above operation, in addition to signal amplification, gamma correction is performed in one circuit.

Therefore, in this embodiment, since the operating range is expanded from the linear characteristic area to the nonlinear characteristic area, the restriction on the dynamic range is relaxed and the amplitude of the input signal can be increased.

Also, the characteristic curve is variable resistance 6. By adjusting the variable resistor 6, the slope and the nonlinear ratio can be varied as shown in FIG. 5, and the desired gamma characteristic can be easily obtained. In a general differential amplifier, since a linear region is used, a variable resistor 5. If the resistance values of the variable resistors 6 are not the same, there is a problem that the dynamic range will be very narrow, but since the present invention uses a nonlinear region, the variable resistors 6. The variable resistors 6 do not need to have the same resistance value, but can be set to any desired resistance value in order to obtain a desired characteristic curve.

Note that the curves in FIG. 5 are shown only for the region shown in FIG. 4, and other regions are omitted.

Furthermore, in video signal processing, it is necessary to suppress not only white but also black and both black and white. However, according to the present invention, by setting the operating point and setting the dynamic range of the input amplitude by the variable bias power supply 9, black suppression, black and white suppression, etc. can be achieved by arbitrarily using the characteristics shown in the shaded area shown in FIG. It can be easily applied to a wide range of video signal processing.

Even if the nonlinear processing voltage thus obtained is amplified as necessary via an amplifier at a later stage to be supplied to the CRT, the effect of the nonlinear operation will not be impaired in any way.

Furthermore, it goes without saying that if the subsequent amplifier is not a linear amplifier but has nonlinearity, the same effect can be obtained by making operational settings that take this into consideration.

In one embodiment of the present invention, the output terminal is taken from the NPN transistor 4, but the same effect can be obtained from the NPN) transistor 3, and the same effect can be obtained even if the NPN) transistor is replaced by a PNP) transistor. Needless to say.

Effect of the invention As described above, according to the present invention, the following effects are achieved.

(1) Signal amplification and gamma correction can be configured in one simple circuit.

(2) Any gamma characteristic can be obtained by changing the emitter resistance and bias.

(3) It can handle not only white suppression but also black suppression and both black and white suppression.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a gamma correction circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional gamma correction circuit, and FIG. 3 is a characteristic diagram showing a general differential range of a differential amplifier. FIG. 4 is a characteristic diagram explaining the present invention in detail, and FIG. 5 is a characteristic diagram showing the variable resistance 6.
．． FIG. 6 is a characteristic diagram showing the change in characteristics due to the variable resistor 6. FIG. 6 is a characteristic diagram showing the usage range of black suppression and both black and white suppression in the characteristic curve. 1...Input terminal, 2...Capacitor,
3, 4...NPN) transistor, 5, 6...
...Variable resistance, 7゜8...Load resistance, 9.
...Variable bias power supply, 1°...Current source, 11.12...Resistor, 13...Output terminal. Name of agent: Patent attorney Akira Okaji and 2 others No. 1
Figure II! 3 Figure input signal Vln -CV+-Vt) Figure 4 One small λ force signal Vln=(V・-Vt) Large-Figure 5 d'1ゝ A 214 No. V II+-(Ml-
Vz) Big 61st! 1

Claims (1)

[Scope of Claims] Consisting of a first transistor, a second transistor, a first variable resistor, a second variable resistor, a variable bias power supply, a current source, and an input terminal, the input terminal is the first variable bias power supply is connected to the base of the first transistor, the variable bias power supply is connected to the base of the second transistor, and the first variable bias power supply is connected to the base of the second transistor; A resistor and the second variable resistor are connected in series, a connection point between the first variable resistor and the second variable resistor is connected to ground through the current source, and the first transistor and the second variable resistor are connected to the ground through the current source.
The transistors constitute a differential amplifier, and by adjusting the operating point of the differential amplifier according to the voltage level of the variable bias power supply, the input/output characteristics are made nonlinear, and the transistors of the first variable resistor and the second variable resistor are made nonlinear. A gamma correction circuit characterized by being able to vary the slope of input/output characteristics by changing the resistance value.