JPH0346871A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To preclude overdeviation at the time of modulation due to the increase in the amplitude of a color difference signal which is caused by an irregular signal by providing an amplitude limiting circuit on the pre-stage of a modulating circuit. CONSTITUTION:As the pre-stage of 1st and 2nd FM-modulating circuits 35 and 36, 1st and 2nd amplitude limiting circuits 38 and 39 are provided. Amplitude limiting operation is performed based upon the horizontal fly-back line section level of an output R-Y signal G, so similar amplitude limiting operation is performed as to an R-Y signal which has only a level higher than the horizontal fly-back line section or an R-Y signal having only a lower level. Consequently, the amplitude limiting operation is performed without distorting the waveform to preclude the overdeviation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a video signal processing circuit used when recording video fIA signals as components.

2. Description of the Related Art The conventional video signal processing circuit described above will be explained based on the configuration diagram of FIG.

The NTSC signal A input to the video signal processing circuit is Y,
The /C separation circuit 37 separates the modulated color difference signal 8 and the luminance signal F, and the seismic intensity signal F passes through the AGC circuit 34 which performs amplitude control by capturing changes in the amplitude of the synchronizing signal.
The FM modulation circuit 37 performs FM modulation. Further, the modulated color difference signal B passes through an ACC circuit 32 that performs amplitude control by capturing changes in the amplitude of the burst signal, and is further processed by a color difference signal demodulation circuit 33 to convert the R-Y signal to the B signal.
The color difference signals are demodulated into Y@signal E, and E is the first
and FM modulated by second FM modulation circuits 35 and 36.

These FMWl-toned I! The 11 degree signal and the two color difference signals are recorded by independent recording heads, or by performing frequency multiplexing by setting appropriate frequency allocation, and recorded by one recording head.

In addition, although Fig. 3 shows the case where the color difference signal and E are independently FM modulated, the color difference signal is line-sequentially
It may also be M-modulated.

Problems to be Solved by the Invention In the conventional configuration shown in FIG. 3, regarding the luminance signal F,
Since an AGC circuit 34 is provided that performs amplitude control by capturing changes in the amplitude of the synchronization signal, even if the input NTSC signal A signal width fluctuates, the frequency deviation when performing FM modulation in the third FM modulation circuit 37 will be reduced. There is no problem because the maximum value of is kept constant. However, if the ratio of the burst signal amplitude of the modulated color difference signal B is lower than the specified value to the signal amplitude, the ACC
Due to the operation of the circuit 32, the amplitude of the output signal C increases, and the amplitude of the R-Y signal and the 8Y@signal E, which are the outputs of the color difference signal demodulation circuit 33, also increases.
It will be sent to M modulation circuits 35 and 36.

1st and 2nd FM! The setting of the frequency deviation by the so-called circuits 35 and 36 is based on the R-Y signal level and the 8-Y signal level that are determined by the color difference signal W tone circuit 33 when the ratio of the burst signal amplitude and the signal amplitude of the modulated color difference signal 8 is normal. Since this is performed on the signal amplitude of the signal pressure, in the case of an irregular signal where the ratio of the burst signal amplitude of the modulated color difference signal B described above is lower than the specified signal amplitude, the preset frequency deviation range (hereinafter referred to as overdeviation), which causes phenomena such as J3 distortion during playback.

Furthermore, when FM modulating the color difference signal E, the level of the horizontal blanking interval is generally fixed, so even if the amplitude of the color difference signal that has only a level higher or lower than the level of the horizontal blanking interval increases, The six defenses that had the problem of overdeviation causing blurring during playback are intended to solve the above problem, and provide a video signal processing circuit that does not cause overdeviation even with irregular signals. The purpose is to

Means for Solving the Problems In order to solve the above problems, the video signal processing circuit of the present invention comprises:
A voltage control amplification circuit that amplifies the color difference signal according to a control input signal, as a preceding stage of a modulation circuit that modulates the color difference signal separated from the video signal and demodulated;
Horizontal I of the color difference signal output from the Jtllll amplifier circuit
R1! ! a clamp circuit that holds the section at a constant voltage; an amplitude detection circuit that detects the amplitude #A of the color difference signal output from the clamp circuit with reference to the clamp level of the clamp circuit; and an output signal level of the amplitude detection circuit; a comparison circuit that compares predetermined levels and outputs a melodic control input signal to the voltage control amplifier circuit according to the level difference;
Said voltage control l11111@! An amplitude limiting circuit is provided for outputting the color difference signal amplified by the circuit to the modulation circuit.

Effect: With the above configuration, the clamp circuit holds the horizontal retrace section of the color difference signal output from the voltage-controlled S amplifier circuit at a constant voltage, and the amplitude detection circuit detects the amplitude of the color difference signal using the clamp level of the clamp circuit as a reference. The comparator circuit then outputs a control input signal to the voltage control amplifier circuit according to the increase/decrease of this amplitude amount to control the gain 1a of the voltage control amplifier circuit. Therefore,
When the amplitude of the color difference signal exceeds a certain level, the output amplitude of the color difference signal is suppressed by the amplitude limiting circuit.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. It should be noted that the same components as those of the conventional example shown in FIG.

FIG. 1 is a block diagram of a video signal processing circuit showing an embodiment of the present invention.

The video signal processing circuit of the present invention operates as a preceding stage of the first and second FM modulation circuits 35 and 36, respectively, to generate the first and second vibration @I! 117 limit circuits 38 and 39 are provided.

The first amplitude limiting circuit 38 will be explained based on the configuration diagram of FIG. Note that the configuration of the second amplitude limiting circuit 39 is the same as that of the first amplitude limiting circuit 38, and a description thereof will be omitted.

The R-Y signal input to the first amplitude limiting circuit 38 is
Amplified by the voltage control amplifier circuit 1, its output R-Y signal G
is the first FM! g! ! 1 circuit 35 and input to the clamp circuit 2 , where the horizontal retrace section of the output RY signal G is clamped to the clamp level set by the clamp level setting circuit 3 .

In addition, the output signal @H of the clamp circuit 2 is
is input to the peak hold circuit 4.5, the first peak hold circuit 4 holds the peak at a level higher than the clamp level, and the second peak hold circuit 5 holds the peak at a level higher than the clamp level.
Peaks at a level lower than the clamp level are held.

Further, the first and second differential amplifiers 6.7 have equal gains, and the first differential amplifier 6 adjusts the voltage of the output signal J of the first peak hold circuit 4 to the clamp level. The second differential amplifier 7 inverts and amplifies the voltage of the output signal of the second peak hold circuit 5 with respect to the clamp level. Furthermore, the outputs of the first and second differential amplifiers 6.7 are connected via a diode 8.9 at a connection point P, and the connection point P is connected to a comparator 11.
is input to the negative input of Therefore, the diode 8.9 allows the first and second differential amplifier 6.7
The output signal of M, which has a larger voltage, is input to the negative input of the comparator 11. That is, the clamp level, that is, the horizontal retrace level of the output R-Y signal G, is The amplitude of the output RY signal G is detected with reference to .

On the other hand, the positive input of the comparator 11 is connected to the operating point setting circuit 1.
A voltage set by 0 is input, and its output signal N is input to the control input of the gain control circuit of the voltage control amplifier circuit 1. Therefore, voltage controlled amplifier circuit 1
The gain of the voltage control amplifier circuit 1 can be automatically changed by increasing or decreasing the amplitude of the output R- and the Y signal G based on the horizontal retrace interval level, and the set voltage of the operating point setting circuit 19 can be adjusted appropriately. If you keep it set at a certain level, the voltage #J1
11 The gain remains constant until the amplitude of the output R-Y signal G of the amplifier circuit 1 reaches a certain level with reference to the horizontal retrace interval level, and it is possible to change the gain after exceeding that level. Therefore, even if a RY signal having an excessively large amplitude is input, the output RY signal G has a constant amplitude, making it possible to realize a vibration mHJ limit operation.

In addition, since the swing 41i [limiting operation is performed based on the horizontal retrace section level of the output R-Y signal @G, the R-Y signal has only a level higher than the horizontal retrace section level, or the R-Y signal has only a lower level. A similar amplitude limiting circuit can be implemented for the Y signal as well.

In this embodiment, the case where the color difference signals and E are independently FM modulated has been described, but the color difference signals and E are independently FM modulated.
This is also effective when FM modulating the line-sequential data.

In addition, the amplitude limiting circuits 38 and 39 in this embodiment are different from so-called limiters that use nonlinear elements such as diodes, so they limit the width without causing waveform distortion to prevent overdeviation. be able to.

Effects of the Invention As described above, according to the present invention, by providing an amplitude limiting circuit before the modulation circuit, it is possible to suppress the amplitude of the color difference signal input to the modulation circuit when the amplitude exceeds a certain level. This makes it possible to prevent overdeviation during modulation caused by an increase in the amplitude of the color difference signal due to an irregular signal.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a video signal processing circuit showing an embodiment of the present invention, Fig. 2 is a block diagram of an amplitude limiting circuit which is a main component of the video signal processing circuit, and Fig. 3 is a block diagram of a conventional video signal processing circuit. FIG. 2 is a configuration diagram of a signal processing circuit. 1... Voltage control amplifier circuit, 2... Clamp circuit, 3
...Clamp level setting circuit, 4.5...Peak hold circuit, 6.7...Differential amplifier circuit, 8,9...
Diode, 10... Operating point setting circuit, 11... Comparison circuit, 35, 38... FM modulation circuit, 38.39.
...Amplitude limiting circuit, A...NTSC signal (video signal)
, D...RY signal, E...B-Y signal, G...
Output RY signal.

Claims (1)

[Claims] 1. As a pre-stage of a modulation circuit that modulates a color difference signal separated from a video signal and demodulated, a voltage control amplifier circuit that amplifies the color difference signal according to a control input signal, and a color difference output from the voltage control amplifier circuit. a clamp circuit that holds a horizontal blanking section of the signal at a constant voltage; an amplitude detection circuit that detects the amplitude of the color difference signal output from the clamp circuit with reference to the clamp level of the clamp circuit; and an output of the amplitude detection circuit. a comparison circuit that compares a signal level with a predetermined level and outputs the control input signal to the voltage control amplifier circuit according to the level difference, and outputs the color difference signal amplified by the voltage control amplifier circuit to the modulation circuit. A video signal processing circuit equipped with an amplitude limiting circuit.