JPS5827493A - Video reproducing device - Google Patents

Abstract

PURPOSE:To obtain a reproducing signal of PAL-M system, by providing each color subcarrier oscillator of the PAL-M and NTSC systems and using a means which converts a chroma signal of the NTSC system into that of the PAL-M system. CONSTITUTION:Each system can be changed over with each other, by providing a subcarrier wave oscillator 16 for the PAL-M system, a subcarrier wave oscillator 18 and switches 1a, 1b and 1c which change over the oscillators and output terminals 17. In inputting a reproducing signal of the PAL-M system to an input terminal 2, the oscillator 16 is connected to an APC loop including a voltage controlled oscillator 9 and a signal through a balancing modulator 4 is obtained from the terminal 17. On the other hand, in supplying a signal of the NTSC system to the input terminal 2, the oscillator 18 is connected to the APC loop including the voltage controlled oscillator 9. A signal through a band pass filter 11 is replaced with a subcarrier wave burst of the PAL-M system at a burst replacing 19 and outputted from the terminal 17 as a signal of the PAL-M system. Thus, the signal of the PAL-M system can be obtained from the signal recorded with the NTSC system.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video playback device that plays back color television signals from recording media such as video discs and video tapes, and in particular, the present invention relates to a video playback device that plays back color television signals from recording media such as video discs and video tapes, and in particular, plays back color television signals of the PAL-M system adopted in Brazil and other countries. The present invention relates to a video playback device suitable for playback.

The color television signals have the same horizontal and vertical definition scanning frequencies, and there is no difference in the luminance signal components, only the chroma signal components differ. This point (where fH is the horizontal scanning frequency) is shifted by 3.9 3 4 kHz, and the chroma signal vector is reversed every IH (+ horizontal scanning period) around the BY axis. It is.

Therefore, in a video playback device designed to play back a color television signal from a recording medium recorded according to either the NTSC or PAL-M system, the It was impossible to reproduce color television signals.

The present invention has been made in view of these points, and is
The object of the present invention is to provide a video playback device that can play back not only a recording medium recorded in the ALM system but also a recording medium recorded in the NTSC system.

The present invention will be described below with reference to embodiments shown in the drawings. 1st
The figure shows a block diagram of one embodiment of the present invention, and in this embodiment, a case where both NTSC and PAL-M video tapes recorded on a VH8 video tape recorder are played back is taken as an example. explain in detail.

First, the operation for reproducing a normal PAL-M color television signal from a VH3 standard videotape recorded in accordance with the PAL-M method will be described. In this case N
The TSC-PAL-M changeover switches ta+tb+tc are previously switched to the PAL-M terminal (■) side shown in the figure.

Now, when a reproduced video signal is derived from the input terminal 2 during reproduction of the VH8 video tape recorder, only the low frequency component, that is, the chroma signal is derived through the low-pass filter 3, and this is supplied to the balanced modulator 4. Ru. This chroma signal has a subcarrier frequency of 40 fH or 629.87 kHz and is phase shifted by 90° (90°
rotation). Although this chroma signal includes uneven rotation of the magnetic head in the video tape recorder and fluctuation components in the tape running system, these fluctuation components are removed by the APC or AFC circuit operation described later.

On the other hand, at this time, 1 oscillated by +60 fH oscillator 5
The oscillation signal of 60 fH is divided by one frequency by a frequency divider 6 and then applied to a 90° rotation circuit 7, where the phase is shifted by 90° for each lH based on the horizontal pulse (90° rotation). ) to be done.

The 40 fH signal thus rotated by 90° is supplied to the balanced modulator 8. Also, at this time, the 3,575,611 MHz oscillation signal oscillated by the voltage controlled oscillator 9 is applied to the balanced transformer 8, where it is balanced modulated with the 90° rotation signal of 40f. As a result, 4.20 of the sum of both signals is passed through the bandpass filter 0.
A 42O498 90° rotation signal is applied to the balanced modulator 4.

Therefore, the balanced modulator 4 uses a chroma signal of 629.87 kHz obtained from the Rono filter 3 and a chroma signal of 420498 MHz obtained from the bandpass filter 0.
(7) The rotation signal is balanced modulated, and at this time, the difference between the two signals is 3.57
A chroma signal of 5611 MHz is obtained, which is derived via a changeover switch IC.

The chroma signal of 3,575,611 MH2 obtained in this way has the 90° rotation component canceled out and becomes a color television signal conforming to the PAL-M system with a constant 0° phase.

Here, in the 16 OfH oscillator 5, oscillation is controlled based on the output of the phase comparison of the horizontal pulse width obtained from the 160 fH signal and the reproduced video signal in the phase ratio modulator 13, so this control component balance modulator 8 , are applied to the balanced modulator 4 via the band-pass filter 10, thereby canceling out and removing frequency fluctuation components in the chroma signal supplied to the balanced modulator 4 via the low-pass filter 3.

That is, the AFC circuit operation is performed by these.

On the other hand, 8
, 575,611 MHz are applied to the burst gate circuit 14, where only the burst signal is separated and derived and supplied to the phase comparator 15. Further, a reference oscillation signal of 3.575611 MHz is supplied to the phase comparator from the PAL-M reference oscillator I6 via the changeover switch 1b, and the comparison output is supplied to the voltage controlled oscillator 9. As a result, the oscillator 9 always has 3.5
The 75611 MHz signal is not precisely oscillated, but the oscillation frequency is controlled according to the burst signal included in the reproduced chroma signal. Since this controlled oscillation output is supplied to the balanced modulator 4 via the balanced modulator 8 and the bandpass filter 10, the phase modulation component in the reproduced chroma signal is canceled out and removed in the balanced modulator 4.

That is, the APC circuit operation is performed in this manner.

As described above, when playing back a videotape recorded in accordance with the PAL-M system, the 3,575,611 MHz signal from which frequency fluctuations and phase fluctuations have been removed is output to the output terminal I7.
A regular chroma signal of is derived.

Next, in the same video tape recorder as above, the NTS
A case will be described in which a videotape recorded in advance using the C method is played back. In this case, first NTSC-P
AL-M changeover switch la.

1b and 1c are NTSC terminals.

In this case as well, the same AFC and APC circuit operations as in the case of playing back the PAL-M videotape described above are performed, and frequency fluctuations and phase changes caused by rotational unevenness of the magnetic head are processed through the bandpass filter 11. A chroma signal with fluctuations removed is obtained, but in this case, the NTSC reference oscillator 18 and the voltage controlled oscillator 9 oscillate at a frequency of 3.579545 MH2 in accordance with the NTSC system, so the bandpass filter 11 The subcarrier of the chroma signal obtained through the chroma signal is also a chroma signal that conforms to the NTSC system and has a frequency component of 3579545 MHz.

Next, a signal conversion operation for converting the thus obtained reproduced chroma signal of the NTSC system into a chroma signal compatible with the PAL-M system will be explained. In order to make this operation easier to understand, it is assumed here that the reproduced chroma signal obtained from the bandpass filter 11 has the same vector component for each scanning period, as shown in FIG.

First, the chroma signal is supplied to the burst gate circuit 14 and also to the burst exchange circuit 19, and the burst signal separated by the burst gate circuit 4 is supplied to the phase circuit 20. At this time, the phase of the burst signal is shifted by 45 degrees in the phase circuit 20 as shown in FIG. In the burst switching circuit 19, based on the horizontal pulse, only the burst switching circuit in the chroma signal shown in FIG. 2 is replaced with a burst signal shifted by 45 degrees as shown in FIG. A ROMA signal is supplied to the balanced modulator 21 as shown in FIG.

On the other hand, at this time, the voltage controlled oscillator 9 oscillates a signal of 3,579,545 MHz that matches the burst signal in the reproduced chroma signal, which is doubled by the doubler 22.
A signal of 7.159090 MHz is supplied from the doubler 22 as a modulation signal to the balanced modulator 21. Therefore, at this time, the chroma signal is balanced modulated in the balanced modulator 21 at a frequency of 7.159090 MHz.

By passing the balanced modulation output through a 3.579545 MHz band-pass filter 23 and extracting only the low-frequency components, a chroma signal with the vector component reversed with respect to the <B-Y axis as shown in FIG. This is supplied to the IH switching circuit 24. Further, the IH switching circuit 24 is supplied with a chroma signal obtained from the burst switching circuit 19, as shown in FIG. This is because a slight phase delay occurs when the chroma signal is normally passed through the bandpass filter 23, so the delay circuit 23
5 has a delay time that matches this phase delay, thereby matching the phases of the two chroma signals supplied to the IH switching circuit 24.

Next, in the above-mentioned IH switching circuit 24, the two chroma signals shown in FIG. A modulator 25 IC is provided. In the balanced modulator 25, the chroma signal is balanced modulated by the 7,155155 signal oscillated by the reference signal oscillator 26. If the balanced modulated output is passed through a 3.5756+IMHz bandpass filter 27 to extract only the low frequency components, a chroma signal compatible with the PAL-M system is derived from the output terminal 17 via the changeover switch 1c. be done.

Note that there is no difference in the luminance signal components of both the NTSC and PAL-M systems, so by superimposing the NTSC brightness signal in the reproduced video signal with the PAL-M chroma signal as is, the PAL-M color television signals can be obtained.

In the above embodiment, the case where a video tape is played back in a VH8 video tape recorder has been particularly described, but the present invention is of course not limited to such a video tape recorder, but can also be implemented when playing a video disc. can.

As described above, according to the video playback device of the present invention, the NTSi
Q system color television signals can be converted to PAL-M system color television signals, so not only recording media recorded according to the PAL-M system, but also NT
Recording media recorded in accordance with the SC system can also be easily reproduced by simply switching a switch, and in this case, can be viewed on a PAL-M television receiver.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the apparatus of the present invention, and FIG. 2 is a signal vector diagram for explaining the operation of the embodiment. 1a, 1b, 1c-NTSC” PAL
M changeover switch, 19...burst switching circuit, 2
1...Balanced modulator, 22...2 multiplier, 23...
Bandpass filter, 24...IH switching circuit, 25.
...Equilibrium modulator 1, agent Patent attorney Aihiko Fuku ■ Δ−＼−入− 2nd review ＼−X−

Claims (1)

[Claims] 1. NTSC system and PAL-M depending on the content of the recording medium.
NTSC-PAL-M switching means for switching between the N
A video playback device comprising a signal conversion means for converting a TSC system chroma signal into a PAL-M system chroma signal. 2. The signal conversion means includes a burst switching circuit that replaces the burst signal in the chroma signal of the NTSC system with a burst signal whose phase is shifted by 45 degrees, and modulation at a frequency twice as high as the color subcarrier frequency of the chroma signal of the NTSC system. a doubler that generates a wave signal, a balanced modulator that balance-modulates a chroma signal obtained from the burst switching circuit with the modulated wave signal, and a low-frequency component of the modulated wave output obtained from the balanced modulator. a bandpass filter that filters to obtain an inverted chroma signal on the BY axis; an IH switching circuit that alternately switches and derives both chroma signals obtained from the burst switching circuit and the bandpass filter for each IH; The video reproducing device described in the patent, characterized in that it comprises a second balanced modulator that converts the frequency of the chroma signal obtained from the IH switching circuit.