JPS5820090A - Signal converter - Google Patents

Abstract

PURPOSE:To ensure a simple conversion of a signal of the NTSC system into the PAL-N system for a signal converter, by converting the chroma signal of the NTSC system into that of the PAL-N system and then superposing said chroma signal on the luminance signal of the NTSC system. CONSTITUTION:The burst signal in a chroma signal of the NTSC system is replaced with another burst signal with a phase shifted by 45 deg.. Then a modulated signal which has two times of the chrominance carrier frequency of the chroma signal of the NTSC system is produced from a double multiplier 6. With this modulated signal, the burst signal given from the circuit 2 is modulated through a balanced modulator 7. The low frequency component of the modulated wave output is filtered through a BPF8. The chroma signal having the inverted B-Y axis given from the BPF8 is switched with the chroma signal obtained by delaying the output of the circuit 2 through a 1H switch circuit 9 at every 1H and then applied to a balanced converter 11 to receive a frequency conversion through the converter 11 by the signal given from a reference signal oscillator 12. Then a PAL-N chroma signal is delivered.

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. This difference is because the color subcarrier frequency of the chroma signal is the same! -5H (where 5H is the horizontal scanning frequency), that is, shifted by j2j41 KHz, and the vector of the chroma signal is inverted every /H (/horizontal scanning period) around the BY axis.

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

Especially with this invention! ,,MHz NTSC color subcarrier signal on f796! ! 7j11/MHz PAL-
The PAL-M color television signal is obtained by converting the signal into an M system color subcarrier signal and at the same time inverting it every lH with respect to the By axis.

The present invention will be described below with reference to embodiments shown in the drawings. 1st
The figure shows a block diagram of an embodiment of the present invention, in which an NTSC chroma signal of J, 52 MHz is supplied from the input terminal to the burst switching circuit and the burst gate circuit 3. .

In order to make the operation easier to understand, it is assumed that the chroma signal supplied to the input terminal / has the same vector component for each scanning period, as shown in Figure 1 (2).

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 and the synchronous oscillator j. At this time, the phase shift circuit 1 shifts the phase of the burst signal by j''' as shown in Figure 1 (■) and supplies it to the burst switching circuit 2. On the other hand, the synchronous oscillator j converts the burst signal into a burst signal based on the burst signal. Synchronized 367ri!+', 5MH
A signal of z is oscillated, this is multiplied once by a multiplier g, and a signal of 7. A signal of /690 OMHz is supplied to the balanced modulator 2 as a modulation signal.

Also, in the above burst switching circuit, based on the horizontal pulse,
Only the burst signal component shown in FIG. 1 (■) is replaced with a burst signal shifted by 5@ as shown in FIG. 1 (■), and a ROMA signal as shown in FIG. Therefore, at this time, the chroma signal is balanced modulated in the balanced modulator 2 at a frequency of 77.5° OMHz. The balanced modulation output is 3!7 j41. By passing it through a jMHz band-pass filter ♂ and extracting only the low-frequency components, a chroma signal with the vector component inverted with respect to the B-Y axis is obtained as shown in Figure ♂, and this is supplied to the /H switching circuit. Further, the /H switching circuit is supplied with a chroma signal as shown in FIG. When a signal is passed through a bandpass filter, a slight phase lag occurs, so the delay circuit /θ has a delay time that matches this phase lag.
The phases of the two chroma signals supplied to the H switching circuit are matched.

Next, in the /H switching circuit, the two chroma signals shown in Figure 1 and 2 are switched alternately every 1H based on the horizontal pulse, and a ROMA signal as shown in Figure 0 is derived, and this is balanced. modulator//. In the balanced modulator l/, the chroma signal is oscillated from the reference signal oscillator/-.
j, f/, t, j MHz (this is Ko5c + upper SH, that is, Ko x 352rij41jMI (!+-Xθ0157J41M
Hz) is balanced by a reference signal.

The balanced modulated output is J, 676t//MHz
If only the low-frequency components are extracted through the band-pass filter 3 of J,! 7. A chroma signal compatible with the PAL-M system of ft//M)lx is derived.

In this way, according to the above signal conversion device, one balance degree 1i
Instrument 7, // and two bandpass fills! , /3, /H switching circuit, burst switching circuit 2, etc., allows NTSC system chroma signals to be PA.
It can be converted into an LM system chroma signal.

Note that there is no difference in the luminance signal components of both the NTSC and PAL-M systems, so by simply superimposing the NTSC brightness signal with the PAL-M chroma signal, you can create a PAL-M color television. I can get a signal.

As described above, according to the signal conversion device of the present invention, NTSC
It is relatively easy to convert PAL color television signals to PAL.
Since it can be converted to M system color television - Chiron signal,
For example, if a videotape recorded according to the NTSC system is played back using a VTR, and the reproduced color television signal is once converted into a PAL-M system color television signal by the apparatus of the present invention, the PAL-M system television set can be received. You can easily watch it on your computer as well.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the apparatus of the present invention, and FIG. 1 is a signal vector diagram for explaining the operation of the embodiment. Co...burst switching circuit, 2...balanced modulator, ♂
・・・Band pass filter, ri.../H switching circuit. Agent Patent Attorney Aihiko Fukushi

Claims (1)

[Claims] 1. Burst switching means for replacing the burst signal in the chroma signal of the NTSC system with a burst signal whose phase is shifted by 5'', and generating a modulated wave signal having a frequency that is one times the color subcarrier frequency of the chroma signal of the NTSC system. means for balanced modulating the chroma signal obtained from the burst exchanging 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 to invert the BY axis. band and /f filter means for obtaining the chroma signal obtained by the burst switching means and the band pass filter means; 1. A signal conversion device comprising means for frequency converting a chroma signal obtained from a switching means, and converting an NTSC system chroma signal into a FA-LM system chroma signal.