JPS6147473B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a multiple output circuit suitable for use in, for example, a color signal processing section of a video tape recorder (hereinafter abbreviated as VTR). Generally, in a VTR, the periphery of a comb filter for separating a luminance signal and a color signal in a composite video signal is constructed as shown in FIG. First, during recording, a recording video signal is input to the automatic gain control amplifier 1 via the input terminal. The output of the automatic gain control amplifier 1 is input to the comb filter 3 via the input terminal R of the switch circuit SW2, and is also input to the low pass filter 2. The brightness signal output of the comb filter 3 and the output of the low pass filter 2 are connected to a switch circuit.
It is added to the input terminals X and Y of SW1. This switch circuit SW1 selects one of the input terminals depending on the color killer voltage during recording, and is switched to the input terminal Y side in monochrome mode and to the input terminal X side in color mode. This switch circuit
The output of SW1 is input to a detector 4 for obtaining an automatic gain control voltage. The output of this detector 4 is
It is fed back to the control end of the automatic gain control amplifier 1,
It is used for automatic gain control of the luminance signal separated by the comb filter 3 during recording. The comb filter 3 is used for cross color removal. The color killer voltage switches the switch circuit SW1 to the input terminal X side when the burst signal level of the recording color signal is above a predetermined level, and is obtained from a circuit that detects the burst signal. If the burst signal is at a predetermined level or higher during recording, the color mode is set. Furthermore, when the burst signal is below a predetermined level (during black-and-white broadcasting or in a weak electric field), the mode becomes black-and-white mode, and the automatic gain control amplifier 1
The output luminance signal is input to the detector 4 via the low-pass filter 2. That is, when the color burst signal is below a predetermined level, automatic gain control is performed on the video signal obtained through the low-pass filter 2 rather than through the comb filter 3 in order to prevent resolution deterioration. On the other hand, during playback, switch circuit SW2,
SW3 is switched to the input end P side. Further, the color signal frequency-converted to a predetermined frequency is input to the input terminal P of the switch circuit SW2. Then, the switch circuit SW1 is switched to the input terminal Y side,
In this case, a reproduced color signal is obtained from the comb filter 3 while the recording mode is forcibly set to monochrome mode. The reproduced color signal input to the input terminal P of the switch circuit SW2 is extracted by the comb filter 3. The signal is then input to the reproduced color signal amplifier 5 via the switch circuit SW3, amplified, and then input to the mixer with the luminance component. In the above circuit, the killer voltage generating circuit for controlling the switch circuit SW1 and the reproduced color signal amplifier 5 each exist independently, and each has an output pin when integrated circuit. However, focusing on the above operation, the function of the reproduced color signal amplifier 5 is used only during reproduction, and separate color killer signal paths are required during recording and reproduction. This invention was made in response to the above-mentioned circumstances, and aims to improve the circuit utilization rate and integrate the circuit by reducing the number of external pins and making effective use of the pins. It is an object of the present invention to provide a multiple output circuit configured to be used as a color killer control signal transmission line depending on the mode. Embodiments of the present invention will be described below with reference to the drawings. Note that portions having functions corresponding to those of the circuit portion shown in FIG. 1 are designated by the same reference numerals, and description thereof will be omitted. In FIG. 2, reference numeral 11 denotes an input terminal for a reproduced color signal, into which a color signal during reproduction is input. This input end 11 is connected to a reproduction color signal amplifier 12. The reproduction color signal amplifier 12 is provided with a killer detection signal input terminal 13 and a recording/reproduction switching signal input terminal 14. The output terminal of this reproduced color signal amplifier 12 is led out to a first output terminal 16 via a low-pass filter 15, and a coupling capacitance 1
7 to a second output terminal 18. A killer voltage detection circuit 1 is connected to the killer voltage input terminal 13.
3' output is directly connected. In the above circuit, killer information (DC) is obtained from the first output terminal 16 during recording, and color signal output (AC) is obtained from the second output terminal 18 during reproduction. That is, the reproduced color signal amplifier 12 outputs a color killer control signal during recording, and outputs a reproduced color signal during reproduction. Next, the relationship between the output signal and the input control signal in the above circuit is shown in the table below.

[Table] Next, a specific circuit of the reproduced color signal amplifier 12 is constructed as shown in FIG. In FIG. 3, E _B is a DC bias power supply, which is connected to the base of transistor Q ₁ via resistor R ₁ and to the base of transistor Q ₂ via resistor R ₂ . A comb filter 3 is connected to the base of transistor Q ₁ .
The reproduced color signal extracted by is input. Transistors Q ₁ and Q ₂ form a differential amplifier circuit, and the emitters of transistors Q ₁ and Q ₂ are resistors, respectively.
They are commonly connected through R ₃ and R ₄ and connected to the reference potential end through resistor R ₅ . Transistor Q ₁
The collector of transistor _Q2 is connected to the DC power supply Vcc through the resistor _R6 .
and the base of transistor _Q3 . The collector of this transistor Q ₃ is connected to the reference potential end, and the emitter is connected to the base of a transistor Q ₄ forming an emitter follower circuit, and is also connected to the DC power supply Vcc via resistors R ₈ and R ₇ in series. . A resistor _R9 is connected between the base and emitter of the transistor _Q4 , and the collector of the transistor _Q4 is connected to the DC power supply Vcc via a resistor _R10 . Also this transistor
The emitter of Q ₄ is connected to the reference potential terminal via a resistor R ₁₁ and also to the output terminal OUT.
Further, the collector of a transistor _Q5 forming a control signal input circuit is connected to the connection point between the resistors _R8 and _R7 . The emitter of this transistor _Q5 is connected to the reference potential terminal. This transistor _Q5
The collector of the transistor Q ₆ is connected to the base of the transistor Q 6 , and the killer detection signal input terminal 13 is also connected to the base of the transistor Q 6 via a resistor R ₁₂ . Also transistor
The emitter of _Q6 is connected to the reference potential terminal. A recording/reproduction switching signal input terminal 14 is provided at the base of the transistor _Q6 via a resistor _R13 . Further, the output terminal OUT of the above circuit is connected to the first output terminal 16 via the low-pass filter 15, and the second output terminal 18 via the coupling capacitor 17.
connected to. During recording, the reproduction color signal amplifier 12
No color signal is supplied via SW3 to
Furthermore, the input terminal 14 is at a low level, and the transistor _Q6 is off. Therefore, during recording, the transistor _Q5 is controlled to be turned on or off depending on the killer voltage obtained from the output of the killer voltage detection circuit 13'. Here, in the color mode during recording when the killer voltage is at a high level, the transistor
Q ₅ turns on and the emitter of transistor Q ₃ falls almost to ground potential. Therefore transistor Q ₄
The emitter potential of is also approximately the ground potential. At this time, a DC potential close to ground potential is obtained at the output terminal OUT. The low-level DC potential generated at the first output end of the low-pass filter 15 turns the key switch K1 into a conductive state. When the killer switch K1 becomes conductive, the color signal whose frequency has been converted to a low frequency band is applied to the mixer M1, and the color signal is processed. in this case,
The output voltage of the first output terminal 16 is determined by a switch circuit.
It is also used as a control signal for SW1, making the killer switch K1 conductive and connecting the switch circuit SW1 to the input terminal X side. For this reason, from the signal whose frequency has been converted to a low frequency for recording,
AGC operation is performed on the luminance signal separated using the comb filter 3. On the other hand, in the black and white mode during recording, the detection voltage of the killer voltage detection circuit 13' is low and the transistor _Q5 is off, so the transistor
The emitter potential of _Q4 becomes approximately the same potential as the collector of transistor _Q2 . At this time, the potential of the output terminal OUT is higher than that in the color mode. Therefore, the killer switch K1 is cut off for the color signal which has been converted to a low frequency by the potential of the output terminal OUT, and a color killer operation is performed. At this time, the high potential of the first output terminal 16 connects the switch circuit SW1 to the Y terminal side, and performs AGC operation on the luminance signal passed through the low-pass filter 2. That is, the extraction of the luminance signal by the comb filter 3 is stopped, and a color killer operation is performed on the recording signal.
In this way, the first output terminal 16 can provide high level, low level color or black and white switching output. Next, during reproduction, the potential at the reproduction switching signal input terminal 14 becomes a high level, and since the transistor Q ₆ is on, the transistor Q ₅ is off regardless of the killer potential, and therefore the first output terminal 16 is at a high level. It remains as it is. Therefore, SW1 is connected to the Y terminal side, but this does not affect the reproduction signal system. The reproduced color signal is input from the comb filter 3 to the reproduced color signal amplifier, and the reproduced color signal amplified by the differential amplifier is obtained at the second output terminal 18. According to the multiple output circuit configured as described above,
During recording and reproduction, the control signal in one mode and the processed signal in the other mode can be delivered to the same output terminal. In this way, signals with different properties in both modes can be led out to the same output terminal, and desired signals can be separated and extracted for each predetermined mode. Therefore, when integrated, extremely effective effects such as a reduction in the number of pins, an improvement in circuit utilization, and a reduction in the number of external circuits can be achieved. As described above, the present invention can provide a multiple output circuit configured to reduce the number of external pins and make effective use of the pins in terms of improving the circuit utilization rate and integrating the circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the circuit configuration around a comb filter in a VTR, FIG. 2 is a diagram illustrating the basic configuration of a multiple output circuit according to an embodiment of the present invention, and FIG. 3 is a diagram showing the configuration of the circuit shown in FIG. It is a specific circuit diagram. _Q1 to _Q6 ...transistor, _R1 to _R13 ...resistance,
13...Killer voltage input terminal, 14...Switching signal input terminal, 15...Low pass filter.

Claims (1)

[Scope of Claims] 1. A differential amplifier circuit that amplifies a color signal applied to an input terminal, an emitter follower circuit that derives an output terminal from the emitter of a transistor to which this output is applied, and a differential amplifier circuit that is connected in parallel to the output terminal of this emitter follower circuit. A first output terminal provided via a low-pass filter, a second output terminal provided via a coupling capacitor, and one control signal input terminal are provided with a low level during recording and a high level during playback. - A reproduction state switching signal is input, and a color killer detection signal of high level in color mode and low level in black and white mode is applied to the input terminal of the other control signal, and according to the logic of both signals, the emitter follower is The input side bias circuit section of the emitter follower circuit is controlled so that the output potential of the first output terminal of the circuit corresponds to the change in the color killer detection signal, and during playback, the output voltage is changed according to the change in the recording/playback state switching signal. 1. A multiple output circuit comprising: a control signal input circuit that is inactive with respect to an emitter follower circuit. 2. In the differential amplifier circuit, the DC bias power supply is connected to the base through the first and second resistors, and each emitter is connected to the fifth resistor in common after passing through the third and fourth resistors. a first transistor and a second transistor connected to a reference potential terminal via a first transistor;
A system for inputting a color signal to the base of the transistor, a system for supplying DC power to the collector of the first transistor, and a sixth resistor provided between the collector of the second transistor and the DC power supply. The bias circuit section includes a third transistor whose base is connected to the collector of the second transistor, whose collector is connected to a reference potential terminal, and whose emitter is connected to a DC power supply through a seventh and eighth resistor in series. The emitter follower circuit has a base connected to the emitter of the third transistor, a ninth resistor connected between the base and emitter, and a collector connected to a DC power supply via a tenth resistor, and the emitter follower circuit a fourth transistor connected to a reference potential terminal via an eleventh resistor and led out to the only output terminal; A fifth transistor has a collector connected to the terminal, an emitter connected to the reference potential terminal, and a color killer detection signal input terminal set to the base via the twelfth resistor, and a collector connected to the base of this transistor, the emitter is connected to the fifth transistor. A sixth transistor is connected to a reference potential terminal, and a recording/reproduction switching signal input terminal is set to the base via a thirteenth resistor.
Multiple output circuit described in section. 3. In an image recording and reproducing device, a reproduction color amplifier having an output terminal for amplifying an input reproduction color signal during image reproduction and deriving the amplified reproduction color signal via an output buffer circuit; During recording, a color killer detection signal is applied to the buffer circuit input terminal, a DC potential corresponding to this detection signal is buffered, and a DC potential corresponding to this detection signal is output to the buffer circuit in the recording/playback mode. a low-pass filter having a first output terminal for extracting a color killer signal from the output terminal in a recording mode; and a low-pass filter having a first output terminal for extracting a color killer signal from the output terminal in a playback mode; and a capacitor having a second output terminal connected to the output terminal to block DC components from the amplified reproduced color signal, and derive a color killer signal to the first output terminal during recording. . A multiple output circuit, wherein a reproduced color signal is obtained at the second output terminal during reproduction.