JPS61102897A - Chrominance signal recording and reproducing circuit - Google Patents

Abstract

PURPOSE:To correct the jitter of chrominance signals in high accuracy by providing an independent circuit for correction of the jitter of pilot signals and, by using the VCO in common for decoding the low-band conversion chrominance signals for reproduction, because this jitter correction circuit comprises a VCO that has the jitter component. CONSTITUTION:A VCO 29 is controlled by a phase-locked loop (PLL) circuit comprising of a frequency converter 37, a BPF 38, a phase comparator 26, an LPF 31, a VCO 29, a primary frequency converter 40, a BF 41, and an oscilla tor 24 so as to correct the jitter included in the divided pilot signals. The output of the VCO 29 is converted to signals (t) for demodulating a low frequency conversion chrominance signals by a phase shifter 30, a primary frequency converter 27, and the oscillator 24. The reproducing band conversion chrominance signals separated by an LPF 21 are decoded to the reproduction chrominance signals by the decording signal, (t) at a frequency converter 22. Therefore, the jitter component of the reproduction chrominance signal which occurs at the time of frequency conversion is offset.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a color signal recording and reproducing circuit for a magnetic recording and reproducing device. In particular, the video tape recorder (hereinafter referred to as V)
The present invention relates to a color signal recording/reproducing circuit suitable for use in a color signal recording/reproducing circuit (abbreviated as TR).

[Background of the invention]

Conventionally, as a video signal recording and reproducing method in a general home VTR (for example, Ml (S method)), a method is used in which a luminance signal is FM-modulated and then frequency-multiplexed with a color signal converted to a low frequency band for recording and reproducing. For example, as shown in ``NHK Home Video Technology'' PP, edited by Japan Broadcasting Corporation, 94-95, in the color signal recording and reproduction method, so-called jitter such as frequency fluctuation and phase fluctuation of the color subcarrier during reproduction is corrected. As a means for this, a method is used in which a continuous signal synchronized with the reproduced color synchronization signal (color burst) is generated, and this continuous signal is used to perform frequency conversion with the reproduced color signal to cancel jitter. Figure 3 shows a conventional example of a recording circuit for luminance signals and color signals.NTS
In the case of the O method, only a composite video signal in which a 1R degree signal and a color signal are frequency multiplexed is input. V11iS
In the case of this method, after separating the luminance signal and the color signal, they are processed separately, and then frequency-multiplexed and recorded using the same magnetic head. Specifically, a low-pass filter (hereinafter referred to as LP)
After the luminance signal 4 is separated by the 7M modulation circuit (hereinafter abbreviated as MOD) 2, a 7m1 degree signal is obtained. Next, the color signal will be explained. A color signal fts is generated by a band pass filter (hereinafter abbreviated as BPIF) 3.
Separate. f8 represents the frequency of the color signal. color signal f
s is the second frequency conversion circuit (Maix conv in the figure,
It is expressed as ) 4 to the low frequency LPI
After removing unnecessary frequency components by P5, the signal is mixed with the FM luminance signal 6 by the mixing circuit 6, and recorded on the tape by the recording amplifier 7 and the magnetic head 8. Next, a method of generating the conversion signal d input to the second frequency conversion circuit 4 for converting the color signal into a low frequency band will be described. Horizontal synchronization signal fH
, by a frequency control circuit (hereinafter abbreviated as AFO) 14 and a voltage controlled oscillation circuit (hereinafter abbreviated as VCO) 15, 1
A signal 4 with a frequency of 60 fH is obtained, and a signal t with a frequency of 40 fH is obtained by a frequency dividing circuit (denoted as kp, s in the figure) 16. Burst extraction circuit 102 Phase comparison circuit 11. A signal with a frequency of 5.58 MH2 synchronized with the burst signal is obtained by LPF12 and VO (N3?) and the signal is provided by the first frequency conversion circuit (
In the figure, the frequency is converted by 9 (denoted as dub 0onv), and a converted signal d is obtained.

Next, the reproducing circuit will be explained. FIG. 4 shows a specific example of the reproducing circuit. A bypass filter (hereinafter referred to as H
A reproduced FM luminance signal is separated from a demodulation circuit (hereinafter abbreviated as DEMO) 19 into a reproduced luminance signal D. On the other hand, LP? The reproduced low frequency conversion color signal S separated by '21 is converted into a reproduced color signal by the conversion signal l in the second frequency conversion circuit 22, and is further converted into a reproduced color signal by the conversion signal l.
P? 23 removes unnecessary frequency components. Next, a method of generating the conversion signal l will be described. Burst extraction circuit 2
51 oscillation circuit (hereinafter abbreviated as OSC) 24, phase comparator circuit 26 and LPF 31 control VOO29 u fd U
is obtained. The control signal U also includes a component corresponding to jitter, and the oscillation frequency of the VOO 29 includes the jitter component of the reproduced color signal. Further, the VCC 529 is controlled to prevent the oscillation frequency error from becoming extremely large by the discriminator 28 and the reproduced horizontal interval borrow fH'. '
From the signal ν obtained by i'o029, the starting circuit 30.
A converted signal l is obtained by the first frequency conversion circuit 27 and 0S024. The converted signal l contains a frequency or phase variation component corresponding to jitter, and the jitter of the reproduced color signal is corrected by performing frequency conversion with the reproduced low-pass converted color signal in the first frequency conversion circuit 22.

This method has the drawback that the range for correcting fluctuations in the process of creating a continuous signal from the reproduced color synchronization signal is limited, and the fluctuations cannot be sufficiently corrected.

In order to compensate for this drawback, for example, as shown in Japanese Patent Publication No. 55-45656 and Japanese Patent Publication No. 49-2410, a pilot signal is frequency-multiplexed into a low-frequency conversion color signal and an FM luminance signal, and recorded and reproduced. A method of correcting jitter using a pilot signal is known. However, these methods have drawbacks such as the frequency at which the pilot signal is multiplexed and recorded is near the lower limit of the band that can be recorded and reproduced on a magnetic tape, and the band of the video signal is limited.

On the other hand, an excellent method is to select the frequency of the pilot signal to be a frequency between the low frequency conversion color signal and the IFM luminance signal, perform multiple recording, and use the pilot signal during playback to satisfactorily correct jitter.

[Purpose of the invention]

An object of the present invention is to correct the jitter contained in the reproduced color signal using a reproduced pilot signal in the jitter correction circuit for the color signal with high precision, thereby improving the signal-to-noise ratio (hereinafter referred to as S/N) of the color signal. The purpose of the present invention is to provide a circuit that significantly improves the

[Summary of the invention]

The present invention provides an independent circuit for correcting the jitter of the pilot signal, and since the WOO used in the jitter correction circuit has a jitter component, this circuit is also used for the subsequent use of the reproduced low-frequency conversion color signal. [Embodiments of the Invention] The present invention will be described below in detail based on specific embodiments. First, recorded Byron signals will be described. Second
The figure shows an example of the frequency relationship between a pilot signal, a low frequency conversion color signal, an FM luminance signal, an FM audio signal, etc. In the case of the MTSO system, when the horizontal synchronization signal frequency is f, the pilot signal frequency f is selected as the following frequency.

In this embodiment, a case where a pilot signal is generated by multiplying fH by 96 using a phase-locked loop circuit and is recorded and reproduced will be described. An embodiment of the present invention will be described below with reference to FIG. The luminance signal of the words reproduced from the magnetic tape by the Video Rad 8 and preamplifier 17 is HP
718 and the demodulator 19, the luminance signal t is sharply modulated.

On the other hand, the pilot signal P is separated by Bpy3s and then frequency-divided by the frequency dividing circuit 66. The frequency f of the divided pilot signal is f, -96x! -fm
-40fm Color synchronization signal (color burst) of low frequency conversion color signal
is equal to the frequency of Therefore, since the divided reproduced pilot signal includes a jitter component equal to that of the reproduced low-pass converted color signal, it is possible to share the control signal for correcting the jitter of the pilot signal and the color signal. This point will be discussed in more detail. Second frequency conversion circuit 37BP
738. Phase comparison circuit 26. LPF31. VOO2
9. First frequency loss conversion circuit 40. B P IP41.
A phase-locked loop (hereinafter P
LL) circuit controls the VCO 29 to correct jitter included in the frequency-divided pilot signal. Further, the VOO 29 is controlled by the disk IJ minator 28 to prevent changes in the oscillation frequency from becoming extremely large. The output of VOO29 is sent to phase shifter 30. The first frequency conversion circuit 271 is converted by the oscillator 24 into a signal for demodulating the low frequency conversion color signal. The reproduced band-converted color signal separated by the LPF 21 is demodulated into a reproduced color signal by a demodulated signal l containing a jitter component in the second frequency conversion circuit 22. Therefore, the jitter component of the reproduced color code is canceled during frequency conversion. Since the jitter of the reproduced color signal is corrected using the jitter information contained in the continuous pilot signal, it is possible to correct the jitter with extremely high precision and stability compared to the case where the intermittent signal described above is used. Furthermore, although the above-described embodiments are based on the HTsO system, the same thing can be said for the PAL or SICOAM systems.

〔Effect of the invention〕

As described above, according to the present invention, unlike the conventional jitter correction method using an intermittent signal such as a reproduced color synchronization signal, jitter is corrected using a continuous pilot signal. Jitter correction becomes possible. Therefore, there is an effect of greatly improving the S/N ratio in recording and reproducing color signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a color signal reproducing circuit according to the present invention.
FIG. 2 is a frequency spectrum diagram showing the frequency relationship between a pilot signal and a video signal, FIG. 3 is a block diagram of a conventional signal recording circuit, and FIG. 4 is a block diagram of a conventional 1M number reproduction circuit. 35... B PF s 67... Second frequency conversion circuit, 38... B PF5 26... P, /DN 31... DPIF. 29... v 00. 40...First frequency conversion circuit-41-B P'F. Representative Patent Attorney Akio Takahashi - ゛ - Flute 1 Fig. 2 Fig. 1, t; Figure 14

Claims (1)

[Claims] In magnetic recording and reproducing circuits that record and reproduce pilot signals and video signals by frequency multiplexing, low frequency conversion is performed on the voltage or current controlled oscillator circuit present in the phase synchronization circuit, which is controlled to correct the jitter of the reproduced pilot signal. A color signal recording/reproducing circuit characterized in that it is also used for demodulating color signals.