JP3048884B2 - VTR video signal reproduction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal reproducing circuit of a VTR for reproducing a video signal in a home VTR, and more particularly to a video signal of a VTR in which the performance of a noise removing circuit is improved and the number of filters is reduced. The present invention relates to a signal reproducing circuit.

[0002]

2. Description of the Related Art In a reproduction circuit of a home VTR, it is necessary to remove various noises from a Y (luminance) signal and a C (color) signal. First, a so-called YNR using the correlation around 1H (H is a horizontal synchronization signal period) is applied to the Y signal.
(A luminance signal noise elimination circuit). After that, high-pass noise removal is performed.

In addition, a color signal is subjected to crosstalk removal (color signal noise removal circuit) for removing interference from an adjacent track. This crosstalk removal also requires a 1H delay circuit. For this reason, a circuit which is also used as a 1H delay circuit for removing YNR and crosstalk is used.

FIG. 2 shows a video signal reproducing circuit of such a VTR. A video signal from a reproducing head (not shown) is supplied from an input terminal (1) to an LPF (2) and a BPF (3).
Is applied to LPF (2) is 629 in the video signal.
A color signal of KHZ is extracted, and a BPF (3) extracts a Y signal in the video signal. The 629 KHz color signal is returned to the original frequency of 3.58 MHz by the frequency conversion circuit (4).

The Y signal from the BPF (3) is FM-demodulated by an FM demodulation circuit (5) and applied to an LPF (6). The LPF (6) removes an unnecessary component generated when the FM demodulation is performed by the FM demodulation circuit (5) and an interfering wave such as a remaining chroma signal and extracts a necessary Y signal. The addition circuits (7) and (8), the limiter (9), the coefficient circuit (10), and the 1H delay circuit (11) form a YNR. The Y signal from which noise has been removed is supplied to the terminal (1).
It is derived in 2).

The 3.58 MHz color signal from the terminal (13) of the frequency conversion circuit (4) is applied to the terminal (14). The adding circuit (15) and the 1H delay circuit (11) constitute a crosstalk removing circuit (16). Therefore, the 3.58 MHZ color signal from the terminal (14) is subjected to noise removal by the crosstalk removing circuit (16), and the output terminal (1
7) is derived.

However, 3.58M from the terminal (14)
The HZ color signal is added to the addition circuit (1
8) Unwanted components (white noise,
Non-linear distortion (especially present in 3.2 MHZ) associated with magnetic recording is added. Therefore, a trap circuit (19) having a trap point near 3.2 MHZ is provided for the purpose of removing remaining unnecessary components near 3.2 MHZ from the terminal (12).

Although the trap circuit (19) also deletes the Y signal component, there is no problem because it is in the YNR loop.
Thus, the Y signal is applied to the 1H delay circuit (11) via the trap circuit (19) and the addition circuit (18), and is applied to the YNR (20). As a result, the terminal (1
In 2), a Y signal from which noise is removed by YNR is obtained.
The signal is applied to the non-linear de-emphasis circuit (21). The non-linear de-emphasized Y signal is
The noise is further removed by the two high-pass noise removing circuits (22) and (23), and the noise is led to the output terminal (24).

[0009] In the reproduced Y signal, around 1 MHZ, 3 to
A lot of unnecessary components are generated near 3.5 MHZ. Therefore, the high-pass noise removal circuit (22) reduces unnecessary components near 1 MHz. Further, the high-pass noise removing circuit (23) reduces unnecessary components in the vicinity of 3 to 3.5 MHz.

Therefore, according to the apparatus shown in FIG. 2, the Y signal and the C signal are shared by using the YNR and the 1H delay circuit for removing the crosstalk.
Various noise removal can be performed on the signal.

[0011]

However, since the device shown in FIG. 2 requires a large number of filters, there are problems such as the need for a large capacity and an increase in the current consumption due to an increase in the number of elements when the IC is formed. Was. Therefore, it has been desired to reduce the number of filters in the apparatus shown in FIG.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been made in consideration of the above problems.
A high-pass noise removing circuit for removing a noise component in a frequency band from HZ to 4 MHz, a YNR for removing an unnecessary component in an output signal of the high-pass noise removing circuit, and a YNR
An adder circuit for adding the output signal of the adder and the color signal whose frequency has been converted to the original value; a delay circuit for delaying the output signal of the adder circuit by one horizontal synchronizing signal period and applying the same to the YNR; A crosstalk removing circuit for removing crosstalk of a color signal using input / output signals, wherein a luminance signal is extracted from the YNR and a color signal is extracted from the crosstalk removing circuit. And

[0013]

According to the present invention, the characteristics of the conventional high-pass noise removing circuit for removing unnecessary components near 3 to 4 MHz are changed so that the 3.58 MHz chroma (color) component can also be removed. The noise elimination circuit was arranged before YNR. Therefore, the high-pass noise elimination circuit can simultaneously perform the conventional high-pass noise elimination function and the trap function. Therefore, the number of filters can be reduced.

[0014]

FIG. 1 shows a video signal reproducing circuit of a VTR according to the present invention, wherein (25) shows a characteristic of a high-pass noise removing circuit for removing unnecessary components near 3 to 4 MHZ, and 3.58.
This is a high-pass noise elimination circuit having a characteristic of removing a chrominance (color) component of MHZ.

In FIG. 1, the same circuit elements as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. FIG. 1B
A filter circuit such as a PF includes a plurality of differential amplifiers and capacitors. High-pass noise removal circuit (2
5) is provided between the LPF (6) and the YNR (20). As described above, the high-pass noise removing circuit (25) has the characteristics of a high-pass noise removing circuit for removing unnecessary components near 3 to 4 MHZ, so that the high-pass noise required in the subsequent stage of the nonlinear de-emphasis circuit (21) is obtained. One removal circuit is not required.

The high-pass noise removing circuit (2)
5) has a characteristic of eliminating unnecessary components near 3.58 MHZ, so that the trap circuit provided in the preceding stage of the adder (18) becomes unnecessary. In YNR (20), noise removal is performed by comparing Y signals around 1H, but it is necessary to accurately delay 1H at that time. Therefore, Y
It is desirable that there is no circuit that disturbs the phase of the passing signal as much as possible in the NR loop. If there is a trap in the loop as in the prior art, it is difficult to accurately delay, and as a result, the noise cannot be sufficiently removed.

On the other hand, if the high-pass noise removing circuit (25) is arranged in front of the YNR as shown in FIG. 1, the phase problem is eliminated and the YNR can be accurately performed. FIG.
FIG. 2 shows a specific circuit example of the high-pass noise removing circuit (25) of FIG. 1, in which a signal from an input terminal (26) is applied to an adding circuit (27). The signal from the input terminal (26) is supplied to the adder circuit (2) via the HPF (28), the limiter (29), the phase adjustment circuit (30), and the coefficient circuit (31).
7) is applied.

This will be described with reference to FIGS. FIG. 4 is a spectrum diagram of a signal from the input terminal (26) and noise mixed therein. The frequency band a in FIG. 4 shows noise around 3 to 4 MHz. The noise in this band is relatively large compared to the others. Then, when the noise and the signal in the band are extracted by the HPF (28), the spectrum diagram of the output signal of the HPF (28) is as shown in FIG. When the signal and noise in FIG. 5 are amplitude-limited by the limiter (29), only the signal level is reduced, and the spectrum of the output signal of the limiter (29) is as shown in FIG.

The components shown in FIG. 6 correspond to the phase adjustment circuit (3
0) and the result is inverted and applied to the addition circuit (27) via the coefficient circuit (31). Then, the frequency band a of FIG.
The noise component cancels out for the component of. As a result, the spectrum diagram of the output signal of the adding circuit (27) is as shown in FIG. 7, and it is possible to reduce a large noise.

This noise elimination is a type in which the amount of attenuation varies depending on the noise level, and is called non-linear noise elimination. FIG. 8 shows the relationship between the noise level and the attenuation. As the magnitude of the noise is smaller (−40 dB), the attenuation is larger, and as the magnitude of the noise is larger (−10 dB).
The amount of attenuation is small. In the actual circuit, a color signal trap circuit is provided immediately before the signal from the 1H delay circuit (11) is applied to the adder circuit (7), but is omitted in FIG.

[0021]

As described above, according to the present invention, 3 to 3
The characteristics of the high-pass noise elimination circuit that removes unnecessary components near 4 MHZ are changed so that the chroma (color) component of 3.58 MHZ can also be eliminated, and the high-pass noise elimination circuit is disposed before YNR. Therefore, the high-pass noise elimination circuit can simultaneously function as a conventional high-pass noise elimination function and a trap function, and the number of filters can be reduced.

Therefore, the number of elements and power consumption can be reduced. Further, since the element causing the phase shift is not included in the YNR loop, the YNR can be accurately calculated.
It has the advantage that it can be done.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a video signal reproducing circuit of a VTR according to the present invention.

FIG. 2 is a block diagram showing a conventional video signal reproducing circuit of a VTR.

FIG. 3 is a block diagram showing a specific circuit of a high-pass noise removing circuit (25) of FIG.

FIG. 4 is a characteristic diagram for explaining FIG. 3;

FIG. 5 is a characteristic diagram for explaining FIG. 3;

FIG. 6 is a characteristic diagram for use in explaining FIG. 3;

FIG. 7 is a characteristic diagram for explaining FIG. 3;

FIG. 8 is a characteristic diagram for explaining FIG. 3;

[Explanation of symbols]

 (11) 1H delay circuit (16) Crosstalk elimination circuit (20) YNR (25) High-pass noise elimination circuit

Claims (2)

(57) [Claims] 1. A video signal reproducing circuit of a VTR for reproducing a video signal recorded on a magnetic tape, comprising: a high-pass noise removing circuit for removing a noise component in a frequency band of 3 MHz to 4 MHZ of a reproduced luminance signal subjected to FM demodulation. A YNR for removing unnecessary components in an output signal of the high-pass noise removing circuit; an adding circuit for adding the output signal of the YNR and a color signal whose frequency has been converted to an original value; an output of the adding circuit A delay circuit for delaying a signal by one horizontal synchronizing signal period and applying the signal to the YNR; and a crosstalk removing circuit for removing a crosstalk of a color signal using an input / output signal of the delay circuit.
A video signal reproducing circuit for a VTR, wherein a luminance signal is extracted from the NR and a color signal is extracted from the crosstalk removing circuit. 2. A video signal reproducing circuit of a VTR for reproducing a video signal recorded on a magnetic tape, comprising: a first high-pass for removing a noise component in a frequency band from 3 MHZ to 4 MHZ of an FM demodulated reproduced luminance signal. A noise removing circuit; a YNR for removing unnecessary components in an output signal of the first high-pass noise removing circuit; an adding circuit for adding the output signal of the YNR and a color signal whose frequency has been converted to an original value; A delay circuit that delays an output signal of the adder circuit by one horizontal synchronizing signal period and applies the same to the YNR; a crosstalk removing circuit that removes crosstalk of a color signal using input / output signals of the delay circuit; A second high-pass noise elimination circuit that eliminates a noise component in a frequency band near 1 MHz of the reproduced luminance signal from the YNR. A video signal reproducing circuit for a VTR, wherein a luminance signal is extracted from the crosstalk removing circuit and a color signal is extracted from the crosstalk removing circuit.