JPH04150178A - Video mixing amplifier - Google Patents

Abstract

PURPOSE:To attain video signal mixing with an excellent cross fade characteristic by shaping a blanking signal with a control signal so as to generate two gain control signals whose polarity is reversed to each other and mixing two video signals while each output level is controlled. CONSTITUTION:A blanking generating circuit 15 generates a blanking signal B from a control signal C1(C2) to generate a control signal C3 and a correction circuit 16 applies S-shape correction to the control signal C3 preferably to form a control signal C4. The control signal C4 is inputted to an inverting amplifier circuit 17, in which the signal is converted into gain control signals C5, C6 whose polarity is reversed to each other, they are fed to gain control circuits 11, 12, which control an output level of video signals V1, V2 in response to the gain control signals C5, C6 and sends the result to a mixing circuit 13. Thus, the video mixing amplifier in which the linearity of the cross fade characteristic is excellent is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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, this type of video mixing amplifier is as shown in Figure 3.
It includes gain control circuits 21 and 22 that control and output the signal levels of video signals V1 and V2 according to control signals C1 and C2, and a mixing circuit 23 that mixes the video signals from the gain control circuits 21 and 22. The ratio at which the video signals are mixed is set by control signals CI and C2. Normally, control signals CI and C2 change in opposite directions to each other by faders (not shown), and control signal C
1 and C2 are generated so that the sum of the signal levels is constant. By doing this, level fluctuations of the mixed video signal (1)0 are suppressed and cross-fade characteristics are improved.

[Problem to be solved by the invention]

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

In addition, although a transistor differential amplifier circuit is used for the gain control circuit, due to the diode characteristics between the base and emitter of the transistor, the gain control characteristics for the control signal are figure-8 characteristics, and the range of linear variation is limited. The problem was that it was narrow.

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

[Means for Solving the Problems] The video mixing amplifier of the present invention mixes first and second video signals generated by the same blanking signal, and the video mixing amplifier mixes first and second video signals generated by the same blanking signal. a blanking shaping circuit that shapes the blanking signal; and an inverting circuit that generates first and second gain control signals that change symmetrically in opposite directions based on the output signal from the blanking shaping circuit; first and second gain control amplifier circuits that change output levels of the first and second video signals according to the first and second gain control signals; and the first and second gain control amplifiers. and a mixing circuit that mixes video signal outputs from the. Further, the configuration may include a correction circuit that performs nonlinearity correction of the gain control amplifier circuit on the output signal from the blanking shaping circuit.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of the present invention, in which a gain control circuit 11 controls and outputs video signals V1 and V2 generated by the same blanking signal according to gain control signals C5 and C6. and]-2, gain control circuit 1
] - and a mixing circuit 1-3 that mixes the video signals outputted by 12, and a switch that selects one of the control signals C1 and C2 that are generated to change in opposite directions by a fader (not shown). A circuit 1-4, a blanking forming circuit 15 that forms and outputs a blanking signal B based on a control signal from a fader, a correction circuit 16 that corrects the figure-8 characteristic of the gain control amplifier circuit, and outputs signals whose polarities are inverted to each other. The inverting amplifier circuit 17 is also provided.

Next, the operation will be explained. FIG. 2 is a diagram showing the process of generating gain control signals C5 and C6 shown in FIG. 1. 3(a) shows the blanking signal B of the video signal, and FIG. 2(b) shows the control signal CI. 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. The control signals C1 and C02 change in opposite directions, and one of them is selected depending on the direction of change of the fader. The blanking shaping circuit 15 is a type of gate circuit, and shapes the blanking signal B using the control signal C1 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 a figure-8 characteristic as shown in FIG. The control signal C3 is subjected to character-8 characteristic correction by the correction circuit 16, and becomes a control signal C4 as shown in FIG. 4(e). The control signal C4 is input to the inverting amplifier circuit 17, where it is converted into gain control signals C5 and C6 having inverted polarities as shown in FIG. Ru.

Gain control circuits 11 and 12 control the output levels of video signals V1 and V2 according to gain control signals C5 and C6, and send them to mixing circuit 13. In this way, since the control signals C5 and C6 are generated from one control signal C4 that has been corrected for the figure-8 characteristic of the gain control circuit, it is possible to set the sum of the signal levels of the control signals C5 and C6 constant. is easy. Therefore, it is possible to improve the cross-fade characteristics and linearity of the video signal Vo mixed at the mixing circuit N1B.

〔Effect of the invention〕

As explained above, the present invention shapes a blanking signal using a control signal generated by a fader, corrects the figure-8 characteristic of a gain control amplifier circuit, and then generates two gain control signals with opposite polarities. and supplying this gain control signal to each of the two gain control amplifier circuits.
By controlling and mixing the respective output levels of the two video signals, a video mixing amplifier capable of performing video mixing with good cross-fade characteristics and linearity can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the process of generating the gain control signal shown in FIG. 1, and FIG.
The figure is a block diagram showing an example of a conventional video mixing amplifier. 11.12, 21.22-...Gain control circuit, 1
3.23...Mixing circuit, 14...Switching circuit, 15...Blanking forming circuit, 16...
.--Correction circuit, 17..... Inverting amplifier circuit,
B... ~Blanking signal, CI, C2...
--Control signal, C5, C6...Gain control signal, VO, Vl, V2...Video signal.

Claims (1)

[Claims] 1. In a video mixing amplifier that mixes first and second video signals generated by the same blanking signal, a blanking signal is shaped by a mixing control signal applied from the outside. a ranking forming circuit; an inverting circuit that generates first and second gain control signals that change symmetrically in opposite directions based on the output signal from the blanking forming circuit; and the first and second gains. first and second gain control circuits that change the output levels of the first and second video signals according to a control signal; and mixing that mixes the video signal outputs from the first and second gain control circuits. A video mixing amplifier comprising a circuit. 2. The video mixing amplifier according to claim 1, further comprising a correction circuit for correcting nonlinearity of the gain control circuit on the output signal from the blanking shaping circuit.