JPS6221474B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal conversion device suitable for converting an NTSC color television signal to a PAL-M color television signal adopted in Brazil and other countries.

Generally, color television signals of the NTSC system and the PAL-M system have the same horizontal and vertical scanning frequencies, and there is no difference in the luminance signal component, only the chroma signal component. The difference is that the color subcarrier frequency of the chroma signal is shifted by 1/4H (where H is the horizontal scanning frequency), that is, 3.934KHz, and the vector of the chroma signal is shifted by 1H (1 horizontal This point is inverted every scanning period).

The present invention has been made in view of the above points, and provides a signal conversion method that can easily convert an NTSC color television signal obtained from a broadcasting station, VTR, etc. into a PAL-M color television signal. It provides equipment.

In particular, in the present invention, a 3.579545 MHz NTSC color subcarrier signal is converted into a 3.575611 MHz PAL-M color subcarrier signal, and at the same time, the PAL-M color signal is inverted every 1H with respect to the B-Y axis. It is used to obtain television signals.

The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a block diagram of an embodiment of the present invention, in which input terminal 1 is first connected to burst switching circuit 2 and burst gate circuit 3 at 3.579545 MHz.
NTSC chroma signals are supplied. To make the operation easier to understand, it is assumed that the chroma signal supplied to the input terminal 1 has the same vector component for each scanning period, as shown in FIG. 2a. In the burst gate circuit 3, only the burst signal component is separated from the chroma signal based on the horizontal pulse, and the burst signal is supplied to the phase shift circuit 4 and the synchronous oscillator 5. At this time, the phase shift circuit 4
Then, the burst signal is phase-shifted by 45 degrees as shown in FIG. 2b and is supplied to the burst switching circuit 2. On the other hand, the synchronous oscillator 5 oscillates a 3.579545MHz signal synchronized with the burst signal based on the burst signal, which is doubled by the doubler 6, and the 7.159090MHz signal from the doubler 6 is balanced as a modulation signal. The signal is supplied to a modulator 7.

Also, in the burst switching circuit 2, based on the horizontal pulse, only the burst signal component shown in FIG. 2a is replaced with a burst signal shifted by 45 degrees as shown in FIG. 2b, and as shown in FIG. 2c. A chroma signal is supplied to a balanced modulator 7. Therefore, at this time, in the balanced modulator 7, the chroma signal is
Balanced modulation at a frequency of 7.159090MHz. By passing the balanced modulation output through a 3.579545MHz bandpass filter 8 and extracting only the low-frequency components, a chroma signal with the vector component inverted with respect to the BY axis is obtained as shown in Figure 2d, and this is the chroma signal that is used in the 1H switching circuit. 9. Further, the 1H switching circuit 9 is supplied with a chroma signal as shown in FIG. 2c obtained from the burst switching circuit 2 after being slightly delayed via a delay circuit 10. Normally, when the chroma signal is passed through the bandpass filter 8, a slight phase delay occurs, so the delay circuit 10 is provided with a delay time that matches this phase delay.
The phases of the two chroma signals supplied to the switching circuit 9 are matched.

Next, in the 1H switching circuit 9, the 2
The two chroma signals are alternately switched every 1H based on the horizontal pulse, and a chroma signal as shown in FIG. 2e is derived, which is supplied to the balanced modulator 11. In the balanced modulator 11, the chroma signal is oscillated by the reference signal oscillator 12 at 7.155155MHz.
(This is 2C+1/4H or 2×3.579545MHz+1
/4 × 0.015734MHz). If the balanced modulated output is passed through a 3.575611MHz bandpass filter 13 to extract only the low frequency components, the output terminal 14 will have a frequency converted by 1/4H.
A chroma signal compatible with the 3.575611 MHz PAL-M system is derived.

In this way, the above signal conversion device has a simple configuration using two balanced modulators 7, 11, two bandpass filters 8, 13, a 1H switching circuit 9, a burst switching circuit 2, etc. It is possible to convert a PAL-M system chroma signal into a PAL-M system chroma signal.

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

As described above, according to the signal conversion device of the present invention,
Since it is possible to convert an NTSC color television signal to a PAL-M color television signal relatively easily, for example, even a videotape recorded in the NTSC format can be played back using a VTR and the reproduced color television signal can be converted to a PAL-M color television signal. Once the signal is converted into a PAL-M color television signal using the apparatus of the present invention, it can be easily 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. 2...Burst switching circuit, 7...Balanced modulator,
8...Band pass filter, 9...1H switching circuit.

Claims (1)

[Claims] 1 The burst signal in the chroma signal of the NTSC system
burst switching means for replacing a burst signal with a 45° phase shift; means for generating a modulated wave signal having a frequency twice the color subcarrier frequency based on the burst signal in an NTSC chroma signal; and said burst switching. means for balanced modulating the chroma signal obtained by the means with the modulated wave signal; and means for filtering the low frequency component of the modulated wave output obtained from the balanced modulating means.
bandpass filter means for obtaining an inverted Y-axis chroma signal, and both chroma signals obtained from the burst exchange means and bandpass filter means;
1H switching means that alternately switches and derives every 1H;
A signal conversion device comprising means for frequency converting a chroma signal obtained from the 1H switching means, and converting an NTSC system chroma signal into a PAL-M system chroma signal.