JPS614375A - Signal inserting device - Google Patents

Abstract

PURPOSE:To obtain stable contrast irrespective of the size of video signal level and dispersion of constituting elements by making the level of inserted signals the first and second level values according to the size of video signal level using a clamping circuit, a clipping circuit and an adder. CONSTITUTION:When a composite video signal in the figure A is supplied to an input terminal 1, and controlling signal in the figure B is supplied to an input terminal 4, A switch S2 of the terminal 4 is closed for the period H, and the output (base potential of TrQ1) is raised by the second level value U2=R1.I3 and becomes a signal in the figure C. Further, a switch S1 is closed for the period and the base potential of a TrQ2 becomes voltage V1, and the synchronizing signal side of the signal of an output terminal 6 is clipped to the potential of the first level value (V'1=V1-VBE2) and becomes D in the figure. When Vp denotes potential of pedestal part of the composite video signal in the output terminal 6, the level of an inserted signal is determined by the first level value V'1 when the video signal level Us is Us<V'1-Vp-U2, and the level is determined by the sum of video signal level Us and the second level value U2 when Us>V'1-Vp-U2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a simple signal insertion device for inserting white characters and figures into a composite video signal used in magnetic recording/reproducing devices, television devices, etc. It is something.

Conventional configuration and its problems FIG. 1 shows an example of a conventional signal insertion device.

In FIG. 1, a composite video signal is applied to a first input terminal 1, and after the potential at the tip of the synchronizing signal is clamped by a clamp circuit 2, it is supplied to a clip circuit 3. The clip circuit 3 is composed of transistors Q1 and Q2, a current source 1, a voltage source V1, and a switch S1.The output of the clamp circuit 2 is supplied to the base of the transistor Q1, and the output of the clamp circuit 2 is supplied to the base of the transistor Q2. , the second input terminal 4
A voltage source v1 is connected via a switch S1 which is opened and closed by a control signal supplied to the switch S1, the collector of the transistor Q1 is connected together with the collector of the transistor Q2 to the power supply terminal 5, and the emitter of the transistor Q1 is connected together with the emitter of the transistor Q2. , are grounded via the current source 1 and connected to the output terminal 6.

In the signal insertion device having various configurations as described above, a composite video signal such as the one shown in FIG. 2 is supplied to the first input terminal 1,
When a control signal as shown in FIG. 2B is supplied to the second input terminal 4, the switch S1 is closed only while the second input terminal 4 is at the H level, and the base potential of the transistor Q2 is changed to the voltage source v1. The output voltage becomes v1, and the voltage at the output terminal 6 is shown as C in Figure 2.
V'1 only during the period when the second input terminal 4 is at H level as shown in
A signal clipped to a potential of = V 1 - VBE2 can be obtained. (
However, VBE2 is the base-emitter voltage of the transistor Q2. ) That is, by means of a control signal supplied to the second input terminal 4, characters or figures that appear white on the television screen can be inserted into the composite video signal supplied to the first input terminal 1.

However, if the clipping potential decreases relatively due to variations in the clamping potential of the clamp circuit 2, variations in the output voltage v1 of the voltage source v1, etc., the video signal level is high as shown in the second diagram, that is, on a bright screen, insertion is not possible. The signal that should be used is video 4. . -1 yes, yes 7, yes.

Furthermore, if a signal insertion circuit with the above configuration is installed in the gain control loop of an automatic gain control device for video signals, if the inserted signal becomes larger than the white level of the video signal, the gain of the video signal will become abnormal. There was also the drawback that it was too small to fit properly.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional examples, and has a relatively simple configuration, with little change in the inserted signal level due to variations in component elements or changes in the video signal level, and automatic processing of the video signal. An object of the present invention is to provide an excellent signal insertion device that does not disturb gain control operation even when installed in a gain control loop of a gain control device.

Structure of the Invention The present invention includes a clamp circuit that clamps the DC potential at the leading end of a synchronization signal of a composite video signal input to a first input terminal to a constant potential, and a clamp circuit that clamps the DC potential of the synchronization signal tip of a composite video signal input to a first input terminal, and connect the synchronizing signal side of the clamp circuit output signal to the first
and an adder that adds a voltage corresponding to a second level value to the output signal of the clamp circuit in synchronization with a control signal input to the second input terminal. , when the video signal level is relatively low, the level of the inserted signal is determined mainly by the first level value, and conversely, when the video signal level is relatively high, it is mainly determined by the second level value. The above object is achieved by configuring the system as follows.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows an embodiment of a signal insertion device according to the present invention.
The same parts as in FIG. 1 are indicated by the same numbers. In FIG. 3, a composite video signal is applied to a first input terminal 1, and after the potential at the tip of the synchronization signal is clamped to a constant potential by a clamp circuit 2, it is supplied to an adder 7. Adder 7
are transistor Q3, resistor R1, and current source I2. I3
and Swissos S2, and transistor Q3
The output of the clamp circuit 2 is supplied to the base of the clamp circuit 2, and the emitter is connected to the current source I2. through a resistor R1. It is connected to one end of the switch S2 and the input side of the clip circuit 2, and its collector is connected to the power supply terminal 5. switch S2
is opened and closed by a control signal supplied to the second input terminal 4, and the other end thereof is connected to the electric current engineer 3.

The clip circuit 3 includes transistors Q1. Q2, a current source 1, a voltage source v1, and a switch S1, the base of the transistor Q1 is supplied with the output of the adder, and the base of the transistor Q2 is connected to a second input terminal 4.
A voltage source v1 is connected through a switch S1 which is opened and closed by a control signal supplied to the transistor Q11Q2.
The collectors of both are connected to the power supply terminal 6, and the emitters of both are grounded via the current wire 1 and connected to the output terminal 6.

In the signal insertion device configured as described above, a composite video signal as shown in FIG. 4A is supplied to the first input terminal 1,
When a control signal as shown in FIG.
The base potential of 1 is the second level value, that is, U2=R
The signal increases by 1 and 3, resulting in a signal as shown in Figure 4G.

Further, the switch S1 is closed for a period when the second input terminal 4 is at the white level, and the /<-segment level of the transistor Q2 becomes the output voltage v1 of the voltage source v1, and the signal obtained at the output terminal 6 is at the first level. The synchronizing signal side is clipped to a potential of v'1 - 1 - vBE2, resulting in the result as shown in the fourth diagram. However, VBH3 is the base-emitter voltage of transistor Q2. That is, the second input terminal 4
By means of control signals supplied to the first input terminal 1, characters and figures that appear white on the television screen can be inserted into the composite video signal supplied to the first input terminal 1. In addition, the potential of the pedestal portion of the composite video signal at the output terminal 6 is set to Vp.
Then, the level of the signal to be inserted is such that the video signal level Us is Us(V'1-Vp-U2 (in case D, the first level j value v'1 is determined)V'1- In the case of vp-U2 (7), it is determined by the sum of the video signal level Us and the second level value U2.

Therefore, regardless of the J% of the video signal level Vs or the variations in the constituent elements, the level of the inserted signal is smaller than the minimum level variation determined by the first level value v'1. Also, the level difference between the inserted signal and the video signal is never smaller than the minimum variation value of the second level value U2, so stable contrast and stable brightness can be achieved on the television screen. In addition, even when a signal insertion device is installed in the gain control loop of an automatic gain control device for video signals in order to rationalize peripheral circuits, the first level value v′1 of the video signal By setting the gain to be slightly smaller than the white level, the gain of the video signal is determined by the synchronization signal level, the video signal level, and the second level value U.
This is advantageous because the gain is not suppressed more than the gain for which the sum with 2 becomes a normal level value.

In the above example, the output of the adder 7 which receives the output of the clamp circuit 2 as an input is supplied to the clip circuit 3, but conversely, the output of the clip circuit 3 which receives the output of the clamp circuit 2 as an input Exactly the same effect can be obtained even if the configuration is such that the adder 7 is supplied with .

As described in detail, according to the present invention, with a very simple configuration, it is possible to maintain stable contrast and stable brightness on a television screen, regardless of the magnitude of the video signal level or variations in component elements. An excellent signal insertion device that can insert white characters and figures and does not require any additional circuitry even when installed in the gain control loop of an automatic gain control device for video signals has been realized. , which is extremely useful in practice.

[Brief explanation of drawings]

1 is a circuit diagram showing an example of a conventional signal insertion device; FIG. 2 is a waveform diagram for explaining its operation; FIG. 3 is a circuit diagram showing an embodiment of the signal insertion device according to the present invention; The figure is a waveform diagram for explaining the operation. 1...First input terminal, 2...Clamp circuit, 3...Clip circuit, 4...1 second
Input terminal, 6... Power supply terminal, 6...
...Output terminal, 7...Adder. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure-3;

Claims (1)

[Claims] A clamp circuit that clamps the DC potential at the tip of the synchronization signal of the composite video signal input to the first input terminal to a constant potential, and a clamp circuit output signal in synchronization with the control signal input to the second input terminal. a clip circuit that clips the synchronization signal side of the synchronous signal side to a potential of a first level value, and adds a voltage of a second level value to the output signal of the clamp circuit in synchronization with a control signal input to the second input terminal. 1. A signal insertion device comprising: an adder.