JPS59208A - Gain controlling circuit - Google Patents

Abstract

PURPOSE:To realize satisfactorily both of a dissolving operation and an add- mixing operation, by switching an input signal to an amplifier, at the time of said two operations. CONSTITUTION:In case when dissolve-mixing is executed, (k) and (l) are connected by switching circuits 9, 10. A video signal inputted to a terminal 1 is inputted to an input terminal (a) of a circuit 5. The video signal inputted to a terminal 3 is inputted to an input terminal (b) of a circuit 6. The gain of the circuit 5 is kept constant, and a good dissolving operation can be realized. In case when add-mixing is executed, (k) and (m) are connected by the switching circuits 9, 10. The circuit 5, 6 can amplify the video signal inputted separately to each terminal 1, 3, therefore, the add-mixing can be executed by deciding the gain independently each other.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a television transmission system, and more particularly to a gain control circuit for television signals.

Conventionally, in TVSILON transmission systems, control from the fader lever has been used to attenuate the video signal, mix two video signals, or switch the screen between two video signals. A gain control circuit is used that controls the gain using a signal. For example, in order to perform a so-called dissolve operation in which two video screens are simultaneously increased and decreased in opposite directions and changed to another screen with a temporal inclination, one of the video screens can be changed using a control signal from a fader lever. A gain control circuit is configured to increase the video signal and attenuate the other video signal. In the case of the dissolve operation, there are many cases where both video signals to be screen changed are the same, such as when mixing columns are replaced, and in such cases, the output level of the gain control circuit changes due to the dissolve operation.

That is, there were gain control circuits with poor cross-fade characteristics. Furthermore, such gain control circuits also have the disadvantage that gain fluctuations may occur depending on the circuit configuration. In order to solve these drawbacks, is the output of the gain control circuit changed to a gain control circuit? A gain control circuit with good cross-fade characteristics and little gain fluctuation was devised and put into use by providing negative feedback to the constituent gain control amplifiers.

FIG. 1 is a circuit diagram showing an example of a conventional gain control circuit with good cross-fade characteristics.
are each supplied with an input video signal.

Input terminal 101 is connected to the base of transistor 104, and input terminal 102 is connected to the base of transistor 115. Transistors 104 and 105, transistors 108 and 109, and transistors 110 and 11
1, transistors 114 and 115, and transistor 1
18, 119 and transistors 120 and 121 constitute a differential circuit, respectively. Transistor 104.1
The emitter of transistor 05 is connected to the collector of transistor 106, and the emitter of transistors 108 and 109 is connected to transistor 1.
04, the emitter of transistor 110.111 is connected to the collector of transistor 105, the emitter of transistor 114.115 is connected to the collector of transistor 116, the emitters of transistors 118 and 119 are connected to the collector of transistor 114, and the emitter of transistor 120.1 is connected to the collector of transistor 114.
The emitters of 21 are connected to the collectors of transistors 115, respectively. Further, the emitter of the transistor 106 and the emitter of the transistor 116 are connected to a negative power supply through a resistor 107 and a resistor 117, respectively. The bases of transistors 106 and 116 are held at a suitable bias voltage VB. Also, the transistor 109,1
The collectors of 10°118 and 121 are respectively connected to the positive power supply. On the other hand, the collectors of transistors 108 and 120 are resistors 112? Through the transistor 111゜11
The collectors of 9 are each connected to a positive power supply via a resistor 113. Transistor 109.110.

The bases of 119 and 120 are each connected and maintained at an appropriate bias viewing pressure VRFiF. On the other hand, transistor 10
The bases of 8.111 and 118.121 are connected respectively,
It is connected to the control voltage input terminal 103.

The collectors of transistors 108 and 120 are connected to the base of transistor 122, and the collectors of transistors 111 and 119 are connected to the base of transistor 123, respectively. Transistors 122 and 123tj: Completely constitutes a differential circuit, and the emitters of transistors 122 and 123 are connected to the positive power supply via a resistor 124k.

Further, the collectors of transistors 122 and 123 are connected to a negative power supply via resistors 125 and 126, respectively. The collector of transistor 122 is also connected to the base of transistor 127. The emitter of transistor 127 is connected to the positive power supply through resistor 128, and
The collector of 7 is connected to the negative power supply.

Further, the emitter of the transistor 127 is connected to the output terminal 129 and the bases of the transistors 105 and 114, respectively.

In this figure, transistors 104 to 111 or a first gain control section, transistors 114 to 121, or a second gain control section are each configured with resistors 112 and 113 as a common load, and transistors 122, 123 and 127 are configured as amplifiers. It consists of Now, if the input voltage of the control voltage input terminal 103 is higher than the bias voltage 1 voltage VRgF, each of the transistors 108, 111, 118, and 1121 becomes conductive, so that the video signal supplied from the signal input terminal 101 is When the input voltage of the input terminal 103 is lower than the bias voltage V RgF, the transistors 109 and 110
. transistor 1
The signal is taken out from the collectors of transistors 08 and 120 and transistors 111 and 119, and input to the bases of transistors 122 and 123, where it is amplified. The amplified video signal appears at the emitter of the transistor 127, is output from the output terminal 129, and is simultaneously 100% negatively fed back to the bases of the transistors 105 and 114.

Therefore, the gain of this gain control circuit is equal to the gain tG1. of the first gain control section. 1st. If the gain of the gain control section is 'tG2, it will always be 01-02=constant (ioo%), and when the voltage at the control voltage input terminal 103 is changed by 10 to 100%, this control Iil! Gl and G2 are determined by the pressure ratio, but the overall gain is constant. Therefore.

When the same video signal signal level is applied to the signal input terminals 101 and 102, the voltage at the control voltage input terminal 103 is changed by 10 to 100%, that is, the video signal at the output terminal 129 is always constant even if the Gesolve operation is performed. Good loss fade causticity and gain fluctuation characteristics are obtained.

In such a gain control circuit, the cross-fade characteristic is good, but on the other hand, the total gain Gt -1-02 is always constant, so G102 must be set at a predetermined value (100%) or higher, that is, the gains for both video signals are independently controlled. It had the disadvantage that it could not be mixed.

In broadcasting stations, etc., when obtaining the effect of mixing and adding both video signals, it is necessary not only to mix the sum level of both video signals to a constant level (desolp mixing with good cross-fade characteristics), but also to
Mixing (hereinafter referred to as additive mixing) is often required, in which both signals are amplified independently according to the faders corresponding to both signals, and the width signals are added as they are (hereinafter referred to as additive mixing). The control circuit has the drawback of not being able to meet these demands.

An object of the present invention is to provide a gain control circuit that can perform Tesolp mixing with good cross-fade characteristics and can also perform additive mixing if necessary.

The gain control circuit according to the present invention includes a circuit that amplifies the signals received at the first and second input terminals so that the gain ratio t for each signal is a value corresponding to the control voltage, and a circuit that amplifies the signals received at the first and second input terminals. first and second circuits each comprising a circuit for mixing signals and a negative feedback circuit for guiding the output of the mixing circuit to the amplifier circuit to keep the sum of the respective gains in the amplifier circuit constant; means for selecting a signal to be applied to the second input terminal of the circuit from either the signal received at one input terminal of the second circuit or a predetermined critical voltage; When all the signals received at the one input terminal of the circuit are selected, is the mixing circuit output of the first circuit? and conductive means to mix the mixing circuit outputs of the first and second circuits to the output terminal when the one selection means selects the predetermined voltage. It is composed of:

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a configuration diagram showing an embodiment of the present invention.

First video signal input terminal 1. First control voltage input terminal 2
%Second video signal input terminal3. Second control voltage input terminal 4. 5. A first circuit that controls the gain of the first video signal and the second video signal using the first control voltage. 6. A second circuit that controls the gain of the second video signal using a second control voltage. Resistor 7 for mixing the outputs of the first circuit 5 and the first second circuit 6
When the 8° mixing operation is Desorge mixing, the first circuit controls the second and second video signals at the first control voltage; According to the switching circuits 9 and 10, which switch to mix after each gain control in the first and second circuits 5 and 6, the total gain is the same in the case of Desorge mixing as in the case of additive mixing. It consists of a resistor 11 to be set and an output terminal 12.

The first and second circuits 5 and 6 are, for example, as shown in FIG. 1, a gain control amplifier whose gain changes so that two signals are inversely increased or decreased in response to an external control signal, and an output of this gain control amplifier. The output amplifier is configured to negatively feed back the output of the output amplifier to the gain control amplifier to improve cross-fade characteristics. Here, a of the first and second circuits 5 and 6 are connected to the signal input terminal 101 in FIG.

Similarly, b corresponds to the input terminal 102, C corresponds to the pressure input terminal 103 for the control 611, and d corresponds to the output terminal 129. The switching circuits 9 and 1o operate in conjunction, and the terminals 11 and 11 are connected to each other by desolde mixing, and the terminals -m and 10 are connected to each other by addition mixing. Therefore, the signal is input to a and b of the desorge mixing circuit 5, gain control is performed with good cross-fade characteristics using the control voltage from the control voltage input terminal 2, and the signal is sent out from the output terminal 12 via the resistor 7. Here, the resistor 11 is connected to the output terminal 12 during dissolve mixing, and is a resistor for matching the total gain to the gain during additive mixing.
and set to the DC potential of the d terminal of the second circuit 5.6.

Further, the input terminal bVi of the second circuit 6 is maintained at an appropriate bias voltage VREF. On the other hand, during addition and mixing operation, the first video signal is connected to a of the first circuit 5, the second video signal is connected to a of the second circuit 6, and the control voltage input terminals 2 and 4 are connected to each other. The gain is independently controlled by the control voltage, mixed by resistors 7 and 8, and sent to the output terminal 12. At this time, the input terminals of the first and second circuits 5, 6 are kept at a suitable bias voltage VREFVc.

With this configuration, when mixing two video signals using the fader lever, switching screens, etc., by switching the switching circuits 9 and 10 according to the selection of either dissolve mixing or addition mixing, In the case of desolp mixing, mixing with good cross-fade characteristics can be performed, and in the case of additive mixing, the gains of both video signals can be controlled independently to add and mix the two signals.

As described above in detail, according to the present invention, desolp mixing with good cross-fade characteristics can be performed.

Moreover, a gain control circuit capable of performing additive mixing as required can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional gain control circuit, and Fig. 2 is an embodiment of the present invention. FIG. 101.102...Video signal input terminal, 103
...... Control voltage input terminal, 104, 105, 10
6,108°109.110,111,114,115
,116°118.119,120,121,122,
123°129...transistor, 107,1
12,113°117.124,125,126.12
8...Resistor. 129...Video signal output terminal, 1,3...
...Video signal input terminal, 2, 4... Control voltage input terminal, 5... First circuit, 6... Second circuit, 7, 8.11 ...Resistor, 9.10
......Switching circuit, 12...Video signal output terminal. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] A circuit that amplifies the signals received at the first and second input terminals so that the ratio of ρ gain becomes a value corresponding to the control voltage, and a circuit that mixes these amplified signals. and a negative feedback circuit that leads the output of the mixing circuit to the amplifier circuit to keep the sum of the respective gains in the amplifier circuit constant.
a circuit, and means for selecting either a signal tl applied to the second input terminal of the first circuit, a signal received at one input terminal of the second circuit, or a predetermined 7cr9r constant voltage; When this selection means selects the signal received at the one input terminal of the @20 circuit, the mixing circuit output of the first circuit is guided to the output terminal, and the selection means selects the signal received at the one input terminal of the @20 circuit. a gain control circuit comprising means for mixing the mixing circuit outputs of the first and second circuits and guiding the mixture to an output terminal when all voltages are selected.