JPS5929029B2 - Sampling method of carrier color signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sampling a carrier color signal included in a color video signal, and in particular, a method for sampling the carrier color signal directly with a sampling pulse selected at a frequency within the carrier color signal band. It was designed to be sampled.

Generally, as a method for directly sampling the carrier color signal, there is a method of selecting a sampling pulse at a frequency twice or three times the color subcarrier frequency coarse fs of the carrier color signal. The disadvantage was that it was expensive and occupied a wide band.

The present invention eliminates such drawbacks, and changes the sampling frequency (fa) to fa■fs+yofH (however,
fH: horizontal scanning frequency, n: any integer, m: any positive integer) and within the band of the carrier color signal, the sampling frequency is low and the occupied band can be narrowed. This is what I did.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a block diagram for explaining the principle of the present invention. In the same figure, a carrier color signal applied to an input terminal 1 is transmitted through a sampling gate circuit 2, a sample output terminal 5, a low-pass filter 6, a balanced modulator T, and a comb filter 8.
The signal is then output to the output terminal 9. The output signal of the oscillator 3 is supplied to the sampling gate circuit 1 circuit 2 via the sampling pulse generation circuit 4. The output signal of another oscillator 12 is fed to the balanced modulation circuit T. Next, the first
The operation in the configuration shown in the figure will be explained.

An NTSC carrier color signal is applied to the input terminal 1. The frequency spectrum of this is shown in FIG. In the figure, the upper side wave is shown in white, and the lower side wave and color subcarrier frequency are shown in black. A carrier color signal having such a spectrum is sampled by the sampling gate circuit 2. Here, sampling gate circuit 2
The sampling pulse applied to is obtained as follows. First, let the oscillation frequency fa of the oscillator 3 be fa=fs
It is selected near +2n+1□fH and within the band of the carrier color signal.

(However, fH: horizontal scanning frequency, n■ arbitrary integer, m:
(any positive integer) Here, for example, if n=0 and m1 are selected, fa=f5+ifH.

By supplying such a signal to the sampling pulse generation circuit 4, a sampling pulse of frequency fa7fS++fH is obtained. When this sampling pulse is applied to the sampling gate circuit 2, a sampled carrier color signal is obtained at the sampling output terminal 5. Note that this operation will be equivalently explained with reference to FIG. In FIG. 2, the same reference numerals are given to the blocks that operate in the same way as in FIG. In FIG. 2, a carrier color signal applied to an input terminal 1 is balanced-modulated by a balanced modulator 10, and its low-frequency components are transmitted to a low-pass filter 1.
1, sampled by the sampling gate circuit 2, and the sampled carrier color signal is output to the sample output terminal 5. The sampling pulse is obtained in the same manner as in FIG. 1 by applying the source of the frequency Fa generated by the oscillator 3 to the sampling pulse generation circuit 4. Further, the output signal of the oscillator 3 is applied to the balanced modulator 10 . That is, as shown in FIG. 3, the balanced modulator 10 has F8=1, F
Since a carrier color signal having a spectrum with FH intervals above and below H as the center and a carrier wave with the above frequency Fa=f8+-4fH are added, the output end of the low-pass filter 11 has the upper and lower spectrum as shown in FIG. A carrier color signal whose sidebands are interleaved while maintaining the -FH relationship is obtained. Next, this interleaved carrier color signal is sampled by the sampling gate circuit 2 using a sampling pulse whose frequency Fa is Fa=Fa+-4fH, so that the sample output terminal 5 shown in FIG. A sampled carrier color signal similar to that obtained in is obtained.

Normally, the sample output terminal 5 is connected to a transmission path including a known encoding circuit, a video tape recorder, etc., and a transmission system such as a known encoding/decoding circuit.

Here, it is assumed that the sampled carrier color signal is transmitted to those transmission systems, and the first
This will be explained with reference to the figure. By applying the sampled carrier color signal to the low-pass filter 6, a carrier color signal with interleaved upper and lower sidebands similar to the output signal of the low-pass filter 11 shown in FIG. 2 is produced at its output end. can get.

This 5-interleaf carrier color signal is sent to a balanced modulator 7.
The balance is modulated by The carrier wave for balanced modulation is supplied from the oscillator 12 and its frequency is Fa=F8+-4fH
Selected nearby. FIG. 5 shows the frequency spectrum of the output signal of the balanced modulator 7. By supplying a signal having such a frequency spectrum to the comb filter 8, a carrier color signal having a spectrum similar to that shown in FIG. 3 is restored at the output terminal 9. The comb filter 8 is composed of a well-known 1H (horizontal scanning period) delay line and an arithmetic circuit, and its frequency characteristics are as shown in FIG.

Here, a 1H delay line was used as the delay line constituting the comb filter 8, but this was because m was selected to be 1 at the oscillation frequency Fa-F8+FH of the oscillator 3 (
This is supported.

For example, if m=2 is chosen, it is necessary to use a 2H delay line. As is clear from the above description, according to the present invention, since the sampling frequency for directly sampling the carrier color signal is selected within the band of the carrier color signal, the occupied band is narrow. The effects are very large.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the basic example of the present invention.
FIG. 2 is a block diagram for equivalently explaining the present invention;
FIGS. 3, 4, and 5 are diagrams showing signal spectra, and FIG. 6 is a diagram showing an example of frequency characteristics of a comb filter. 1... Input terminal, 2... Sampling gate circuit, 3... Oscillator, 4... Sampling pulse generation circuit, 5... Sample Output terminal.

Claims (1)

[Claims] 1. When sampling the carrier color signal included in a color video signal, the frequency f_a of the sampling pulse is f_a=f_s+(2n+1)/(4m)f_H (where f_s: color subcarrier frequency, f_H: horizontal scanning frequency, n: A method for sampling a carrier color signal, characterized in that sampling is performed near an arbitrary integer (m: an arbitrary positive integer) and within a band of the carrier color signal.