JPH05198088A - Dropout detector - Google Patents

Abstract

PURPOSE:To detect long and short dropouts by comparing the output signal of a voltage dividing circuit with a regenerative signal by a comparator and ORing the output signals of a dropout end detection part and a start detection part which are generated in a specific period. CONSTITUTION:The voltage of the envelope detection signal (b) from an envelope detecting circuit 11 is divided at a voltage-dividing and smoothing part 13 by resistances R5 and R6, and the signal is smoothed by a capacitor C4 to generate a reference voltage (d). The resistances R5 and R6 form a voltage dividing circuit, and the comparator IC1 compares its output signal with the regenerative signal of a voltage (d). The start of a dropout of the regenerative signal is detected from the output signal of the comparator IC1. Consequently, the dropout start detection part 17 generates its output signal during a specific period and the dropout end detection part 15 detects the dropout of the regenerative signal from the output signal of the circuit 11 and generates its output signal in a specific period before its end. An OR means 14 ORs the output signals of the detection parts 15 and 17 to easily detect the long and short dropouts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dropout detector for detecting a dropout of a reproduced signal.

[0002]

2. Description of the Related Art In a magnetic recording device such as a high-density magnetic recording device for data backup, in order to ensure reliability when reproducing data from a magnetic tape by a reproducing magnetic head, a recording magnetic head is recorded on the magnetic tape. When recording data with, the reproduction magnetic head located immediately after the recording magnetic head reproduces the data from the magnetic tape immediately after recording and checks it, and the level of the reproduction signal from the reproduction magnetic head is used as a reference. When it becomes smaller than the voltage (when there is a dropout), the read signal is cut by cutting the playback signal, and the data with the same content as the cut playback signal is rewritten (recorded again) to another location on the magnetic tape. By doing so, the part that drops out the data on the magnetic tape is not used.

In such a recording apparatus, the dropout detector detects that the level of the reproduction signal from the reproduction magnetic head becomes lower than the reference voltage (there is a dropout of the reproduction signal). FIG. 5 shows an example of the dropout detector, and FIG. 6 shows its timing chart.

In a magnetic recording device such as a high-density magnetic recording device for data backup, data is divided into blocks and recorded on a magnetic tape by a recording magnetic head, and a reproduction signal reproduced from the magnetic tape is amplified by a preamplifier. Then, it is input to the non-inverting input terminal of the comparator 1. This reproduction signal A is supplied from the reference voltage source 2 to the comparator 1
The dropout is detected by comparing with the reference voltage B input to the inverting input terminal of the comparator 1 and the mono-multivibrator 3 is triggered by the rise of the output signal C of the comparator 1 to output the pulse signal D having a constant time width. Occur. The time width of the pulse signal D is set to be longer than the maximum value of the data cycle and output to the gate 4. The output signal of the preamplifier is differentiated by a differentiator through a low-pass filter and then compared with a zero-cross point by a zero-cross comparator to be read data E. The read data E is supplied to the gate 4 of the monomultivibrator 3. The output signal D removes the dropout portion and outputs it to the demodulator.

[0005]

However, in the above dropout detector, the level of the reproduction signal A input to the comparator 1 fluctuates due to the output level of the reproducing magnetic head, variations in the gain of the preamplifier, and the like. , Drop-out detection level (reference voltage B from reference voltage source 2
Of the preamplifier or the level of the reference voltage B from the reference voltage source 2,
Both the number of parts and the number of man-hours for adjustment increase, resulting in cost increase.

The present invention solves the above-mentioned drawbacks and provides a dropout detector capable of keeping the dropout detection level constant without adjustment for variations in the output level of the recording magnetic head and the gain of the preamplifier. The purpose is to do.

[0007]

In order to achieve the above object, the present invention provides an envelope detecting circuit for detecting the envelope of a reproduction signal, a voltage dividing circuit for dividing the output signal of the envelope detecting circuit, and this voltage dividing circuit. A comparator for comparing the output signal of the circuit with the reproduction signal, and a dropout for detecting the start of the dropout of the reproduction signal from the output signal of the comparator and generating an output signal in a predetermined period from the start of the dropout. A start detector,
A dropout end detection unit that detects the end of the dropout of the reproduction signal from the output signal of the envelope detection circuit and generates an output signal in a predetermined period before the end of the dropout, and the output of the dropout end detection unit And a logical sum means for calculating a logical sum of the signal and the output signal of the dropout start detection unit.

[0008]

The envelope of the reproduction signal is detected by the envelope detection circuit, and the output signal of this envelope detection circuit is divided by the voltage dividing circuit. The output signal of the voltage dividing circuit and the reproduction signal are compared by the comparator, and the dropout start detection unit detects the start of the dropout of the reproduction signal from the output signal of the comparator and outputs the dropout start within a predetermined period. Generate a signal. The dropout end detection unit detects the end of the reproduction signal dropout from the output signal of the envelope detection circuit and generates an output signal in a predetermined period before the end of the dropout. The logical sum of the output signal and the output signal of the dropout start detection unit is calculated.

[0009]

1 shows an embodiment of the present invention, and FIG. 2 shows a timing chart of this embodiment. Transistor T
The r, the resistors R1 to R3, and the capacitors C1 and C2 form an envelope detection circuit 11, and a reproduction signal is input from the outside. The capacitor C3 and the resistor R4 are the time constant circuit 12
And an input terminal to which a reproduction signal is input from the outside,
It is connected to the non-inverting input terminal of the comparator IC1. Voltage dividing circuit consisting of resistors R5 and R6 and capacitor C4
And the partial pressure smoothing unit 13 and the envelope detection unit 11
Is connected to the output terminal of the comparator IC1 and the inverting input terminal of the comparator IC1.

An envelope end detector 15 is connected between the output terminal of the envelope detector 11 and the OR circuit 14, and the envelope end detector 15 has a resistor R7,
It is composed of R8, capacitor C5, and comparator IC2. The resistors R7 and R8 form a voltage dividing circuit, and the voltage dividing circuit and the capacitor C5 form a voltage dividing / smoothing unit 16. The voltage dividing / smoothing unit 16 may also be used as the voltage dividing / smoothing unit 13, and the output signal d of the voltage dividing / smoothing unit 13 may be input to the non-inverting input terminal of the comparator IC2. Further, the output terminal of the comparator IC1 and the OR circuit 1
4, a dropout start detection unit 17 is connected to the dropout start detection unit 17, and the dropout start detection unit 17 includes retriggerable mono multivibrators MM1 and MM2.

In a magnetic recording device such as a high-density magnetic recording device for data backup, data is divided into blocks and recorded on a magnetic tape by a recording magnetic head, and a reproduction signal reproduced from the magnetic tape is amplified by a preamplifier. After that, it is input to the envelope detection circuit 11. The reproduced signal a has dropouts as shown in FIG. 2, for example, and the envelope is detected by the envelope detection circuit 11 to detect the envelope detection signal b as shown in FIG.
Becomes

The envelope detection signal b from the envelope detection circuit 11 is divided into resistors R5 and R in the voltage division smoothing section 13.
The voltage is divided by 6 and smoothed by the capacitor C4, and becomes the reference voltage d as shown in FIG. Then, the reproduction signal a from the preamplifier is compared with the reference voltage d from the voltage dividing / smoothing unit 13 through the time constant circuit 12 and the comparator IC, and the signal from which the dropout portion is removed as shown in FIG. It becomes e.

Here, the time constant circuit 12 includes resistors R5 and R6.
And the time constant of the capacitor C4 is set sufficiently large with respect to the duration of the dropout, so that the dropout detection level (reference voltage d) does not decrease in the dropout portion of the reproduction signal and is made unadjusted. The out detection level d (ratio to the maximum level of the reproduction signal a) can be arbitrarily set by changing the ratio of the resistors R5 and R6.

Retriggerable mono multivibrator MM
1 is triggered by the rising edge of the output signal e of the comparator IC as shown in FIG. 2 to generate the output signal f of a constant cycle,
The generation period of the output signal f is extended by being triggered by the rising edge of the output signal e of the comparator IC during the generation period of the output signal f. The falling edge of the output signal f of the retriggerable monomultivibrator MM1 is delayed from the falling edge of the output signal e of the comparator IC (beginning of dropout) by a constant time t ₁ , and the output signal e of the comparator IC drops out. The start is detected with a delay of a fixed time t ₁ .

Retriggerable mono multivibrator MM
2 is triggered by the trailing edge of the output signal f of the retriggerable mono multivibrator MM1 and outputs the output signal g of a constant period t ₂ . Here, t ₁ and t ₂ are set to be longer than the maximum period of the cycle of the output signal e of the comparator IC for a normal reproduction signal. If the output signal e of the comparator IC for a normal reproduction signal is 4 bits or less, it is not known whether it is data or dropout, so t ₁ and t ₂ are set to a time longer than the 4 bits.

Therefore, when there is a short dropout in the reproduction signal a as shown in FIG. 3, an output signal g is output from the retriggerable mono multivibrator MM2,
Even a short dropout can be detected. However, when the reproduction signal a has a long dropout as shown in FIG. 4, the output signal g of the retriggerable mono multivibrator MM2 disappears within the period where the reproduction signal a has a dropout. Therefore, the envelope end detection unit 15 detects the end of the dropout of the reproduction signal a from the output signal b of the envelope detection circuit 11 and generates the output signal in a predetermined period before the end of the dropout.

That is, in the envelope end detecting section 15, the output signal b of the envelope detecting circuit 11 is divided by the resistors R7 and R8 and smoothed by the capacitor C5 to become a reference voltage, and the envelope detecting circuit 11
Output signal b is compared with the reference voltage by the comparator IC2 and binarized. The output signal h of the comparator IC2 is generated before the end time of the dropout of the output signal e of the comparator IC, and the envelope end detection unit 15 detects the end of the dropout of the reproduction signal a and is reset before the end of the dropout. The output signal is generated in a predetermined period before the fall of the output signal g of the triggerable mono multivibrator MM2.

The OR circuit 14 takes the logical sum of the output signal h of the envelope end detector 15 and the output signal g of the retriggerable monomultivibrator MM2, and the output signal i of the OR circuit 14 is shown in FIG. As described above, the output signal e of the comparator IC has a waveform substantially corresponding to the dropout period T, and the dropout can be accurately detected even if the reproduction signal a has a long dropout.

[0019]

As described above, according to the present invention, an envelope detecting circuit for detecting the envelope of a reproduction signal, a voltage dividing circuit for dividing the output signal of the envelope detecting circuit, and an output signal of the voltage dividing circuit. Since it has a comparator for comparing with the reproduction signal, it is possible to make the dropout detection level constant without adjustment for the output level of the recording magnetic head and the variation of the gain of the preamplifier.
The cost can be reduced by reducing the number of parts and the adjustment man-hours. In addition, the dropout start detection unit that detects the start of the dropout of the reproduction signal from the output signal of the comparator and generates the output signal for a predetermined period from the start of this dropout, and the reproduction signal from the output signal of the envelope detection circuit. A dropout end detection unit that detects the end of dropout and generates an output signal in a predetermined period before the end of this dropout, and an output signal of this dropout end detection unit and an output signal of the dropout start detection unit Since it has a logical sum means to take a logical sum,
Long and short dropouts can be detected with a simple configuration.

[Brief description of drawings]

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

FIG. 2 is a timing chart of the same embodiment.

FIG. 3 is a waveform diagram for explaining the same embodiment.

FIG. 4 is a waveform diagram for explaining the same embodiment.

FIG. 5 is a block diagram showing a conventional dropout detection circuit.

FIG. 6 is a timing chart of the dropout detection circuit.

[Explanation of symbols]

 11 Envelope detection circuit R5, R6 voltage divider circuit IC1 comparator 14 OR circuit 15 Dropout end detection unit 17 Dropout start detection unit

Claims (1)

[Claims] 1. An envelope for detecting an envelope of a reproduced signal.
The rope detection circuit and the output signal of this envelope detection circuit
The voltage dividing circuit that divides the signal and the output signal of this voltage dividing circuit
This comparator and a comparator that compares the playback signal
From the output signal of the data
Start of detection and a predetermined period from the start of this dropout
A dropout start detector that produces an output signal at
Of the reproduction signal from the output signal of the envelope detection circuit
The end of the dropout is detected and this dropout's
A dropout that generates an output signal in a predetermined period before the end
End detection unit and the output of this dropout end detection unit
Between the signal and the output signal of the dropout start detector
Doro characterized by having a logical sum means for taking a Riwa
Up-out detector.