JPH06189343A - Driver output circuit - Google Patents

Abstract

PURPOSE:To reduce the cost and to decrease the current consumption resulting from separate provision of an output circuit by using one output circuit for a line output circuit and an output circuit for an S terminal (Y) in common. CONSTITUTION:A composite signal being a mixture of a luminance signal and a chroma signal is inputted to a noninverting input terminal of an operational amplifier A1 being a component of an output circuit 3. Furthermore, a chroma signal from a Y/C separate circuit 2 is inputted to an inverting input terminal of the operational amplifier A1 being a component of the output circuit 3. Then the operational amplifier A1 is used for an adder or a subtractor through the changeover of a switch SW4 to generate a composite video signal or a chroma signal. Then either of the generated composite video signal and chroma signal is outputted to a line output terminal or an S(Y) terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video tape having an output terminal for outputting a composite signal in which a luminance signal and a chroma signal are mixed, and an S terminal for outputting a luminance signal and a chroma signal separately. Regarding recorders, etc.

[0002]

2. Description of the Related Art Currently, in addition to an external output terminal for outputting a composite signal in which a luminance signal and a chroma signal are mixed, a high resolution device such as a stationary video tape recorder, a camcorder, or a laser disc player is used. What is called an S terminal that outputs a luminance signal and a chroma signal separately is generally added as a part of the external output terminal.

FIG. 3 shows the configuration of a driver output circuit of a conventional general video tape recorder.

The video signal from the line input terminal is video A
After passing through the GC circuit 1, it is output to the Y / C separation circuit 2, and one of them is impedance-converted to 75Ω by the output circuit 3 and output from the line output terminal. Here, the output circuit 3 is an operational amplifier type driver, and
By selecting the values of the resistors R2 and R3 and the coupling capacitor C2, the feedback signal to the negative side of the operational amplifier A1 is determined and used for output level adjustment and sag correction.

On the other hand, the signal input to the Y / C separation circuit 2 is separated into a luminance signal and a chroma signal, which are individually processed and recorded on a magnetic tape. Then, the separated luminance signal is output from the S terminal (Y) as an S terminal luminance signal via the output circuit 4. Here, the output circuit 4 is also an operational amplifier type driver like the above-mentioned output circuit 3, and includes two resistors R5 and R6 and a coupling capacitor C.
By selecting the value of 4, the feedback signal to the negative side of the operational amplifier A2 is determined and used for output level adjustment and sag correction.

The separated chroma signal is output from the S terminal (C) as an S terminal chroma signal via the output circuit 5.

Generally, a luminance signal processing IC incorporates the video AGC circuit 1, the Y / C separation circuit 2 and the output circuit 3 in the IC, but the output circuits 4 and 5 are not formed in the IC. Instead, it must be configured as an external circuit. This is because the output circuit 5 can be driven at 75Ω without any problem in use due to the increase in the current of the emic follower type, but since the output circuit 4 requires a resistor, a feedback capacitor, an operational amplifier, etc., the circuit scale is small. This is because it becomes large and the cost becomes high when integrated into an IC. Further, when these output circuits 4 and 5 are incorporated in the luminance signal processing IC, the current consumption of the output circuit increases by several tens of mA, which is an obstacle in IC design.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. One output circuit combines the line output circuit and the output circuit for the S terminal (Y), and a separate output circuit is provided. The purpose is to reduce the cost increase and the current consumption increase due to the provision of the.

[0009]

According to the present invention, there is provided a first external output terminal for outputting a composite video signal in which a luminance signal and a chroma signal are mixed to an external device, and a composite
A plurality of second and third external output terminals that separately output a luminance signal and a chroma signal from a video signal and a plurality of impedances that match the impedance of the signals from the first, second, and third external output terminals. The output circuit of the first external output terminal and the second external output terminal are also used as the driver output circuit.

[0010]

In the present invention, the composite signal in which the luminance signal and the chroma signal are mixed is input to the plus side input terminal of the operational amplifier which constitutes the output circuit, and the chroma signal from the comb filter constitutes the output circuit. Input to the negative input terminal of. Then, by switching the switch, either the composite signal or the chroma signal is selected from the operational amplifier and output to the respective external output terminals.

[0011]

FIG. 1 shows the first embodiment of the present invention.

Normally, a composite video signal, which is a mixture of a luminance signal and a chroma signal input from a line input terminal, passes through a video AGC circuit 1 and then is passed through a Y / C separation circuit 2 to produce a luminance signal and a chroma signal. And is output to each recording signal processing circuit (not shown). On the other hand, a part of the output of the video AGC circuit 1 is impedance-converted to 75Ω by the operational amplifier A1 of the output circuit 3 and output.

SW1 is a first external output terminal, and is a mechanical switch which is turned on when an external cable is connected to the line output RCA pin jack. SW2 is a second external output terminal and is a mechanical switch that is turned on when an external cable is connected to the S (Y) terminal. SW3 is a third external output terminal, which is normally pulled up, and is HIGH, but when the cable is connected to the S (C) terminal, it is electrically connected to the GND of the cable to be LOW by being short-circuited. It is a switch.

In FIG. 1, in the case of output from a general line, a composite video signal whose impedance is converted to 75Ω through the signal path as described above is obtained at the line output terminal and output to the outside. At this time, SW4 is set to be OFF.

Next, in the case of the output from the S terminal, first, the composite signal is delayed by the CCD delay line 6 in the Y / C separation circuit 2 by 1H in the NTSC system and 2H in the PAL system. Here, in order to separate the luminance signal and the chroma signal, the luminance signal is subtracted by adding the original signal and the signal passed through the CCD delay line 6, and the original signal and the signal passed through the CCD delay line 6 are subtracted. This creates a chroma signal. The signal that has passed through the CCD delay line 6 is BPF7.
Then, only the chroma component is allowed to pass through, and then the level and phase adjusted by the amplifier 8 is input to the negative side input terminal of the operational amplifier A1. Therefore, the operational amplifier A
From 1, a signal obtained by subtracting the chroma signal from the composite signal, that is, a luminance signal is output. When outputting from the S terminal, SW4 is set to be turned on.

On the other hand, the chroma signal from the Y / C separation circuit 2 is impedance-converted to 75Ω by the emitter follower operational amplifier 5, and then output from the S (C) terminal to the outside.

By configuring as described above, in a device having an S terminal function, a composite video signal in which a luminance signal and a chroma signal are combined and an S terminal Y signal
Since one output circuit can be used in common, cost reduction can be achieved.

Next, FIG. 2 shows a second embodiment of the present invention.

The switch and the structure of each output circuit are the same as in the first embodiment.

In FIG. 2, in the case of output from the line,
The luminance signal separated by the Y / C separation circuit 2 is input to the plus side terminal of the operational amplifier A1 that constitutes the output circuit 3. Further, the chroma signal separated by the Y / C separation circuit 2 passes through SW4 and is input to the negative side terminal of the operational amplifier A1 forming the output circuit 3. Then, in the operational amplifier A1, the above-mentioned luminance signal and chroma signal are added and output as a composite video signal from the line output terminal to the external cable. At this time, SW4 is
Contrary to the first embodiment, when the S terminal is not connected, it is turned on.

Next, in the case of output from the S terminal, by setting SW4 to be OFF, only the luminance signal separated by the Y / C separation circuit 2 from the output circuit 3 is S.
It operates so as to be supplied to the outside from the (Y) terminal.

Since SW1 and SW2 are for mechanically switching the output from the line and the output from the S (Y) terminal, even if these output selection switches are provided on the external device side. good.

[0023]

According to the present invention, with the above-described configuration, a driver output circuit for the S (Y) terminal output is conventionally required in addition to the driver output circuit for the line output terminal. By also using the driver output circuit of, it is possible to reduce the driver output circuit,
Cost reduction. In addition, the reduction of the driver output circuit reduces the current consumption and facilitates the integration into an IC.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a driver output circuit of the present invention.

FIG. 2 is a block diagram showing a conventional driver output circuit.

FIG. 3 is a block diagram showing a second embodiment of the driver output circuit of the present invention.

[Explanation of symbols]

 1 Video AGC Circuit 2 Y / C Separation Circuit 3 First Output Circuit 4 Second Output Circuit 5 Third Output Circuit 6 CCD Delay Line 7 BPF A1 Operational Amplifier A2 Operational Amplifier

Claims (1)

[Claims] 1. A first external output terminal for outputting a composite video signal in which a luminance signal and a chroma signal are mixed to an external device, and a first external output terminal for separating a luminance signal and a chroma signal from the composite video signal and outputting each separately. The second and third external output terminals, and a plurality of output circuits that match the impedances of the signals from the first, second, and third external output terminals, and the first external output terminal and the A driver output circuit which is also used as an output circuit of a second external output terminal.