JPS5919494A - Noise canceller device - Google Patents

Abstract

PURPOSE:To obtain a color reproduced image without noise and to eliminate the deterioration in the color resolution, by attenuating a part at the outside of a side band of a chrominance carrier only when there exists the horizontal correlation in luminance signals. CONSTITUTION:A signal reproduced from a magnetic tape 1 and amplified at an amplifier 11 is applied to a low pass filter 21, a chrominance carrier signal is extracted and applied further to an adder 16 via an ACC circuit 22, a frequency converter 23 and a filter circuit 25. The adder 16 adds this chrominance carrier signal and the luminance signal to transmit a color video signal. A detecting circuit having a level comparison circuit 32 and the like detects the horizontal correlation of the luminance signals to control the filter circuit 25 and only when the horizontal correlation exists, the outside part of side band of the chrominance carrier signal is attenuated.

Description

Detailed Description of the Invention In a color VTR, if pre-emphasis is performed on the carrier color signal during recording and de-emphasis is performed on the carrier color signal during playback, the carrier color signal can be recorded with a good S/N ratio. Can be played.

However, this method cannot be applied to a color VT)t for which the signal format has already been determined, for example, a beta format color T'fL. .

In view of this point K, the present invention attempts to improve the 87N of the carrier color signal even if the signal format has already been established.

Now, if we only perform de-emphasis on the carrier chrominance signal during reproduction, i.e., we modulate the carrier chrominance signal; - the outer part of the sideband of the carrier chrominance signal so that the high-frequency components of the chrominance signal are attenuated. By attenuating the noise component, the noise component is attenuated, but at the same time, the high frequency component of the color difference signal demodulated from the carrier color signal is also attenuated. Since the high frequency component of the color difference signal corresponds to a color changing portion in the horizontal direction of the reproduced screen, the attenuation of the color difference signal causes deterioration of the color resolution in the horizontal direction of the reproduced screen.

Therefore, in the present invention, the 87N of the carrier color signal is improved as follows.

That is, in portions of the reproduced screen where the color changes greatly in the horizontal direction, the horizontal correlation of the carrier color signal is small, but in portions where the color does not change, the horizontal correlation is large. In addition, on a general television screen, the correlation of the luminance signal and the correlation of the carrier color signal almost always match. Therefore, in this invention, the horizontal correlation of the luminance signal is detected, and the detected output is Accordingly, only when the horizontal correlation force t is present, the portion outside the site of the carrier color signal is attenuated.

An example of this will be explained below.

In Fig. 1, (1) indicates a magnetic tape, and on this tape (1), an addition signal 8a processed from a color video signal by a normal color VTR is recorded as one diagonal magnetic track for each l field. recorded sequentially. That is, the sum signal Sa&ma and luminance signal sy are F'M
The carrier color signal Ss is converted into the signal Sf, and the carrier color signal Ss is converted into the signal Sf.
This is a signal obtained by frequency-converting the M signal 8f to the lower frequency side, and adding the frequency-converted carrier color signal aS and its FM signal 8f.

It is also assumed that the luminance signal sy is pre-emphasized when converted into the FM signal 8f, and that the amount of pre-emphasis becomes smaller as the level of the signal 8y becomes larger.

And two rotating magnetic heads (2A) and (2B)
are rotated at a frame frequency with an angular spacing of 180° from each other, and a tape (1
) is run around an angular range of more than 180°, and the added signal Sa is reproduced from the tape (1) by the heads (2A) and (2B). And this signal 8a is
The signal Sf is supplied to the pass filter (121) through the regenerative amplifier θD, and the FM signal Sf is taken out. is supplied to the adder circuit (16) through the de-emphasis circuit (151 (details will be described later)).

Furthermore, the signal Sa from the amplifier αB is supplied to the low-pass filter 0211 and is converted into a low frequency carrier color signal 8.
g is taken out, and this signal Ss is supplied to the frequency converter (c) through the 〇〇 circuit (221), and
fI”c/APC1 [1 path Ca is supplied with an alternating signal for frequency conversion, and the signal SS is the carrier color signal S of the original band.
The frequency is converted to C. Then, this signal SC is supplied to an adder circuit αQK through a filter circuit (e) of band erinne (reverse bell characteristic), which will be described later, and is added to the luminance signal By, and the original color video signal is displayed on the terminal surface. taken out.

In this case, the de-emphasis circuit 0 (g) is configured as follows, for example. That is, as a nonlinear circuit, the emitters of the transistors Ql and Q2 are connected to the constant current source A1 to form an IJ j ivy (151), and the demodulation circuit I
The luminance signal Sy from the 15-bit voltmeter is supplied to the base of transistor Q1 through resistor R1 and to the base of transistor Q2 through a filter (152) having resistor R2 and capacitor C2.

The output signal 815 of the transistor Q2 is supplied to the subtraction circuit (153), and the luminance signal sy from the demodulation circuit is supplied to the subtraction circuit (153).

Therefore, the luminance signal 8y is applied to the base of the transistor Q1.
is supplied as is, and the low frequency component of the luminance signal sy is supplied to the base of the transistor Q2, so the output signal 8ts of the transistor Q2 is the difference component of the base power, that is, the high frequency component of the luminance signal sy. Becomes an ingredient. and,
The high frequency component S1s of this signal Sy is sent to the subtraction circuit (153)
Since the signal is subtracted from the signal sy, the subtraction circuit (1
53), the high-frequency attenuated luminance signal 8y, that is,
A de-emphasized luminance signal Sy is extracted.

Furthermore, at this time, since the transistors Ql and Q2 form a beam (151), the higher the level of the luminance signal 8y from the demodulation circuit I, the more the transistor Q2
The amplitude of the high-frequency component 815 from the de-emphasis circuit (1ω) becomes smaller as the level of the signal 8y becomes larger, and has complementary characteristics with pre-emphasis.

A filter circuit (25) for the carrier color signal 8C
is configured as follows, for example. That is, as a nonlinear circuit, the transistors Q12 and Qla are connected to the constant current source A12 to form a current source (251), and the carrier color signal Sc from the converter (23) is supplied to the emitter follower transistor QIIK. At the same time, its emitter is connected to the bases of transistors Q1g and Qt3 through resistors Ro and R12, and the signal 8c is connected to the base of transistor Q13 as a bandpass filter whose pass band is mainly around the center of the carrier color signal 8c.
A parallel resonant circuit (252) whose resonant frequency is the carrier frequency (''; -3,58 MHz) is connected.
C11 is a DC cut capacitor, and All is a constant current source.

Then, the output signal 825 of the transistor Q13 is supplied to the subtraction circuit (253) through the emitter follower transistor Q14 and further through the resistor R1s, and the signal Sc from the converter r2■ is supplied to the subtraction circuit (253).
3). Note that Ala is a constant current source.

Furthermore, a detection circuit (K) that detects the horizontal correlation of the luminance signal Sy and controls the filter circuit 0ω is configured as follows. That is, a signal -81s having a phase opposite to that of the signal 81s is obtained at the collector of the transistor Q1, but this signal -81! + is supplied to the base of transistor Q5 through transistor Q3 of the engineered follower, and
Signal S15 is applied to the base of transistor Q6 through emitter follower transistor Q4. In addition,
A2. All is a constant current source.

The emitters of transistors QB, Q6, and C7 are connected to constant current source A4, and transistors p Qy
A reference voltage Vr is supplied to the base of the level comparison circuit 6.
2 is configured, and the output signal 831 of the collector of transistor Q7 is supplied to the base of transistor Q9 through the emitter follower transistor Qa. The collector of transistor Q9 is connected to the output terminal of resistor R13 through capacitor C2.

Note that the circuits 051, cll) and (251) are each formed into a l-chip IC as indicated by the chain lines, and the capacitors C1°C2, C1l and the resonant circuit (252) are externally connected.

Therefore, the carrier color signal 8C supplied to transistor Qo
is supplied from its emitter through resistor Ro to the base of transistor Q120. -! In addition, at this time, the signal 8c at the emitter of the transistor Q11 is connected to the resistor R12.
However, since the resonant circuit (252) is connected to this base, the part of the signal 8c outside the sideband (this modulates the signal Sc) (corresponding to the high frequency component of the color difference signal) is bypassed through the resonant circuit (252), and only the component near the center of the signal 8c is supplied to the base of the transistor Q1B.

Therefore, the output signal 82 at the collector of transistor Q13
s is the transistor Q12. This is the difference component of the base input of Q13, that is, the part outside the sideband of signal 8c.

Then, if the transistor Q9 is off, a portion 825 outside the sideband of this signal Sc is supplied to the subtraction circuit (253) through the transistor Q14,
In this subtraction circuit (253), from signal Sc to signal 8
Since 2B is subtracted, the subtraction circuit (253) outputs a signal 8c in which the outside portion of the sideband is attenuated. Further, at this time, the noise included in this signal 8c is also attenuated.

Furthermore, at this time, since the transistors Qlz and Q13 constitute a vine (251), the level of the signal 8C from the converter (c) increases, and the signal 8
The amplitude of 2B is compressed, and therefore the amount of attenuation in the outer part of the sideband becomes smaller as the level of signal 8c becomes larger.

That is, if the transistor Q9 is off, attenuation is performed on the outer side band of the carrier color signal Sc, and the amount of attenuation becomes smaller as the level of the signal 8C becomes higher.

Furthermore, if the transistor Q9 is on, the signal 825 is no longer supplied to the subtraction circuit (253), so that the portion outside the sideband of the carrier color signal 8c is not attenuated.

On the other hand, it is assumed that the luminance signal sy from the demodulation circuit (141) is changing at the time t1, t2 K level, as shown in FIG. Then, this signal Sy is supplied to the base of the transistor Q1, and is also supplied to the low-pass filter (152) to produce the signal shown in FIG. 2B, and this signal is supplied to the base of the transistor Q2, so that The difference signal 815 of the transistor Q2 becomes a differential signal (high frequency component of the signal sy) at time K, time 1..12, as shown in FIG. Also, the signal -815 is as shown in the second diagram.

Then, the signal S1a is supplied to the transistor Q6 through the transistor Q4 and is compared in level with the voltage Vr, so that at time t1, the signal S1a is 5K, as shown in FIG.
”. Also, since the signal -815 is supplied to the transistor Q5 through the transistor Q3 and compared in level with the voltage Vr, the signal -815 is supplied to the transistor Q5 through the transistor Q3, so that the signal -815 is level-compared with the voltage Vr.
s=“1”. Therefore, the signal 8al indicates the horizontal correlation of the luminance signal sy, and when the horizontal correlation is large, 831=
83s=“l” when it is “0” and small.

Then, this signal Sat passes through the transistor Q8,
Since the transistor Q9 is supplied with K, the transistor Q9 is off when 8ss="O", and 531="11'"
It turns on when . Therefore, when the horizontal correlation of the luminance signal BY is small (S31-'1''), heating of the outside part of the side band of the carrier color signal Sc is not performed, but when the horizontal correlation is large, the side band of the carrier color signal Sc is not heated. Attenuation of the outer part of the band is performed.

As mentioned at the beginning, the horizontal correlation of the carrier color signal Sc is small in the portions of the reproduced screen where the color changes are large in the horizontal direction, and the horizontal correlation of the carrier color signal Sc is small in the portions where the color changes are small.
The horizontal correlation of c becomes large, and in most cases, on a general television screen, the correlation of the luminance signal and the correlation of the carrier color signal match.

Therefore, in the portion of the reproduced screen where the color change is small in the horizontal direction, the portion outside the sideband of the carrier color signal Sc is attenuated, so at this time, the carrier color signal 8
The noise contained in C is reduced, and a color image with less noise can be obtained.

Further, in a portion of the reproduced screen where the color change is large in the horizontal direction, the portion outside the sideband of the signal Sc is not attenuated, so there is no deterioration in color resolution.

Furthermore, even when attenuation is performed, when the level of the carrier color signal Sc is high and the S/N is originally good,
The amount of attenuation is small and the level of the carrier color signal Sc is small.
When /N is bad, the amount of attenuation becomes large, so noise removal is effective.

Also, when converting to an IC, the external components are capacitor C1,
Since it is only C2, C1l and the resonant circuit (252), the IC
The number of external terminals can be reduced, and the effect of using an IC is significant.

In the above description, the circuits Q5) and C25) are of a feedforward type, but they can also be configured as a feedback type as shown in FIG.

[Brief explanation of drawings]

1 and 3 are connection diagrams of an example of the present invention, and FIG. 2 is a diagram for explaining the same. (121 is a bypass filter, αXun is an FM demodulation circuit, C
υ is a low-pass filter (the second floor is a WdR number condenser).

Claims (1)

[Claims] The pass band is mainly located near the center of the carrier color signal, and
It has a filter circuit whose input/output characteristics are non-linear, and a detection circuit that detects the horizontal correlation of the luminance signal, and when the detection output of this detection circuit indicates that the horizontal correlation of the luminance signal is small, the filter circuit is disabled. The noise canceller device extracts the carrier color signal as it is, and when the horizontal correlation of the luminance signal is large, the filter circuit operates to remove noise from the carrier color signal and extract it.