JPH03232393A - Reproducing video signal processing circuit - Google Patents

Abstract

PURPOSE:To improve an S/N by providing a luminance signal processing circuit composed of a level-down circuit for lowering the level of a separated luminance signal and a noise cancel circuit for canceling a noise component, and a chrominance signal processing circuit adding a burst level varying circuit to vary the burst level of the separated chrominance signal. CONSTITUTION:Since a noise cancel circuit 26 is arranged in the rear step of a level-down circuit 23, the noise cancel amount can be relatively leveled up by 20% by inputting the 20% level-down luminance signal. A chrominance signal C is divided and leveled down by a burst level varying circuit 31 with a ratio between resistors R4 and R5, and on the other hand, a burst gate pulse P to be obtained through a synchronizing separator circuit 29 and a burst gate pulse generating circuit 30 is inverted by an inverter 32 and it is controlled that a switch SW4 can be opened for the pulse generating period through a switch SW2.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (a) Field of Industrial Application The present invention relates to a reproduced video signal processing circuit for a video tape recorder.

(b) Conventional technology market i: Rental video tapes on the market are often played repeatedly many times, and when these soft tapes are played back, they sometimes feel noisy. As a countermeasure against this problem, some videotape recorders are equipped with a switch called a so-called rental position on the node side. For example, the June 1989 issue of the monthly magazine Radio Technology (pages 177 to 178) or the published publication JP-A-64
-69194 (HO4N9/83).

Figure 4 shows the circuit block diagram. In the figure, when the rental position is selected, the luminance signal is transmitted through the IH delay element (1), adder (2) (5'), filter (3),
After passing through the luminance signal comb filter circuit (6) for removing vertical noise consisting of a limiter (4), a bypass filter (7), a limiter (8), a low-pass filter (9), and A reproduced luminance signal output from which minute level noise has been removed is obtained through a horizontal noise canceller circuit (10) composed of an adder. Note that (15) is the bypass filter (11) and limiter (11) for normal playback.
12) and low-pass filter (13) and addition!
(14) This is a horizontal noise canceller circuit configured as shown in FIG.

(c) Problems to be Solved by the Invention The luminance signal processing circuit according to the above-mentioned prior art produces noise that appears to have increased due to the decrease in output during tape playback when the tape has been repeatedly played back and the playback output has decreased. By increasing the noise cancellation amount of the component, the relative signal-to-noise ratio (S/
N), and the corresponding circuit configuration is not necessary if the soft tape is of good quality. Moreover, since the method mainly reduces the high-frequency noise component of the luminance signal output and does not take any measures for the color signal output, 1, the image effect received from the entire screen is hardly felt.

Generally, cathode ray tubes in television receivers are designed to be used in bright places, and the brightness level is set high to reduce the influence of external light. When playing back a soft tape, the brightness level of the reproduced video signal is lowered to match the surrounding brightness, resulting in a white screen, but the chroma level is relatively emphasized, resulting in an unnatural screen. Therefore, it is necessary to lower the chroma level at the same time, but if you simply lower it, the ACC (auto chroma)
There is a problem that the control circuit returns to the original level.

(d) Means for Solving the Problems In the present invention, after a reproduced video signal is separated into a luminance signal and a color signal, the luminance signal is reduced to a level near the tuning frequency (approximately 1.5 MHz) using a level down circuit equipped with a tank circuit. A moderate luminance signal is obtained by passing the luminance signal with a frequency characteristic whose peak value is lowered by a certain amount through a noise canceling circuit, and for the color signal, the chroma level other than the burst signal period is lowered by a predetermined amount by resistor division. Sir-t 6/
A color signal with a high burst-to-chroma signal ratio is output through the <-st level variable circuit.

(e) Effect With the above-described configuration, if, for example, a rental soft tape on the market is played back and the playback screen of the soft tape is a noisy screen, switching to the above-mentioned circuit by external operation will convert the played video signal into a luminance signal. After separating the chrominance signal and the chrominance signal, the luminance signal has high-frequency noise removed and the level of the frequency characteristic having a peak around 1.5 MHz is lowered, and the chrominance signal has the chroma level other than the burst signal lowered by a predetermined amount. A color signal with a relatively large burst signal output is obtained, and a reproduced screen with noise removed is obtained.

(f) Examples Specific examples of the present invention will be described below. FIG. 1 is a block diagram of the present invention, FIG. 2 is a frequency characteristic diagram of the luminance signal output, and FIG. 3 is a noise canceling characteristic diagram of the luminance signal output.

In FIG. 1, (21) is a reproduced video signal amplifier, (2
2) is a luminance signal processing unit that extracts a luminance signal from the reproduced video signal, and (23) is a tuning circuit (2) consisting of resistors R2, R1, and L, C, , R elements tuned at 1.5 MHz.
(4) is a level down circuit that attenuates the luminance signal output by resistor division; (26) is a noise canceling circuit that removes noise components; (28) is a color signal processing unit that extracts color signals from the reproduced video signal; 29) is a sync separation circuit that separates a horizontal sync signal from the separated luminance signal;
30) is a burst gate pulse generation circuit for creating a burst extraction pulse from the separated synchronization signal, and (31) is a resistor R4, R3 and an analog switch (
S W + ) and an inverter (32).
), the level of the color signal is lowered by dividing the color signal between resistors R1 and R6. The signal is a switch (SW)
, ) via the analog switch <S W , >
Since it is opened, the chroma level down circuit becomes inactive only during the burst signal period, and the burst signal passes through as the original signal. Therefore, the burst signal increases relative to the chroma level. That is, the level ratio of the burst signal to the chroma signal increases. , (35) is an adder circuit, (37) is an audio signal amplification circuit, (38) is an audio signal processing circuit, and (39) is a low frequency enhancement circuit equipped with a differential amplifier (40).

In addition, (25), (27), (33), (34), (36
), (41) are signal amplification circuits, (42) are external operation switches (43), (44), (45), and (46) are output terminals, (47) and (48) are magnetic heads, and T is a tape. shows. Next, the present invention will be explained in detail.

In the figure, in the normal case, the tape (T) is reproduced and the signal obtained from the magnetic head (47) is transmitted to the video signal amplification circuit (2).
After amplification in step 1), the brightness signal processing unit (22) converts the brightness signal (
Y) is separated into an output terminal (43) via an amplifier circuit (25), a noise canceling circuit (26), and an amplifier circuit (27).
), the reproduced luminance signal is output. Color signal processing section (28)
The color signal (C) separated and processed by the amplifiers (33) (34)
), the color signal is output to the output terminal (44). A composite video signal obtained by adding a luminance signal and a color signal by an adder (35) is output to an output terminal (45).

On the other hand, the audio signal (S) reproduced by the magnetic head (48)
is the output terminal (
46), the audio signal is output.

Now play the tape (T) and press the external operation switch (42).
When operated, each switch sw, sw, , SW4 is closed (ON), and switch SW is switched to 1] contact. 5 Therefore, the brightness signal (Y) is 1/bell-down circuit
As shown in Figure 2, 1.5NiH
The frequency characteristic (50) has a tuning point at z, and the level is about 2 dB lower than the frequency characteristic (49) of normal reproduction. Around 1.5 MHz, the level is down to about ldb, so overall it is 1.5 MHz.
The frequency characteristics around z are increased by about ldb. A noise canceling circuit (
26), by inputting luminance whose level has been reduced by 20% to a noise canceling circuit having a constant noise canceling amount, the noise canceling amount can be relatively increased by 20%. FIG. 3 shows the input versus output of the noise canceling circuit (26) of the luminance signal during reproduction, and (51) is during normal reproduction, that is, when the switch (SW, ) is open (off).
(52) shows the case where the switch (SWl) is closed (ON). (2) 1 is the luminance signal level down amount.

In addition, the color signal (C) is transmitted through a burst level variable circuit (31).
On the other hand, the burst gate pulse (P) obtained via the synchronization separation circuit (29) and the burst gate pulse generation circuit (30) is divided by the ratio of the resistor R4 and the resistor R6, and the level is lowered. ) is inverted with Lo
The level control signal is passed through the switch (SW2) and the switch (S W h ) is opened during the pulse generation period (o
ff). Therefore, the chrominance signal (C) remains at the original burst signal level without being lowered in level during the burst signal period, and only the chroma signal is lowered in level by a predetermined amount. In this case, without changing the chroma level,
It may be configured to increase only the burst signal level.

After that, the output terminal (
44), the color signal is output.

Since the audio signal (S) has one switch (SW+) switched to the contact point, the audio signal with enhanced low frequencies passes through the reduction/augmentation circuit (land) and is sent to the output terminal (46) via the amplifier circuit (41). is output from.

(G) Effects of the Invention According to the purchase of the present invention, by operating an external switch depending on the playback tape, the brightness level can be lowered and the amount of noise cancellation can be relatively increased more than usual, resulting in signal correction. The noise ratio is improved. Furthermore, the burst signal to chroma signal ratio of the color signal is increased, and the luminance signal level and the color signal level are simultaneously lowered, which has the effect of making it possible to obtain a good-quality image with a sharp reproduced screen.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a reproduced video processing circuit according to an embodiment of the present invention, and FIG. 2 is a frequency characteristic diagram of a luminance signal in the circuit diagram.
FIG. 3 is a diagram showing the input level versus output level of the luminance signal noise cancellation circuit in the same circuit diagram, and FIG. 4 is a block diagram of a conventional reproduced luminance signal processing circuit. 23... Level down circuit, ■"... Tuning circuit, 2
6... Noise cancellation circuit, 31... Burst level variable circuit, SW, SW, SW,... Switch, 42... Operation switch.

Claims (3)

[Claims] (1) In a reproduced video signal processing circuit that separates a reproduced video signal into a luminance signal and a color signal and processes the signals, a level down circuit that lowers the level of the separated luminance signal and a noise cancellation circuit that cancels noise components are provided. 1. A reproduced video signal processing circuit comprising: a luminance signal processing circuit comprising a luminance signal processing circuit; and a color signal processing circuit including a burst level variable circuit for varying the burst level included in the separated color signal. (2) The reproduced video signal processing circuit according to claim 1, wherein the level down circuit includes a tuning circuit. (3) The reproduced video signal processing circuit according to claim 1, wherein the burst level variable circuit is constituted by a resistor divider circuit, and the resistor divider circuit is made inoperable only during the burst period.