JPH0273571A - Information reproducing circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction of a data discriminating circuit by adding automatically a pulse in order to shorten the period of a noise pulse at the time of reading an area where information is not recorded. CONSTITUTION:When a noise signal appears in an output (a) of a magnetic head 1, while a noise pulse appears in an output (b) of a shaping circuit 2, a 1st monostable circuit 3 is triggered to come under an unstable state for a period set as longer than a prescribed max. period of digital data. Then, the moment the state is restored to its original stable state a 2nd monostable circuit 4 is triggered to produce a pulse having a short pulse width in its output (d). The logical sum of the noise pulse of the output (b) of the shaping circuit 2 and the pulse of the output (d) of the 2nd monostable circuit 4 is made by an OR-circuit 5, and a pulse of an output (e) of the OR-circuit 5 is shorter than the original noise pulse in period, and hence even when the read operation is shifted from an area where information is not recorded to an area where information is recorded, the malfunction of the data discriminating circuit is hardly generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an information reproducing circuit that reproduces a reproduced analog signal read from an information recording medium as a digital signal.

[Prior Art] A magnetic recording information reproducing circuit usually performs the following signal processing. Magnetization information on the magnetic recording medium is read by a magnetic head and becomes a reproduced analog signal. This reproduced analog signal is converted into digital data through amplification, waveform correction, peak detection, etc. A clock signal synchronized with this digital data is generated. The above-mentioned digital data is subjected to data discrimination at the timing of this clock signal and becomes a read signal.

[Problems to be Solved by the Invention] When a magnetic recording medium has a portion where information is recorded and a portion where information is not recorded, the following problem occurs.

Assume that information is recorded using MFM modulation. In this case, if the shortest magnetization reversal interval is T, then T, 1.5T
Information is recorded at three types of magnetization reversal intervals: , 2T. When the part where information is recorded is read with a magnetic head, it becomes a reproduced analog signal, based on which digital data is created, and a synchronized clock signal is created based on this digital data. However, when a magnetic head reads a portion where no information is recorded, only noise appears in the reproduced analog signal. Undefined digital data is also created from this noise. The period of this child digital data is usually the longest magnetization reversal interval 2
T''. A synchronized clock signal is also generated from such digital data. This synchronized clock signal has a longer period and is unstable than the synchronized clock signal when reading the MFM modulation data. Become something.

Of course, the read signal obtained from the reproduced analog signal containing only noise is considered to be normal data. ! , not recognized. Therefore, no matter what the synchronous clock signal is at this time, it should not be horizontal. However, later, when reading the MFM modulated data, the synchronized clock signal created from the noise will have an adverse effect.

That is, the magnetic head records information from the part where no information is recorded. The moment you move to the part marked with %,
A synchronous clock signal made from noise will be used. Of course, the synchronized clock signal immediately shifts to the optimal period. However, there is a risk that the data discrimination circuit may malfunction due to the use of a temporally inappropriate synchronization clock signal.

This invention was made in view of these circumstances, and its purpose is to record j1. To provide an information reproducing circuit capable of preventing malfunction of a data discrimination circuit by shortening the cycle of noise pulses obtained from the part even if there is a part in the body where no information is recorded.

[Means for Solving the Problems] In order to achieve the above-mentioned object, an information reproducing circuit according to the present invention has the following configurations (a) to (d).

(a) A shaping circuit that converts a reproduced analog signal read from an information recording medium into digital data.

[b) a first monostable circuit that is triggered by the output of the old error shaping circuit, the period of the unstable state being set to be longer than a predetermined longest cycle of the digital data;
The first monostable circuit is of a type that resets the period of instability when retriggered during the instability.

(c) a second monostable circuit triggered by the output of the first monostable circuit, the period of the unstable state being set to be approximately the same as the pulse width of the digital data;
Second monostable circuit.

(d) an OR circuit that ORs the output of the shaping circuit and the output of the second monostable circuit;

Due to its nature, the information reproducing circuit of the present invention is not only applicable to magnetically recorded information reproducing circuits, but also to other recording/reproducing systems such as optical discs.

[Function] In order to keep the synchronization clock signal at an appropriate value while reading the part where no information is recorded,
All you have to do is shorten the period of the digital signal obtained from the noise appropriately. In this invention, when there is a noise pulse, a new pulse is automatically generated when the period of instability 7B of the first monostable circuit has elapsed from that point. Then, the noise pulse and the new pulse are logically summed to shorten the pulse period.

To explain this invention in detail, first, a reproduced analog signal read from an information recording medium is converted into digital data by a shaping circuit. This digital data triggers the first monostable circuit. Then, the first monostable circuit shifts from a stable state to an unstable state. The period of instability is
It is set longer than the predetermined longest cycle of digital data.

The "predetermined longest period of digital data" is determined for each modulation method of information recorded on a recording medium, and is 2T in the above-mentioned MFM modulation method as an example. This first monostable circuit is of a type that, when retriggered during an unstable condition, resets the period of the unstable condition. Therefore, as long as the area in which information is recorded is being read, the next pulse is always input to the first monostable circuit before the unstable state ends. As a result, the unstable state is reset. In other words, the first monostable circuit continues to be in an unstable state.

When an area where no information is recorded is read, the first monostable circuit is triggered by the first noise pulse and goes into an unstable state. However, after a predetermined period of time, it returns to a stable state. At this moment, the second monostable circuit is in turn triggered to produce a pulse with a short pulse width. Then, in the OR circuit, the noise pulse and the output pulse of the second monostable circuit are ORed. As a result, the period of the output pulse of the OR circuit becomes shorter than the period of the original noise pulse.

[Example" Next, embodiments of the invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. In this embodiment, the present invention is applied to a playback circuit of a floppy disk device. Information is recorded using MFM modulation.

This regeneration circuit consists of a shaping circuit 2, two monostable circuits 3,
- 4 and an OR circuit 5. The same contents as the conventional device, such as a synchronous clock regeneration circuit and a data discrimination circuit, are omitted. The output a of the magnetic head 1 is input to a shaping circuit 2. The output of the shaping circuit 2 is input to an OR circuit 5 and a first monostable circuit 3. The output C of the first monostable circuit 83 is input to the second monostable circuit 4. The output d of the second monostable circuit 4 is input to the OR circuit 5. The output e of the OR circuit 5 is sent to a data discrimination circuit (not shown).

Next, the function of each component will be explained with reference to FIG. 1 and FIG. 2, which is a timing chart thereof.

The output a of the magnetic head 1 becomes a reproduced analog signal 10. The shaping circuit 2 amplifies and amplifies the reproduced analog signal 10.
Digital data 20 is obtained by performing waveform correction, peak detection, etc. The shaping circuit 2 itself is the same as that of the conventional device.

The first monostable circuit 3 is triggered by the rising edge of the digital data 20 pulse. Then, the state shifts from a stable state to an unstable state. The period T1 of the unstable state is set longer than the longest period T1.8 of MFM modulation data. When the unstable state period T1 ends, the original stable state returns. By the way, when this first monostable circuit is retriggered during an unstable state, the period T1 is reset.

The second monostable circuit 4 is triggered by the fall of the output C of the first monostable circuit 3. As a result, pulses 40, 41, and 42 with small pulse widths are output.

That is, the period T2 during which the second monostable circuit 4 is in an unstable state is set to be very short. This period T2 is approximately the same as the pulse width of the digital data 20.

The OR circuit 5 performs the OR of the digital data 20 and the output d of the second monostable circuit 4.

Next, the operation of this reproducing circuit will be explained.

First, a case will be described in which the magnetic head 1 reads out an area A in which information is recorded using the MFM modulation method. At this time, the digital data 2 appearing at the output of the shaping circuit 2
0 is a normal pulse train. That is, the pulse period is T, 1.5T, or 2T. longest period T
. , 8 are 2T. If the first monostable circuit 3 is triggered by such a pulse, its unstable state will continue.

This is because the period T1 of the unstable state of the first monostable circuit 3
This is because T is set longer than T. When the first monostable circuit 3 in an unstable state is retriggered,
Since T1 is reset from the time of re-triggering, the unstable state will continue indefinitely. In other words, the output C of the first monostable circuit 3 remains at the high level 30. Therefore, the second monostable circuit 4 is not triggered,
No pulse appears at its output d. As a result, area A
, the OR circuit 5 receives the digital data 20
Only the pulse of
The output is That is, limited to region A, the output is the same as that of the conventional reproducing circuit.

Next, the magnetic head]
Let's explain the case where it is read. At this time, a noise signal 11 appears at the output a of the magnetic head 1, and noise pulses 21 and 22 appear at the output of the shaping circuit 2. The period TN of the noise pulse is random, generally T. , longer than . When the first monostable circuit 3 is triggered by the noise pulse 21, it enters an unstable state 31 for a period T1 and then returns to the original stable state. Then, at the falling edge when returning to a stable state, the second monostable circuit 4 is triggered. Then, a pulse 41 appears at the output d. Similarly, when the next noise pulse 22 occurs, a pulse 42 appears at the output d of the second monostable circuit 4. In the OR circuit 5, the noise pulse 2
1.22 and the output pulse of the second monostable circuit 4 41.42
It can be logically summed with. Therefore, in region B, the period T8 of the noise pulse is divided into T1 and TN1 and shortened.

In region B, the pulse period has been shortened in this way, so that the period of the synchronous clock signal in region B is
The period is not far different from the period of the synchronous clock signal in region A. Therefore, when area A follows area B, there is less possibility that the data discrimination circuit will malfunction.

In addition, in the timing chart of FIG. 2, if the period TN of the noise pulse becomes very long, even if T
1, it is unavoidable that the pulse period T N l at the output e of the OR circuit 5 becomes longer. However, it is certain that this embodiment greatly improves the prevention of malfunction of the data discrimination circuit.

[Effects of the Invention] As described above, the present invention adds pulses so that the period of noise pulses becomes shorter when reading out an area where no information is recorded. Therefore, the period of the synchronous clock signal in this region does not deviate far from the period of the synchronous clock signal when reading the original information. As a result, even when a read operation is transferred from an area where no information is recorded to an area where information is recorded, the data discrimination circuit is less likely to malfunction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a timing chart of this embodiment. 2-Shaping circuit 3...first monostable circuit 4...second monostable circuit 5...OR circuit T1...period T2 of the first monostable circuit in an unstable state...
・Period of unstable state of the second monostable circuit T 11111...Longest period of digital data Figure 1 Patent applicant: NEC Corporation Representative, Patent attorney Toshiyuki Meki

Claims (1)

[Claims] An information reproducing circuit having the following (a) to (d). (a) A shaping circuit that converts a reproduced analog signal read from an information recording medium into digital data. (b) a first monostable circuit triggered by the output of the shaping circuit, the period of which is in an unstable state is set to be longer than a predetermined longest period of the digital data, and which is retriggered during the unstable state; a first monostable circuit of the type in which the period of instability is reset when the period of instability is reset; (c) a second monostable circuit triggered by the output of the first monostable circuit, the period of the unstable state being set to be approximately the same as the pulse width of the digital data;
Second monostable circuit. (d) an OR circuit that ORs the output of the shaping circuit and the output of the second monostable circuit;