JPS60169286A - Magnetic reproducing device - Google Patents

Abstract

PURPOSE:To obtain a jitter correcting means leading to low cost and high performance by using an oscillated frequency of a VCO so as to modulate a high frequency portion of a reproduced luminance signal and providing nearly same jitter component as that of the reproduced luminance signal to the oscillated frequency of the VCO. CONSTITUTION:An FM luminance signal reproduced from a head 3 is amplified by a preamplifier 4 and the frequency is corrected by a peaking circuit 5. After the high frequency of an output of the peaking circuit 5 is converted at a high frequency converting circuit 11, one frequency is extracted by a BPF12 and demodulated by a demodulation circuit 6. On the other hand, a horizontal synchronizing signal (h) separated from the luminance signal by a synchronizing separator circuit 9 is compared for the phase with a reference signal hr at a phase comparator 15 and its output (v) is fed to the VCO17 via an LPF16. As a result, an output of the VCO17 has nearly the same jitter component as the reproduced luminance signal and the reproduced luminance signal is subject to high frequency conversion by a high frequency converting circuit 11 based on the signal, then the luminance signal suppressed with jitter component is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention relates to a magnetic reproducing device f (hereinafter referred to as a VTR) having a frequency fluctuation (hereinafter abbreviated as jitter) correcting means.

[Background]

FIG. 1 shows a recording signal spectrum of a home VTR (for example, VH8 system), and shows how an FM-modulated luminance signal 1 and a low-frequency converted color signal 2 are frequency-multiplexed.

FIG. 2 shows a conventional FM luminance signal reproducing circuit. The FM luminance signal reproduced from the head 3 is amplified by a preamplifier 4, its frequency characteristics are corrected by a peaking circuit 5, and then demodulated by a demodulation circuit 6 and sent to an LPF.
7 and becomes the luminance signal. In the case of a home VTR, since signals are recorded and reproduced using a magnetic head installed on a rotating drum, collectors occur due to uneven rotation of the drum, making the reproduced screen unstable.

FIG. 3 shows a conventional example of correcting the jitter generated by the above circuit. This conventional circuit uses a variable delay line 8 such as a CCD to correct the jitter-containing luminance signal output from the LPF 7. This is a correction. That is,
A horizontal synchronization signal including jitter is separated from the luminance signal by a synchronization separation circuit 9, thereby changing the clock frequency of a clock oscillator 10. The delay time of the variable delay line 8 is uniquely determined by the clock frequency, and by changing the clock frequency according to jitter, the delay time is changed, and finally a jitter-free luminance signal L 2 is obtained.

omp, the jitter correction circuit shown here has the following drawbacks.

(1) A variable delay line for passing wideband video signals is very expensive.

(2) S/N deteriorates due to clock leakage.

Since the conventional jitter correction circuit has the above-mentioned drawbacks, it is difficult to apply it to home VTRs in terms of cost and performance. Furthermore, the so-called digital time base collector using the converter of 1-A, the N-A converter, and the memory also has drawbacks such as extremely high cost.

〔the purpose〕

SUMMARY OF THE INVENTION An object of the present invention is to provide a jitter correction means which eliminates the above-mentioned conventional drawbacks and which leads to low cost and high functionality.

〔overview〕

The present invention is characterized by a means for high-frequency conversion of a reproduced luminance signal;
means for separating the horizontal synchronization signal from the demodulated signal; means for comparing the horizontal synchronization signal and the reference signal; a filter for extracting a control voltage from the phase comparison output; and a voltage at which the oscillation frequency changes when the control voltage is applied. A controlled oscillator (hereinafter abbreviated as VCO) is provided, and the reproduced luminance signal is converted to a high frequency using the oscillation frequency of the VCO, and feedback control is performed so that the oscillation frequency of the VCO has approximately the same jitter component as the reproduced luminance signal. The key point is that jitter in the reproduced luminance signal is suppressed.

〔Example〕

The BA of the present invention will be described in detail below based on specific examples. FIG. 4 shows a first embodiment of the invention.

This embodiment differs from the conventional example of the third factor in the following points.

(1) A high frequency conversion circuit 11 and a BPF 12 are provided between the peaking circuit 5 and the demodulator 6.

(2) The horizontal synchronization signal separated from the luminance signal by the synchronization separation circuit 9 is outputted from the reference signal generator 13 through the multiplier and branching circuit 14, and the reference signal hr and the phase comparator 15. be compared.

(3) The output of the phase comparator 15 becomes the control voltage V which is limited by the LPF 16, and the voltage controlled oscillator (hereinafter referred to as V
The output of the VCO 17 is input to a high-frequency conversion circuit 11, and the reproduced luminance signal that has passed through the peaking circuit 5 is high-frequency converted according to the oscillation frequency of the VCO 17.

The control voltage V of the VCO 17 is expressed as follows.

y=x v0±ΔV Here, vμ reference potential, lv, is an error voltage corresponding to a jitter component.

The VCO 17 is a linear -f converter as shown in FIG. 5, for example, v=V. When , the frequency f of the output signal
When fi f = f, v = Vo+:jv, f
=fo±Δf. Here, fo is the high frequency conversion frequency in the standard state.

Now, if the center frequency of the reproduced luminance signal is represented by fY, the frequency of the output of the high frequency conversion circuit 11 will be f-1:fY. BPF12 is fl=f+fY or f,=f
Take out the signal with one frequency of -fY and take the signal υ
The peaked signal is demodulated by a demodulation circuit 6. here,
The actual reproduced luminance signal includes jitter, and in this case, the center frequency fY of the reproduced luminance signal is fy = fy. +, jf.

The aim of the present invention is to adjust the frequency of the output signal of VCO 17 to ±
The purpose of this invention is to improve the above jitter ±jf by forming a feedback loop that varies lf.

In the following, a case where the frequency f1 selected by the BPF 12 is used and a case where the frequency f is used as the demodulated signal will be explained separately.

(1) When using fX-f+ta, if fY=fYO±jf, the frequencies #j and f1 of the output signal of the BPF 12 are as follows.

f, = f + fy = f + fyo ± jf Therefore, the output frequency f of VCO 17 is f = fO + -, il
If control is applied so that the frequency 11 of the output signal of the BPF 12 becomes f, the knock can be corrected as follows.

f, = f eye j f + f work. ±jf=f0+fa.

This means that when the frequency fY of the reproduced luminance signal increases due to disturbance etc., the oscillation frequency f of the VCO 17 decreases.
A decrease in yield means more control than an increase in yield.

Note that the codes that appear in each of the above equations are decoded in the same order. The same applies to each formula below.

(2) When using f, = f − fY, fY””fY
o±If, the frequency 1 of the output signal of BPF12
2 becomes as follows.

f, =f-fY xf-fY0 If Therefore, the output frequency f of the VCO 17 is f=fo±Δ
If control is applied so that the frequency f of the output signal of the BPF 12 becomes f, the jitter can be corrected as follows.

b-f, f　If　-fYo乎Δf! fo-f,.

This means that when the frequency fY of the reproduced luminance signal increases (or decreases) due to disturbance or the like, control is applied to increase (or decrease) the oscillation frequency af of vC017.

The actual jitter improvement effect is determined by the loop gain of the feed bank cruise, and the jitter of the signal ±j4 is ±Δf/(loop gain).

FIG. 6 shows a second embodiment of the invention. This embodiment differs from the first embodiment shown in FIG. 4 by using one peaking circuit 1 instead of the peaking circuit 5 and BPF 12 shown in FIG.
8 is a point existing between the high frequency conversion circuit 11 and the demodulator 60.

As the peaking circuit 18 of this embodiment, a surface acoustic wave filter (hereinafter abbreviated as SAW filter) can be used. FIG. 7 shows an example of the characteristics of the SAW filter.

FIG. 7 shows an example of the characteristics when the FM luminance signal is converted into a high frequency range by about 10 degrees.

As is clear from FIG. 7, the group delay characteristic 19 of the SAW filter is almost flat. Further, the SAW filter can obtain desired gain characteristics 20.

Therefore, the signal output from the high frequency conversion circuit 11 is
It is possible to receive desired peaking without being subjected to distortion by the SAW filter. Furthermore, it is clear from the gain characteristic 20 that the SAW filter functions as a BPF.

Note that when peaking a high-frequency converted luminance signal, an LC filter cannot obtain a high Q, but a SAW filter can obtain a satisfactory Q. In addition, the SAW filter is
Its size is almost determined by the wavelength of the surface acoustic wave, and the higher the frequency it handles, the smaller it will be and the cost will be lower.

From the above, according to this embodiment, the first
There is an advantage that the peaking circuit 18 can also be used as the BPF 12 of the embodiment. Furthermore, this embodiment is particularly effective when a SAW filter is used as the peaking circuit 18 because the SAW filter has the characteristics and characteristics described above.

In this example, f
If the characteristics of the SAW filter required when using +f formula = f1) are as shown in Figure 7, then the high-frequency conversion brightness i (i
When using t −tY< −rt) as the signal, the characteristics of the SAW filter are approximately 14 M as shown in FIG.
It is necessary to make the characteristics shown in FIG. 7 axially symmetrical at Hz.

In each of the embodiments of the present invention described above, a multiplier and frequency divider circuit 1 is provided between the reference signal generator 13 and the phase comparator 15.
4 is provided, but this circuit 14 is not necessary when the reference signal generator 13 generates a horizontal frequency. Furthermore, it goes without saying that depending on the frequency d of the reference signal generator 130, only one of a multiplier or a frequency divider circuit may be required. Further, as the reference signal generator 13, a 3.58 h crystal oscillator used in color systems may be used.

〔effect〕

As described above, in the present invention, v
Feedback is applied so that the oscillation frequency of the CO has a frequency fluctuation that corrects the jitter of the reproduced FM luminance signal, so jitter can be reduced, which is extremely effective in stabilizing the reproduced screen and improving image quality. There is.

Furthermore, if the configuration is such that severe keying is applied to the SAW filter after high-frequency conversion, there is no deterioration of the waveform characteristics, and the distortion of the reproduced waveform can be reduced, which is a great effect.

[Brief explanation of drawings]

Figure 1 is the spectrum of the luminance signal and color signal, Figure 2 is a block diagram of a conventional FM luminance signal reproducing circuit, and Figure 3 is the spectrum of the luminance signal and color signal.
Figure 4 is a block diagram of a conventional FM luminance signal reproducing circuit including a jitter correction circuit, Figure 4 is a block diagram showing the first embodiment of the present invention, Figure 5 is a VCo mar-f conversion characteristic diagram, Figure 6 FIG. 7 is a block diagram showing a second embodiment of the present invention, and FIGS. 7 and 8 are characteristic diagrams showing an example of characteristics of the USAW filter. 11...High frequency conversion circuit, 12...BPF, 13...
・Reference signal generator, 14... multiplier and frequency divider circuit,
15--Phase comparator, 16-LPF, 17-VC
o. 1B-・-B#:yf circuit, 19・5AWf)i'
F! Time delay, 20...Gain characteristics of SAW Attorney Michihito Hiraki 1st figure 2 if figure 3 figure 4 figure 5 figure 6

Claims (4)

[Claims] (1) In a magnetic reproducing device that reproduces an FM-modulated luminance signal, a means for correcting the frequency characteristics of the reproduced signal, a means for high-frequency conversion of the reproduced signal, a means for demodulating the high-frequency conversion signal, and synchronization from the demodulated signal. A means for separating signals, a means for comparing the phase of the synchronizing signal with a reference signal, a filter for extracting a control voltage from the phase comparison output, and a voltage-controlled oscillator whose oscillation frequency changes depending on the control voltage. Equipped with at least
The oscillation frequency of the voltage controlled oscillator is used to convert the reproduced signal to a high frequency, and feedback control is applied so that the oscillation frequency of the voltage controlled oscillator has the same jitter component as the reproduced signal. A magnetic reproducing device characterized by: (2) The frequency of the reproduced signal is fY1, the oscillation frequency of the voltage controller oscillator is f, and the demodulation means (f+fY
), when the frequency fY of the reproduced signal increases (or decreases) due to disturbance etc., control is applied to prevent the oscillation frequency of the voltage controlled oscillator from decreasing (or increasing). 1. A magnetic reproducing device according to Patent No. 1, characterized in that: (3) The frequency of the reproduced signal is fY1, the oscillation frequency of the voltage-controlled oscillator is f, and the demodulation means (f-fY
), when the frequency fY of the reproduced signal increases (or decreases) due to disturbance etc., control is performed so that the oscillation frequency of the voltage controlled oscillator increases (or decreases). 2. The magnetic reproducing device according to claim 1, wherein the magnetic reproducing device is configured such that the magnetic reproducing device has a magnetic reproducing device. (4) The magnetic reproducing apparatus according to claim 1, wherein the frequency characteristics of the reproduced signal are corrected using a surface acoustic wave filter after the Takagi transformation.