JPH0491570A - Gamma correction circuit - Google Patents

Abstract

PURPOSE:To make the response speed of the title circuit faster by impressing input signals upon one input sides of plural differential amplifying means and bias voltages having different values upon the other input sides. CONSTITUTION:Base-emitter capacities CBE exist between the bases and emitters of transistors Tr3 and Tr5, but the charging and discharging speeds of the base-emitter capacities CBE are fast, since no resistance is inserted into the bases of the transistors Tr3 and Tr5. In addition, the base-emitter capacities CBE are not charged further after the transistors Tr3 and Tr5 are once turned on, because, when their base potentials rise, their emitter potentials also rise and the voltages between the bases and emitters are maintained at fixed levels. Therefore, the falling response speed can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gamma correction circuit, and particularly to a gamma correction circuit used in a video signal processing circuit or the like.

[Prior Art] Generally, in a color picture tube, the grid signal voltage and the light emission output are not linear, and the actual light emission output is proportional to about the 2.2 power of the signal voltage applied to the grid. Therefore, before applying the signal to the color picture tube, the input pressure characteristic is approximately 1/2.2
It is performed to pass through a nonlinear circuit such that the power is multiplied. Such a nonlinear circuit is called a gamma correction circuit.

Conventionally, there has been a gamma correction circuit as shown in FIG.

In FIG. 4, Tr7 to Tr12 are transistors, R
4-R7 is a resistor, l is an input section, 2 is an output section, 3 is a power input section, and 4 is a constant current circuit. Also, ■4 to ■6
represents a constant voltage having the relationship o<v4<v+t<Va<Vcc.

The operation of the gamma correction circuit will be explained below.

(I) V4<V. When ur<Va, transistors Tr9 and Trll are in the OFF state, so 1
．． =I, =O. At this time, 1,=I. =I-I4
・ ・ ・■ becomes, and the above ■.

■From Than this, 0LIT =Vcc-Re ■.

V OLI? =Vcc Rs ■.

■ (n) ■.

<VOUT <　V　s When Transistor Tri 1 is in the OFF state, so l7=0.

At this time, Is = Ig + Ia ■ 1, =I-I4 ・・・・■ VOUa = Above formula ■.

Substituting ■ into the above formula ■, we get (I[I) < When V o u t Is = Is + I? +Ia ・O Above formula ■.

■.

Substituting ■ into O, we get 0UT V+N-V4 Than this, V OLI T ・0 =Vcc-Is R6 In such a gamma correction circuit, Input part l The output waveform Vout when the sawtooth waveform VIN is input to the The result will be as shown in Figure 5.

In the figure, [Problems to be Solved by the Invention] However, in the above-mentioned conventional gamma correction circuit, there is a base-emitter capacitance CSZ+ atz between the base and emitter of the transistor Tr9°Trll. Therefore, when the transistor Tr9 is turned on, the base-emitter capacitance C is passed through the resistor R6.
When m t + is charged and the transistor Tr11 is turned on, the base-emitter capacitance CIEI is charged through the resistor Ry.

Similarly, transistor Tr9. Tr11 is O
When in the FF state, the base-emitter capacitance Cst+
, Cmt* are charged to the resistors R,,R, respectively.
, discharge through.

Therefore, the response speed of rising and falling becomes slow. Especially when the input voltage VIN falls sharply,
The output voltage Vout does not fall sufficiently and has a waveform delayed by time t1, as shown in FIG.

As described above, conventional gamma correction circuits have the problem of not being able to handle high-speed signal processing.

[Means for Solving the Problems] The gamma correction circuit of the present invention includes a plurality of differential amplifying means, an input signal is applied to one input side of each differential amplifying means, and an input signal is applied to the other input side. It is characterized by applying different bias voltages to each.

Note that in the present application, the gamma correction circuit is not limited to a nonlinear circuit whose input/output characteristics are approximately 1/2.2 power, but is applied to a nonlinear circuit with desired characteristics.

[Function] The present invention provides a plurality of differential amplification means, and applies an input signal to one input side of each differential amplification means, and applies different bias voltages to the other input side. The purpose is to improve the rise and fall response speed of the gamma correction circuit.

[Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform diagram showing the output voltage when the input voltage V+, 4 is a sawtooth waveform voltage.

In FIG. 1, a transistor Tri and a transistor T
r2, transistor Tr3 and transistor Tr4, and transistor Tr5 and transistor Tr6 each constitute a differential amplifier.

Also, constant voltage V,, V2. The magnitude relationship of V is vl<vl
<Vs With Te, the current flowing through the resistors R, , R* and R is 1. ．． 1. ．． 1. shall be.

In this embodiment, the output voltage ■ is when the input voltage ■IH is a sawtooth waveform voltage. uT is the voltage level of the sawtooth voltage (
The voltage level of the input voltage V Ill is as follows.

(I) V+, I<Vt<Vx (7)
When (II) When V x < V + s < V z ■ 3 = 0, and the current flowing through the resistor R1 is
I2), so Vout = Vcc R+ (I II +I2
) (I[I) When Va < Vs < VIN, the resistance R
Since the current flowing through 1 is (I-I,), Vout ”
Vcc-R+ (I - I + ) current is (I
II +I2 +I3), so VOut = V
cc-R+ (I-11+Ia +rs)...
・・・・・・■ ・・・・・・・・・・・・■ From the formulas ■, ■, and ■ shown above, if the input voltage v1 is a sawtooth waveform voltage, the output voltage Vau is It is expressed as a polygonal line, and the slope of each line is as shown in Figure 2.

As shown in FIG. 1, in this embodiment as well, transistors Tr9. Tr4
1, the base-emitter capacitance CB! between the bases and emitters of transistors Tr3 and Tr5! exists, but
In this embodiment, transistors Tr3. Since no resistor is inserted into the base of Tr5, charging and discharging of the base-emitter capacitance CIIE is fast. In addition, the transistor Tr
After the 3° Tr5 is turned on, when the base potential rises, the emitter potential also rises, and the base-emitter voltage is kept constant, so that no further charging of the base-emitter capacitance CIE occurs.

Therefore, the falling response speed becomes particularly fast.

FIG. 3 is a circuit configuration diagram showing a second embodiment of the present invention.

In this embodiment, as shown in the figure, transistors Tr3,
Constant current source 5 on the emitter side of Tr5 (however, I'<I)
may also be provided, and the same effects as in the first embodiment can be obtained.

In the embodiments described above, if the number of differential amplifier stages is increased to four or five stages, an output waveform consisting of a large number of polygonal lines can be obtained, and a more accurate gamma correction circuit can be constructed. Further, in the above-mentioned embodiments, the circuit was constructed using NPN type transistors, but it may also be constructed using PNP-type transistors, and the same effects as in the above-mentioned embodiments can be obtained6.

[Effects of the Invention] As described above in detail, according to the gamma correction circuit of the present invention, it is possible to configure a gamma correction circuit with faster response.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention. FIG. 2 is a waveform diagram showing the output voltage when the input voltage (2)+s is a sawtooth waveform voltage in the first embodiment. FIG. 3 is a circuit configuration diagram showing a second embodiment of the present invention. FIG. 4 is a circuit diagram of a conventional gamma correction circuit. FIG. 5 is a waveform diagram showing the output voltage when the input voltage VIN is a sawtooth waveform voltage in the second embodiment. In FIG. 2, 1 is an input section, 2 is an output section, 3 is a power supply input section, 4.5 is a constant current circuit, Tri, Tr2, Tr3, Tr4, Tr5 are transistors, R,, R,. R1 is resistance. Agent Patent Attorney Sekihei Yamashita

Claims (1)

[Claims] (1) Gamma correction characterized by comprising a plurality of differential amplifying means, applying an input signal to one input side of each differential amplifying means, and applying different bias voltages to the other input side. circuit.