JPS62171288A - Recording picture quality compensation circuit for video tape recorder - Google Patents

Abstract

PURPOSE:To prevent the extreme deterioration in the S/N of a reproduced picture even when the electric field strength is low by changing the compensation quantity of a low amplitude high frequency component of a recording luminance signal in response to the electric field strength of a broadcast radio wave. CONSTITUTION:Only a high frequency component whose low frequency band is cut off is extracted from a recording luminance signal 300 separated by a luminance/ chrominance signal separator circuit 15 by a high pass filter 21, amplified by an amplifier circuit 22 and the low amplitude component 800 of a prescribed level or below in the high frequency component of the recorded luminance signal is extracted by an amplitude limit circuit 23, the result is attenuated by a variable attenuation circuit 24 to form a low amplitude high signal component 900, which is inputted to an adder circuit 25, a correction recording luminance signal 400 adding the component 900 to the signal 300 is outputted from the adder circuit 25. In this case, detection signal 600 obtained from the detection signal from an AGC detection circuit 17 through the DC amplification by an AGC amplifier circuit 20 is inputted to the variable attenuation circuit 24 and when the amplitude of the detection signal 600 is lowered, the attenuation of the circuit 24 is controlled to be larger.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a video tape recorder recording quality compensation circuit suitable for being installed in a video tape recorder (VTR) equipped with a television broadcast signal receiving circuit.

J Invention's technical blueprint and its problems] In home high-density recording VTRs, etc., after separating a composite video signal into a luminance signal and a chrominance signal, the luminance signal is first emphasized and then converted to a low carrier FM signal. converted into a signal. On the other hand, the chrominance signal is 700KH, which is lower than the FM band of the luminance signal.
After the signal is converted into a low frequency converted color signal having a frequency around 2, the signal is recorded on a tape while being superimposed on the low carrier FM signal of the luminance signal. Among these, regarding the recording of luminance signals, the recording bandwidth and track width are narrower than that of broadcasting VTRs that use direct color processing, etc.
There is a problem that a sufficient S/N ratio cannot be obtained. Conventionally, in order to deal with this problem, a reproduction image quality compensation circuit as shown in FIG. 6 has been used during reproduction. The input reproduced luminance signal 100 has its low frequency components cut by a high-pass filter 1, is amplified by an amplifier 2, and then amplitude-limited by an amplitude limiting circuit 3, resulting in a visually noticeable high frequency component. Only component noise is extracted. The level of this high frequency component noise is attenuated by the attenuation circuit 4 and input to the subtraction circuit 5 . Further, the reproduced luminance signal 100 is directly input to this subtraction circuit 5, and the reproduced luminance signal @2 is obtained by subtracting the high frequency component noise from the reproduced luminance signal 100.
00 is output from this subtraction circuit 5. Since this reproduced luminance signal 200 has high frequency component noise removed, the noise is reduced, but the low amplitude high frequency component signal, which is essentially indistinguishable from noise, also disappears at the same time. This has the disadvantage that the reproducibility of fine pattern parts is impaired.

Therefore, in order to avoid this drawback, a circuit as shown in FIG. 7 is used which compensates the recorded luminance signal during recording. The recorded luminance signal @300 has low frequency components cut by a high-pass filter 1, amplified by an amplifier circuit 2, and then limited by an amplitude 1+11 limiter circuit 3 to produce high-frequency components below a certain level. Only frequency signal components are extracted. After this is attenuated to an appropriate level by the attenuation circuit 4, it is input to the addition circuit 6. The recording luminance signal 300 is directly input to this adder circuit 6 and added to the above-mentioned high frequency component, and the resulting corrected recording portion i degree signal 400 is output from this adder circuit 6. In this case, since the high frequency components that are lost during reproduction can be emphasized during recording, deterioration in the definition of image quality can be prevented even when the circuit shown in FIG. 6 is used during reproduction.

Note that the correction ♀ of the recording image quality compensation circuit shown in FIG. 7 can be changed as shown in FIG. 8 by changing the attenuation mother of the attenuation circuit 4.

In this case, for a small amplitude signal, the amount of compensation is large as shown in FIG. 8A, and for a large amplitude signal, the amount of compensation is zero as shown in FIG. 8A.

By the way, the recording compensation circuit shown in FIG. 7 certainly exhibits its effect when the S/N of the recording luminance signal 300 is sufficient. However, if the S/N of the recording luminance signal becomes poor, as shown in the circuit diagram shown in Figure 7, h
This has the drawback that the O arithmetic circuit 6 adds 1 part of the noise, and when this is recorded and reproduced, the S/N of the reproduced luminance signal decreases, resulting in extreme deterioration of image quality. Ta.

Such a situation becomes noticeable when a home VTR or the like having a receiving circuit for television broadcast waves receives broadcast waves in various environments, particularly radio waves in a medium-weak electric field, and performs recording and reproduction.

[Object of the Invention] In view of the above-mentioned drawbacks, the object of the present invention is to provide a video tape recorder that prevents extreme S/N deterioration of the screen that records and reproduces broadcast waves even when the electric field strength of broadcast waves is at a low level. The purpose of this invention is to provide a recording image quality compensation circuit.

``Summary of the Invention 1 The present invention is capable of changing the amount of compensation for low-amplitude high-frequency components of a recorded luminance signal according to the electric field strength of broadcast radio waves, so that even when the electric field strength is low, extreme S /
This achieves the purpose of preventing a drop in N.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing one implementation of a recording quality compensation circuit for a video tape recorder according to the present invention. 11 is a tuner that selects a predetermined frequency from the television broadcast QIOOO and converts it into an intermediate frequency signal; 12 is an intermediate frequency amplification circuit that amplifies the intermediate frequency signal; and 13 is an intermediate frequency amplified signal that is input. Composite video signal (video signal)
14 is a video amplification circuit that amplifies the composite video signal; 15 is a luminance and chrominance signal separation circuit that separates the luminance signal and chrominance signal from the composite video signal; 16 is a noise remover that removes noise from the input video signal. 17 is an automatic gain control detection circuit (AGC detection circuit) that detects the amplitude level of the input video signal; 18 is an AGC amplifier circuit that DC amplifies the detection signal output from the AGC detection circuit 17; is supplied to the intermediate frequency amplification circuit 12 and outputted to the tuner AGC amplification circuit 19. 19 DC amplifies the detection signal provided from the AGC amplifier circuit 18 and provides an output signal T100 to the tuner 11. Reference numeral 20 denotes an AGC amplification circuit that DC amplifies the detection signal output from the AGC detection circuit 17, and outputs its output signal 600 to the variable attenuation circuit 24. 21 is a high-pass filter that cuts low frequency components and extracts high frequency components from the input recording luminance signal 300; 22 amplifies the high frequency components and outputs them to the amplitude limiting circuit 23; an amplifier circuit; 23 is an amplitude 111 limiting circuit that limits the amplitude of the input signal to extract low amplitude components; 24 is an AGC amplifier circuit 20;
A variable attenuation circuit 25 changes the amount of attenuation according to the AGC detection signal 600 supplied from the variable attenuation circuit 24.
This is an adding circuit that adds the low amplitude high frequency component and the recording luminance signal component inputted from the controller 1 and outputs the normal recording luminance signal 400.

FIG. 2 is a circuit diagram showing an example of the variable attenuation circuit shown in FIG. 1. The emitters of NPN transistors 241 and 242 are commonly connected via emitter resistors 243 and 244 to form a differential amplifier circuit.

A common connection point of the emitter resistors 243 and 244 is grounded via the collector and emitter of a transistor 245 and the emitter resistor 246 of this transistor 245. The low amplitude high frequency component 800 of the recording luminance signal output from the amplitude limiting circuit 23 is directly input to the base of the transistor 241, and the resistor 2, ! 17.248 to the base of transistor 242. Furthermore, a collector resistor 249 is connected to the collector of transistor 2/11.
A voltage source Vcc is applied through the collector, and an output signal is taken out from the collector. In addition, the resistors 247 and 2
A reference voltage from a reference voltage source 250 is applied to the connection point 48.

Figure 3 shows the electric field strength of broadcast radio waves and the above AGC detection circuit 17.
This shows the output relationship of the AGC detection circuit 17 as the electric field strength decreases, that is, the recording luminance signal @
300 indicates a decrease in one-breadth level.

Next, the operation of this embodiment will be explained. The tuner 11 selects a predetermined broadcasting station signal from the high frequency signal 1000 inputted from the antenna, converts it into an intermediate frequency signal, and outputs it to the intermediate frequency amplification circuit 12. The intermediate frequency signal amplified by the intermediate frequency amplification circuit 12 is sent to the video detection circuit 13.
The image is detected at . After the composite video signal output from the video detection circuit 13 is amplified by the video amplification circuit 14,
The signal is input to a luminance and color signal separation circuit 15 and a noise removal circuit 16. The luminance and chrominance signal separation circuit 15 separates a recorded luminance signal 300 and a recorded chrominance signal @ 700 from the input composite video signal.
The recording color signal 700 is output to the next stage (not shown).

On the other hand, the composite video signal from which noise has been removed by the noise removal circuit 16 is subjected to AGC detection by the AGC detection circuit 17, and after the detected signal is amplified by the AGC amplifier circuit 18,
The ΔGG detection output 500 is inputted to the intermediate frequency amplification circuit 12. Further, the AGO detection signal amplified by the AGC amplifier circuit 18 is amplified by the tuner AGC amplifier circuit 19 to become a detection signal 1100, which is input to the tuner 11. However, as shown in Figure 3, the AGC double wave signal of the rAGc detection circuit 17 increases in proportion to the electric field strength of the broadcast radio wave, so the tuner 11 detects the input detection signal 1100
When the level of 00 decreases, control is performed to increase the amplification factor of the first stage. At the same time, the intermediate frequency amplification circuit 12
performs control to increase the amplification factor when the level of the input detected signal @500 decreases. Therefore, juna 1
1 and the intermediate frequency amplification circuit 12, the level of the composite video signal output from the video amplification circuit 14 changes slowly with respect to increases and decreases in the electric field strength of broadcast radio waves.

On the other hand, the recording luminance signal 300 separated by the luminance and color signal separation signal 15 has its low frequency band cut by the high-pass filter 21 to extract only the high frequency component. The signal is amplified by the amplifier circuit 22 and input to the amplitude limiting circuit 23 . The amplitude limiting circuit 23 extracts a low amplitude component 800 below a certain level from among the high frequency components of the recording luminance signal, and this is extracted by the variable attenuation circuit 2.
4, the signal is attenuated into a low-amplitude high-frequency signal component 900, which is input to the adder circuit 25. Since the recording luminance signal 300 is directly input to this adding circuit 25, a corrected recording luminance signal 400 obtained by adding the low amplitude high frequency signal component 900 to this recording luminance signal 300 is output from this tightening circuit 25. . At this time, the variable attenuation circuit 24 receives either the detection signal from the AGC rectification circuit 17 or the detection signal 600 that is DC amplified by the AGC amplifier circuit 20, and when the amplitude of this detection signal 600 decreases, the variable attenuation circuit 2
Control is performed to increase the amount of attenuation in step 4.

The operation of the variable attenuation circuit 24 will now be explained with reference to FIG. The low amplitude high frequency component 800 of the recording luminance signal outputted from the amplitude limiting circuit 23 is the 1-transistor 2
41.242 and its output signal 900
is taken out from the collector of transistor 241. At this time, the common emitter current of the transistors 241 and 242 is converted into a wave signal q600 given from the AGC amplifier circuit 20.
a transistor 24 whose collector current is controlled by
5, the level of the output signal 900 is changed.

According to this embodiment, the electric field strength of broadcast radio waves is reduced,
When the amplitude level of the composite video signal output from the video amplification circuit 14 becomes low, the amplitude level of the recording luminance signal 300 becomes low. However, at this time, the amount of attenuation of the variable attenuation circuit 24 is increased, and the recording luminance signal 300 is
Low amplitude high frequency component 900 of the recording luminance signal to be added to
The quantity to reduce the amount of is set to zero. For this reason, the electric field strength of the broadcast radio waves decreases, and the S/N of the recording luminance signal 300 decreases.
When the recording brightness signal 300 has a low amplitude and high frequency component, the compensation port for the low amplitude high frequency component is reduced or made zero, even when recording and reproducing by receiving broadcast radio waves with a medium-weak electric field.
A significant drop in S/N of reproduced images can be prevented.

FIG. 4 is a block diagram showing the main parts of another embodiment of the present invention. In this example, the denoised composite video signal 1
The detected voltage of the AGC detection circuit 17 that detects the amplitude level of 200 is input to the voltage comparison circuit 26, where it is compared with the reference voltage vr. That is, in the voltage comparison circuit 26, when the voltage level of the input detection voltage becomes lower than the reference voltage vr, the control voltage J output to the variable attenuation circuit 24:
Let E1300 be a low level. As a result, the attenuation interval of the variable attenuation circuit 24 increases, so that the low amplitude high frequency component of the recording luminance signal added to the recording luminance signal 300 in the adding circuit 25 is reduced or set to zero. Similarly, when the electric field strength of broadcast radio waves becomes low, it is possible to prevent the S/N of recorded and reproduced images from drastically decreasing.

FIG. 5 (This is a block diagram showing the main part of still another embodiment of the present invention. A composite video signal 120 from which noise has been removed.
0 is input to the AGC detection circuit 17, where it is converted into an AG (J wave), and the detected voltage is input to the GG amplification circuit 20. This AGC amplification circuit 20 amplifies this detection voltage,
variable attenuation circuit 24 and variable high-pass filter 2, respectively
7 and a variable level amplitude limiting circuit 28. In this example, the variable high-pass filter 27 changes its characteristics depending on the AGC detection voltage supplied from the AGC amplifier circuit 20, and the variable level amplitude limiting circuit 28 changes the amplitude limiting level. The attenuation circuit 24 changes its attenuation amount. Therefore, the variable high-pass filter 27, the variable level amplitude limiting circuit 28, and the variable attenuation circuit 24 are controlled to have optimal characteristics according to the electric field strength of the broadcast radio wave, and the recording brightness is controlled by the adding circuit 25. signal 30
By optimizing the low-amplitude high-frequency component added to 0 for the electric field strength at that time, the S/
It is possible to prevent a decrease in N.

[Effects of the Invention] As described above, according to the recording quality compensation circuit of the videotape recorder of the present invention, the compensation ♀ of the low amplitude high frequency component of the recording 'R degree multiplied signal is changed in accordance with the electric field strength of the broadcast radio wave. Thereby, even when the electric field strength is low, it is possible to prevent the S/N of the recording/reproducing screen from being extremely reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the recording quality compensation circuit for a video tape recorder according to the present invention, FIG. 2 is a circuit diagram showing a detailed example of the variable attenuation circuit shown in FIG. 1, and FIG. is a diagram showing an example of the characteristics of the AGC detection circuit shown in FIG. 1, FIG. 4 is a block diagram showing another embodiment of the invention, and FIG. 5 is a diagram showing still another embodiment of the invention. 6 is a block diagram showing an example of a conventional video tape recorder playback image quality compensation circuit, FIG. 7 is a block diagram showing an example of a conventional recording image quality compensation circuit, and FIG. 8 is a block diagram showing an example of a conventional recording image quality compensation circuit. FIG. 3 is a diagram showing the change characteristics of compensation (♀) by the attenuation circuit shown in the figure. 11...Tuner 12...Intermediate frequency amplification circuit 13...Video detection circuit 15...Brightness, color signal separation circuit 17...△GC detection circuit 20...AGC amplification circuit 21...High Band-pass filter 23... Amplitude limiting circuit 24... Variable attenuation circuit 25
... Sleeping circuit 26 ... Voltage comparison circuit 27 ...
・Variable high-pass filter 28...Variable level amplitude limiting circuit Representative Patent attorney Nori Chika Yudo Hiroshi Uji Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] A recording quality compensation circuit of a video tape recorder that extracts a low-amplitude high-frequency component from a recorded luminance signal and adds the extracted low-amplitude high-frequency component to the recorded luminance signal detects the electric field strength of the received broadcast radio wave. A recording quality compensation circuit for a video tape recorder, comprising: a detection circuit; and a compensation amount variable circuit that changes the level of a low amplitude high frequency component to be added to the recording luminance signal according to the electric field strength.