JP2890786B2 - Video mixing amplifier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video mixing amplifier, and more particularly to a video mixing amplifier that mixes two video signals by changing them symmetrically in opposite directions.

[Conventional technology]

Conventionally, as shown in FIG. 3, this type of video mixing amplifier controls gain levels of video signals V1 and V2 in accordance with control signals C1 and C2 and outputs the same.
2. A mixing circuit 23 for mixing the video signals from the gain control circuits 21 and 22 is provided. The rate at which the video signals are mixed is set by the control signals C1 and C2. Normally, the control signals C1 and C2 are generated by faders (not shown) so that they change in opposite directions, and the sum of the signal levels of the control signals C1 and C2 is constant. By doing so, the level fluctuation of the mixed video signal V0 is suppressed and the cross-fade characteristics are improved.

[Problems to be solved by the invention]

In the above-described conventional video mixing amplifier, two control signals that change symmetrically in opposite directions are generated by a fader circuit and supplied to the two gain control circuits to independently control the level of the video signal. I have. However, there is a limit in the improvement of the cross-fade characteristics due to fluctuations in control signals and circuit fluctuations, and it has been difficult, for example, to suppress the level fluctuation when mixed to 5% or less.

Further, although a transistor differential amplifier circuit is used for the gain control circuit, the gain control characteristic for the control signal becomes an S-shaped characteristic due to the diode characteristic between the base and the emitter of the transistor, and the range in which the gain changes linearly varies. There was a problem that it was narrow.

An object of the present invention is to provide a video mixing amplifier having good cross-fade characteristics and linearity.

[Means for solving the problem]

A video mixing amplifier according to the present invention is a video mixing amplifier that mixes first and second video signals generated by the same blanking signal, wherein the levels of the first and second video signals are set to first and second levels. A first and a second gain control circuit that respectively change the gain control signal in accordance with the gain control signal, a switching circuit that selects one of the mixed control signals that change in opposite directions generated by the fader, A blanking signal that is formed by the mixing control signal selected by the switching circuit, clamps a blanking pulse to a fixed level, and outputs the blanking pulse; and a gain control circuit that outputs the blanking signal to the output signal of the blanking signal. And a first and a second gain that change symmetrically in opposite directions from an output signal of the correction circuit. Configured to include an inverting circuit for generating a control signal, and a mixing circuit for mixing an output signal of the first and second gain control circuit.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.
Video signal V1 and V1 generated by the same blanking signal
Gain control circuits 11 and 12, which control and output V2 in accordance with gain control signals C5 and C6, mix video signals output by gain control circuits 11 and 12, and are inverted by a fader (not shown). A switching circuit 14 for selecting one of the control signals C1 and C2 generated so as to change in a direction, a blanking shaping circuit 15 for shaping and outputting a blanking signal B by a control signal from a fader, and a gain control. A correction circuit 16 for correcting the S-shaped characteristic of the amplifier circuit and an inverting amplifier circuit 17 for outputting signals whose polarities are inverted are provided.

Next, the operation will be described. FIG. 2 is a diagram showing a process of generating the gain control signals C5 and C6 shown in FIG. FIG. 3A shows a blanking signal B of a video signal, and FIG. 3B shows a control signal C1. When the switching circuit 14 selects the control signal C1, the blanking signal B and the control signal C1
Are supplied to the blanking forming circuit 15. Control signal C1
And C2 change in opposite directions, and one of them is selected in accordance with the change direction of the fader. The blanking shaping circuit 15 is a kind of gate circuit, shaping the blanking signal B by the control signal C1, and clamping the blanking pulse to a certain level to generate a control signal C3 as shown in FIG. On the other hand, it is assumed that the gain control circuits 11 and 12 have an S-shaped characteristic as shown in FIG.
The control signal C3 is subjected to S-character correction by the correction circuit 16 to become a control signal C4 as shown in FIG. Control signal
C4 is input to the inverting amplifier circuit 17, and (f) and (g) in FIG.
Are converted into gain control signals C5 and C6 whose polarities are inverted, and sent to the gain control circuits 11 and 12. Gain control circuits 11 and 12 are provided with gain control signals C5 and C5.
The output levels of the video signals V1 and V2 are controlled according to C6 and sent to the mixing circuit 13. Thus, the control signals C5 and C6
Is generated from one control signal C4 in which the S-shaped characteristic of the gain control circuit is corrected, so that it is easy to set the sum of the signal levels of the control signals C5 and C6 constant. Therefore, the cross-fade characteristics and the linearity of the video signal V0 mixed by the mixing circuit 13 can be improved.

〔The invention's effect〕

As described above, the present invention forms a blanking signal using a control signal generated by a fader, corrects the S-shaped characteristic of a gain control amplifier circuit, and then generates two gain control signals having inverted polarities. Generating and supplying this gain control signal to each of the two gain control amplifier circuits,
By controlling and mixing the output levels of the two video signals, a video mixing amplifier capable of performing video mixing with good cross-fade characteristics and linearity is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a process of generating the gain control signal shown in FIG.
FIG. 1 is a block diagram showing an example of a conventional video mixing amplifier. 11,12,21,22 ... Gain control circuit, 13,23 ... Mixed circuit, 14
... Switching circuit, 15 ... Blanking forming circuit, 16 ... Correction circuit, 17 ... Inverting amplifier circuit, B ... Blanking signal, C1, C2 ... Control signal, C5, C6 ... Gain control signal, V0, V
1, V2 ... Video signal.

Claims (1)

(57) [Claims] A first blanking signal generated by the first blanking signal;
A video mixing amplifier for mixing the first and second video signals, wherein the first and second video signals change in level according to the first and second gain control signals, respectively.
And a second gain control circuit, a switching circuit for selecting one of mixed control signals generated by a fader and changing in opposite directions, and the switching circuit for selecting the blanking signal supplied from the outside. A blanking shaping circuit for shaping with the mixed control signal thus obtained and clamping and outputting a blanking pulse to a constant level, a correction circuit for performing nonlinearity correction of the gain control circuit on an output signal of the blanking shaping circuit, An inverting circuit that generates the first and second gain control signals that change symmetrically in opposite directions from an output signal of the correction circuit; and the first and second inverting circuits.
And a mixing circuit that mixes the output signals of the gain control circuits.