JPH075739Y2 - Automatic color signal control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of an automatic color signal control circuit for holding a carrier color signal at a constant level in a video tape recorder.

<Prior Art> A video signal recording / reproducing system of a video tape recorder uses a video signal obtained by superimposing a carrier color signal on a frequency-modulated luminance signal by at least two magnetic heads to produce a first video signal and a second video signal on a magnetic tape. This is a system in which the tracks are alternately recorded, and the video signals recorded on the first and second tracks on the magnetic tape are alternately reproduced to demodulate the luminance signal and the carrier color signal.

In such a video signal recording / reproducing system, a first carrier color signal and a second carrier color signal reproduced from the first video track are recorded.
Automatic color signal control circuit (hereinafter ACC) that keeps the level of the second carrier color signal reproduced from the video track of
Circuit), but this ACC circuit has the following configuration.

FIG. 2 will be described with reference to the drawings.

2 shows a carrier color signal recording circuit in a color video signal recording system, and FIG. 3 shows a carrier color signal reproducing circuit in a color video signal reproducing system.

At the time of recording, the carrier color signal of 3.58MHz extracted from the color video signal is amplified by the video amplifier circuit (1R),
The level is adjusted to a constant level through the ACC circuit (2R). The output of this ACC circuit (2R) is the frequency conversion circuit (3R).
Is input to, mixed with a 4.21 MHz signal, and converted into a 629 KHz low-frequency conversion carrier color signal. The low-frequency carrier color signal is mixed with the FM modulation luminance signal by the recording amplifier circuit (4R) and recorded on the magnetic tape by the magnetic head.

During playback, 629 KHz low-frequency conversion carrier color signal video amplifier circuit (1
After being amplified by P), its level is adjusted to a constant level through the ACC circuit (2P). The output of the ACC circuit (2P) is input to the frequency conversion circuit (3P), mixed with a 4.21MHz signal and converted into a 3.58MHz carrier color signal, mixed with a luminance signal and output as a video signal.

The ACC circuit is an average value control type, and has a role of maintaining and adjusting the level of the carrier color signal of 3.58 MHz during recording and the level of the low frequency conversion carrier color signal of 629 KHz during reproduction.

On the other hand, a video tape recorder employs a helical scan method recording / reproducing method using two or more magnetic heads, so that, for example, in the case of two heads, the characteristics of the two heads are different. As shown in FIG. 4, the output differs between the first magnetic head (A head) and the second magnetic head (B head). Therefore, it takes time to control the level of the low-frequency conversion carrier color signal of 629 KHz to be constant for each level fluctuation of each head.

Therefore, conventionally, an ACC circuit as shown in FIG. 5 has been proposed.

The levels of the carrier color signal (A) corresponding to the first magnetic head (A head) and the carrier color signal (B) corresponding to the second magnetic head (B head) are set to the first and second filters (5A). ，
(5B) respectively detect the detected output (average value) of the first and second output transistors (6A), (6B)
, And outputs the average values from the respective emitters.

Then, the first and second output transistors (6A), (6B)
Of the carrier color signal (A) and the carrier color signal (B) are taken out by switching the output of the switch (7) by the switch circuit (7), and the voltage control type amplifier circuit (8) is obtained by these mean values. Is controlled to keep the levels of the carrier color signals (A) and (B) constant.

Further, as a conventional example, it is disclosed in Japanese Utility Model Laid-Open No. 62-152585, which detects a color burst signal level in a head output signal obtained by sequentially switching a plurality of heads of a rotary magnetic head device. To control the level of the chroma signal obtained in the head output signal.
A color video signal reproducing apparatus having an ACC circuit, wherein the ACC circuit has a parallel burst peak hold circuit that is switched corresponding to switching of the magnetic head,
As a ACC circuit used when reproducing a color signal from a video tape recorder, a parallel burst peak hold circuit that can be switched corresponding to the switching of multiple heads is provided to reduce the dedicated area of the ACC circuit for the printed circuit board. This is a device of a "color video signal reproducing device" that has the effect of being able to.

<Problems to be Solved by the Invention> The first and second filters (5A) and (5B) detect the average value of each of the carrier color signal (A) and the carrier color signal (B),
These are held, but these holding voltages are the first and second
It is always consumed as the base bias current (about 1 microampere) of the output transistors (6A) and (6B).

Therefore, if the switching time of the switch circuit (8) becomes long, the first and second filters (5A), (5B)
There is a problem in that the average value holding voltage fluctuates, and it takes time to control so that the level of the low-frequency conversion carrier color signal of 629 KHz becomes constant each time the level of each head fluctuates.

<Means for Solving the Problems> Referring to FIG. 1 showing a typical embodiment (principal part) of the present invention, the present invention relates to an ACC circuit of a video tape recorder. Second and third switch circuits (9A) and (9B) for connecting and disconnecting the first and second output transistors (6A) and (6B) in parallel with the output transistors (6A) and (6B) of Respectively, and the first
Switch circuit (10) of the first output transistor (6A)
This first output transistor (6
A) is conducted, the second output transistor (6B) is cut off,
When the first switch circuit (10) is switched to the second output transistor (6B) side, the second output transistor (6B) is turned on and the first output transistor (6A) is turned off. It is characterized in that the first, second and third switch circuits (10), (9A) and (9B) are interlocked.

<Operation> When the first switch circuit (10) is switched to the first output transistor (6A) side, the second switch circuit (9)
A) is OFF (open state), 3rd switch circuit (9B) is ON
Since it is in the (closed state), the first output transistor (6A)
Is turned on, and the second output transistor (6B) is turned off. Therefore, the base bias current of the second output transistor (6B) stops flowing, and the second filter (5B)
Since there is no discharge, the average voltage can be maintained for a long time.

When the first switch circuit (10) is switched to the second output transistor (6B) side, the second switch circuit (9A) is turned on (closed state) and the third switch circuit (9B) is turned on.
Since it is turned off (open state), the first output transistor (6
A) shuts off and the second output transistor (6B) becomes conductive. Therefore, the base bias current of the first output transistor (6A) ceases to flow, and the discharge of the first filter (5A) disappears, so that the average value voltage can be held for a long time.

<Embodiment> A typical embodiment (main part) of the present invention will be described with reference to FIG. In the drawing, the same parts as those of the conventional example of FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted.

(5A) is the first filter, (5B) is the second filter,
(6A) is a first output transistor, (6B) is a second output transistor, and (8) is a voltage-controlled amplifier circuit.

These first and second output transistors (6A) and (6B) are arranged in parallel with the first and second output transistors (6A) and (6B).
Second and third switch circuits (9A) that conduct and cut off the
(9B) respectively, and the first switch circuit (10)
To the first output transistor (6A) side, the first output transistor (6A) is turned on, the second output transistor (6B) is turned off, and the first switch circuit (10) is turned on. When the second output transistor (6B) is switched to the second output transistor (6B) side, the second output transistor (6B) conducts,
The first, second and third switch circuits (10), (9A) and (9B) so as to cut off the output transistor (6A) of
Interlock.

That is, when the first switch circuit (10) is switched to the first output transistor (6A) side, the second switch circuit (9A) is turned off (open state) to turn on the first transistor (6A). Set to the conductive state and connect the third switch circuit (9B).
It is turned on (closed state), and the collector and emitter of the second output transistor (6B) are short-circuited to cut off the state.

On the contrary, when the first switch circuit (10) is switched to the second output transistor (6B) side, the second switch circuit (9A) is turned on (closed state) and the first output transistor (10) is turned on. 6A) collector-emitter is short-circuited to cut off the state, the third switch circuit (9B) is turned off (open state), and the second transistor (6B) is turned on.

Although the embodiments considered to be typical of the present invention have been described above, the present invention is not necessarily limited to only the structures of these embodiments, and the constitutional requirements referred to in the present invention and the purpose referred to in the present invention can be obtained. The present invention can be carried out with appropriate modifications within the scope of achieving the following effects.

<Effect of Device> As is apparent from the above description, the device of the present invention is such that when the first, second and third switch circuits are interlocked and the first switch circuit is switched to the first output transistor side. The first output transistor is turned on and the second output transistor is turned off, and the first switch circuit is turned on to the second switch.
When switching to the output transistor side of, the average voltage of the first and second filters can be held for a long time by cutting off the first output transistor and turning on the second output transistor. There is an effect that an ACC circuit having a long switching time of the switch circuit can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a typical embodiment (main part) of an automatic color signal control circuit of the present invention, and FIG. 2 is a configuration of a carrier color signal recording circuit in a color video signal recording system of a video tape recorder. FIG. 3 is a diagram showing the structure of a carrier color signal reproducing circuit, FIG. 4 is a diagram showing output waveforms of A and B heads, and FIG. 5 is a conventional automatic color signal control circuit. It is a figure which shows the structure of (main part). In the figure, (5A) is a first filter, (5B) is a second filter, (6A) is a first output transistor, (6B) is a second output transistor, and (8) is a voltage-controlled amplifier circuit. (1
0) is the first switch circuit, (9A) is the second switch circuit, and (9B) is the third switch circuit.

Claims (1)

[Scope of utility model registration request] 1. A video signal in which a carrier color signal is superimposed on a frequency-modulated luminance signal is alternately recorded on first and second video tracks on a magnetic tape by at least two magnetic heads, and the video signal is recorded on the magnetic tape. In the video signal recorder / reproducer type video tape recorder, the video signals recorded in the first and second tracks are alternately reproduced to demodulate the luminance signal and the carrier color signal. A first carrier color signal reproduced from the first carrier color signal and a second carrier color signal reproduced from the second video track, respectively. Of the first carrier (5A) for detecting the level of the second carrier color signal and holding the average value thereof, and the second filter (5B) of detecting the level of the second carrier color signal and holding the average value thereof.
And first and second output transistors (6A) and (6B) for deriving the outputs of the first and second filters (5A) and (5B).
And the first and second output transistors (6A) and (6B)
A first switch circuit (10) for switching the output of the first and second carrier colors by controlling the voltage control type amplifier circuit (8) by the output of the first switch circuit (10). An automatic color signal control circuit for keeping a signal level constant, said first and second output transistors (6A), (6B)
In parallel with these first and second output transistors (6
A second and a third switch circuit (9A) and (9B) for respectively connecting and disconnecting A) and (6B) are provided, and the first switch circuit (10) is connected to the first output transistor (6A) side. When switching, the first output transistor (6A) is turned on,
The second output transistor (6B) is turned off, and when the first switch circuit (10) is switched to the second output transistor (6B) side, the second output transistor (6B) is turned on, Of the first, second and third switch circuits (10), (9) so as to cut off the output transistor (6A) of
An automatic color signal control circuit characterized by interlocking A) and (9B).