JPH0684115A - Agc circuit of magnetic recording/reproducing apparatus - Google Patents

Abstract

PURPOSE:To obtain an AGC circuit of a magnetic recording/reproducing apparatus which can stabilize sampling clocks and shorten a gap area. CONSTITUTION:A continuous controlling system with an envelope detecting circuit 2 and a comparator 3 and, a discrete controlling system with a sample holder 4 and a level detector 5 are arranged in parallel in the rear stage of a gain variable amplifier 1 amplifying reproducing signals. The AGC circuit of a demodulating system of a magnetic recording/reproducing apparatus of a partial response type controls the gain of the gain variable amplifier 1 by feeding back a signal of either one of the controlling systems through a change- over switch 6 from a loop filter 7 to the gain variable amplifier 1. The AGC circuit is provided with a comparing means 8 for comparing the amplitude of a sampling signal from the sample holder 4 with a target value of an envelope signal thereby to generate an error signal. Moreover, the AGC circuit consists of a controlling system switching means 9 for detecting whether or not the error signal is within a predetermined range and connecting the loop filter 7 from the continuous controlling system to the discrete controlling system by switching the change-over switch 6 when the error signal is within the predetermined range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an AG of a magnetic recording / reproducing apparatus.
More specifically, the present invention relates to an automatic amplitude control circuit (AGC) in a demodulation system of a magnetic disk device using the partial response method. 2. Description of the Related Art In recent years, a magnetic disk device has a high recording density in order to achieve miniaturization and large capacity of the device, and intersymbol interference of reproduced signals has increased. Therefore, recently, a partial response type magnetic disk utilizing intersymbol interference has been put into practical use. In this partial response type magnetic disk device, in order to suppress the amplitude fluctuation caused by the nonuniformity of the recording medium of the magnetic disk, an automatic amplitude control circuit (Automatic Gauge) for the reproduced signal is used.
in Control: hereafter referred to as AGC) is indispensable, and the ability of this AGC circuit to perform or not greatly affects the characteristics of amplitude detection. Therefore, there is a demand for an AGC circuit of a magnetic disk device having high performance.

[0002]

2. Description of the Related Art FIG. 8 shows an AGC of a conventional magnetic disk device.
This figure shows the configuration of the circuit 80. In this figure, the magnetic disk and head of the magnetic disk device are omitted, and only the reproduction signal from the head is shown. A reproduction signal read by a head from a magnetic disk on which data is recorded is amplified by a variable gain amplifier 81, and then a continuous control system including an envelope detection circuit 82 and a comparator 83, a sample holder 84 and a level detector. It is branched into two systems of a discrete control system consisting of 85. One of the continuous control system and the discrete control system is connected to the loop filter 87 in the subsequent stage by the changeover switch 86, and the signal from the loop filter 87 is fed back to the variable gain amplifier 81. The changeover switch 86 performs the changeover operation by the output of the timing generation circuit 90 to which the read gate signal is input. In addition, the sample holder 8 of the discrete control system
The sampled signal from 4 is input to the clock recovery circuit 88 and the demodulation circuit 89. Clock recovery circuit 8
In 8, the clock is extracted from the input sampling signal, and this clock is input to the sample holder 84. Further, the demodulation circuit 89 demodulates the data by, for example, maximum likelihood detection to obtain reproduced data. Since the reproduction of these clock signals and the reproduction of data are not the gist of the present invention, further description will be omitted.

In the AGC circuit 80 of the conventional partial response type magnetic disk device configured as described above, there is a gap area before the data area of the magnetic disk, and the changeover switch 8 by the timing generation circuit 90 is used.
By switching 6 the reproduction signal passes through the continuous control system when reproducing the gap area and the reproduction signal passes through the discrete control system when reproducing the data area. A training signal whose envelope is all 1's is recorded in the gap region, and the envelope of the reproduction signal from this gap region is detected by the envelope detection circuit 82, compared with the target value by the comparator 83, and its error signal is detected. A variable gain amplifier 81 via a loop filter 87.
Be fed back to. In this process, the amplitude of the reproduced signal is kept constant. After that, when the reproduction of the data area is started, the changeover switch 86 is switched to the discrete control system by the timing generation circuit 90, the level of the signal sampled by the sample holder 84 is detected by the level detector 85, and the amplitude of the reproduced signal is detected. Was kept constant.

[0004]

However, in the AGC circuit of the conventional magnetic disk device, the feedback system is switched from the continuous control system to the discrete control system at a fixed time by the timing generation circuit 90, so that the gap region is changed. There is a problem that the training signal to be recorded in must have a sufficient margin to stabilize the system, the gap area becomes long for the data area, and the frame efficiency deteriorates. When the gap area is shortened, the AGC is performed before the sampling clock is fixed.
Since the system is switched to the discrete control, the AGC malfunctions and under the influence of this, the clock system also falls into an unstable state, and there is a problem that reproduction cannot be performed in the data area.

Therefore, in the present invention, the phase of the sampling clock is determined by comparing the amplitude of the sampled signal with the target value of the slope while detecting the slope of the all-1 training signal and keeping the amplitude constant. It is judged whether or not it is done, and when it approaches the target value, AG
It is an object of the present invention to provide an AGC circuit of a magnetic recording / reproducing apparatus in which a sampling clock is stable, an AGC malfunction does not occur, and a gap region can be shortened as much as possible by switching a C system to discrete control. .

[0006]

FIG. 1 shows the principle configuration of an AGC circuit of a magnetic recording / reproducing apparatus of the present invention for achieving the above object. As shown in FIG. 1, the present invention is an AGC circuit of a magnetic recording / reproducing apparatus for controlling a signal level to a demodulation circuit for demodulating a reproduction signal from a magnetic recording / reproducing apparatus using a partial response system, which is a magnetic recording medium. In the subsequent stage of the variable gain amplifier 1 for amplifying the reproduction signal read from
A continuous control system including an envelope detection circuit 2 and a comparator 3 that compares the envelope signal with a target value, and a discrete control system including a sample holder 4 and a level detector 5 for the sampling signal are provided in parallel, and a changeover switch is provided. 6, the signal of either one of the two control systems is fed to the loop filter 7
In order to control the gain of the variable gain amplifier 1 by feeding back to the variable gain amplifier 1 via, the amplitude of the sampling signal from the sample holder 4 is compared with the target value of the envelope signal to generate an error signal. And the comparison means 8 for determining whether the error signal is within a predetermined range. When the error signal is within the predetermined range, the changeover switch 6 is switched to make the loop filter 7 a continuous control system and a discrete control system. And a control system switching means 9 connected to the.

In the AGC circuit of this magnetic recording / reproducing apparatus, the control system switching means 9 comprises a filter 10 and a comparator 11, and the average error of the error signals from the comparison means 8 is the comparator 1.
The connection destination of the changeover switch 6 may be switched from the continuous control system to the discrete control system when the value becomes smaller than the threshold value of 1. In the case where the control signal holding means 12 is provided in the feedback path of the control signal from the loop filter 7 to the variable gain amplifier 1 and the average error of the comparator 11 does not become smaller than the threshold value during the reproduction of the gap area of the magnetic recording medium. , The amplitude control signal detected by the envelope of the continuous control system is held by this holding means 12, and when the average error becomes smaller than the threshold value, the control system switching means 9 separates the connection destination of the changeover switch 6 from the continuous control system. You may make it switch to a control system.

Further, the target value in the comparing means 8 may be the output of the voltage divider 13 which divides the output of the envelope detection circuit 2 by a factor of 1 / √2, and the loop filter 7 may be a changeover switch. It may be provided in the continuous control system and the discrete control system in the preceding stage of the changeover switch 6 instead of the latter stage.

[0009]

According to the AGC circuit of the magnetic recording / reproducing apparatus of the present invention, continuous automatic amplitude control is performed by detecting the slope of the reproduced signal from the gap area, and the amplitude of the training signal becomes constant regardless of the clock. Then, when the phase of the sampling clock matches when the amplitude of the training signal is constant, the amplitudes of the discrete signals in the gap area are +1, + 1, -1, -1, +1, + 1, It converges to the target amplitude level of -1, -1 .... In this way, it is determined that the phase of the sampling clock has been fixed because the error between the amplitude of the discrete signal and the target value has become small, and the AGC system is switched to the discrete control.

[0010]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 2 shows the configuration of the AGC circuit 20 of the magnetic disk device according to the first embodiment of the present invention. The same components as those of the AGC circuit 80 of the conventional magnetic disk device shown in FIG. Is attached. In the AGC circuit 20 of the magnetic disk device of FIG. 2, the magnetic disk and head of the magnetic disk device are omitted, and only the reproduction signal from the head is shown.

The magnetic disk apparatus of this embodiment is also of the partial response type, and the magnetic disk has a gap area prior to the data area, in which a training signal whose envelope is all 1 is recorded. . AGC circuit 2 of the magnetic disk device of this embodiment
Even at 0, the reproduction signal is amplified by the variable gain amplifier 81, and then the envelope detection circuit 82 and the comparator 83 are used.
And a discrete control system including a sample holder 84 and a level detector 85. One of the continuous control system and the discrete control system is connected to the loop filter 87 in the subsequent stage by the changeover switch 86,
The signal from the loop filter 87 is fed back to the variable gain amplifier 81.

Further, the sampled signal from the sample holder 84 of the discrete control system is a clock recovery circuit 88.
Is input to the demodulation circuit 89. The clock recovery circuit 88 extracts a clock from the input sampling signal and inputs the clock to the sample holder 84.
Further, the demodulation circuit 89 demodulates the data by, for example, maximum likelihood detection to obtain reproduced data.

In the AGC circuit 80 of the conventional magnetic disk device, the changeover switch 86 is changed over by the output of the timing generation circuit 90 to which the read gate signal is input, but in this embodiment, the timing generation circuit 90 is used.
Instead of, the control system switching circuit 25 including the first comparator 21, the filter 22, and the second comparator 23 switches the changeover switch 86. The first comparator 21 compares the amplitude of the sampling signal from the sample holder 84 with the target value of the envelope signal input to the comparator 83 to generate an error signal. This error signal is smoothed by the filter 22 and then input to the second comparator 23, where it is compared with a threshold value. When the error signal is larger than this threshold value, the changeover switch 86 is connected to the continuous control system, and when it is within the threshold value, the changeover switch 86 is changed over and the loop filter 7 is connected from the continuous control system to the discrete control system.

3 (a), 3 (b), and 3 (c) show the output waveform of the variable gain amplifier in the AGC circuit 20 of the magnetic disk device of FIG. 2, the output waveform of the sample holder 84, and the envelope detection circuit 82, respectively. It shows an output waveform.
The cross mark in FIG. 3A indicates the sampling time. In the AGC circuit 20 of the magnetic disk device of this embodiment, the reproduction signal from the gap area passes through the continuous control system,
At this time, continuous automatic amplitude control is applied by detecting the slope, and the amplitude of the training signal becomes constant irrespective of the clock, as shown in FIG. 3 (a). Then, when the phases of the sampling clocks match when the amplitude of the training signal is constant, the amplitudes of the discrete signals in the gap area are +1, +1,-, as shown in Fig. 3 (b). 1,
It converges to the target amplitude level of -1, +1, +1, -1, -1 .... and the envelope width becomes constant.

When the first comparator 21 and the second comparator 23 detect that the error between the discrete signal amplitude and the target value is small, the phase of the sampling clock changes. It is determined that it has been decided, and the AGC system is switched from the continuous control system to the discrete control system. That is,
When the average error in the second comparator 23 becomes smaller than the threshold value, the continuous control system is switched to the discrete control system.

As described above, in the embodiment described above, since the continuous control system is switched to the discrete control system in the state where the phase of the sampling clock is fixed, the pull-in in the discrete control system becomes faster and the training signal becomes shorter. Becomes
Frame efficiency is improved. FIG. 4 shows the configuration of the AGC circuit 40 of the magnetic disk device according to the second embodiment of the present invention. The same constituent members as the AGC circuit 20 of the magnetic disk device of the first embodiment described in FIG. Are given the same reference numerals. AG of the magnetic disk device of this embodiment
The C circuit 40 is the AGC circuit 2 of the magnetic disk device of FIG.
In 0, it is possible to deal with the case where the average error in the second comparator 23 does not become smaller than the threshold value at the end of reproduction of the gap area. Therefore, FIG.
2 is different from the AGC circuit 20 of the magnetic disk device of the embodiment of FIG. 2 in that the AGC circuit 40 of the magnetic disk device of the embodiment of FIG.
The holding circuit 41 is only provided between the loop filter 87 and the variable gain amplifier 81.

FIG. 5 is a flowchart showing the operation of the current affairs circuit 41. In step 501, it is first determined whether or not the training signal written in the gap area is being reproduced. During the reproduction of the training signal, the routine proceeds to step 502, where it is determined whether the error in the comparator 23 is smaller than the threshold value. According to this determination, if threshold value ≦ error, the process proceeds to step 503. In step 503, it is determined whether the training signal has ended, that is, whether the reproduction of the gap area has ended. When the reproduction of the gap region is completed, the average error in the second comparator 23 has not become smaller than the threshold value in the engine of the gap region, so the holding circuit 41 holds the input data as it is. The output does not change depending on the input.

On the other hand, when it is determined in step 501 that the training signal is not being reproduced, step 502
In the case where the threshold value is larger than the error in the step S1 and the training signal is not ended in the step 503, the process proceeds to the step 505 to output the data input to the holding circuit 41 as it is. As described above, in the AGC circuit 40 of the magnetic disk device of the embodiment of FIG. 4, when the average error in the comparator 23 does not fall below the threshold value during the training signal period, the amplitude control signal by envelope detection is changed. It is held by the holding circuit 41, and the discrete control is started when the average error becomes smaller than the threshold value in the comparator 23 during the period of the next training signal.

FIG. 6 shows the configuration of the AGC circuit 60 of the magnetic disk device according to the third embodiment of the present invention.
A of the magnetic disk device according to the first embodiment described in
The same components as those of the GC circuit 20 are designated by the same reference numerals. The difference between the AGC circuit 60 of the magnetic disk device of this embodiment and the AGC circuit 20 of the magnetic disk device of the embodiment of FIG. 2 is that the target value of the first comparator 21 is the target value of the comparator 83 of the continuous control system. It is not a value but only the output voltage value of the voltage divider 61 that divides the output of the envelope detection circuit 82 of the continuous control system by 1 / √2.

In this way, when the clock recovery circuit pulls in, 1 / th of the envelope of the training signal
Since the sample hold value matches the √2 times the amplitude, the loop can be quickly switched to the sample system AGC, and as a result, the training signal is short and the frame efficiency can be improved. FIG. 7 shows the configuration of the AGC circuit 70 of the magnetic disk device according to the fourth embodiment of the present invention, and it has the same components as the AGC circuit 20 of the magnetic disk device of the first embodiment described in FIG. Are given the same reference numerals. AGC of the magnetic disk device of this embodiment
The circuit 70 is different from the AGC circuit 20 of the magnetic disk device of the embodiment of FIG. 2 in that the loop filter 87 arranged at the subsequent stage of the changeover switch 86 is eliminated, and in the continuous control system, it is between the comparator 83 and the changeover switch 86. In the discrete control system, the loop filters 71 and 72 are provided between the level detector 85 and the changeover switch 86, respectively. When the loop filter is provided in each of the continuous control system and the discrete control system as described above, the loop filter can be optimally set in each system, and the phase of the sampling clock can be determined quickly.

[0021]

As described above, according to the present invention,
In the state where the amplitude of the training signal of all 1s is detected and the amplitude is kept constant, it is judged whether the phase of the sampling clock is confirmed by comparing the amplitude of the sampled signal with the target value of the slope, and the target value is set. By switching the AGC system to discrete control when approaching, the sampling clock is stable and there is no malfunction of AGC, and moreover, the pull-in in discrete control of the AGC circuit becomes faster, so the training signal becomes shorter and the frame efficiency becomes shorter. Has the effect of improving. .

[Brief description of drawings]

FIG. 1 is a principle configuration diagram showing a configuration of an AGC circuit of a magnetic recording / reproducing apparatus of the present invention.

FIG. 2A of the magnetic disk device of the first embodiment of the present invention
It is a block circuit diagram which shows the structure of a GC circuit.

3A and 3B show operation waveforms in the main part of FIG. 2, where (a) is an output waveform diagram of the gain control amplifier, (b) is an output waveform diagram of the sample holder, and (c) is an output waveform diagram of the envelope detection circuit. is there.

FIG. 4A of a magnetic disk device according to a second embodiment of the present invention
It is a block circuit diagram which shows the structure of a GC circuit.

5 is a flowchart showing an operation of the holding circuit of FIG.

FIG. 6A of a magnetic disk device according to a third embodiment of the present invention
It is a block circuit diagram which shows the structure of a GC circuit.

FIG. 7A of a magnetic disk device according to a fourth embodiment of the present invention
It is a block circuit diagram which shows the structure of a GC circuit.

FIG. 8 is a block circuit diagram showing a configuration of an AGC circuit of a conventional magnetic disk device.

[Explanation of symbols]

 1 ... Variable gain amplifier 2 ... Envelope detection circuit 3 ... Comparator 4 ... Sample holder 5 ... Level detector 6 ... Changeover switch 7 ... Loop filter 8 ... Comparison means 9 ... Control system switching means 10 ... Filter 11 ... Comparator 12 ... Holding means 13 ... Voltage divider 20, 40, 60, 70 ... AGC circuit 21 according to the embodiment of the present invention 21 ... First comparator 22 ... Filter 23 ... Second comparator 41 ... Holding circuit 61 ... Voltage divider 71 ... 72 Loop filter 81 ... Variable gain amplifier 82 ... Envelope detection circuit 83 ... Comparator 84 ... Sample holder 85 ... Level detector 86 ... Changeover switch 87 ... Loop filter 88 ... Clock recovery circuit 89 ... Demodulation circuit

Claims (5)

[Claims] 1. An AGC circuit of a magnetic recording / reproducing apparatus for controlling a signal level to a demodulation circuit for demodulating a reproduced signal from a magnetic recording / reproducing apparatus using a partial response system, which is read from a magnetic recording medium. An envelope detection circuit is provided after the variable gain amplifier (1) that amplifies the reproduction signal.
(2) and a comparator that compares the envelope signal with the target value (3)
And a discrete control system including a sample holder (4) and a sampling signal level detector (5) are provided in parallel, and a changeover switch (6) selects one of the two control systems. In one that controls the gain of the variable gain amplifier (1) by feeding back one signal to the variable gain amplifier (1) via a loop filter (7), the sampling signal from the sample holder (4) Of the error signal is compared with the target value of the above-mentioned slope signal to generate an error signal, and it is determined whether or not this error signal is within a predetermined range. In some cases, the magnetic recording / reproducing device is provided with a control system switching means (9) for connecting the continuous control system to the discrete control system by switching the selector switch (6) to connect the loop filter (7). Device AGC circuit. 2. The control system switching means (9) is a filter (10).
And a comparator (11), and when the average error of the error signal from the comparison means (8) becomes smaller than the threshold value of the comparator (11), the connection destination of the changeover switch (6) is continuously connected. The AGC circuit of the magnetic recording / reproducing apparatus according to claim 1, wherein the control system is switched to a discrete control system. 3. A control signal holding means (12) is provided in a feedback path of a control signal from the loop filter (7) to the variable gain amplifier (1), and the control signal holding means (12) is provided during reproduction of a gap region of the magnetic recording medium. If the average error in the comparator (11) does not become smaller than the threshold value, the amplitude control signal by the envelope detection of the continuous control system is held by this holding means (12), and at the time when the average error becomes smaller than the threshold value, 3. The AGC circuit of the magnetic recording / reproducing apparatus according to claim 2, wherein the control system switching means (9) switches the connection destination of the changeover switch (6) from a continuous control system to a discrete control system. 4. A target value in the comparison means (8) is an output of a voltage divider (13) for dividing the output of the envelope detection circuit (2) by a factor of 1 / √2. The AGC circuit of the magnetic recording / reproducing apparatus of claim 2 or 3. 5. The loop filter (7) is arranged not in the latter stage of the changeover switch (6) but in the changeover switch (6).
The AGC circuit of the magnetic recording / reproducing apparatus according to any one of claims 1 to 4, wherein the AGC circuit is provided in each of the continuous control system and the discrete control system in the preceding stage.