JPH067675B2 - Color burst signal insertion circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color burst signal insertion circuit for time-sequentially inserting a color burst signal into a video signal forming a color television signal, and more particularly to a color difference signal. And the insertion of a color burst signal in a modulation circuit section for obtaining a carrier color signal from a color subcarrier.

[Conventional technology]

As shown in FIG. 4, the color television signal includes a horizontal cycle signal a, a color burst signal b, a carrier color signal c ₁ ,
c ₂ and the luminance signal d. The color burst signal b is obtained by inserting a minimum of 8 cycles of color subcarriers on the rear side (back porch) of the horizontal synchronizing signal a in the horizontal blanking period t _H , and a color difference signal, that is, RY on the receiving side.
And BY signals (where R represents red, B represents blue, and Y represents luminance).

[Problems to be solved by the invention]

Conventionally, regarding the insertion of this color burst signal, for example, a color difference signal B- of a matrix circuit for obtaining color difference signals RY and BY from color signals R (red), G (green) and B (blue)
A burst gate pulse is inserted into the output side of Y via the level adjusting means at a timing suitable for the back porch of the horizontal synchronizing signal, and the inserted burst gate pulse is B
A color burst signal composed of a color subcarrier whose time and time are specified in accordance with the burst gate pulse during modulation of the color subcarrier along with the Y signal in addition to the balanced modulator. There is something to insert.

When a burst gate pulse is inserted in the latter part of such a matrix circuit, it is impossible to substitute the pedestal clamp pulse with the burst gate pulse, and it is difficult to adjust the burst level.
There are drawbacks such as a complicated circuit configuration and unstable insertion of a color burst signal.

Therefore, an object of the present invention is to provide a color burst signal insertion circuit that realizes stable insertion of a color burst signal with a simple circuit configuration.

[Means for solving problems]

As shown in FIG. 1, the color burst signal insertion circuit 2 of the present invention uses a balanced modulator 4a installed on the color difference signal side having a phase difference of 180 ° with respect to the color burst signal to respond to the color burst gate pulse. Output control means (transistors 60 and 66 of the embodiment shown in FIG. 1) forcibly bringing them into an inverted output state and outputting a color subcarrier at a specific time set by the color burst gate pulse.
Circuit comprising the transistor 6 of the embodiment shown in FIG.
1) is installed.

[Action]

As shown in FIG. 2, the color television signal has a phase difference of 90 ° with the color difference signals BY and RY, and the color burst signal CB has a phase difference of 180 ° with respect to the color difference signal BY. have.

Therefore, the color burst signal insertion circuit of the present invention utilizes such a relationship between the color burst signal CB and the color difference signal BY to balance the modulator on the side for modulating the color subcarrier by the color difference signal RY. The color subcarrier is output at a specific time set by the color burst gate pulse by forcibly switching to the inversion output state in response to the color burst gate pulse and inserting the color burst signal into the color television signal. Has been realized.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of a color burst signal insertion circuit of the present invention.

As shown in FIG. 1, the color burst signal insertion circuit 2
Is a balanced modulator 4a, 4b for obtaining a carrier color signal by quadrature two-phase modulation from the color difference signals BY and RY and the color subcarrier.
Is added to the balanced modulator 4a on the chrominance signal BY side in the modulation circuit section consisting of, and the balanced modulator 4a is forcibly controlled to an inverted output state at a certain time and time by a color burst gate pulse. As a result, a normal color signal is formed and a color burst signal is inserted in time series to the output of the color signal.

That is, the color difference signal BY is input to the input terminal 6a of the balanced modulator 4a, and the color difference signal RY is input to the input terminal 6b of the balanced modulator 4b. Each is added from the matrix circuit.
Therefore, the color difference signals BY and RY are set to specific levels via the clamp circuits 8a and 8b, respectively, and then individually added to the balanced modulators 4a and 4b provided for each color difference signal. There is.

Each of the balanced modulators 4a and 4b has a multiplier circuit configuration, and includes a first switch circuit 14 including transistors 10 and 12, a second switch circuit 20 including transistors 16 and 18, and an emitter side via a resistor 22. Amplifier 2 consisting of transistors 24 and 26 coupled together
8. Transistors 30 and 32 and resistors 34 and 36 as constant current sources for supplying a drive current to the transistors 24 and 26, respectively. In this case, the voltage V _cc is applied to the collectors of the transistors 10 and 16 from the driving power supply via the resistor 38, and the collectors of the transistors 12 and 18 are supplied from the driving power supply to the voltage V _cc via the resistor 40. Has been added. In addition, the transistor 4 is provided at the base of each of the transistors 30 and 32.
2, diodes 44, 46 and resistors 48, 50, 52
A constant voltage is applied from a constant voltage circuit 54 consisting of, and a constant current set by the resistors 34 and 36 flows through the transistors 30 and 32.

The clamp circuit 8a supplies the color difference signal BY to the base of the transistor 24 of the balanced modulator 4a.
The color difference signal R-Y is applied from the clamp circuit 8b to the base of the transistor 26 of FIG.
A constant bias voltage is applied by a common voltage source 56 to the bases of the transistor 26 on the side and the transistor 24 on the side of the balanced modulator 4b.

In addition, between the bases of the transistors 10 and 18 on the side of the balanced modulator 4a and the bases of the transistors 12 and 16, the color subcarrier E ₁ on the side of the color difference signal BY and the transistors 10 and 18 on the side of the balanced modulator 4b are connected. Base and transistor 12,1
The color subcarrier E on the color difference signal RY side is provided between the base 6 and
₂ has been added individually. In this case, the color subcarriers E ₁ and E ₂ both have a frequency of 3.58 MHz (nominal), and the color subcarrier E ₂ has a phase difference of 90 ° with respect to the color subcarrier E ₁ .

Therefore, in such balanced modulators 4a and 4b, the transistors 10 and 18 and the transistors 12 and 16 of the first and second switch circuits 14 and 20 alternately have a frequency of 3.58 depending on the polarities of the color subcarriers E ₁ and E _2. While switching at MHz, the transistors 24 and 26 on the side of the balanced modulator 4a are alternately turned on and off according to the level of the color difference signal BY, and the transistors 24 and 26 on the side of the balanced modulator 4b are alternately turned on and off. Repeat the state. by this,
A modulation output based on the color difference signals RY and RY is obtained at each of the balanced modulators 4a and 4b.
After being combined on the output side of a, 4b, output terminals 58a, 5
It is output from 8b as a carrier color signal.

A color burst signal inserting circuit 2 for inserting a color burst signal into the modulated output is added to the balanced modulator 4a side. The color burst signal insertion circuit 2 of this embodiment constitutes a constant current source as output control means for forcibly setting the balanced modulator 4a to the inverted output state with respect to the collector of the transistor 26 constituting the differential amplifier 28. The transistor 60 and the variable resistor 62 as a level adjusting means are installed, and a constant voltage is applied to the base of the transistor 60 from the emitter of the transistor 42 of the constant voltage circuit 54 via the resistor 64. It is configured to be controlled by the switching operation of the transistor 66 as a switching element.
That is, the transistor 66 forms a bypass circuit with respect to the base-emitter circuit of the transistor 60,
A color burst gate pulse CGP is applied to the input terminal 68 provided on the base.

The color burst gate pulse CGP is added at an appropriate time on the back porch side of the horizontal synchronizing signal a in the color television signal shown in FIG. 4, and its low (L) level section is the insertion section of the color burst signal. Represent.

Therefore, when the input terminal 68 is set to the L level by the color burst gate pulse CGP, the transistor 6
6 is turned off, a constant voltage is supplied from the constant voltage circuit 54 to the base of the transistor 60 via the resistor 64, the transistor 60 becomes conductive, and the transistor 60 is turned on.
Draws a constant current from the second switch circuit 20 side. As a result, the output of the balanced modulator 4a is forcibly controlled to the inverted output state in the section of the color burst gate pulse CGP, the color subcarrier E ₁ is output from the balanced modulator 4a, and output from the output terminals 58a and 58b. Taken out.

As described above, as a result of outputting the color subcarrier E ₁ with one mode of the modulation operation of the balanced modulator 4a to realize the insertion of the color burst signal, as shown in FIG.
Color burst signal C with a phase difference of 180 ° with respect to
B is inserted.

Since the input terminal 68 is maintained at the high (H) level in the section where the color burst gate pulse CGP does not arrive, the transistor 66 maintains the conductive state, and in this state, the constant voltage is supplied to the base of the transistor 60. Then, the transistor 60 is turned off, and the balanced modulator 4
a performs normal balanced modulation operation.

Since the color burst signal insertion circuit 2 is added to the balanced modulator 4a in this manner, it is superimposed on the modulation operation of the balanced modulators 4a and 4b, and is a mode of the modulation operation that is a specific output control state of the balanced modulator 4a. Therefore, the color burst signal can be inserted in a stable state at an appropriate time in the carrier color difference signal.

The color burst signal to be inserted is the variable resistor 6
It can be directly adjusted by adjusting the value of 2 and can be easily set to an arbitrary level.

As shown in FIG. 3, the color burst signal insertion circuit 2 may be composed of a transistor 61 and a variable resistor 62 and installed on the emitter side of the transistor 32 of the balanced modulator 4a.

By doing so, the transistor 61 is turned on by the color burst gate pulse CGP applied to the input terminal 68, so that the current set by the variable resistor 62 flows on the emitter side of the transistor 32 and the color burst gate pulse is generated. In the H level section of CGP, the balanced modulator 4a is controlled to the inverted output state. As a result, the color subcarrier E ₁ is output from the balanced modulator 4a as a color burst signal, whereby the color burst signal is time-sequentially inserted into the carrier color signal.

Further, in the L level section of the color burst gate pulse CGP, the transistor 61 is turned off, and the balanced modulator 4a is not affected at all. However, in the case of the circuit shown in FIG. 3, it is necessary to invert the logic of the color burst gate pulse CGP.

〔The invention's effect〕

As described above, according to the present invention, the balanced modulator on the color difference signal side having a phase difference of 180 ° with respect to the color burst signal is forcibly made to respond to the color burst gate pulse to be in the inverted output state. By this, the color subcarrier can be output at a specific time set by the color burst gate pulse, and the insertion of the color burst signal into the color television signal can be realized. With a simple circuit configuration, the color burst of any level can be achieved. The signal can be stably inserted, and the color burst signal to be inserted can be easily adjusted to an arbitrary level.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a color burst signal insertion circuit of the present invention, FIG. 2 is a diagram showing a phase difference between a color difference signal and a color burst signal, and FIG. 3 is a color burst signal insertion circuit of the present invention. FIG. 4 is a circuit diagram showing another embodiment, and FIG. 4 is a diagram showing a color television signal. 2 ... Color burst signal insertion circuit, 4a ... Balanced modulator, 60, 61, 66 ... Transistor as output control means.

Claims (1)

[Claims] 1. A balance modulator installed on the color difference signal side having a phase difference of 180 ° with respect to a color burst signal is forcibly set to an inversion output state in accordance with the color burst gate pulse, and the color burst gate pulse is used. A color burst signal insertion circuit comprising an output control means for outputting a color subcarrier at a set specific time.