JPH07203484A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a high speed search picture for a VTR with high quality by making a signal input amplitude to an A/D converter stable and eliminating a fluctuation in an output level of a D/A converter. CONSTITUTION:In the VTR having a time base correction circuit using a digital memory, a 1st automatic gain control circuit 13 is provided to a pre-stage of an A/D converter 15 giving a digital signal to the digital memory as an amplitude stabilizing means. Furthermore, a 2nd automatic gain control circuit 6 is provided to a post-stage of a D/A converter applying D/A-conversion to an output of the time base correction circuit as an amplitude stabilizing means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus such as a VTR, and more particularly to a magnetic recording / reproducing apparatus for improving the correction accuracy of time axis error in a reproducing system circuit.

[0002]

2. Description of the Related Art In a VTR, a luminance FM signal and a chrominance signal are A / D converted at the time of reproduction and written in a digital memory, and a device for correcting a time axis error is disclosed in, for example, Japanese Patent Laid-Open No. 64-48580. The techniques described may be mentioned. In this prior application, a reproduction signal is A / D converted and written in a digital memory, and then a time axis error is corrected by a sync signal separated from the signal obtained by demodulating the reproduction signal, and D / A conversion is performed. To obtain an output.

[0003]

By the way, in the prior art disclosed in the above-mentioned prior application, no consideration is given to the input level of the A / D converter which requires high accuracy. That is, when the circuit shown in the above-mentioned prior application is applied to the VTR, the signal amplitude of the reproduction signal obtained from the magnetic head is the sensitivity of the magnetic tape, the sensitivity of the magnetic head, the mechanical contact state of the head with the tape, and the VHS. In the standard, the tape speed corresponding to the standard / 3 times mode is greatly affected. In particular, when the circuit shown in the prior application is applied during the search in the special reproduction mode, the relative speed of the magnetic tape and the magnetic head changes as compared with that during normal reproduction, and accordingly, the signal of the reproduction signal obtained from the magnetic head. The amplitude also changes. Therefore, if the circuit shown in the above-mentioned prior application is used as it is for a VTR, the input level of the A / D converter is not taken into consideration, so that it does not fall within the target value of the signal input level of the A / D converter. The problem arises.

Therefore, the problem to be solved by the present invention is to solve the above-mentioned problems of the prior art. The purpose is to stabilize the signal amplitude of the reproduction signal obtained from the magnetic head, The signal input level of the A / D converter is kept within the target value, whereby a highly accurate and stable time axis correction operation is realized, and a high quality reproduction signal is obtained.

[0005]

In order to achieve the above-mentioned object, a luminance signal is FM-modulated and a color signal is frequency-converted into a low frequency band of the luminance signal to record the luminance FM signal and the color signal on a magnetic recording medium. Then, in reproduction, in the magnetic recording / reproducing apparatus for correcting the time axis error by performing analog-digital conversion of the luminance FM signal and the chrominance signal by an A / D converter, and writing the same in the digital memory of the time axis correction circuit,
An automatic gain control circuit (hereinafter referred to as an AGC circuit) is provided as an amplitude stabilizing means on the front side of the A / D converter.

Further, an AGC circuit is also provided as an amplitude stabilizing means on the subsequent stage side of a D / A converter for D / A converting the output of the time axis correction circuit.

[0007]

The AGC circuit provided on the front side of the A / D converter operates according to the sensitivity of the magnetic tape, the sensitivity of the magnetic head, the mechanical contact state of the head with the tape, the tape speed, and the relative speed of the tape and the head. Thus, even if the output level of the magnetic head changes greatly, the output value is controlled to the target value of the AGC circuit with high accuracy. Then, the output of the AGC circuit is input to the A / D converter, and the signal input level of the A / D converter is set within the target value, thereby realizing a highly accurate and stable time base correction operation.

Further, another AG provided on the rear side of the D / A converter for D / A converting the output of the time axis correction circuit.
Even if the output level of the D / A converter varies, the C circuit controls the output value to the target value of the AGC circuit with high accuracy in the same manner as above. Therefore, the signal processing circuit in the subsequent stage of the AGC circuit is not affected by the variation in the output level of the D / A converter, and a high quality reproduced signal can be obtained.

[0009]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a block diagram showing a reproducing circuit system of a VTR (magnetic recording / reproducing apparatus) according to the first embodiment of the present invention.
Here, regarding the application of the time axis correction circuit to the VTR, 2
You can think of the street. The first is to absorb time-axis fluctuations (jitter) of the magnetic tape running system during normal reproduction. The other is the time discontinuity (skew) of the synchronization signal generated during the search for running the magnetic tape at a higher speed than during recording, and the continuous time axis deviation caused by the change in the relative speed between the tape and the head. To remove. The embodiment shown in FIG. 1 is applied to the latter high speed search.

In FIG. 1, 1 is a magnetic tape, 2 is a recording / reproducing magnetic head (hereinafter referred to as a magnetic head), 3 is a preamplifier, 4 is a signal selection switch (hereinafter referred to as a switch), and 5 is a high-pass filter (hereinafter referred to as a high-pass filter). , HPF),
6 is an automatic gain control circuit (hereinafter, referred to as RFAGC circuit) that keeps the amplitude level of the FM luminance signal constant, 7 is an equalizer (FM equalizer) for equalizing the frequency characteristic in the band of the FM luminance signal, and 8 is the FM. Luminance signal processing circuit for processing the luminance signal such as demodulation, de-emphasis, noise reduction, 9 is a low-pass filter (hereinafter referred to as LPF), 10 is a chroma ACC circuit for keeping the color signal amplitude level at a constant value, and 11 is, for example, a VHS type In the case of a VTR, a chroma signal processing circuit for converting a color signal, which has been frequency-converted into a low frequency band of a luminance signal at the time of recording, to an original frequency again, or removing an interference from an adjacent track by a comb filter, 12 is a luminance signal. And a video output terminal for adding and outputting color signals. Further, 13 is an automatic gain control circuit (hereinafter, referred to as RFAGC circuit) that stabilizes the input level to the A / D converter, 14 is an LPF, and 15 is A.
/ D converter, 16 is a time axis correction circuit having a digital memory, 17 is a D / A converter, 18 is an LPF, 19 is an equalizer having the same characteristics as the equalizer 7, 20
Is an FM demodulator, and 21 is a sync separation circuit for extracting a horizontal sync signal from the demodulated video signal.

The flow of the reproduction signal in FIG. 1 is as follows. First, during normal reproduction, the luminance FM signal and the low frequency conversion color signal are read from the magnetic tape 1 via the magnetic head 2 and the preamplifier 3. Next, the output of the preamplifier 3 is selected during normal reproduction by the switch 4 that selects the reproduction signal during normal reproduction and the reproduction signal during high-speed search. Next, the HPF 5 extracts a luminance signal component from the output signal of the switch 4,
On the other hand, the LPF 9 extracts the color component.
Further, the luminance signal component from the HPF 5 has its amplitude fixed by the RFAGC circuit 6 for keeping the FM signal amplitude level constant, and then equalized within the band of the FM luminance signal in which the high frequency band is lowered in the tape / head system by the equalizer 7. Are equalized in frequency characteristics, and further, by the luminance signal processing circuit 8, F
Processing such as demodulation, de-emphasis and noise reduction of the M luminance signal is performed. Also, the color component is LP
The signal is input from F9 to the chroma ACC circuit 10 and controlled so that the amplitude of the burst portion of the color signal becomes constant. Further, this signal is converted by the chroma signal processing circuit 11 into a color signal whose frequency is converted into the low frequency range of the luminance signal again to the original frequency, and the comb-shaped filter removes interference from the adjacent track. The luminance signal from the luminance signal processing circuit 8 described above is added by an adder and output from the video output terminal 12 as a composite video signal.

On the other hand, when the VTR is in the high speed search state, the switch 4 is switched to select the output of the LPF 14. The signal output from the preamplifier 3 is input to the RFAGC circuit 13, where
The sensitivity of the tape, the sensitivity of the magnetic head, the mechanical contact state of the head with the tape, the change of the track width due to the mode change of the tape speed, and the fluctuation of the output level depending on the relative speed of the tape and the head are eliminated. The output signal of the RF AGC circuit 13 has a band component of ½ or more of the sampling frequency in the A / D converter 15 removed by the LPF 14, and then the A / D converter 15 outputs, for example, 8
It is converted into a bit digital signal. Also, RFAG
The output signal of the C circuit 13 is also input to the equalizer 19,
The equalizer 19 having the same characteristic as the equalizer 7 equalizes the frequency characteristic in the band of the FM luminance signal in which the high frequency is lowered, and then the FM demodulator 20 demodulates the luminance signal including the synchronization signal. Further, the sync separation circuit 21 extracts only the sync signal. Then, the VCO in the time axis correction circuit 16 in which the synchronization signal is phase-controlled
The clock signal generated by the (voltage controlled frequency oscillator) causes the above 8-bit digital signal to be written in the line memory. By this operation, even if the reproduction signal contains a continuous time axis deviation caused by the change in the relative speed of the tape and the head, the clock signal synchronized with the reproduction signal is written in the line memory. The digital signal has the time axis error removed.

Next, the digital signal in the line memory is read by a clock signal having a very small time-axis fluctuation like a crystal, converted into an analog signal again by the D / A converter 17, and out of band by the LPF 18. The aliasing component of is removed and added to the switch 4 for selecting a reproduction signal for normal reproduction and a reproduction signal for high-speed search. At the time of high-speed search, the time-axis-corrected signal is selected by the switch 4, and thereafter, as in the case of normal reproduction, the brightness signal is passed through the HPF 5, RF AGC circuit 6, equalizer 7, and brightness signal processing circuit 8. And the color signal that has passed through the LPF 9, the chroma ACC circuit 10 and the chroma signal processing circuit 11 are added by an adder and output from the video output terminal 12 as a composite video signal.

Here, the input amplitude level of the A / D converter 15 is very important for accurately converting the reproduced signal into a digital signal. Generally, the target value of the input amplitude level peculiar to the A / D converter is determined by the following restrictions. The minimum input amplitude is determined because the signal amplitude is sufficient for the quantization noise generated when the signal is sampled by the A / D converter. On the other hand, the maximum input amplitude is, for example, 1 in the case of 8-bit quantization when the amplitude corresponding to the minimum resolution is determined to be 1 mV.
It is a value that is uniquely determined, such as mV × 2 ⁸ = 256 mV, and cannot exceed this value. Therefore, in general, A
The input amplitude level of the / D converter needs to be set with high accuracy and without variation with respect to the target center input level.

However, when the time base correction function which requires such an A / D converter is applied to the high speed search of the VTR without using the RF AGC circuit 13 of the present embodiment, the A / D converter described above is used. There is a problem that the input amplitude level of the D converter 15 changes greatly. For example VHS
In the expression VTR, when a search is performed at a tape speed which is about 40 times as high as the normal standard recording / reproducing mode (normal mode), the relative speed between the tape and the head is 23 as shown in FIG.
% Will also fluctuate. FIG. 2 shows a VHS type VTR in the normal standard reproduction mode and 40
The FM carrier frequency of each reproduction signal is shown at the time of fast-forward search and fast-reverse search at a tape speed about twice as fast. In the case of standard reproduction in which the tape feeding direction and the tape feeding speed are the same as those in the normal recording, the FM carrier frequency defined by the VHS standard is obtained as shown by A in FIG. Since the head (rotary magnetic head) and the magnetic tape move in the same direction, the frequency of the FM carrier of the reproduced signal becomes 23% lower as shown by B in FIG. On the contrary, in the case of rewind (REW), the rotary head and the magnetic tape move in opposite directions, so that the FM carrier of the reproduction signal is 2 as shown by C in FIG.
3% higher frequency.

When the FM carrier signal having a large frequency variation is passed through the magnetic head 2 and the preamplifier 3 shown in FIG. 1, the inductance of the magnetic head 2 and the preamplifier 3 are increased.
The output amplitude of the preamplifier 3 largely changes due to the reproduction gain frequency characteristic generated by the input capacitance of. For example, a reproduction FM carrier A during normal reproduction and an FM during reverse search
Comparing the amplitudes of the carrier C, although not shown here, the amplitude of the FM carrier C at the time of fast-return search is lower than the reproduced FM carrier A at the time of normal reproduction by 20% or more.

In addition to the amplitude fluctuation due to the FM carrier having a large frequency fluctuation as described above, there are the following problems. That is, in general, the magnetic tape 1, the magnetic head 2, and the preamplifier 3 have variations in sensitivity. In particular, the magnetic head 2 has 20 to 30 depending on the head structure and material.
It has an output variation of up to%. The preamplifier 3 also has a gain of about 1000 times, and has a gain variation of 10 to 20% due to the precision variation of the elements inside the integrated circuit. Further, in the high-speed search state, the mechanical contact state of the magnetic tape 1 with the magnetic head 2 may change greatly due to changes in the tension of the magnetic tape. Furthermore, the magnetic tape to be reproduced is not limited to the one recorded by the reproducing device itself, but may be reproduced in a compatible manner. In this case, an azimuth deviation between the recording device and the reproducing device or a recording level deviation occurs. Will end up. Eventually, the reproduction output obtained from the preamplifier 3 causes each of the above-mentioned variations to overlap with each other, causing a very large fluctuation.

Here, the RFAGC which is a feature of the present invention
By providing the circuit 13 as shown in FIG. 1, the above-mentioned problem can be solved. The RF AGC circuit is a generally known circuit that keeps the amplitude of an RF signal constant, and includes an envelope detection circuit and a gain control amplifier. FIG. 3 shows the RFAGC circuit 1 according to this embodiment.
3 shows the characteristics of the input signal amplitude level versus the output signal amplitude level of FIG. As shown in FIG. 3, even if the input signal amplitude level changes from 50 mV to 1000 mV by a factor of 20, the output is a small change of 450 mV to 500 mV, and the above-mentioned FM carrier frequency fluctuation, magnetic head sensitivity variation, etc. Even if there is, the output amplitude of the RFAGC circuit 13 can be kept almost constant. Due to this effect,
The input level of the A / D converter 15 is stabilized and
A signal amplitude sufficiently large with respect to the quantization noise of the D converter 15 can be input to the A / D converter 15. Also, the maximum input amplitude does not exceed the upper limit value of the quantization of the A / D converter 15.

Further, another RF AGC circuit 6 is provided.
Is known to be arranged in front of the luminance signal processing circuit 8 and the FM equalizer 7 as shown in FIG.
The following effects can be obtained by operating the GC circuit 13 at the same time. The purpose of the second RF AGC circuit 6 is to arrange it in the preceding stage of the luminance signal processing circuit 8 and the FM equalizer 7 so as to stabilize the signal input level of the FM limiter circuit of the luminance signal processing circuit 8 and the FM equalizer 7 and always It is to keep the distortion to a minimum and suppress the fluctuation of the frequency characteristic after FM demodulation. On the other hand, as described above, the circuit of FIG.
When used for high-speed R search, the first RFAGC circuit 1
By 3, the reproduction amplitude fluctuation up to the A / D converter 15 can be suppressed. However, the D / A converter 17 also has a factor that causes a gain variation, and when the second RF AGC circuit 6 is not provided, the output amplitude of the D / A converter 17 needs to be individually adjusted. Further, the first RF AGC circuit 13 operates so as to make the amplitude of the signal to which the color components are added constant. Therefore, when the reproduced signal includes a color signal with high saturation, the output amplitude of the luminance signal of the first RFAGC circuit 13 is reduced. However, by inputting the above-mentioned signal to the second RF AGC circuit 6, the variation of the D / A converter 17 and the decrease of the output amplitude of the luminance signal when the reproduced signal includes a color signal of high saturation are canceled. You can do it.

In the first embodiment of FIG. 1 described above, two RF AGC circuits are used.
The second RF AGC circuit 6 can be omitted if the second embodiment of the present invention shown in FIG. FIG. 4 is a block diagram showing a reproducing circuit system of a VTR (magnetic recording / reproducing apparatus) according to the second embodiment of the present invention. In FIG. 4, components equivalent to those in FIG. I will omit the explanation.

In FIG. 4, when the VTR is in the normal reproduction, the switch 4 is on the upper side, and the output of the RFAGC circuit 13 is selected. On the other hand, during the high speed search, the switch 4 is on the lower side, and the time axis correction is performed. In this embodiment, the first RFA
AGC for detecting the signal amplitude of the RF signal in the GC circuit 13
A chromatographic wrap circuit 26 for removing color signal components is added in front of the detection section 25 (a chromatographic wrap circuit 26 is added to the input system of the control signal for envelope detection of the RF AGC circuit). This allows
Even if the reproduced signal includes a color signal with high saturation, the operation is performed so that the amplitude of the luminance signal component becomes constant. RFAG
The output of the C circuit 13 is the LPF as in the first embodiment.
It is input to the A / D converter 15 via 14 and the input amplitude of the A / D converter 15 is made constant. However, since only the luminance signal component is made constant as compared with the first embodiment of FIG.
It is necessary to take a margin equal to the amplitude of the color signal component with respect to the maximum quantized amplitude of the D converter 15. Further, since the second RF AGC circuit 6 is not provided, the variation of the D / A converter 17 cannot be canceled. Therefore, it is necessary to provide the gain adjuster 27 after the D / A converter 17.

According to this embodiment, the time axis correction function can be accurately operated with a simple circuit configuration having only one RF AGC circuit.

[0023]

As described above, according to the present invention, for example, V
The input amplitude level of the A / D converter can be made constant against changes in the FM carrier amplitude that occur when the high-speed search speed of TR is very fast, such as 40 times. Magnetic tape,
The input amplitude level of the A / D converter can be stabilized against variations in sensitivity due to the magnetic head and preamplifier, variations in tension of the magnetic tape, and variations in reproduction level that occur during tape compatible reproduction. Further, by providing the second RF AGC circuit in the present invention, the influence of the sensitivity variation of the D / A converter and the color saturation in the reproduced signal can be eliminated.
It is possible to stabilize the signal input level of the FM limiter circuit and the like in the luminance signal processing circuit, and suppress fluctuations in frequency characteristics after FM demodulation. As described above, the stable and highly accurate operation of the time axis correction means can be secured, and a high-quality reproduced image of high-speed search can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a reproducing circuit system of a VTR according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing how the reproduced FM signal carrier frequency fluctuates when the VTR is set to a high-speed search mode.

3 is a characteristic diagram showing a relationship between an input signal level and an output signal level of the RFAGC circuit 13 in FIG.

FIG. 4 is a block diagram showing a reproducing circuit system of a VTR according to a second embodiment of the present invention.

[Explanation of symbols]

6 FM automatic gain control (RFAGC) circuit for making the amplitude level of the luminance signal constant 7 Equalizer 8 Luminance signal processing circuit 11 Chroma signal processing circuit 13 A / D converter Automatic gain control (RFAGC) circuit for stabilizing the input level 15 A / D converter 16 Time axis correction circuit 17 D / A converter 19 Equalizer A FM carrier frequency defined by the VHS standard B FM carrier frequency during tape fast-forward C FM carrier frequency during tape fast-reverse 25 AGC detector 26 Chromatography Wrap circuit

Claims (5)

[Claims] 1. A brightness signal is FM-modulated, and a color signal is frequency-converted into a low frequency band of the brightness signal to record the brightness FM signal and the color signal on a magnetic recording medium.
In a magnetic recording / reproducing apparatus for correcting a time axis error by performing analog-digital conversion of a signal and a color signal by an A / D converter and then writing the digital memory of a time axis correction circuit, a signal input path of the A / D converter. A magnetic recording / reproducing apparatus characterized in that at least an amplitude stabilizing means for the luminance FM signal is provided on the side. 2. The luminance signal is FM-modulated and the color signal is frequency-converted into a low frequency band of the luminance signal to record the luminance FM signal and the color signal on a magnetic recording medium.
In a magnetic recording / reproducing apparatus for correcting a time axis error by performing analog-digital conversion of a signal and a color signal by an A / D converter and then writing the digital memory of a time axis correction circuit, a signal input path of the A / D converter. The first amplitude stabilizing means provided on the side, the output signal from the D / A converter that digital-analog converts the output signal of the time axis correction circuit, and the output of the preamplifier that amplifies the signal extracted from the magnetic head. A magnetic recording / reproducing apparatus comprising: a switch for switching between a signal and a signal; and a second amplitude stabilizing means provided on the signal output path side of the switch. 3. The magnetic recording / reproducing apparatus according to claim 2, wherein the magnetic recording / reproducing apparatus has a mode in which the time axis correction is not performed, and the second amplitude stabilizing means is used in a mode in which the time axis correction is not performed. A magnetic recording / reproducing apparatus, which is also used as a means. 4. The magnetic recording / reproducing apparatus according to claim 1, 2 or 3, wherein the amplitude stabilizing means includes an envelope detection circuit for a luminance FM signal and a variable gain amplifier. 5. The magnetic recording / reproducing apparatus according to claim 4, wherein means for removing the color signal is provided on a signal input path side of an envelope detection circuit for the luminance FM signal.