JPH04373364A - Video signal processing device - Google Patents

Abstract

PURPOSE:To solve the problem that a digital video signal processing device used in the reproducing system of a digital VTR can be used in both of the SVHS system and the VHS system but S/N is degraded by remaining of the noise component on the outside of the signal band at the time of reproducing in the VHS system. CONSTITUTION:An input video signal is connected to first and second LPFs 2 and 19, and one of their outputs is selected by a first switch 11 and is connected to an A/D converter 3 and is supplied to a recording mode discriminating circuit 5 and a reproduced signal processing circuit 4. The output of the reproduced signal processing circuit 4 passes a D/A converter, and the output passes third and fourth LPFs 7 and 12, and one of their outputs is selected by a second switch 13 and is outputted. First and second switches 11 and 13 are controlled by the output of a recording mode discriminating circuit 5 to automatically switch the bands of LPFs in accordance with the SVHS system and the VHS system, and the out-band noise component does not remain to prevent the degradation of S/N at the time of VHS reproducing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital video signal processing apparatus used in a reproduction system of a digital video tape recorder.

0002

2. Description of the Related Art In recent years, video tape recorders (hereinafter abbreviated as VTR) having high resolution, that is, compatible with high bands, have become popular.

[0003] In such a high-band compatible VTR, it is necessary to record and reproduce video signals in a plurality of formats on the same magnetic tape. In this case, the user generally selects the format using a switch when recording, and the VTR automatically determines and switches the format during playback.
During playback, automatic format discrimination is performed. This method is the same whether the reproduced video signal processing is analog processing or digital processing.

A conventional video signal processing device will be explained below. As shown in FIG. 2, the video signal applied to input terminal 1 is passed through a first low-pass filter (hereinafter abbreviated as LPF).
2 and is supplied to the A/D converter 3. A/D converter 3
The output of the reproduction signal processing circuit 4 is supplied to the reproduction signal processing circuit 4 and the recording mode discrimination circuit 5, the output of the recording mode discrimination circuit 5 is supplied to the reproduction signal processing circuit 4, and the output of the reproduction signal processing circuit 4 is supplied to the D/A
It is supplied to converter 6. The output of the D/A converter 6 passes through a second LPF 7, and a reproduced video signal is output from an output terminal 8. On the other hand, the output of the reference clock generation circuit 9 is A
/D converter 3, reproduction signal processing circuit 4, recording mode discrimination circuit 5, and D/A converter 6, respectively.

The detailed operation of the video signal processing apparatus that operates as described above will be explained below. Here, as an example, consider a case where the conventional video signal processing apparatus shown in FIG. 2 is used in a reproduction system of a VTR compatible with the VHS system and the SVHS system. The video signal applied to the input terminal 1 is an FM modulated video signal having a frequency band as shown in FIG. That is, as shown in FIG. 3A, in the VHS system, sidebands are distributed around a luminance signal carrier wave of 3.4 MHz to 4.4 MHz and a color signal carrier wave of 0.63 MHz. Moreover, as shown in FIG. 3(b), S
In the VHS system, sidebands are distributed around a luminance signal carrier wave of 5.4 MHz to 7.0 MHz and a color signal carrier wave of 0.63 MHz. A/D input analog video signal
When converting into a digital signal with the converter 3, if there is an input signal with a frequency higher than half of the clock frequency input from the reference clock generation circuit 9 (hereinafter referred to as the Nyquist frequency), it cannot be converted into an accurate digital signal due to aliasing distortion. Therefore, an LPF 2 that passes only frequencies lower than the Nyquist frequency is inserted in front of the A/D converter 3. The digitally converted video signal is discriminated as SVHS or VHS by the recording mode discriminating circuit 5, and as a result, is FM demodulated in the reproduction signal processing circuit 4, subjected to VTR reproduction signal processing, and then converted into a digital signal by the D/A converter 6. A reproduced analog signal of the VTR is output from an output terminal 8 after being converted into an analog signal and passed through a second LPF 7 for removing harmonics such as a clock frequency.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional configuration, the band of the LPF before the A/D converter and the LPF after the D/A converter both pass the wide band of the SVHS system. Therefore, when an FM modulated signal recorded in the VHS format is input, even signals outside the band are taken into the A/D converter, FM demodulated, reproduced signal processed, D/A converted, and sent to the LPF. However, since the band of the LPF after D/A conversion is wide, the output reproduction signal has a noise component outside the band, resulting in a problem that the S/N ratio decreases.

The present invention solves the above-mentioned conventional problems, and automatically switches the band of the LPF before the A/D converter and the band of the LPF after the D/A converter based on the output of the recording mode discrimination circuit. Accordingly, it is an object of the present invention to provide a video signal processing device that does not cause S/N deterioration even during VHS format playback.

[0008]

[Means for Solving the Problems] In order to achieve the above object, a video signal processing device of the present invention includes first and second low-pass filters into which an angle-modulated video signal is input;
a first selection means for selecting an output of the second low-pass filter; and an M-bit (M is an arbitrary integer) digital image by using a clock signal from a reference clock generator to select the output of the first selection means. An A/D converter that converts into a signal, and an A/D
Recording mode determining means for determining the recording mode of the digital video signal output from the converter; Reproduction signal processing means for processing the digital video signal as a reproduction signal; and converting the digital video signal output from the reproduction signal processing means into an analog video signal. a D/A converter for selecting a D/A converter; third and fourth low-pass filters for inputting the analog video signal output from the D/A converter; and a third and fourth low-pass filter for selecting outputs of the third and fourth low-pass filters. 2 selection means, and has a configuration in which the output of the first and second selection means is switched by the output of the recording mode discrimination means.

[0009]

[Operation] With the above-described configuration, the present invention provides a
By having independent LPFs for signals in different bands, such as those for HS, it is possible to sufficiently remove noise outside the band even when playing VHS with a narrow band, eliminating S/N deterioration. Become.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a block diagram of this embodiment, and the same parts as those in FIG. 2 are given the same reference numerals and the explanation thereof will be omitted.

As shown in FIG. 1, the video signal applied to the input terminal 1 is supplied to the first LPF 2 and the second LPF 10, and their outputs are input to one and the other input of the first switch 11. Supplied to the terminal. The output of the first switch 11 is A
/D converter 3. The output of the A/D converter 3 is supplied to a reproduction signal processing circuit 4 and a recording mode discrimination circuit 5.
The output of the recording mode discrimination circuit 5 is supplied to the reproduction signal processing circuit 4, and the output of the reproduction signal processing circuit 4 is supplied to the D/A converter 6. The output of the D/A converter 6 is supplied to the third LPF 7 and the fourth LPF 12. 3rd and 4th LPF7
, 12 are supplied to one and the other input terminals of the second switch 13, and the output of the second switch 13 is outputted as a signal from the output terminal 8. The output of the recording mode discrimination circuit 5 is the first
, to the control input terminals of the second switching devices 11 and 13. On the other hand, the output of the reference clock generation circuit 9 is transmitted to the A/D converter 3, the reproduction signal processing circuit 4, the recording mode discrimination circuit 5, the D/D converter 3, the reproduction signal processing circuit 4, the recording mode discriminating circuit 5, the
It is supplied to the A converter 6.

The operation of the above video signal processing apparatus will be explained in detail using FIGS. 1 and 3. here,
For example, a VTR compatible with VHS and SVHS systems.
Consider a case where the video signal processing apparatus of the present invention shown in FIG. 1 is used in a reproduction system. The video signal applied to the input terminal 1 is an FM modulated video signal having a frequency band as shown in FIG. The first LPF 2 is used for SVHS with a band of 10 to 12 MHz, and the second LPF 10 is used for VH.
The band for S is set to about 6 MHz, and the A/D converted digital video signal is discriminated as SVHS or VHS by the recording mode discrimination circuit 5, and is FM demodulated by the playback video signal processing circuit 4 and becomes the playback signal of the VTR. Processing is done, D
/A converter 6 converts the signal into an analog signal, third and fourth LPFs 7 and 12 remove harmonic components, and switch 1
The reproduction signal of the VTR selected in step 3 is output from the output terminal 8. The third LPF7 band is 5MHz, the fourth LPF
12 is set to 3 MHz, when the recording mode discrimination circuit 5 discriminates as SVHS, the first LPF 2 and the third LPF 7 are selected, and when it discriminates as VHS,
By controlling the control inputs of the first switch 11 and the second switch 13 so as to select the second LPF 10 and the fourth LPF 12, even when a VHS system playback signal is played, the LPF is adjusted to the band. This makes it possible to sufficiently remove out-of-band noise components and prevent S/N deterioration.

[0014]

As described above, the present invention automatically switches the band of the LPF before the A/D converter and the band of the LPF after the D/A converter using the output from the recording mode discrimination circuit. , it is possible to select an LPF suitable for each band of VHS and SVHS, and even when playing VHS format, noise components outside the band can be sufficiently removed, resulting in excellent video signal processing without deterioration of S/N. The device can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a video signal processing device according to an embodiment of the present invention.

[Figure 2] Block diagram of a conventional video signal processing device

[Figure 3]
(a) is a frequency allocation diagram for the VHS system (b) is a frequency allocation diagram for the SVHS system

[Explanation of symbols]

2 First LPF 3 A/D converter 4 Reproduction signal processing circuit 5 Recording mode discrimination circuit 6 D/A converter 7 Third LPF 9 Reference clock generation circuit 10 Second LPF 11 First switch 12 4th LPF 13 Second switch

Claims (1)

[Claims] Claim 1: A first device for inputting an angle-modulated video signal;
a second low-pass filter; first selection means for selecting outputs of the first and second low-pass filters;
an A/D converter that converts the output of the selection means into an M-bit (M is any integer) digital video signal using a clock signal from a reference clock generator; and an output from the A/D converter. A recording mode determining means for determining the recording mode of a digital video signal, a reproduction signal processing means for processing a reproduction signal of the digital video signal, and a D/A for converting the digital video signal outputted from the reproduction signal processing means into an analog video signal. a converter, third and fourth low-pass filters that input the analog video signal output from the D/A converter, and a second filter that selects the outputs of the third and fourth low-pass filters. 1. A video signal processing device, comprising: a selection means, wherein outputs of the first and second selection means are switched based on an output of the recording mode discrimination means.