JPH0646802B2 - Signal processing circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a signal processing circuit suitable for use in a clamp circuit in a video device, and more particularly to a technique effective in expanding a horizontal synchronizing signal to a desired level.

[Background technology]

In video equipment such as a VTR, the level of the horizontal synchronizing signal and the level of the video signal are set to a ratio of 3: 7. The signal processing is performed with the pedestal level as a reference, and a clamp circuit is used to hold the pedestal level. Regarding the clamp circuit, "VTR-related basic course" (published on September 10, 1981, publishing company, Radio Technology Co., pp162-163)
It is described in.

In the case of performing the above signal processing, there is a problem that so-called sync contraction occurs in the horizontal synchronizing signal, and the ratio of 3: 7 cannot be obtained, which makes it difficult to synchronize. Therefore, a sink expansion circuit utilizing the non-linearity of the germanium diode was examined and configured to correct the contraction of the original signal, but the sync expansion circuit cannot be provided in the IC. .

As a result, it has been clarified by the present inventors that the number of external connection pins of the IC increases and the number of external parts increases, which is one of the causes of the decrease in the degree of integration and the decrease in mounting density.

To solve the above problems, there is no choice but to form a signal processing circuit for performing sync extension in the IC integrally with other circuits.

Therefore, the present inventors have found that the above problem can be solved by amplifying a video signal with a single amplifier having a common input circuit, amplifying a horizontal synchronizing signal with another amplifier, and then synthesizing the two signals. He came to propose an invention.

[Object of the Invention]

It is an object of the present invention to form a signal processing circuit capable of expanding the level of a horizontal synchronizing signal or the like in an IC together with other circuits.

The above and other objects and novel features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

[Outline of Invention]

The following is a brief description of the outline of the typical inventions among the inventions disclosed in the present application.

That is, an input signal having two signal components is commonly supplied to two amplifiers having different amplification values and a reference value for amplification, and the two signal components are compared with the reference value and individually amplified by the two amplifiers. The object of the present invention is to expand the level of a desired signal component by expanding and then combining the two signal components.

〔Example〕

An embodiment of a signal processing circuit to which the present invention is applied will be described below with reference to FIGS. 1 to 3. In addition, FIG. 1 shows a VTR
2 is a block diagram showing a circuit configuration of a main part of FIG. 2, FIG. 2 is a circuit diagram of a signal processing circuit for performing sync expansion, and FIG. 3 is a characteristic diagram for explaining a circuit operation.

The feature of this embodiment is that an amplifier for amplifying a horizontal synchronizing signal and an amplifier 2 for amplifying a video signal are provided in parallel as shown in FIG. 2 and the output signals of both are combined. .

First, for convenience of explanation, the circuit structure of the VTR will be described with reference numeral 1 to a magnetic tape, 2 to a reproducing head, and 3 to a preamplifier. The reproduction signal V ₁ is supplied to the luminance signal processing circuit A and the color signal processing circuit B. The luminance signal processing circuit A will be described below in sequence. Reference numeral 4 is an AGC circuit, 5 is a limiter circuit, and 6 is an FM demodulator, and its output signal includes a luminance signal and a horizontal synchronizing signal.

Reference numeral 7 is de-emphasis, 8 is a noise canceller, and 9 is a mixing circuit which mixes a luminance signal and a color signal supplied from a color signal processing circuit, and supplies them to a video signal or a video amplifier 10 which is a combination of both. To be done.

A signal processing circuit to which the present invention is applied is provided between the noise canceller 8 and the mixing circuit 9 or the mixing circuit 9
And the video amplifier 10.

Referring to the signal processing circuit 11 shown in FIG. 2, a video signal V _in having a waveform as shown in FIG. 3 is supplied from the first terminal.

Regarding the input signal V _in , the horizontal synchronizing signal V _S is assumed to be compressed.

Amplifier 21 composed of transistors Q ₁ and Q ₂
Is for amplifying the horizontal synchronizing signal V _S , and its gain is set by the current I _o by the constant current circuit CS ₂ .
Amplifier 2 composed of transistors Q ₃ and Q ₄
2 amplifies the video signal V _V , and its gain is set by the ratio of the resistors R ₁ and R ₂ .

The transistor Q _{6 supplies the} reference voltage determined by V _ref -V _BQ6 to the transistors Q ₁ , Q ₃ , and the diode D ₁ , the resistor R ₁ supplies the reference voltage determined by V _ref -V _FD1. Supply to the transistor Q ₂ .

When the input signal _{V in} is supplied, the other transistors _Q 1 to Q ₃ by the base voltage of the transistor _{Q 4} is V _ref1
Since it is set to a level higher than the base voltage of, the voltage above the pedestal level, in other words, the video signal V _V is amplified by the amplifier 22. Then, the voltage equal to or lower than the pedestal level, in other words, the horizontal synchronizing signal V _S is amplified by the amplifier 21.

The outputs of the amplifiers 21 and 22 are obtained as a voltage drop across the resistor R ₂ and drive the transistor Q ₅ . Therefore, if the gain of the amplifier 21 is made high and the characteristics shown in FIG. 3 are obtained, the output signal V _out obtained by expanding the horizontal synchronizing signal V _S is obtained.
Is obtained.

〔effect〕

(1) Expanding the horizontal sync signal to a desired level by connecting amplifiers having different gains and amplification reference levels in parallel and individually amplifying the video signal and the horizontal sync signal and then combining the output signals, The effect is obtained.

(2) Since the amplifier can be composed of a silicon transistor, there is an effect that it can be composed of an IC together with other circuits.

(3) By the above (2), it can be formed as an insertion circuit in a conventional video amplifier or the like, and the added value of the IC is improved.

(4) The expansion of the horizontal sync signal provides stable synchronization, thus improving the image quality.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. There is no end.

For example, the current control by the constant current circuit CS ₂ may be performed by a control signal from the outside.

[Field of application]

In the above description, the case where the invention made by the present inventor is mainly applied to the VTR which is the field of application which is the background has been described, but the present invention is not limited thereto, and for example, various display devices using a picture tube. Can be used for.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts of a VTR showing an embodiment of the present invention, FIG. 2 is a circuit diagram of a signal processing circuit to which the present invention is applied, and FIG. 3 is a circuit operation of the signal processing circuit. It is a characteristic diagram. 11 ... Signal processing circuit, 21, 22 ... Amplifier, V _ref , V _ref1 ... Reference voltage, Q _{1 to} Q ₅ ... Transistor, D ₁ ... Diode, V _S ... Horizontal sync signal, V _V
... video signal, V _in ... input signal, V _out ... output signal.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shigehisa Yamamoto 1479 Kamimizumotocho, Kodaira-shi, Tokyo In-house Hitachi Mycro Computer Engineering Co., Ltd. (56) Reference JP-A-56-153816 (JP, A) 50-65320 (JP, U)

Claims (1)

[Claims] 1. An input terminal to which an input signal composed of two signal components of a horizontal synchronizing signal and a video signal is supplied, and a first transistor to which the input signal is supplied to its base via the input terminal, A second transistor having an emitter coupled to the emitter of the first transistor and having a first reference voltage supplied to the base; and a resistance element provided between the collector of the second transistor and a power supply terminal, A first amplifier including a constant current circuit provided on the emitter side of the first and second transistors, a third transistor to which the input signal is supplied to its base via the input terminal, and an emitter The collector of the third transistor is connected to the emitter of the second transistor, the collector of the second transistor is commonly connected to the collector of the second transistor, and the second reference voltage is A second amplifier provided with a fourth transistor supplied to the second transistor and a constant current circuit provided on the emitter side of the third and fourth transistors, and a first reference voltage source that forms the first reference voltage. A signal processing circuit configured to obtain an output from the collectors of the second and fourth transistors, the signal processing circuit including: a second reference voltage source that forms the second reference voltage; A voltage higher than one reference voltage, the horizontal synchronizing signal component in the input signal is expanded and amplified substantially only by the first amplifier, and the video signal component in the input signal is substantially the second amplifier. A signal processing circuit, wherein the signal processing circuit is configured to amplify only by.