JPS6123493A - Chrominance signal processing circuit - Google Patents

Abstract

PURPOSE:To improve the S/N of a phase noise of a reproducing chrominance signal by applying waveform shaping to a burst signal to improve the S/N of the burst signal itself. CONSTITUTION:A limit amplifier 3 receives a chrominance signal (a) from a signal source 1 in the period of a burst signal s1 in a chrominance signal and the signal s1 is subjected to amplification and amplitude limit and waveform shaping into a rectangular wave. The signal s1 subjected to waveform shaping is given to a load circuit 6 via a switch circuit 4. On the other hand, the signal (a) from the signal source 1 is given directly to the circuit 6 via the circuit 4 during the period other than the burst signal of the chrominance signal. Only the burst signal of the chrominance signal (c) is waveform-shaped into a rectangular wave. Then only phase information given substantially to the burst signal is extracted from the burst signal superimposed with noises by the electromagnetic converting system, the S/N of the burst signal is improved and the S/N of the phase noise of the chrominance signal is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a color signal processing circuit used in a VTR or the like.

[Prior Art] The prior art will be explained below using a home VTR as an example. In a home VTR, a composite video signal is recorded as follows. That is, the luminance signal component is a low carrier FM
while the color signal components are recorded at low frequencies (e.g. VH
8-NTSC system, it is converted to 629KHz),
The luminance signal is multiplied by the low carrier FM signal and recorded on the magnetic tape.

To reproduce this, first separate the low carrier FM signal and the low frequency converted color signal using a filter, then the low carrier FM signal is subjected to FM'atR to become a luminance signal, and the low frequency converted color signal is converted to a high frequency signal. and mixed with the luminance signal. When converting the color signal to a higher frequency band, i.e. back to the normal color subcarrier frequency, the I
! In order to reduce the phase noise received by the magnetic conversion system, a PLL is applied to match the phase of the burst signal with the phase of the reference phase oscillator.

Such a conventional color signal high frequency conversion circuit is effective when the burst signal and the color information signal in the color signal are simultaneously subjected to phase noise. However, if only the burst signal portion of the color signal receives phase noise, the PLL causes the color information signal portion to receive phase noise instead.

[Summary of the Invention] Therefore, an object of the present invention is to provide a color signal processing circuit that can waveform shape a burst signal to increase its S/N ratio, thereby improving the S/N ratio of phase noise of a color signal. It is to be.

According to the invention, the color signal processing circuit receives a color signal from a color signal source having a reference burst signal. The burst signal in the color signal is subjected to waveform shaping processing, and the processed color signal is provided to a load circuit.

[Embodiments of the Invention] This invention will be described below with reference to FIGS. 1 to 3.
The following describes an example in which the present invention is applied to a color signal reproducing circuit.

FIG. 1 is a schematic block diagram showing a color signal processing circuit according to a preferred embodiment of the present invention. A color signal consisting of a burst signal and a color information signal is supplied from a signal source 1 to a burst signal waveform shaping circuit 2. In this embodiment, the color signal supplied from the signal source 1 corresponds to a low frequency converted color signal reproduced from a magnetic tape (not shown). This signal is illustrated in Figure 2a. Signal S1
indicates a burst signal, and signal S2 indicates a color information signal.

Furthermore, a burst gate pulse as already shown in FIG. 2 is applied to the burst signal waveform shaping circuit 2. The burst signal waveform shaping circuit 2 operates to shape only the burst signal S1 in response to the burst gate pulse. A color signal including a burst signal whose waveform has been shaped in this manner is shown in FIG. 2C. This signal 0 is given to the load circuit 6. In this embodiment, the load circuit 6 corresponds to a color signal high frequency conversion circuit for changing the color signal to a high frequency range.

Referring now to FIG. 3, a block diagram illustrating the burst signal waveform shaping circuit 2 in further detail is shown. The burst signal waveform shaping circuit 2 includes a limiting amplifier 3 and a switch circuit 4. Switch circuit 4 has two input terminals and one output terminal. , one of the two input terminals is connected to the output of the limiting amplifier 3, and the other input terminal is directly connected to the signal 8!1. The input of the limiting amplifier H3 is connected to the signal source 1. An output terminal of the switch circuit 4 is connected to a load circuit 6.

A burst gate pulse is applied from a burst gate pulse input terminal 5 as an i control input of the switch circuit 4 . When the burst gate pulse input is high, the switch circuit 4 is connected to the limiting amplifier 3 during the period of the burst signal S1 in the color signal. On the other hand, when the burst gate pulse input is low, that is, during periods other than the burst signal S1 in the color signal, the switch circuit 4 is connected to the signal source 1 side.

During the period of the burst signal S1 in the color signal, the limiting amplifier 3 receives the color signal a from the signal source 1 and outputs the burst signal S1.
Amplify and limit the amplitude of the signal to shape it into a square wave. This waveform-shaped pulse 1-Hakutan S1 is applied to the load circuit 6 via the switch circuit 4. On the other hand, in a period other than the burst signal @ in the color value code, the color signal a from the signal source 1 is directly applied to the load circuit 6 via the switch circuit 4. In this way, the color signal applied to the load circuit 6 has only the burst signal 61 shaped into a square wave, as shown in FIG. 2C. As a result, only the phase information originally possessed by the burst signal is extracted from the burst signal on which noise is superimposed in the electromagnetic conversion system, improving the S/N ratio of the burst signal, and thus improving the S/N ratio of the phase noise of the color signal. ratio is improved.

In the above-mentioned embodiment, the burst signal waveform shaping circuit 2 is inserted before the load circuit 6 (color signal range conversion circuit), but it is inserted after the load circuit 6 (color signal range conversion circuit), but it is inserted after the load circuit 6 (color signal range conversion circuit). The waveform of only the burst signal may be shaped. In this case as well, the same effects as in the above embodiment can be achieved.

In the above-described embodiment, the present invention is applied to a color signal reproducing circuit of a VTR, but the present invention can also be applied to a color signal recording circuit.

FIG. 4 shows another preferred embodiment of the invention, in which VT
This is a case where the present invention is applied to an R color signal recording circuit. In the figure, a low frequency conversion circuit 7 receives a color signal and performs low frequency conversion on the color subcarrier frequency. The low frequency converted color signal is applied to the burst signal waveform shaping circuit 2, and only the burst signal is waveform shaped in the same manner as described above. The color signal obtained by waveform-shaping the burst signal is recorded on the magnetic tape 10 by the recording head 8 via a recording amplifier circuit (not shown) serving as a load circuit. The recorded signal is reproduced by the reproduction head 9.

FIG. 5d shows the flow from the burst signal waveform shaping circuit 2 to recording.
Only the burst signal portion of the color signal applied to the tube 8 is shown. The waveform-shaped burst signal shown in FIG. 5d receives noise in an electromagnetic conversion system consisting of recording and reproducing heads 8 and 9 and magnetic tape 10, and is reproduced as a signal as shown in FIG. 58. Since the waveform is shaped into a square wave, there is almost no phase modulation.
Phase noise is significantly reduced.

Note that the burst signal waveform shaping circuit 2 may be placed before the low-frequency conversion circuit 7 to waveform-shape the burst signal before low-frequency conversion of the chrominance signal. It has the effect of

In this invention, the slew rate is increased by shaping the signal waveform, so it is possible that harmonics may interfere with the luminance signal, etc. However, the burst period is not in the visible time period of the luminance signal, so even if harmonic interference Even if it occurs, it will not appear on the television screen.

Although the above embodiment has been explained using a home VTR as an example, this invention is not limited to VTRs, but generally applies to color signals when writing a composite video signal in some form to a recording medium and reading it out. The present invention can be applied to routes, and in this case as well, the same effects as in the above-mentioned embodiments can be achieved.

[Effects of the Invention] As described above, according to the present invention, by waveform shaping the burst signal, the S/N ratio of the phase of the burst signal itself can be improved, and the S/N ratio of the phase noise of the reproduced color signal can be improved.
The N ratio can be improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a color-〇- signal processing circuit which is a preferred embodiment of the present invention, Fig. 2 is a signal waveform of each part of the block diagram of Fig. 1, and Fig. 3 is a burst signal waveform shaping circuit. FIG. 4 is a block diagram showing another preferred embodiment of the present invention, and FIG. 5 shows signal waveforms of each part of FIG. 4 in detail. In the figure, 1 is a signal source, 2 is a burst signal waveform shaping circuit, 3 is a limiting amplifier, 4 is a switch circuit, 5 is a burst gate pulse input terminal, 6 is a load circuit, 7 is a low frequency conversion circuit, and 8 is a recording head. , 9 indicates a playback head, and 10 indicates a magnetic tape, respectively.

Claims (4)

[Claims] (1) A color signal processing circuit that receives a color signal from a color signal source having a reference burst signal, processes the color signal, and supplies the processed color signal to a load circuit, the color signal being included in the color signal. A color signal processing circuit including a waveform shaping means for shaping the waveform of a burst signal. (2) The waveform shaping means includes: a limiting amplifier for amplifying and amplitude limiting the burst signal; and a switching means for activating the limiting amplifier only during the period of the burst signal in the color signal. A color signal processing circuit according to claim 1. (3) The carrier frequency of the color signal supplied from the signal source is a color subcarrier frequency that is low frequency converted, and the load circuit includes a circuit for high frequency conversion of the color signal. A color signal processing circuit according to claim 1. (4) The carrier frequency of the color signal supplied from the signal source is a low-band converted color subcarrier frequency, and the load circuit includes a circuit for recording the color signal on a recording medium. A color signal processing circuit according to claim 1.