JPS60127573A - Drop-out detecting circuit - Google Patents

Abstract

PURPOSE:To enable independently the titled circuit to set the length and depth of drop-out by comparing the instantaneous value of an input signal with two positive and negative reference voltages, and inputting the comparated output to a monostable multivibrator that can make retrigger action to process the detected signal. CONSTITUTION:Detection of drop-out of only types 1, 2 is made possible in modes 1, 2, detection of drop-out of type 1 and type 2 is made possible in mode 3, and detection of drop-out of all types is made possible in mode 4 by using a drop-out detcting circuit. Accordingly, the separation of drop-out of three types, which is impossible by ordinary drop-out detecting circuit is made possibe, and properties relating to the drop-out of a magnetic record reproducing system can be analyzed. Further, by making monostable output pulse of monostable multivibrators 24-26 larger than the minimum time of continuation of drop-out to be detected, the drop-out of any depth determined by reference voltage + or -Vref can be detected accurately, and the interdependence between the length and depth of drop-out is eliminated.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is particularly applicable to a device that detects, analyzes and displays dropouts contained in a playback signal of a magnetic recording and playback device composed of a magnetic head, a magnetic tape, etc. This invention relates to a dropout detection circuit.

[Technical background of the invention and its problems]

The magnetic recording/reproducing device must be capable of erasing and re-recording;
Although it has advantages such as large recording capacity and is widely used, it is difficult to completely avoid partial loss of the reproduced signal due to minute defects in the recording medium such as magnetic tape, dust in the air, etc. It is.

This partial loss of the reproduced signal is usually called a dropout, but the number, length distribution, etc. of these are important parameters that represent the characteristics of the magnetic recording and reproducing system, and the occurrence of dropouts is an error in digital recording. It causes
In analog recording, this causes signal deterioration. Therefore, it is important to reduce this dropout as much as possible, and for this purpose, it is necessary to know the nature of dropout. For this purpose, a device that detects, analyzes and displays dropouts from the reproduced signal (hereinafter referred to as a dropout analyzer) is used, and its basic performance lies in the means for detecting dropouts (hereinafter referred to as a dropout detection circuit). ).

FIG. 1 is a block diagram showing a system in which a reproduction signal from a magnetic head is output as a dropout detection signal. A signal recorded on a recording medium (magnetic tape is shown as an example) 1 is extracted as an electrical signal by a reproducing head 2, amplified and equalized by a preamplifier 3 and an equalization circuit 4, and amplified by a level adjustment amplifier 5. It is adjusted to a level necessary for the operation of the dropout detection circuit 6. The dropout included in this signal is detected by the dropout detection circuit 6 and output as a dropout detection signal. Of the above, the equivalent circuit 4 and the level adjustment amplifier 5 can be omitted, and for example, a single frequency or a constant cycle repetitive signal is recorded on the recording medium 1 and reproduced by the magnetic head 2 to analyze dropouts. In this case, there is no need for an equalization circuit ± to even out the frequency characteristics, and the preamplifier 3 can amplify the minute reproduced signal to the required level and use it as the input signal to the dropout detection circuit 60. It is.

Here, a conventional example of the dropout detection circuit 6 in the general circuit block diagram of FIG. 1 is shown in FIGS. 2 and 3. Figure 2 is a block diagram, and its specific circuit is shown in the third diagram.
The operation will be explained with reference to the time chart of FIG. 4. The input signal to the dropout detection circuit (the waveform shown in FIG. 4a) is converted by the detection circuit to become the waveform shown in FIG. 4. This detection signal is passed through a low frequency pass filter (I, , ,
P, F, )11, a signal representing the envelope of the input signal a (signal shown in FIG. 3a) is obtained, and the reference voltage V
A dropout detection signal (the signal shown in FIG. 3) is obtained by the ref comparison circuit 12. There are three dropouts in which the level contained in the input signal a deteriorates below Vref ((a) shown in FIG. 4a).

Dropout 2 (Fig. 4a)
(b)), the duration is the low frequency pass filter (,f,,
Since it is smaller than the time constant τ of P, F, ) 11, it is not detected as a dropout. That is, from among the dropouts included in the input signal a, only those dropouts having a duration longer than the time constant τ can be selectively detected.

In the conventional concrete example of the dropout detection circuit (Fig. 3), U indicated by a dotted line serves as a composite function of the detection circuit block shown in Fig. 2 and the low frequency pass filter (LP, F,) 11, and the capacitance C When omitted, the circuit block functions as a detection circuit block. That is, the time constant τ (=
RC). In Figure 3, symbol AI, A2 is an amplifier, and A3
- represents a comparator.

Next, let us consider the dropout selection conditions of the conventional dropout detection circuit (FIG. 2) and clarify the problems. No way, dropout 1 (a) in Figure 4 a.
Let us consider as an example a dropout that deteriorates and recovers instantaneously, such as dropout 3 (c), instead of a smooth dropout like dropout 3 (c). FIG. 5 is an explanatory diagram thereof. The waveform e in FIG. 5 represents the envelope of a dropout signal that deteriorates and recovers instantaneously (the envelope of the signal waveform shown in FIG. 4), and the waveform f represents L P, F,
represents the output signal of This signal f can be expressed by the following equation.

1-1゜vo(t)=V8-(VB-V(1)(1-e-)・u
(t-tt)+(VB-Vd)τ However, V8. Vd represents the signal level at normal signal level dropout, and u(t) is a unit step function. If the reference level for dropout comparison is Vref, then the condition for detecting dropout is vo(t3)<Vref (or td'>O) -・
-... Since it is given by (2), the following detection conditional expression can be obtained from equation (1).

The pulse width td' of the dropout detection signal (waveform g in FIG. 5) obtained under this condition is given by the following equation.

Figure 6 is a plot of the drop-out F detection condition given by equation (3) using Vref/Vs as a parameter, with the horizontal axis representing Vd/Vs (in percentage) and the vertical axis representing td/τ. represent. This figure shows, for example, Vr e
When the reference voltage Vref is set so that t/Vs=0.9, td/Vref located at the upper left part of the lowest curve
This means that only dropouts that satisfy the conditions of τ and Vd/Vs are selectively detected. In the figure, Vr
Setting e f /Vs = 0.5, V
The results of measuring the critical point by inputting a simulated dropout signal with varying d/Vs and td/τ are also shown, and are in good agreement with the above-mentioned results.

As is clear from the above results, in the conventional dropout detection circuit, even with a fixed time constant τ and a constant reference voltage Vref, a deep dropout error) (a short dropout error if Vd/Vs is small) (ta/r However, when vci, 'vs is large, however, when Vd < Vr e f , only a long dropout (td/τ is large) can be detected, and the detectable dropout length is It had the disadvantage of interdependence in terms of depth and depth.

[Purpose of the invention]

The present invention improves the above-mentioned conventional drawbacks, and aims to provide a dropout detection circuit that can independently set the length and depth of a detectable dropout.

[Summary of the invention]

The feature of this invention is that the conventional dropout detection circuit
The envelope of the input signal was detected by a detection circuit and a low-frequency pass filter, and then a dropout detection signal was obtained by a comparison circuit.In contrast, the instantaneous value of the input signal is compared with two reference voltages, positive and negative. , After that, each comparator output is input to a monostable multivibrator capable of redriving operation, and the non-oscillation duration of the comparator output obtained from the magnitude relationship of the two reference voltages is determined for the set time tw.
On the other hand, each comparator output is output from an exclusive OR circuit for extracting dropout characteristics and a monostable multivibrator capable of redriving. The objective is to obtain a dropout detection signal by combining the signals obtained by inputting them to the circuit consisting of the following. Here, the dropout detection procedure is reversed; whereas conventional detection circuits rely on analog processing, the present procedure relies on digital processing.

[Embodiments of the invention]

Figure 7 shows an embodiment of the dropout detection circuit according to the present invention, and Figure 8 is a time chart thereof. Hereinafter, the circuit configuration P of this invention will be explained based on these figures.
, its operation, and its effects.

The signal a' shown in FIG. 8 has been changed from the signal a in FIG. 4 to provide a detailed explanation of the present invention, and the dropout shapes are classified into three types. Type 1 (Fig. 8 a'
(a)) has dropouts on both the positive and negative sides,
This is common. On the other hand, Type 2 ((S) in Figure 8 a') is when the reproduced signal is biased towards the positive or negative side, and Type 3 ((C) in Figure 8 a') is when the reproduced signal is biased towards the positive side but not on the negative side. Only one side has dropped out, and these two types are
This problem is not only caused by defects in the magnetic recording medium or dust in the air, but also depends on the characteristics of the read head, and there have been cases of this occurring particularly in magnetoresistive read heads. Therefore, classifying dropouts into three types is by no means a formality, and separating and detecting these three types of dropouts is a must for analyzing the properties of magnetic recording and reproducing systems. This is a practical means.

In FIG. 7 showing the first embodiment of this invention, 2
], , 22 is a comparator or an exclusive OR (Exclusive OR).
ve OR) circuit, 24, 25, and 26 are monostable multivibrators capable of redriving operation, and the other is a logical sum (OR) circuit.
) circuit, η3,29.30 represents a logic (AND) circuit. The operation of these circuits will be explained with reference to FIG.

The regenerated signal a', including dropouts, is connected to two comparator buttons 2. with Vr e f above positive and negative reference voltages. C1 and C2 in FIG. 8 according to the magnitude of the instantaneous value input to U.
It is converted to the waveform shown in . These C1 and C2 are respectively input to the monostable multivibrator 24 and 25, and at the same time, they are also input to the ExcA'u8ive OR circuit port, and the output C1 and C2 of 23 are input to the remaining monostable multivibrator 26. Ru. When these monostable multivibrators 24, 25, and 26 receive A input, IJ is garued at the falling edge of the input signal, so C
I, C2, C1■ Depending on the state of C2, Fig. 8 Ml,
It is converted into waveforms shown as M2 and M3. That is,
Input signals C1, C2, C1■C2 are high level and low
When oscillating between low levels (IJ), the outputs Ml, M2, and M3 maintain low levels by rigger operation, and the adjacent falling time intervals of C1, C2, C1 and C2 are monostable multivibrators. 24,
When it becomes larger than the monostable output pulse width tw of 25.26, the output ■, M2. M3 automatically changes to High level. However, the falling edge of CI and C2 is period Tl, T2
, T3, and falling period TI of C1■C2
, T5, T6, T7, etc. are the monostable output pulse width tw
Needs to be smaller. The signal C thus obtained
I, C2, C1 ■ C2, Ml, M2, M3 are input to the final circuits 27, 28, 29, 30, and dropout detection signals i, j, Il are obtained (see Figure 8). ). These detection signals are divided into 4 depending on their output conditions.
As is clear from FIG. 8, these four modes are classified according to the type of dropout that can be detected.

Table 1 summarizes this.

Table 1 Embodiment - Dropout detection mode in FIG. 7 ◯ indicates that detection is possible, × indicates that detection is not possible.

As is clear from the above explanation, according to the dropout detection circuit of the embodiment of the present invention shown in FIG.
In the model, only type 1 dropout, m
In ode2, only type 2 dropout, mod
In e3, type 1 and type 2 dropouts are
In mode 4, it is possible to detect all types of dropouts.

It becomes possible to separate three types of dropouts, which was not possible with conventional dropout detection circuits, and it is possible to analyze more deeply the dropout-related properties of magnetic recording and reproducing systems. Furthermore, by making the monostable output pulse width tw of the monostable multivibrators 24, 25, and 26 larger than the minimum duration of the drone 1 out to be detected, dropout of any depth determined by the reference voltage ±Vref can be accurately detected. can be detected, and
Since the magnitude of the duration is determined after comparison with ±vref, the interdependence of detectable dropout length and depth, which was a drawback of conventional dropout detection circuits, can be completely eliminated. I can do it.

FIG. 9 shows a second embodiment of the dropout detection circuit according to the present invention, which differs from the first embodiment in that the signal is input to the B input of the monostable multivibrator capable of redriving. (FIG. 7), and therefore requires changes in subsequent signal processing. i.e.%
The circuit shown in Figure 7 is the same as the circuit shown in Figure 9.
has been changed to. However, the results obtained are equivalent and Table 2 represents the dropout detection mode for this second embodiment (FIG. 9).

Table 2 Example/@9 Dropout detection mode in Figure ○ indicates detectable, × indicates undetectable.

〔Effect of the invention〕

As described above, in this invention, by comparing the instantaneous value of the input signal to the dropout detection circuit with two types of reference voltages, a waveform that oscillates when a dropout occurs and does not oscillate when a dropout does not occur. an output signal obtained by creating a waveform and then determining whether the duration of non-vibration is greater than a reference pulse width;
On the other hand, the above two types of comparator outputs are subjected to exclusive OR (Ex
A multi-mode dropout detection signal is obtained by combining the output signal obtained by inputting it to a dropout feature extraction circuit consisting of a comprehensiveOR) circuit and an IJ) monostable multivibrator capable of rigger operation. Therefore, the interdependence of detectable dropout length and depth, which is a drawback of conventional dropout detection circuits, can be completely eliminated. Furthermore, since the three dropout types can be separated, it is also possible to provide a practical means of analyzing the dropout properties of much more powerful magnetic recording and reproducing systems. Since the dropout detection procedure according to the present invention is completely digitally processed, it is more reliable than conventional analog processing, and also has the advantage of being easier to manufacture and greatly reducing the number of parts. It also has

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a system for outputting a dropout detection signal, Fig. 2 is a block diagram showing a conventional dropout detection circuit in Fig. 1, and Fig. 3 is a block diagram showing a conventional dropout detection circuit in Fig. 2. Figure 4 is a time chart showing the operation of Figure 3, Figure 5 is a time chart to explain the conventional problems, Figure 6 is a graph of the calculation results in Figure 5, and Figure 6 is a time chart showing the operation of Figure 3. FIG. 7 is a circuit configuration diagram showing the first embodiment of the present invention, and FIG.
The figure is a time chart showing the operation of Fig. 7, and Fig. 9 is a time chart showing the operation of Fig. 7.
It is a circuit configuration diagram showing a second embodiment of the present invention. (2m) , (4...Comparator @......Exclusive OR circuit (
2), +51. (21... Monostable multivibrator (5).......OR circuit (layer,
@, Rikin......Logic AND circuit Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] In a dropout detection circuit for detecting dropout included in a reproduction signal of a magnetic recording/reproduction device, two comparisons are made to detect whether the instantaneous value of an input reproduction signal is larger than two different reference voltages. and two monostable multivibrators capable of redriving to determine whether the two signals obtained by the two comparators are changing vibrationally, and the two signals obtained by the two comparators. A dropout feature extraction circuit consisting of a monostable multivibrator capable of IJ gar operation (exclusive OR circuit for extracting dropout features from two signals), and a dropout feature extraction circuit consisting of and a logic circuit for separating dropout types.