JPH05174487A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To provide a magnetic recording and reproducing device capable of maxmum improvement of S/N. CONSTITUTION:This device is provided with a FM modulation circuit 2 which frequency-modulates an input signal and a recording equalizer circuit 3 emphasizing the lower sideband wave of a FM signal by K times compared to a specified changing index, then the output of the recording equalizer circuit 3 is recorded in a magnetic tape 6 at the time of recording. Then at the time of reproducing, after a reproducing equalizer circuit 8 corrects the carrier of a reproduced FM signal reproduced from the magnetic tape 6 and the sideband wave in specified relation, a FM demodulation circuit 9 demodulates the reproduced FM signal. The emphasis amount K of the recording equalizer circuit 3 is set near the maxmum value where the changing rate of a second lower sideband wave reproduced output which is a component folding back in the band is not over the changing rate of a first lower sideband wave reproduced output, and also, in an area where the changing rate of a carrier reproduced output is not changed so much.

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 video tape recorder or a video disk.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a recording / reproducing system including an FM modulator / demodulator circuit in a conventional example, and FIG. 5 is a characteristic diagram showing a relationship between carriers and side waves at that time. In FIG.
At the time of recording, the input signal supplied to the input terminal 11 is F
After being converted to an FM signal by the M modulation circuit 12, the recording amplifier 13
Is supplied to the magnetic head 14 and recorded on the magnetic tape 15. Further, at the time of reproduction, the FM signal reproduced from the magnetic tape 15 by the magnetic head 14 is amplified by the reproduction amplifier 16 and then corrected by the reproduction equalizing circuit 17 so that the carrier and the sidebands have a predetermined relationship. The corrected FM signal is
The signal is demodulated by the FM demodulation circuit 18 and output to the output terminal 19.

Next, the relationship between carriers and side waves will be described with reference to FIG. FIG. 5A shows the FM modulation circuit 12
2 shows the relationship between the FM signal carrier and the side wave at the output of FIG. Now, the frequency characteristic of the recording amplifier 13 is flat, and the FM signal remains in the relationship of FIG.
The data is recorded on the magnetic tape 15 via the magnetic head 14.
This is generally called flat equalization.
Next, the FM signal reproduced from the magnetic tape 15 by the magnetic head 14 is amplified by the reproduction amplifier 16. The relationship between the carrier of the FM signal and the side wave at the output of the reproduction amplifier 16 has the relationship shown in FIG. 5C due to the lower side band emphasis effect and the high frequency output lowering characteristic. However, playback amplifier 1
The frequency characteristic of 6 is flat. The output of the reproduction amplifier 16 is the reproduction equalization circuit 1 having the characteristics shown in FIG.
In FIG. 7, after the relationship between the carrier and the side wave is set as shown in FIG. 5 (D), it is demodulated by the FM demodulation circuit 18.

The reproduction equalizing circuit 17 corrects the lower sideband level in the recording / reproducing process and the sideband level changed by the high frequency output lowering characteristic. At this time, even if the demodulated signals have the same frequency characteristics, the equalization characteristics change the margins for the S / N and the inversion phenomenon. Further, this correction has no phase distortion at all, and the frequency characteristic of the amplitude correction is generally called a cosine characteristic. However, in reality, the sideband change rate in which the lower sideband is emphasized and the upper sideband is suppressed, that is, the sideband change rate before demodulation is equalized so as to have a linear descending characteristic, so that the S / N ratio is increased. We are making improvements.

However, in such a recording / reproducing process,
Recording equalize (R
F-emphasis) is well known (for example, JP-A-58-19711). Conventionally, as the S / N improvement method, main emphasis, non-linear emphasis, vertical non-linear emphasis, etc. are well known in the baseband signal region. In that,
Waveform reproduction by clipping becomes a problem, and in nonlinear emphasis, waveform reproduction by a limiter and residual noise near the edge become problems.

On the other hand, the recording equalization utilizes the lower sideband emphasis effect to emphasize the lower sideband in advance during recording,
The slope of the sideband wave change rate is manipulated so that the S / N improvement is maximized during reproduction. This record equalization is
Seen from the baseband signal area before modulation, it is equivalent to emphasis. That is, the modulation index is being manipulated. The advantage of this recording equalization is that it is irrelevant to the waveform reproduction by the limiter or clip and the residual noise because the emphasis is applied by operating the modulation index in the RF signal region. Recording equalization includes, in addition to the lower sideband emphasis (LowBoost) equalization, upper and lower sideband emphasis (Bell type) equalization, upper sideband stop (HighCut) equalization, and the like.
Not only recording equalization but also reproduction equalization can be easily configured, and lower sideband emphasized equalization which is advantageous in both cost and circuit scale is general.

FIG. 6 shows a block diagram of a conventional recording / reproducing system including an FM modulation / demodulation circuit using this recording equalization, and FIG. 7 shows the relationship between the carrier and the side wave at that time. In FIG. 6, at the time of recording, the input signal supplied to the input terminal 21 is converted into an FM signal by the FM modulation circuit 22 and then supplied to the recording equalization circuit 23. The recording equalizer circuit 23 emphasizes the lower sideband of the FM signal. The output of the recording equalizing circuit 23 is supplied from the recording amplifier 24 to the magnetic head 25 and recorded on the magnetic tape 26. Further, at the time of reproduction, the FM signal reproduced from the magnetic tape 26 by the magnetic head 25 is amplified by the reproduction amplifier 27, and then corrected by the reproduction equalizing circuit 28 so that the carrier and the sidebands have a predetermined relationship. The corrected FM signal is F
It is demodulated by the M demodulation circuit 29 and output to the output terminal 30.

Next, the relationship between the carrier and the side wave in the above conventional example will be shown. FIG. 7B shows the relationship between the carrier of the FM signal and the side wave at the output of the FM modulation circuit 22.
The FM signal shown in FIG. 7B has the lower sideband emphasized by the recording equalizing circuit 23 having the characteristic shown in a of FIG. 7A, and becomes the FM signal shown in FIG. 7C. Now, the frequency characteristic of the recording amplifier 24 is flat, and the FM signal is recorded on the magnetic tape 26 via the magnetic head 25 with the relationship of FIG. Next, the FM signal reproduced from the magnetic tape 26 by the magnetic head 25 is amplified by the reproduction amplifier 27. The relationship between the carrier of the FM signal and the side wave at the output of the reproduction amplifier 27 has the relationship shown in FIG. However, the frequency characteristic of the reproduction amplifier 27 is flat. The output of the reproduction amplifier 27 is demodulated by the FM demodulation circuit 29 after the relationship between the carrier and the side wave is set to FIG. 7 (G) in the reproduction equalization circuit 28 having the characteristic shown in FIG. To be done.

[0009]

In recording equalization, the lower sideband enhancement effect is used to enhance the lower sideband in advance during recording and suppress the lower sideband in the playback equalization circuit during playback. Thus, the carrier and the sideband are corrected to a predetermined relationship to improve the S / N. FIG. 8A shows the difference in reproduction equalization depending on the presence / absence of recording equalization. The broken line in the figure shows the reproduction equalization characteristic without recording equalization, and the solid line shows the reproduction equalization characteristic with recording equalization. It can be seen that the lower sideband is suppressed when the recording equalization is applied. FIG. 8B shows the difference in noise distribution depending on the presence or absence of recording equalization in the demodulated baseband signal area. The broken line in the figure shows the noise distribution without recording equalization, and the solid line shows the noise distribution with recording equalization. With recording equalization, the lower sideband is suppressed by reproduction equalization, so that noise is suppressed in the high frequency region.

As described above, when recording equalization is applied, high-frequency noise is suppressed and S / N is improved. However, depending on the amount of equalization (the amount of emphasis on the lower sideband), S / N is reversed.
Was sometimes deteriorated. FIG. 7 shows the relationship between carriers and side waves at that time. FIG. 7B shows the relationship between the FM signal carrier and the side wave at the output of the FM modulation circuit 2.
The FM signal shown in FIG. 7B has the lower sideband emphasized by the recording equalizing circuit 23 having the characteristic shown in b of FIG. 7A, and becomes the FM signal shown in FIG. 7D. Regarding the recording equalization characteristic, the enhancement amount of b is increased as compared with that of a (that is, J _−1a <J _−1b ). Now, the frequency characteristic of the recording amplifier 24 is flat, and the FM signal is recorded on the magnetic tape 26 via the magnetic head 25 with the relationship of FIG.

Next, the magnetic tape 25 is moved by the magnetic head 25.
The FM signal reproduced from is amplified by the reproduction amplifier 27. The relationship between the FM signal carrier and the side wave at the output of the reproduction amplifier 27 is as shown in FIG. 7 (H) due to the lower side band emphasis effect and the high frequency output reduction characteristic. At this time, the reproduction FM at the time of recording equalization having the characteristic shown in a of FIG.
Comparing the signals (F) and (H), the lower side wave (J _-1 )
In regards to ( ₁ ), the reproduction output increases only by being emphasized during recording (that is, J _-1a <J _-1b ), but the reproduction output of the carrier (J ₀ ) decreases (that is, J _0a > J _0b ). However, the frequency characteristic of the reproduction amplifier 27 is flat.

The output of the reproduction amplifier 27 is b in FIG. 7 (E).
In the reproduction equalize circuit 28 having the characteristics shown in
After the relationship between the carrier and the side wave is shown in FIG. 7 (I), it is demodulated by the FM demodulation circuit 29. At this time, noise is suppressed in the high frequency region by the amount of suppression of the lower sideband by the reproduction equalization, but the reproduction output of the carrier (J ₀ ) decreases (the C / N of the carrier decreases). S / N deteriorates.
Further, depending on the amount of equalization at this time, moire due to the return of the second lower side wave may increase.

In view of the above point, the present invention is a folding component into the band in the region where the rate of change of the carrier (J ₀ ) reproduction output does not change much with respect to the lower sideband emphasis amount of the recording equalize circuit. By setting the emphasis amount in the vicinity of the maximum value, which satisfies that the rate of change of the second lower side wave (J _-2 ) reproduction output does not exceed the rate of change of the first lower side wave (J _-1 ) reproduction output, While maximizing S / N improvement,
The present invention provides a magnetic recording / reproducing apparatus in which moire due to folding back of a second lower side wave does not increase.

[0014]

According to a first aspect of the invention, an FM modulation circuit for FM-modulating an input signal at the time of recording, and an F-modulation circuit
The lower sideband of the M signal is K times (K>
1) A reproducing FM having a recording equalizing circuit for emphasizing, recording an output signal of the recording equalizing circuit on a magnetic recording medium, and reproducing the reproduced FM from the magnetic recording medium.
A reproduction equalizer circuit for correcting the carrier of the signal and the sideband to a predetermined relationship, and an FM for demodulating the corrected reproduction FM signal.
It is configured to have a demodulation circuit.

According to a second aspect of the present invention, in the recording equalizing circuit of the first aspect, the enhancement amount K is set in the vicinity of the enhancement amount at which the change rate of the carrier reproduction output changes.

According to a third aspect of the present invention, in the recording equalizing circuit of the first aspect, the enhancement amount K is set to a second lower limit which is a folding component within a region in which the rate of change in carrier reproduction output does not change so much. The configuration is such that the rate of change of the side wave reproduction output does not exceed the rate of change of the first lower side wave reproduction output, and is set near the maximum value.

[0017]

The present invention has the maximum S /
By enabling the N improvement and setting the enhancement amount K to the optimum value, the moire due to the return of the second lower side wave does not increase.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magnetic recording / reproducing apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a recording / reproducing system including an FM modulation / demodulation circuit, which uses lower sideband emphasized equalization.

In FIG. 1, at the time of recording, the input signal supplied to the input terminal 1 is converted into an FM signal by the FM modulating circuit 2 and then supplied to the recording equalizing circuit 3. The recording equalizer circuit 3 emphasizes the lower sideband of the FM signal. The output of the recording equalizing circuit 3 is supplied from the recording amplifier 4 to the magnetic head 5 and recorded on the magnetic tape 6. Further, at the time of reproduction, the FM signal reproduced from the magnetic tape 6 by the magnetic head 5 is amplified by the reproduction amplifier 7 and then corrected by the reproduction equalizing circuit 8 so that the carrier and the sidebands have a predetermined relationship. The corrected FM signal is demodulated by the FM demodulation circuit 9 and output to the output terminal 10.

The emphasis amount K of the recording equalizing circuit at this time
In the invention in which is set near the emphasis amount at which the change rate of the carrier reproduction output changes, the lower side wave (J ₋₁ ) emphasis amount is determined by FIG. FIG. 2 shows a certain modulation frequency (fm)
The relationship between the lower side wave (J _-1 ) enhancement amount, the carrier (J ₀ ) reproduction level, and the lower side wave (J _-1 ) reproduction level in FIG. That is, when the J ₋₁ emphasis amount is increased, the J ₋₁ reproduction level tends to increase monotonically, but the J ₀ reproduction level sharply decreases when a certain J ₋₁ emphasis amount is exceeded. Therefore, in order to maximize the S / N improvement, the J ₋₁ emphasis amount should be set when the J ₀ reproduction level falls. That is,
The lower sideband enhancement amount should be set near the enhancement amount at which the change rate of the carrier reproduction output changes. In this way, by obtaining the optimum emphasis points in some fm, the frequency characteristics of the optimum emphasis points can be obtained and the lower sideband emphasis characteristics of the recording equalizing circuit 3 can be obtained.

On the other hand, the emphasis amount K of the recording equalizing circuit is
It is satisfied that the change rate of the second lower side wave reproduction output, which is a folding component into the band, does not exceed the change rate of the first lower side wave reproduction output within a region where the change rate of the carrier reproduction output does not change so much, In the invention set near the maximum value,
The amount of lower side (J ₋₁ ) enhancement is determined according to FIG. Figure 3
Is a lower side wave (J _-1 ) enhancement amount at a certain modulation frequency (fm), a carrier (J ₀ ) reproduction level and a first lower side wave (J _-1 ) reproduction level, and a folding component into the band. Barrel 2
The relationship of the lower side wave (J _-2 ) reproduction level is shown. That is,
As the J ₋₁ emphasis amount increases, the J ₋₁ reproduction level tends to increase monotonically, but the J ₀ reproduction level sharply decreases when a certain J ₋₁ emphasis amount is exceeded. Therefore, in order to maximize the S / N improvement, the J ₋₁ emphasis amount should be set to a region that does not reach when the J ₀ reproduction level falls.

On the other hand, with respect to the J _-2 reproduction level which is a folding component in the band, when it exceeds a certain J _-1 emphasis amount, it sharply increases with a gradient exceeding the rate of change of the J _-1 reproduction level. That is, the lower sideband emphasis amount is changed within the range where the change rate of the carrier (J ₀ ) reproduction output does not change so much and the change of the second lower side wave (J _-2 ) reproduction output which is a folding component into the band. It should be set near the maximum value that satisfies the condition that the rate does not exceed the rate of change of the first lower side wave (J _-1 ) reproduction output. In this way, by obtaining the optimum emphasis points in some fm, the frequency characteristics of the optimum emphasis points can be obtained, which enables the maximum S / N improvement and the second lower side wave. It is possible to obtain the lower side band enhancement characteristic of the recording equalizing circuit 3 in which the moire due to the folding back of the recording equalizing circuit 3 does not increase.

[0023]

The present invention relates to the lower sideband emphasis amount of the recording equalizer circuit, within the region where the rate of change of the carrier (J ₀ ) reproduction output does not change so much, and the second lower component which is a folding component into the band. The change rate of the side wave (J _-2 ) reproduction output is the first
Lower side wave (J _-1 ) By setting the emphasis amount near the maximum value that does not exceed the change rate of the reproduction output, the maximum S / N can be improved and the second lower side wave can be obtained. The present invention provides a magnetic recording / reproducing device in which the moire due to the folding back is not increased, and its effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetic recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a J ₋₁ emphasis amount and a J ₀ reproduction level and a J ₋₁ reproduction level at a certain modulation frequency.

FIG. 3 is a diagram showing a relationship between a J ₋₁ emphasis amount and a J ₀ reproduction level, a J ₋₁ reproduction level and a J ₋₂ reproduction level at a certain modulation frequency.

FIG. 4 is a block diagram of a conventional recording / reproducing system including an FM modulator / demodulator circuit.

FIG. 5 is a relational diagram of a reproduction equalization characteristic and a carrier and a side wave in an FM signal of each part.

FIG. 6 is a block diagram of a magnetic recording / reproducing apparatus including a conventional recording equalizing circuit.

FIG. 7 is a characteristic diagram showing a recording / reproducing equalization characteristic and a relationship between a carrier and a side wave in an FM signal of each part.

FIG. 8 is a characteristic diagram showing a difference in reproduction equalization characteristics and demodulation noise distribution depending on the presence or absence of recording equalization.

[Explanation of Codes] 1 Input Terminal 2 FM Modulating Circuit 3 Recording Equalizing Circuit 4 Recording Amplifier 5 Magnetic Head 6 Magnetic Tape 7 Reproducing Amplifier 8 Reproducing Equalizing Circuit 9 FM Demodulating Circuit 10 Output Terminal

Claims (3)

[Claims] 1. At the time of recording, an FM modulating circuit for FM-modulating an input signal and a recording equalizing circuit for emphasizing a lower sideband of the FM signal by K times (K> 1) compared with a predetermined modulation index. And reproducing equalization for recording the output signal of the recording equalization circuit on a magnetic recording medium and correcting the carrier and sideband of the reproduced FM signal reproduced from the magnetic recording medium to a predetermined relationship during reproduction. A magnetic recording / reproducing apparatus having a circuit and an FM demodulating circuit for demodulating a reproduced FM signal after correction. 2. The recording equalizing circuit has an enhancement amount K thereof.
2. The magnetic recording / reproducing apparatus according to claim 1, wherein is set in the vicinity of an emphasis amount at which the rate of change in carrier reproduction output changes. 3. The recording equalizing circuit has an emphasis amount K.
Within the region where the change rate of the carrier reproduction output does not change so much, and yet the change rate of the second lower side wave reproduction output, which is a folding component into the band, does not exceed the change rate of the first lower side wave reproduction output. The magnetic recording / reproducing apparatus according to claim 1, wherein the magnetic recording / reproducing apparatus is set to a value close to a maximum value that satisfies the condition.