JPH07322291A - Video signal amplitude control circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for adjustment of a signal amplitude using a variable resistor by controlling automatically an amplitude of the video signal with high accuracy and high reproducibility. CONSTITUTION:A variable gain amplifier circuit 3 varies simultaneously a DC voltage and an amplitude of a luminance signal and gives them to a voltage detection circuit 21 and a voltage detection circuit 58. The voltage detection circuit 21 generates a DC voltage control signal 9 so that a DC voltage VDC 1 and a tip potential of a synchronizing signal of an output video signal are coincident with each other based on a clamp pulse signal 20. The voltage detection circuit 58 generates a signal resulting from superimposing a signal amplifying a voltage between an output video signal and the voltage VDC 1 onto the DC voltage VDCI at an amplifier circuit 8. A charge discharge current corresponding to the voltage between an output of the amplifier circuit 8 and the DC voltage VDC 2 is generated by a voltage current conversion circuit 12, outputted to a capacitor 19 to control the gain of the variable gain amplifier circuit 3 so that the charge / discharge current to the capacitor 19 is made zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal amplitude control circuit, and more particularly to a video tape recorder for converting a video signal into an FM signal and converting a color signal into a low frequency band of the FM signal for recording and reproduction. The present invention relates to a technique effectively used for what is used in a VTR (hereinafter abbreviated).

[0002]

2. Description of the Related Art In a VTR, the amplitude of a video signal output for a monitor (television, etc.) at the time of recording / reproducing, and the potential for clipping a spike signal by an emphasis circuit for emphasizing high frequencies when FM-modulating the video signal at the time of recording The ratio of the image signal amplitude to the video signal amplitude, a so-called white / dark clip level, is defined by the standard. That is, it is necessary to accurately set the amplitude of the luminance signal in the above video signal.

In the conventional video signal processing circuit for a magnetic recording / reproducing apparatus shown in FIG. 3, a video signal amplitude control circuit 24 is used to variably control the video signal amplitude input at the time of recording, and then a desired signal processing such as emphasis is performed. However, since the output signal amplitude does not satisfy the standard due to variations in circuit characteristics, the amplitude is adjusted by a variable resistor in the VTR manufacturing process.

In the video signal amplitude control circuit 24, after passing through a variable gain amplifying circuit 28 which varies and outputs the video signal amplitude input from the recording video signal input terminal 27, the video signal is supplied to a low pass filter circuit 29. An amplitude detection circuit for removing a color signal included in the signal, inputting the video signal for removing the color signal to the clamp circuit 30, clamping the tip end potential of the synchronizing signal of the video signal to a predetermined potential, and detecting the back porch potential. 25, and the gain of the variable gain amplifier circuit 28 is controlled by the control voltage based on the detection.

The video signal whose amplitude is controlled in this way is taken out from the variable gain amplifier circuit 28, amplified by the amplifier circuit 34 through the recording / reproducing changeover switch circuit 33 with a predetermined gain, and output to the monitor video signal output terminal 35. To be done. However, the output video signal amplitude is output by adding the dispersion of the detection characteristics of the amplitude detection circuit 25 and the dispersion of the gain of the low-pass filter circuit 29, so that the output video signal that has dispersion is corrected. Correspondence is required. As a concrete countermeasure example, there is a method of adjusting the detection level of the amplitude detection circuit 25 by the variable resistor 23.

In order to FM-modulate the video signal, the video signal output from the clamp circuit 30 is nonlinearly emphasized in the high frequency range by the non-linear emphasis circuit 31, and is input to the emphasis circuit 38 through the variable gain amplifier circuit 32. The emphasis circuit 38 is provided with a circuit for enhancing the high frequency band of the video signal and clipping the spike signal at a predetermined potential. Here, it is necessary to take measures against variations in the white / dark clip level due to variations in the video signal amplitude at the input of the emphasis circuit 38 due to variations in the detection characteristics of the amplitude detection circuit 25 and variations in the gain of the nonlinear emphasis circuit 31. For example, the variable resistor 26 is used as the variable gain amplifier circuit 32.
Is adjusted to correct the input video signal amplitude of the emphasis circuit 38 to set a desired white / dark clip level. The video signal thus emphasized in the high frequency range is modulated into an FM signal by the FM modulation circuit 37 and then F
It is output to the M signal output terminal 36.

The reason why these two points need to be adjusted is that the factors of variation of the two systems at the time of recording are different as described above, and the video input to the emphasis circuit after the output video signal amplitude for monitor is corrected. It is necessary to correct the signal amplitude.

A concrete circuit of the clamp circuit 30 of the video signal amplitude control circuit 24 described above is shown in FIGS. 5 and 6, and a concrete circuit of the amplitude detection circuit 25 is shown in FIG. Clamp circuit 3
0 is a function of clamping the sync signal tip potential of the video signal input to the amplitude detection circuit 25, and a system as shown in FIG. 5 is adopted, for example. In the figure, a video signal whose sync signal has a negative polarity is input to the emitter of a transistor Q1 of 64 whose base is connected to a DC voltage source 63 via a capacitor 65, and the diode characteristic between the base and emitter of Q1 is shown. It operates to clamp the lowest voltage. Therefore, when waveform distortion or noise that is equal to or lower than the sync signal tip potential is superimposed on the video signal, the lowest voltage of those is clamped, so that the sync signal tip potential of the output video signal varies. There is.

A concrete example of another clamp circuit is shown in FIG.
In this figure, the clamp pulse signal 20 for specifying that it is within the synchronization signal period as shown in FIG. 2 is input through the capacitor 65 by saturating the transistors Q2 and Q3 of 66 and 67 during the HIGH period. The sync signal tip potential of the video signal is set to be equal to the potential near VDC3. This is because the saturation voltage of the switching signals Q2 and Q3 varies and thus the sync signal tip potential of the output video signal varies.

As shown in FIG. 4, the amplitude detection circuit 25 includes an amplifier circuit 47 for amplifying the difference between the clamped video signal and the DC voltage given by the variable resistor 23, and an amplified difference component voltage signal as a voltage. Voltage-current conversion circuit 5 for converting current
1, a capacitor 52 for receiving the output current of the voltage-current conversion circuit 51 to generate a voltage, and a constant current source 53 for discharging the electric charge of the capacitor 52. The voltage generated in the capacitor 52 is used as an amplitude control signal. The signal is supplied to the amplitude control terminal 55 of the variable gain amplifier circuit 28 as 54 to control the gain.

A constant current source 53 is connected to the capacitor 52 so that a constant current I1 for discharging flows, and always operates to increase the gain of the variable gain amplifier circuit 28. For example, in the non-input state, the variable gain amplifier circuit 28 is in the maximum gain state.
On the other hand, the variable gain amplification circuit 28 is output by outputting the charging current generated in the voltage-current conversion circuit 51 to the capacitor 52 according to the potential of the video signal input to the amplitude detection circuit 25.
It works to reduce the gain of. That is, the gain is controlled so that the charge / discharge charge to the capacitor 52 is balanced and the voltage of the capacitor 52 is stable.

Specifically, the keyed pulse signal 22 for specifying that it is within the back porch period as shown in FIG.
During the HIGH period, the voltage-current conversion circuit 51 generates a charging current corresponding to the potential obtained by amplifying the back porch potential of the video signal output from the clamp circuit 30 by the amplification circuit 47 based on the DC voltage obtained by the variable resistor 23. Generated and output to the capacitor 52 via the switch circuit 50, the charge amount by the charging current (Icharge) in the keyed pulse signal period (Tkeyed) and the discharge amount by the constant current source (I1) in one horizontal period (T1H) are calculated. When they match, there is no change in the control voltage applied to the capacitor 52, and the gain of the variable gain amplifier circuit is stable. That is, the state where the following formula (1) is satisfied is the stable state.

Tkeyed × Icharge = T1H × I1 (1) Therefore, Icharge = I1 × T1H / Tkeyed,
The charging current required at the stable point varies due to variations in the pulse width Tkeyed of the keyed pulse signal, and I1
The required charging current also changes with respect to the absolute value of.

As described above, the amplitude detection circuit 25 detects the back porch potential of the video signal whose sync signal tip potential has been clamped by the clamp circuit 30, and the variation and amplification of the sync signal tip potential of the video signal. Variations in the gain of the circuit 47, variations in the pulse width of the keyed pulse signal, and discharge current values cause variations in the amplitude of the video signal input to the amplitude detection circuit 25. This is the variable resistor 23
Is being adjusted.

On the other hand, during reproduction, the FM signal input from the FM signal input terminal 39 shown in FIG.
Then, the signal is demodulated into a video signal in step S1, the high frequency band is suppressed by the de-emphasis circuit 44, and the signal passes through the variable gain amplifier circuit 32. Low pass filter circuit 4
The non-linear de-emphasis circuit 41 suppresses the high frequency band in a non-linear manner, the noise canceller circuit 40 removes the high frequency noise from the video signal, and the switch circuit 33 passes through the amplifier circuit 34 to monitor the video signal. It is output to the output terminal 35. However, since the amplitude of the output video signal is added with the demodulation sensitivity of the FM demodulation circuit and the gain variation of other functions up to the monitor video signal output terminal, the output video signal is corrected. There is a need to. For example, the gain of the variable gain amplifier circuit 32 is adjusted by the variable resistor 43 to correct the amplitude.

[0016]

As described above, since the signal amplitude is adjusted by the external variable resistor in the semiconductor integrated circuit of the conventional video signal processing circuit for the magnetic recording / reproducing apparatus, the component cost of the variable resistor is reduced. And increase the adjustment cost,
In addition, there is a problem that the variable resistance easily changes with time.

It is an object of the present invention to provide a video signal amplitude control circuit capable of automatically controlling the video signal amplitude with high accuracy and reproducibility. Another object of the present invention is to provide a video signal amplitude control circuit that does not require the above-mentioned adjustment of the signal amplitude by a variable resistor. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0018]

The outline of a typical one of the inventions disclosed in the present application will be briefly described as follows. That is, the gain variable circuit means having two terminals for variably controlling the DC voltage and the amplitude of the output video signal, and the potential difference between the sync signal tip potential of the output video signal of the gain variable circuit means and the first DC voltage. According to the first
Means for outputting a charging / discharging current within the synchronizing signal period with respect to the capacitance, and the output of the gain variable circuit means by feeding back the voltage generated in the first capacitance to the DC voltage variable terminal of the gain variable circuit means. Means for clamping the sync signal tip potential of the video signal, the amplifying means for amplifying the potential difference between the output video signal of the gain varying circuit means and the first DC voltage, and superimposing it on the first DC voltage. A means for outputting a charging / discharging current to the second capacitor within the back porch period according to a potential difference between the potential of the output signal of the amplifying means and the second DC voltage based on the first DC voltage; The amplitude of the video signal is controlled by feeding back the voltage generated in the capacitance 2 to the variable gain control terminal of the variable gain circuit means.

[0019]

According to the above means, by fixing the two points of the sync signal tip potential and the back porch potential included in the video signal, the amplitude control with less variation factor is possible and the video signal with the desired amplitude accuracy is provided. Can be obtained.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same numbers indicate equivalent or same parts. FIG. 1 shows a block diagram of an embodiment of a video signal amplitude control circuit according to the present invention. Each circuit block in the figure is formed on one semiconductor substrate such as single crystal silicon by a well-known semiconductor integrated circuit manufacturing technique together with other circuit blocks constituting a signal processing circuit for VTR.

The video signal amplitude control circuit of this embodiment comprises a variable gain amplifier circuit 3, a voltage detection circuit 21, and a voltage detection circuit 5.
8 and. The variable gain amplifier circuit 3 receives the DC voltage control of the DC voltage control signal 9 supplied from the DC voltage control terminal 5 with respect to the video signal input from the input terminal 1, and outputs the video signal to the output terminal 4. The gain of the input / output signal ratio is controlled by the amplitude control signal 6 supplied from the amplitude control terminal 2 to change the output amplitude. That is,
In the variable gain amplifier circuit 3, the DC voltage and the amplitude of the luminance signal are simultaneously varied by the above two control signals to be supplied to the voltage detection circuit 21 and the voltage detection circuit 58, and the output terminal 4 is also provided.
Output to.

In the voltage detecting circuit 21, the DC voltage VD generated by the DC voltage source 17 is generated by the clamp pulse signal 20.
The DC voltage control signal 9 is formed so that the sync signal tip potential of the output video signal and C1 coincide with each other. That is, while the clamp pulse signal 20 is HIGH, the switch circuit 1
4 is made conductive, and the charging / discharging current according to the potential difference between the DC voltage VDC1 and the sync signal tip potential is converted into the voltage-current conversion circuit 1
The DC voltage control signal 9 generated at 5 and supplied to the capacitor 16 to be formed is supplied to the DC voltage control terminal 5. The charge / discharge current for the capacitor 16 is zero, that is, the clamp pulse signal 20
The DC voltage of the output video signal of the variable gain amplifying circuit 3 is variably controlled so that the capacitance 16 does not change in voltage by the sampling operation by, and the sync signal tip potential of the output video signal is made equal to the DC voltage VDC1. Further, the DC voltage control is maintained by the DC voltage control signal 9 held in the capacitor 16 while the clamp pulse signal is LOW.

The voltage detection circuit 58 includes resistors 10 and 11.
An amplifier circuit 8 composed of a differential amplifier circuit 7 and a differential amplifier circuit 7 generates a signal in which a signal obtained by amplifying the potential difference between the output video signal and the DC voltage VDC1 is superimposed on the DC voltage VDC1. The voltage / current conversion circuit 12 generates a charging / discharging current according to the potential difference between the potential of the output signal of the amplifier circuit 8 and the DC voltage VDC2 generated by the DC voltage source 18, and the keyed pulse signal 2 is generated.
Capacitance 1 via switch circuit 13 while 2 is HIGH
Output to 9. The voltage formed in the capacitor 19 is used as the amplitude control signal 6 of the variable gain amplifier circuit 3 in the amplitude control terminal 2
To control the gain of the variable gain amplifier circuit 3 so that the charging / discharging current for the capacitor 19 becomes zero.

Therefore, the sync signal tip potential of the output video signal obtained at the output terminal 4 is controlled to match the DC voltage VDC1 and the back porch potential with respect to the sync signal tip potential is controlled to have a desired potential difference.

In the video signal amplitude control circuit of the present application as described above, the synchronization of the input video signal of the voltage detection circuit 58 is performed by the method of detecting the sync signal tip end potential of the output video signal by the voltage detection circuit 21 and performing feedback control. The DC voltage offset between the signal tip potential and the DC voltage VDC1 can be minimized, and when amplifying the potential difference between the DC voltage VDC1 and the back porch potential, the resistors 10 and 1 are used by using the amplifier circuit 8.
By taking the ratio accuracy of 1, the operation of stabilizing the gain of the variable gain amplifying circuit 3 when the variation of the amplification gain is minimized and the charge / discharge current during the HIGH period of the keyed pulse signal 22 becomes zero. This makes it possible to eliminate the influence of variations in the pulse width of the keyed pulse signal 22.

That is, the amplitude of the output video signal is controlled by automatically controlling the back porch potential with respect to the sync signal tip potential of the output video signal of the variable gain amplifier circuit 3 with high accuracy and reproducibility. About amplifier circuit 8 Differential amplifier circuit 7
Although the circuit system of the two resistors 10 and 11 is shown, another amplifier circuit may be used as long as it is an amplifier circuit that operates as described above.

FIG. 7 is a block diagram showing another embodiment of the video signal amplitude control circuit according to the present invention. In this embodiment, in the video signal amplitude control circuit of FIG.
A voltage-current conversion circuit 56 is provided as a voltage detection circuit for limiting the amplitude of the video signal when the amplitude of the video signal output to the above exceeds a desired value.

The voltage-current conversion circuit 56 determines that the potential of the output video signal is the DC voltage V when the keyed pulse signal 22 is LOW.
When the potential of DC2 is exceeded, the voltage generated in the capacitor 19 generates a current that decreases the gain of the variable gain amplifier circuit 3, and outputs the current to the capacitor 19 via the switch circuit 57. That is, the voltage generated in the capacitor 19 is set to the amplitude control signal 6
Is supplied to the amplitude control terminal 2 to control the amplitude to a desired value and limit the amplitude so as not to exceed the desired value.

FIG. 8 is a block diagram showing still another embodiment of the video signal amplitude control circuit according to the present invention. In this embodiment, a video signal processing circuit 59 for performing band limiting processing and arithmetic processing is provided at the subsequent stage of the variable gain amplifying circuit 3, and the video signal processing circuit 59 for controlling the amplitude of the video signal output to the output terminal 4. Is provided with the voltage detection circuit 21 and the voltage detection circuit 58 shown in the second embodiment, and the variable gain amplifier circuit 3 is provided in the input section. That is, the DC voltage and the amplitude of the video signal input to the video signal processing circuit 59 can be variably controlled, the input dynamic range of the video signal processing circuit 59 can be secured, and the video signal processing circuit 59 can be secured.
It is possible to control the amplitude of the output video signal of 1 to a desired value.

FIG. 9 is a block diagram showing still another embodiment of the video signal amplitude control circuit according to the present invention. In this embodiment, a band limiting circuit 60 is provided at the input of the voltage detecting circuit 58 in order to control the amplitude of a video signal including a color signal in the video signal amplitude control circuit shown in FIG. That is, it is possible to prevent the detection deviation due to the subcarrier of the color signal when detecting the back porch potential of the video signal.

FIG. 10 is a block diagram of an embodiment of a video signal processing circuit for a magnetic recording / reproducing apparatus equipped with a video signal amplitude control circuit according to the present invention. At the time of recording, the conventional video signal amplitude control circuit 24 is used without adjustment in the input section, but is shown in FIG. 9 in which a band limiting circuit 60 for suppressing a color signal is provided between the switch circuit 33 and the amplifier circuit 34. The same video signal amplitude control circuit 62 as that of the embodiment is installed, and the amplitude variation is reduced by outputting to the monitor video signal output terminal 35 to obtain the video signal amplitude within a predetermined value.

Further, the video signal amplitude input to the emphasis circuit 38 is output by adding the variations in the gains of the conventional video signal amplitude control circuit 24 and the non-linear emphasis circuit 31, and is output to the input of the emphasis circuit. The same video signal amplitude control circuit 61 as that of the embodiment shown in FIG. 7 is installed to control the video signal amplitude.

On the other hand, during reproduction, the demodulation sensitivity of the FM demodulation circuit 45 and the gain variations of other functions up to the monitor video signal output terminal 35 are added and output.
The video signal amplitude control circuit 62 used during recording controls the amplitude of the video signal output. Therefore, the white / dark clip level at the time of recording and the amplitude of the video signal output to the monitor video signal output terminal 35 at the time of recording and reproduction can be automatically controlled with high precision and reproducibility.

In the vertical synchronizing signal period of the video signal, sag may occur depending on the CR time constant of the signal transmission system, and to prevent erroneous detection by the voltage detection circuit 58 of the video signal amplitude control circuit of the present application due to this. Then, the detection operation of the voltage detection circuit 58 is stopped within the above period. That is, erroneous detection can be prevented by holding the control voltage of the amplitude control signal during the vertical synchronizing signal period.

At the time of reproduction described in the embodiment shown in FIG. 10, in the video signal amplitude control circuit of the present application in the circuit system for demodulating the FM signal in which the video signal is modulated, an error occurs when the input FM signal is missing. In order to prevent the detection, the two voltage detection operations of the video signal amplitude control circuit are stopped by the signal indicating the loss of the FM signal. That is, erroneous detection can be prevented by holding each control signal voltage.

Although the present invention has been specifically described based on the embodiments, the invention of the present application is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the scope of the invention. .

[0037]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows. That is, according to the invention of claim 1,
The amplitude of the output video signal can be automatically controlled with high accuracy and reproducibility.

According to the second aspect of the invention, the amplitude of the output video signal can be automatically controlled with high accuracy and reproducibility, and the amplitude of the output video signal can be limited.

According to the invention of claim 3, the amplitude of the video signal subjected to the band limitation and the arithmetic processing can be automatically controlled with high precision and reproducibility.

According to the invention of claim 4, the amplitude of the video signal including the color signal can be automatically controlled with high accuracy and reproducibility.

According to the fifth and sixth aspects of the present invention, the amplitude of the output video signal of the video signal processing circuits arranged in parallel can be automatically controlled with high precision and reproducibility.

According to the invention of claim 7, it is possible to eliminate erroneous detection of the amplitude detection circuit which occurs during the vertical synchronizing signal period.

According to the invention of claim 8, in the video signal amplitude control circuit provided in the video signal processing circuit for the magnetic recording / reproducing apparatus, it is possible to eliminate erroneous detection due to the loss of the FM signal input during reproduction. .

With the above effects, adjustment of the signal amplitude by the variable resistance in the semiconductor integrated circuit device including the video signal amplitude control circuit in the VTR or the like becomes unnecessary, the component cost and the adjustment cost can be reduced, and the deterioration of the performance due to the change with time. Can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a video signal amplitude control circuit according to the present invention.

FIG. 2 is a schematic waveform diagram for explaining the circuit operation of FIGS. 1, 4 and 6.

FIG. 3 is a block diagram showing an example of a conventional video signal processing circuit for a magnetic recording / reproducing apparatus.

FIG. 4 is a block diagram showing an example of a conventional video signal amplitude control circuit.

FIG. 5 is a specific circuit diagram showing an example of a conventional clamp circuit.

FIG. 6 is a specific circuit diagram showing another example of a conventional clamp circuit.

FIG. 7 is a block diagram showing another embodiment of the video signal amplitude control circuit according to the present invention.

FIG. 8 is a block diagram showing still another embodiment of the video signal amplitude control circuit according to the present invention.

FIG. 9 is a block diagram showing still another embodiment of the video signal amplitude control circuit according to the present invention.

FIG. 10 is a block diagram showing an embodiment of a video signal processing circuit for a magnetic recording / reproducing apparatus including a video signal amplitude control circuit according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Amplitude control terminal, 3 ... Variable gain amplification circuit, 4 ... Output terminal, 5 ... DC voltage control terminal, 6 ... Amplitude control signal, 7 ... Differential amplification circuit, 8 ... Amplification circuit, 9 ... DC voltage control signal, 10, 11 ... Resistance, 12 ... Voltage / current conversion circuit, 13, 14 ... Switch circuit, 15 ... Voltage / current conversion circuit, 16 ... Capacitance, 17, 18 ... DC voltage source, 19 ... Capacitance, 20 ... Clamp pulse signal, 21 ... Voltage detection circuit,
22 ... Keyed pulse signal, 23 ... Variable resistance, 24 ... Video signal amplitude control circuit, 25 ... Amplitude detection circuit, 26 ... Variable resistance, 27 ... Recording video signal input terminal, 28 ... Variable gain amplification circuit, 29 ... Low pass filter , 30 ... Clamp circuit,
31 ... Linear linear emphasis circuit, 32 ... Variable gain amplification circuit, 33 ... Switch circuit, 34 ... Amplification circuit, 35 ... Monitor video signal output terminal, 36 ... FM signal output terminal, 37
... FM modulation circuit, 38 ... Emphasis circuit, 39 ... FM
Signal input terminal, 40 ... Noise canceller circuit, 41 ... Non-linear de-emphasis circuit, 42 ... Low-pass filter,
43 ... Variable resistance, 44 ... De-emphasis circuit, 45 ...
FM demodulation circuit, 47 ... Amplification circuit, 50 ... Switch circuit,
51 ... Voltage-current conversion circuit, 52 ... Capacitance, 53 ... Constant current source I1, 54 ... Amplitude control signal, 55 ... Amplitude control terminal, 56
... voltage / current conversion circuit, 57 ... switch circuit, 58 ... voltage detection circuit, 59 ... video signal processing circuit, 60 ... band limiting circuit, 61, 62 ... video signal amplitude control circuit, 63 ... DC voltage source, 64 ... transistor Q1 , 65 ... Capacitance, 66 ... Transistor Q2, 67 ... Transistor Q3.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nori Nakagawa 5-22-1 Kamimizuhoncho, Kodaira-shi, Tokyo Inside Hitachi Microcomputer System Co., Ltd. 22-22-1 Hitachi Microcomputer System Co., Ltd. (72) Inventor Katsumi Kaneshiro 52-12-1 Mizumizuhonmachi, Kodaira-shi, Tokyo Inside Hitachi Microcomputer System Co., Ltd.

Claims (8)

[Claims] 1. An output video signal by controlling an input video signal with a first control signal supplied from a first control terminal and a second control signal supplied from a second control terminal. A variable gain amplifier circuit that independently changes and outputs the DC voltage and amplitude of the output video signal, and a sync signal tip potential of the output video signal in a first period that specifies that the output video signal is within the sync signal period. A first voltage detection circuit including a first voltage-current conversion circuit that outputs a charging / discharging current to a first capacity according to a potential difference from the first DC voltage, the output video signal and the first DC voltage An amplifier circuit for amplifying a potential difference between the first DC voltage and the first DC voltage, and an output signal of the amplifier circuit and a first DC voltage in a second period that specifies that the output video signal is within the back porch period. With the second DC voltage based on A second voltage detection circuit including a second voltage-current conversion circuit that outputs a charging / discharging current to the second capacity in accordance with a difference, and a first voltage signal generated in the first capacity. Is supplied to the first control terminal as the control signal of
Further, by supplying the voltage signal generated in the second capacitor as the second control signal to the second control terminal, the synchronizing signal tip end potential of the output video signal is made to coincide with the first DC voltage and the synchronizing signal tip end. A video signal amplitude control circuit for controlling the back porch potential with respect to the potential so as to have a desired potential difference. 2. The second voltage detection circuit according to claim 1, further comprising a third voltage-current conversion circuit connected to the same load as the second voltage-current conversion circuit, the third voltage-current conversion circuit. Receives the output video signal of the variable gain amplifier circuit and the second DC voltage and outputs the gain as the second control signal according to the potential difference when the potential of the output video signal exceeds the second DC voltage except during the second period. A video signal amplitude control circuit for limiting the amplitude of the output video signal by outputting a current in the direction of generating a small voltage to the second capacitor. 3. A video signal, characterized in that the video signal output from the variable gain amplifier circuit according to claim 1 or 2 is input to the first and second voltage detection circuits after being subjected to band limiting processing and arithmetic processing. Signal amplitude control circuit. 4. The method according to claim 1, 2 or 3, wherein the input signal is a video signal including a color signal, and a band limiting circuit for suppressing the color signal is provided in a stage before the second voltage detection circuit. Characteristic video signal amplitude control circuit. 5. A circuit for supplying an input video signal to a plurality of different video signal processing circuits arranged in parallel, wherein each of the output terminals subjected to the video signal processing is provided in each of the output terminals. A video signal amplitude control circuit, characterized in that any one of the video signal amplitude control circuits is provided. 6. The video according to claim 5, wherein the video signal inputted to a video signal processing circuit arranged in parallel is amplitude-controlled by a video signal amplitude control circuit independent of the video signal amplitude control circuit. Signal amplitude control circuit. 7. A video signal according to any one of claims 1, 2, 3, 4, 5, and 6, wherein the operation of the second voltage detection circuit is stopped within the vertical synchronization period of the input video signal. Amplitude control circuit. 8. The method of claim 1, 2, 3, 4, in the process of demodulating and processing an FM signal modulated with a video signal.
The video signal amplitude control circuit according to any one of 5, 6, and 7 is provided, and the operation of the first and second voltage detection circuits is stopped by a signal that means a loss of the FM signal input during demodulation. Video signal amplitude control circuit.