JP2002133791A - Magnetic tape device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence frequency of data errors. SOLUTION: This magnetic tape device is provided with a magnetic tape, a plurality of magnetic heads, pulsing circuits converting regeneration signals into digital signals for individual magnetic heads, phase comparators outputting phase data which are phase differences between the digital signals and discriminating clocks, charge pumps generating the control voltages corresponding to the phase data, voltage control oscillators generating the discriminating clocks based on the control voltages, and a signal processing circuit processing the digital signals. Each charge pump is provided with a gain switching unit switching the gain of the charge pump by an instruction from the signal processing circuit, a charge pump side analog divider dividing the output value of one switched output circuit by a prescribed value and provided on this output circuit, and a charge pump side adder adding a prescribed value to the divided output value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic tape device, and more particularly, to a magnetic tape device having a plurality of magnetic heads.

[0002]

2. Description of the Related Art Conventionally, in a magnetic tape device,
By synchronizing the clock of the bit extraction circuit with the reproduction signal from the magnetic head, the information of the reproduction signal is read. Then, after this signal is interrupted for a long period of time due to the follow-up to jitter and the like in the steady state and the abnormal situation such as dropout,
It is required to have the ability to quickly pull in synchronization. This is because, in the reproduction of a digital signal, for example, even if one bit is read out, a completely different level is represented. Therefore, the clock signal is generated by extracting a bit clock component from the reproduced signal.

The clock signal responds at a high speed when the read speed of the reproduction signal as the basis of the clock signal changes, that is, when the reproduction speed of the magnetic tape changes. Specifically, a voltage controlled oscillator (hereinafter, VCO) that generates a clock signal has two types of response characteristics during reproduction, a high-speed pull-in mode and a stable response mode after the pull-in is completed.
As a result, the control voltage of the VCO is controlled so as to be equal to or less than the target phase in a short time after the start of phase pull-in in the high-speed pull-in mode, and the stable response mode is controlled so as not to perform excessive response after reaching the target phase. ing.

[0004]

However, as for the response characteristics of the VCO at the time of reproduction, there are only two types of response modes, a high-speed pull-in mode and a stable response mode after the pull-in is completed. If it is too large, it will deviate from the feedback loop, cause a malfunction, and the phase response between the read data and the discrimination clock will increase due to the loop response delay, and the frequency of occurrence of data errors will increase.

[0005]

The object of the present invention is to improve the disadvantages of the prior art, and in particular to improve the response speed of the VCO when the magnetic head detects a phase difference in the same direction at the same time, thereby reducing the frequency of data errors. It is an object of the present invention to provide a magnetic tape device capable of suppressing the magnetic tape device.

[0006]

Accordingly, the present invention provides a magnetic tape on which predetermined data is stored and reproduced, a plurality of magnetic heads for storing and reproducing predetermined data on the magnetic tape, and a plurality of magnetic heads. For each magnetic head, a pulse conversion circuit for converting a reproduced signal reproduced from the magnetic tape by each magnetic head into a digital signal, a digital signal and a discrimination clock for separating the digital signal are compared, and the positions of both signals are compared. A phase comparator that outputs phase data that is a phase difference, a charge pump that generates a control voltage corresponding to the phase data, and a voltage-controlled oscillator that generates a discrimination clock based on the control voltage from the charge pump. I have. A signal processing circuit for processing digital signals is provided, and each charge pump is provided with a gain switch for switching the gain of the charge pump in accordance with a command from the signal processing circuit, and one of the switched output circuits is provided. A charge pump-side divider for dividing the output value of the output circuit by a predetermined value is provided. Further, the charge pump is provided with a charge pump side adder for adding a predetermined value to one of the divided output values.

With this configuration, when the speed of the magnetic tape changes, the phase difference between a plurality of magnetic heads operating at the same time, that is, the digital signal reproduced by the phase comparator and the classification clock is changed. The charge pump outputs a control voltage corresponding to the phase difference, and a discrimination clock is output from a voltage controlled oscillator (hereinafter, VCO) based on the control voltage. And
The control voltage is controlled so as to be equal to or less than a predetermined value. When the control voltage is equal to or less than a certain value, the charge pump is switched to one output circuit by the gain switch. The output of the switched charge pump is divided by a predetermined value to lower the gain, thereby suppressing an excessive response due to a jitter component or the like. Further, since a predetermined value is added to the output circuit side, the gain can be increased, the excessive response of the control voltage of the VCO is suppressed, and the phase following characteristic of the discrimination clock which is the output of the VCO is obtained. Can be improved.

[0008] The signal processing circuit may be configured to instruct the gain switch to switch the gain when the control voltage from the charge pump is within a predetermined range. Thus, high-speed control is performed until the control voltage falls within a predetermined range, and when the control voltage falls within the predetermined range, the gain control unit is switched to perform stable response control of the VCO control voltage. In addition, the phase difference between the digital signal and the VCO can be suppressed, and the occurrence of data errors during reproduction can be suppressed.

It is preferable that an arithmetic unit for calculating a value to be input to each charge pump side adder based on predetermined data from each magnetic head is provided. Further, an arithmetic unit-side adder for adding each phase data from each phase comparator corresponding to each magnetic head to this arithmetic unit, and an arithmetic unit-side divider for dividing the added value by a predetermined value Is desirably provided.

With this configuration, the phase data corresponding to the plurality of magnetic heads are added and divided, and the value of the operation result is input to the charge pump side adder. Therefore, in the case of a speed variation in which all the magnetic heads detect a phase difference in the same direction, the detection data from all the magnetic heads can be reflected on the control voltage of the VCO and the gain can be improved appropriately. The phase following characteristic of the discrimination clock can be improved.

Further, the predetermined value in the divider on the charge pump side may be set to one-fifth or less of the predetermined value in the divider on the operation unit side. 20 is desirable. Thereby, when a phase difference is detected in each magnetic head,
The effect of each head can be set at a moderate rate,
When the phase difference is detected by all the magnetic heads due to the speed fluctuation of the magnetic tape, the gain of the charge pump can be increased, and the phase tracking characteristic of the VCO can be improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIGS.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The magnetic tape device in FIG.
Magnetic tape (not shown) on which predetermined data is stored and reproduced
And a plurality of magnetic heads 1 for storing and reproducing predetermined data on the magnetic tape. Then, for each of the plurality of magnetic heads 1, an equivalent amplifier 2 (hereinafter, AGC),
Filter 3, pulsing circuit 4, phase comparator 5, charge pump 6, and voltage controlled oscillator 7 (hereinafter, VCO)
And are provided. Further, the device includes an arithmetic unit 8 for performing arithmetic processing on the output of each of the phase comparators 5 and a signal processing circuit 9 for processing a signal from each magnetic head 1.

Hereinafter, this will be described in detail.

The magnetic tape (not shown) has a predetermined width in a direction perpendicular to the running direction of the tape, and tracks are formed at a predetermined angle with respect to this width. Then, predetermined information is magnetically stored and reproduced in the main data area of the track.

The magnetic head 1 is mounted on a predetermined portion of a magnetic tape device, and scans a track of the magnetic tape. When scanning, the magnetic head 1 stores information on a magnetic tape, or reproduces information already stored. A plurality of the magnetic heads 1 are provided,
It is desirable that the plurality of magnetic heads 1 be used at the same time, that is, operated simultaneously to store and reproduce data.

The AGC 2 amplifies the analog reproduction signal from the magnetic head 1 so as to have a constant amplitude value. The filter 3 shapes the signal amplified by the AGC 2. The pulsing circuit converts the shaped analog waveform into a digital signal 16.

Here, the signal processing circuit 9 mainly performs processing of the converted digital signal 16, and specifically,
The timing for generating a clock for discriminating the signal 16 is detected from the digital signal 16 by pattern detection, and a read gate signal 18 is output to the phase comparator 5. The phase comparator 5 reads the read gate signal 1
At the point when 8 is input, the phase pull-in of the digital signal 16 is started. When the phase pull-in is started, the phase comparator 5 compares the phase of the digital signal 16 with the discrimination clock 17 which is the output of the VCO 7, and uses the compared phase difference as phase data 11 to the charge pump 6 and the arithmetic unit 8. Output.

The arithmetic unit 8 calculates average phase data 14 based on the phase data 11 detected for each magnetic head 1 and outputs the average phase data 14 to the charge pump 6. Charge pump 6
Receives the phase data 11 and the average phase data 14 as inputs, selects a gain by a gain switching signal 13 from the signal processing circuit 9, and outputs the selected gain as a control voltage 15 to the VCO 7. The VCO 7 determines an oscillation frequency based on the control voltage 15 and outputs the determined oscillation frequency to the phase comparator 5 and the signal processing circuit 9 as a discrimination clock 17.

Here, the configuration of the charge pump 6 will be described in detail with reference to FIG. FIG. 2A is a block diagram illustrating a configuration of the charge pump according to the present embodiment.
FIG. 2B is a block diagram illustrating a configuration of a conventional charge pump.

Referring to FIG. 2A, the charge pump 6 according to the present embodiment includes a gain switch 6a for switching the gain of the charge pump 6 in accordance with a command from the signal processing circuit 9, and the switched one. Is provided with a charge pump side divider 6b for dividing the output value of the output circuit by a predetermined value. Further, a charge pump side adder for adding a predetermined value to one of the divided output values is provided. Is provided.

The phase data 11 input from the phase comparator 5 is internally branched, one of which is directly connected to the gain switch 6a, and the other of which has an output value of 1 / M by the charge pump divider 6b. (M is a predetermined value),
Next, after being added to the average phase data 14 by the charge pump side adder 6c, it is input to the gain switch 6a.
The gain switch 6a outputs one of the two data as the control voltage 15 of the VCO 7 according to the gain switching signal 13.

Where "M" is a gain ratio,
This will be described with reference to a block diagram of a conventional charge pump 60 shown in FIG. At the time when the read gate signal 18 is input, the gain switching signal 13 outputs the phase data 11 as the control voltage 15, and when the phase pull-in is completed, the gain switch 60 a uses the charge pump side divider. The 60b output is output as the control voltage 15. Therefore, if the gain at the start of the phase pull-in is “1”, the gain after the phase pull-in is completed is “1 / M”.

The configuration of the arithmetic unit 8 will be described with reference to FIG. Phase comparator 5 provided for each magnetic head 1
Are added by the computing unit-side adder 8a, and then reduced to 1 / L (L is a predetermined value) by the computing unit-side divider 8b. The output is used as average phase data 14 and output to the charge pump 6 provided for each magnetic head 1.

Next, the operation of this embodiment will be described with reference to the drawings. FIG. 4 is an explanatory diagram showing the relationship between the set voltage 15 which is the output of the charge pump and time. FIG.
FIG. 4 is an explanatory diagram showing temporal changes of a tape speed and a phase difference.

Referring to FIG. 5, when the signal processing circuit 9 outputs the read gate signal 18, the phase comparator 5 detects the phase difference, and the control voltage 15 of the VCO 7 is output by the charge pump 6, and the digital signal is output. A feedback loop is configured so that the phase difference between the clock 16 and the discrimination clock 17 becomes zero (see FIG. 1). And the signal processing circuit 9
When the phase acquisition is started, high-speed acquisition is performed, and control is performed so that the phase becomes equal to or less than the target phase in a short time. Control to reduce the loop gain. Here, the target phase is a range of “± a” in FIG. 5, and when the control voltage first reaches the range (first after the set voltage 15 starts to converge) (time A in FIG. 4). , The signal processing circuit 9 outputs a gain switching signal 13.

When the gain switching signal 13 is input to the charge pump 6, the phase switching is switched from the phase data 11 side to the output side of the charge pump side adder 6c by the charge pump side switch 6a, thereby switching the gain of the feedback loop. Done. When the average phase data 14 is not input, the charge pump 6 is equivalent to the configuration of FIG. 2A, which is the configuration of the conventional charge pump 60.

Referring to FIG. 6, assuming that the speed of the magnetic tape fluctuates from the target speed, the phase difference fluctuates from the ideal position (phase difference 0) as shown in FIG. 6 with respect to the speed fluctuation. When the tape speed fluctuates, the phase of the digital signal 16 generated from the magnetic head 1 also fluctuates, and the feedback loop responds to make the discrimination clock 17 follow the phase. At this time, if the speed fluctuation of the magnetic tape is large, the magnetic tape deviates from the feedback loop, and the phase difference between the digital signal 16 and the discrimination clock 17 becomes large due to a loop response delay. Since the fluctuation in the speed of the magnetic tape occurs similarly for all the heads, the phase difference detected by each head is substantially the same. Further, even when the speed fluctuation occurs when data is written to the magnetic tape, the same phenomenon occurs even when the speed fluctuation does not occur during reading.

[0029]

Next, an embodiment will be described.

In the present embodiment, the number N of the magnetic heads 1 used simultaneously, that is, simultaneously storing and reproducing data, is "1".
Consider a feedback gain in a magnetic tape device of N = 16 ″.

In FIG. 2A, the coefficient M of the charge pump-side divider 6b of the charge pump 6 is generally "5 to 5".
20 "is desirable, and in this embodiment," M = 10 "
And

The coefficient L of the calculator 8b of the calculator 8 shown in FIG. 3 is set as follows. Assuming that only the predetermined magnetic head 1 and one other magnetic head 1 have detected a phase difference, the phase amount detected by each magnetic head 1 is defined as "
α ”and“ β ”, the output after the gain switching in the charge pump 6 of the predetermined magnetic head 1 is (α / M +
(α + β) / L). At this time, “M” is set to one fifth of “L” assuming that the weight of β does not affect the weight of α.
In the following, the relationship between “M” and “L” is “M <L / 5”
Becomes If "L" is large, the influence of the other magnetic heads 1 on the predetermined magnetic head 1 is reduced, but the gain at the time of the speed fluctuation cannot be increased. It is assumed that “L = 64” which is four times the number “N”.

According to the above setting, the average phase data 14 is calculated using the phase data 11 from each magnetic head 1, so that the average phase data 14 is 1.56 per magnetic head 1. % (1/64). Therefore, when focusing on one magnetic head 1 and considering the gain of the feedback loop, the maximum gain at the start of pull-in, that is, when the charge pump 6 is in the state shown in FIG. For example, when only a predetermined magnetic head 1 detects a phase difference, the maximum value is 11.56%. This is the result of adding 10% (1/10) of the weight by "M = 10" and the above 1.56%. When all the magnetic heads 1 detect the same phase difference,
The maximum is about 35%. This is 10% and 1.5% as above.
6% × 64 (the number of magnetic heads). On the other hand, in the configuration using the conventional charge pump 60 shown in FIG. 2B, when only a predetermined magnetic head 1 detects a phase difference, the maximum is 10%. When all the magnetic heads 1 detect the same phase difference,
It is up to 10%. Therefore, when only one magnetic head 1 detects the phase difference, no remarkable difference is observed. However, in the case of the speed fluctuation at which all the magnetic heads 1 detect the phase difference in the same direction, the above-mentioned 2
Comparing the two cases, the present example is 35%, whereas the conventional example is 10%, the feedback gain is increased, and the phase tracking characteristic is improved.

[0034]

Since the present invention is constructed and functions as described above, according to this, data is written when rotation fluctuation occurs on a magnetic tape, and this data has a phase fluctuation, When the data is reproduced by the magnetic head, or when the rotation fluctuation occurs during the data reproduction, the phase difference detected by the phase detector in each magnetic head is averaged and added to the control voltage of the VCO of each magnetic head. Therefore, the gain of the charge pump increases, and the VCO can respond to the phase fluctuation caused by the rotation fluctuation at a high speed. The phase fluctuation due to other scratches / deterioration of the magnetic tape is stable. Response can be made. This has an unprecedented superior effect of preventing the occurrence of a VCO mislock due to the occurrence of rotation fluctuation and the like, and reducing the phase difference between the data and the discrimination clock to suppress the occurrence of data errors. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2A is a block diagram illustrating a configuration of a charge pump according to the present embodiment disclosed in FIG. 1, and FIG. 2B is a block diagram illustrating a configuration of a conventional charge pump. .

FIG. 3 is a block diagram illustrating a configuration of a computing unit disclosed in FIG. 1;

FIG. 4 is a diagram illustrating a change over time of a set voltage which is an output of the charge pump disclosed in FIG. 1;

FIG. 5 is a diagram showing a time change of a magnetic tape speed and a phase difference detected by a phase comparator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic head 2 Equivalent amplifier (AGC) 3 Filter 4 Pulsing circuit 5 Phase comparator 6, 60 Charge pump 7 Voltage control oscillator (VCO) 8 Operation unit 9 Signal processing circuit 6a, 60a Gain switch 6b, 60b Charge pump side Divider 6c Adder on charge pump side 8a Adder on operator side 8b Divider on operator side

Claims (6)

[Claims] 1. A magnetic tape on which predetermined data is stored and reproduced, and a plurality of magnetic heads for storing and reproducing predetermined data on and from the magnetic tape, wherein each magnetic head is provided for each of the plurality of magnetic heads. A pulse circuit for converting a reproduced signal reproduced from the magnetic tape into a digital signal, comparing the digital signal with a discrimination clock for discriminating the digital signal, and outputting phase data as a phase difference between the two signals. A phase comparator, and a charge pump that generates a control voltage corresponding to the phase data,
A voltage-controlled oscillator that generates the discrimination clock based on the control voltage from the charge pump; and a signal processing circuit that processes the digital signal. In a magnetic tape device provided with a gain switch for switching the gain of the charge pump according to a command, and a charge pump side divider for dividing the output value of the output circuit by a predetermined value in one of the switched output circuits. A magnetic tape device, wherein the charge pump is provided with a charge pump-side adder that adds a predetermined value to the one of the divided output values. 2. The magnetic tape according to claim 1, wherein the signal processing circuit instructs the gain switch to switch a gain when a control voltage from the charge pump is within a predetermined range. apparatus. 3. The magnetic device according to claim 1, further comprising an arithmetic unit that calculates a value to be input to each of the charge pump-side adders based on predetermined data from each of the magnetic heads. Tape device. 4. An arithmetic unit-side adder for adding the respective phase data from the respective phase comparators corresponding to the respective magnetic heads to the arithmetic unit, and an operation for dividing the added value by a predetermined value. 4. The magnetic tape device according to claim 3, further comprising a unit divider. 5. The magnetic tape device according to claim 4, wherein the predetermined value in the divider on the charge pump side is set to one fifth or less of the predetermined value in the divider on the arithmetic unit side. 6. The magnetic tape device according to claim 1, wherein the predetermined value in the charge pump divider is 5 to 20.