JPH0638233A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To improve fundamental characteristics of video processing for a broad band signal such as the frequency characteristic and crosstalk. CONSTITUTION:A luminance signal is fed to a gain control amplifier 22 and a chrominance signal is fed to a gain control amplifier 24 respectively. Based on variable resistors 26-28, a control circuit 25 extracts control information corresponding to each of the luminance signal and the chrominance signal respectively to control the gain of the gain control amplifiers 22, 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, high-definition television receivers and other high-definition video equipment.
The present invention relates to a video signal processing circuit suitable for application to video processing handling a wideband video signal.

[0002]

2. Description of the Related Art It is common for video equipment such as a television receiver to be provided with a function of adjusting an image by controlling the amplitude of a luminance signal and a color signal such as contrast adjustment and color adjustment. Is. In order to realize such a function, FIG. 4 shows a video signal processing circuit for image adjustment which is generally used.

In FIG. 4, the luminance signal supplied to the input terminal 1 is first supplied to a gain control amplifier 2 which controls the luminance signal independently. The gain control amplifier 2 has a volume 3
The control circuit 4 converts the control voltage determined by the above setting into a current, and controls the gain variable amount. As a result, the gain control amplifier 2 outputs a luminance signal having an amplitude corresponding to the adjustment of the volume 3.

On the other hand, the chrominance signal supplied to the input terminal 5 is also converted into a current in the gain control amplifier 6 by converting the control voltage determined by the setting of the volume 7 in the same manner as the luminance signal.
The control circuit 8 controls the variable gain amount, and the gain control amplifier 6 outputs a color signal having an amplitude corresponding to the adjustment of the volume 7.

As for the luminance signal and the color signal output from the gain control amplifiers 2 and 6, the luminance signal is supplied to the gain control amplifier 9 and the color signal is supplied to the gain control amplifier 11 via the hue adjusting circuit 3. Also here, the control circuit 13 for converting the control voltage determined by the volume 12 into a current and controlling the luminance and color signals controls the gain variable amount, and the luminance and color signals having the amplitudes corresponding to the adjustment of the volume 13 are Output terminals 14 and 15 from the gain control amplifiers 9 and 11 respectively
Output to.

By adjusting the volumes 3, 7 and 12, the controlled luminance signal and color signal are outputted to the output terminal 14.
And 15 and the image can be adjusted arbitrarily.

By the way, the frequency characteristic of the video circuit is particularly important in the video processing handling a wide band signal such as a high definition television receiver and a video equipment for high definition images. In the above video signal processing circuit, the gain control amplifiers 2 and 6 for controlling the luminance signal and the chrominance signal independently and the gain control amplifiers 9 and 10 for controlling the gain signal and the chrominance signal independently.
A two-stage amplifier is required for each axis.

The amplification stage causes a large deterioration of the frequency characteristic, and the conventional video signal processing circuit is not very preferable for the video processing handling a wide band signal. Furthermore, the presence of a plurality of amplification stages complicates the connection and wiring of signal lines, causing an increase in crosstalk.

[0009]

The above-mentioned conventional video signal processing circuit includes a gain control amplifier for controlling the luminance signal and the chrominance signal independently and a gain control amplifier for controlling the gain signal and the chrominance signal in synchronization with each other. Since two stages are required for each axis, this has been a cause of deterioration of frequency characteristics and increase of crosstalk in video processing handling a wideband signal.

In view of the above drawbacks, an object of the present invention is to provide a video signal processing circuit capable of improving basic characteristics of video processing for wideband signals such as frequency characteristics and crosstalk.

[0011]

According to the present invention, there is provided one gain control means per input for a plurality of input signals, and external adjusting means for setting how much the gain of the gain control means is changed. The control information deriving unit derives control information for each input signal according to a plurality of adjustment results in the external adjustment unit and supplies the control information to the gain control unit.

[0012]

By the above means, the image signal for image adjustment can be processed only for each of the luminance signal and the chrominance signal by one amplification stage, so that the frequency characteristic and the crosstalk can be improved.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Luminance signals and color signals are supplied to the input terminals 20 and 21, respectively. The brightness signal is gain control amplifier 22.
In addition, the color signal is supplied to the gain control amplifier 24 via the hue adjustment circuit 23. The gain control amplifiers 22 and 24 independently adjust their respective gains according to the control information of the control circuit 25. The control circuit 25 includes a volume 26 for independent control,
27 and the set results by the synchronous control volume 28 for adjusting in synchronization are all supplied as control information.

Here, the control circuit 25 collectively derives control information such as control voltage or control current for performing control according to each adjustment result of independent control / synchronous control for the luminance signal and the color signal. It is supplied to the gain control amplifiers 22 and 24. As a result, the gain control amplifiers 22 and 24 can obtain desired video outputs at the output terminals 29 and 30 by performing gain control corresponding to the control information on the luminance signal and the color signal.

FIG. 2 shows the correlation between the volume and the gain control amplifier. In the characteristic diagram of FIG. 2, the vertical axis represents the gain of the gain control amplifier, and the horizontal axis represents the synchronization control volume 28.
It is a synchronous adjustment voltage.

Now, it is assumed that the control characteristics of the luminance and color signals in the state where the independent control is not applied are both straight lines a. This indicates that if the volume 28 is reduced, the luminance signal and the chrominance signal are synchronized with each other and the amplitude is reduced as a linear function, as indicated by a straight line a. When it is desired to adjust only the color signal, that is, the independent adjustment voltage for the color signal among the independent adjustment voltages by the independent control volume 27 is changed, and the luminance signal control characteristic remains unchanged as the straight line a. The control characteristic b may be such that only the slope changes without changing the P point of the gain “0” of the gain control amplifier. In addition, the volume 2 which adjusts the brightness signal independently
For 6 as well, similar control may be performed.

In the above description, the control circuit 25 shown in FIG.
It is shown that the control information for satisfying the control characteristic of 1 should be derived. Therefore, taking a luminance signal as an example, the control circuit 25 and the gain control amplifier 22 that satisfy the control characteristics are described.
This will be described with reference to FIG.

Here, it is assumed that IYcnt is given as a variable current source for independent control, Icnt is given as a variable current source for synchronous control, and a control current by each adjusting volume. Reference voltage V
A voltage follower VF1 composed of a transistor Q3 whose ref is connected to the base and transistors Q1, Q2, Q4, resistors R1, R2, and a constant current source Iref1 for biasing the variable current source Icnt and a constant current source Iref2. Is input to obtain an output voltage Vcnt from the collector of the transistor Q4.

Vcnt = Vref−VT · ln [(2Iref−Icnt) / Icnt] (1) However, VT is a thermoelectromotive force, and Iref1 = Iref2 = Iref.

The output voltage Vcnt is input to the comparator 31 whose bias current is the variable current source IYcnt and is composed of the transistors Q5 and Q6, and is compared with the reference voltage Vref. At this time, equation (2) is established, and by substituting equation (1) into it,
From equation (3), the control current IYc is applied to the collector of transistor Q6.
get nt´.

Vref-Vcnt = VT.ln [IYcnt '/ (IYcnt-IYcnt')] ... (2) ∴IYcnt '= [1- (Icnt / 2Iref)] IYcnt ... (3) The control current IYcnt' is the transistor Q7. , Q8 and resistors R3, R4 are folded back by a 1: 1 current mirror circuit to form transistors Q9-Q12 and resistors R5, R6.
, A voltage follower VF2 having the same configuration as the voltage follower VF1, which is composed of a constant current source Iref3 for bias.
To the variable current source Icnt and subtracted from the constant current source Iref4. The collector voltage VCONT of the transistor Q12, which is the output voltage of the voltage follower VF2, can be obtained by the following equation as in the equation (1).

VCONT = Vref−VT · ln [(2Iref−Iadd) / Iadd] (4) where Iref3 = Iref4 = Iref, Iadd = Icnt + I
Ycnt '.

In this circuit example, this collector voltage VCONT
Is output to the gain control amplifier 22 as control information by the control circuit 25. The gain control amplifier 22 is a transistor Q
It is composed of 13, Q14, a load resistor RL, and a bias current source IYin, and the bias current source IYin also serves as an input luminance signal.

The output current flowing through the load resistor RL is now IYO
Then, the following equation is established similarly to the equations (2) and (3).

Vref−VCONT = VT · ln [IYo / (IYin−IYo)] (5) ∴IYo = [1- (Iadd / 2Iref)] IYin (6) Here, Icnt + IYcnt ′ is substituted for Iadd. Further, by substituting the expression (3) for the control current IYcnt ', the relationship between the input / output gain IYo / IYin of the luminance signal and the control current by the independent control and the synchronous control adjustment volumes can be derived as the following expression.

IYo / IYin = (1−IYcnt / 2Iref) · (1−Icnt / 2Iref) (7) Regarding the formula (7), the vertical axis is IYo / IYin, the horizontal axis is Icnt,
If IYcnt is taken as a parameter and plotted in a graph, the circuit shown in FIG. 3 can realize the same control characteristic as that shown in FIG. 2 in which the origin is fixed (2Iref, 0) and the slope changes depending on the parameter. Also, the color signals can be realized in exactly the same manner.

In this way, in the image adjustment for the luminance signal and the color signal, the independent control and the synchronous control are collectively derived to derive the control information according to the adjustment result of each volume, and the gain is obtained for the luminance and the color signal. Since the gain control amplifier is controlled, it is sufficient to provide one stage for each of the luminance and color axes, and it is possible to obtain better frequency characteristics than the conventional one. Further, since the control information deriving circuit can be entirely configured by a DC circuit, the AC circuit of the signal line can be simplified, so that the crosstalk improving effect is great.

[0028]

As described above, according to the video signal processing circuit of the present invention, it is suitable for integration into an integrated circuit, and the basic characteristics in wideband signal video processing such as frequency characteristics and crosstalk can be improved.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram used for explaining FIG.

FIG. 3 is a circuit diagram more specifically showing the main part of FIG.

FIG. 4 is a conventional system configuration diagram.

[Explanation of symbols]

20, 21 ... Input terminals, 22, 24 ... Gain control amplifier,
25 ... Control circuit, 26-28 ... Volume, 29, 30
… Output terminal.

Claims (3)

[Claims] 1. A gain control unit arranged corresponding to each of a plurality of input signals to control the gain of the input signal, an adjusting unit for setting the gain of the gain control unit, and an adjustment result in the adjusting unit. A video signal processing circuit comprising: control means for extracting the control information corresponding to each input signal based on the above, and supplying the control information to the gain control means. 2. The video signal processing circuit according to claim 1, wherein the adjusting means is provided in at least more than the gain controlling means. 3. The video signal processing according to claim 1, wherein the control means derives control information outputs respectively corresponding to the gain control means from all or two or more adjustment results by the adjusting means. circuit.