JPS6232546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection method for a magnetic recording device used in an information processing device.

Conventionally, in this type of magnetic recording device, if the read information transferred to the host device is incorrect, the readout is performed again by a retry command issued from the host device. No occasional state changes were made.

Therefore, if the cause of the error in the transferred read information is due to accidental noise, correct read information can be sent by retrying using the conventional method.
However, if the factor is related to the recording medium, the factor always exists at the readout location, so the conventional method has the disadvantage that it cannot be saved.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional technology. Therefore, in the case of a retry, the purpose of the present invention is to control the signal in the readout circuit by a retry command sent from a host device. It is an object of the present invention to provide a new signal detection method for a magnetic recording device, which detects a signal while reducing the influence of noise related to a recording medium by changing the threshold voltage of a detection circuit, and increases the effect of retry.

In order to achieve the above object, a signal detection method using a variable threshold according to the present invention includes a signal detecting means that compares the peak amplitude of a signal with a threshold voltage and generates a pulse train in accordance with the magnitude of both; noise detection means for detecting the presence or absence of noise; and threshold setting means for changing the threshold voltage when the noise detection means detects noise; The present invention is characterized in that a signal is detected at a point where the noise is detected, and when the noise is detected, the signal in the portion where the noise is detected is read again using a second threshold voltage different from the first threshold voltage.

That is, according to the present invention, the signal amplitude of the amplified readout signal is detected at a certain threshold in the signal detection circuit, and the signal is converted into a pulse and transmitted to the host device. If it determines that there is, it will send a retry command. When the signal detection circuit according to the present invention receives this retry command, it changes the threshold level to another value and performs reading again. In other words, several types of threshold levels are prepared inside the signal detection circuit, and when retrials continue, the threshold levels are changed one after another. When retry is canceled, the threshold level is returned to the initial value.

Noise related to a recording medium occurs in a specific location, and there is a high possibility that a signal recorded in a location where the noise exists will be erroneously detected even at a threshold level determined from the overall condition of the recording medium. Therefore, the present invention is based on the principle that if the threshold level is changed only where the noise is present, the probability of correctly detecting a signal increases.

Next, preferred embodiments of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a signal detection circuit to which the present invention is applied, and FIGS. 2 and 3 show waveforms of each part thereof. This circuit is a readout circuit for signals recorded using the NRZI modulation method.

A signal read from the magnetic head 1 is amplified in voltage amplitude by an amplifier 2, and after unnecessary high frequency components are removed by a multipass filter 3, the signal is input to a signal detector 4. The signal detector 4 compares the output voltage e of the threshold setter 6 with the amplitude voltage of the input signal a, and when the amplitude voltage exceeds the initial output voltage value V ₁ of the voltage e output from the threshold setter 6. A pulse waveform output b is output to. This pulse train is transmitted to the data discriminator 5
The information is decoded into recorded information and transferred to the higher-level device.

If there is noise as shown by the broken line in the waveform of the input signal voltage a, the noise is also output as a signal from the signal detector 4 as its output _b1 . When this output signal b ₁ is transferred to the higher-level device, the higher-level device determines that there is an error in this information and inputs the pulse c ₁ of the pulse train c in FIG. 3 to the threshold value setter 6 as a retry command. Ru. The threshold value setter 6 changes the output voltage to V ₂ as shown in e by inputting the pulse c ₁ , and the signal detector 6 detects the signal with the threshold value as V ₂ and outputs an output pulse train b ₂ . When this information passes through the data discriminator 5 and is transferred to the host device,
The host device determines that there is still an error and inputs the _c2 pulse to the threshold value setter 6. Threshold setter 6 is c ₂
The pulse changes the output voltage to V ₃ . The signal detector 4 performs signal detection with a threshold value of _V3 , and outputs an output pulse train _b3 . Since noise has been removed from this pulse train, when the host device receives the pulse train _b3 , it determines that it is correct and transfers the reset pulse d to the threshold value setter 6. This reset pulse d
As a result, the output voltage of the threshold value setter 6 returns to the initial value _V1 . As described above, it is possible to detect a signal from which the influence of noise has been removed.

FIG. 4 is a diagram showing another embodiment of a signal detection circuit using the present invention, and FIGS. 5 and 6 show waveforms at various parts of the circuit. The circuit shown in FIG. 4 is a circuit for detecting omission of a recording signal as a starting point of recorded information or a timing track.

The signal read from the magnetic head 7 is amplitude-voltage amplified by an amplifier 8, unnecessary high frequency components are removed by a low-pass filter 9, and then input to a full-wave rectifier 10. This input voltage waveform is shown in Figure 5.
The output voltage waveform is shown at g. This output voltage g is input to the signal detector 11. The signal detector 11 compares the voltage of the output n of the threshold value setter 14 with the amplitude voltage of the waveform of the output voltage g, and outputs a detected output voltage h in response to the waveform of g exceeding the voltage of n. The output voltage h is changed to the voltage h by the low-pass filter 12.
The whisker-like voltage portion within is removed, and the output j is transferred by the logic gate 13 to the subsequent circuit as a logic signal k.

Now, if there is noise as shown by the broken line at the point where the input voltage is missing, the signal detector 11 detects that when the output voltage of the threshold value setter 14 is _V4 , the signal detector 11 detects the detected output waveform _h1 . Outputs a voltage waveform with dotted line pulses in the gaps. This is j ₁ , k ₁
When it is formatted as follows and transferred to the subsequent circuit,
It becomes difficult to detect the starting point because the time period during which the gap exists is short, or because there are two gaps. If the starting point cannot be detected within a predetermined period of time, the subsequent circuit sends the l pulse to the threshold value setter 14.
Send to. This causes the threshold setter 14 to change the output voltage to _V5 . When the threshold value becomes _V5 , the output of the signal detector 11 becomes _h2 and is no longer affected by noise. When this signal is shaped like j ₂ and k ₂ and transferred to the subsequent circuit, it is determined that the starting point has been detected and a reset pulse m is sent to the threshold value setter 14. As a result, the threshold value setter 14 The threshold for returns to V ₄ . As described above, it is possible to detect the starting point from which the influence of noise has been removed.

Although the first and second embodiments have been described in detail above, well-known comparators, for example, are used as the signal detectors 4 and 11, and the threshold value setters 6 and 14 are used.
Specifically, the logic gate 13 can be constructed of, for example, a DA converter and an adder, and the logic gate 13 can be composed of, for example, two inverters.

Note that although the first embodiment has been explained using the NRZI modulation method, the present invention can be similarly applied to other modulation methods using level detection.

Further, in the first embodiment, the threshold level is V ₁ ,
A case was explained in which the voltage is changed to three stages, V ₂ and V ₃ , and in the second embodiment, to two stages, V ₄ and V ₅ .
Of course, the number of changes is not limited to the number shown in this embodiment.

As explained above, in the case of normal readout, the present invention detects a signal by reading out with a fixed threshold value, but in the case of retrying, the threshold value is changed and the signal is detected. This improves the effectiveness of resolving errors by retrying, and provides a highly reliable magnetic recording device.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the first embodiment of the present invention in blocks, Figs. 2 and 3 are time charts of voltage waveforms at various parts of the circuit shown in Fig. 1, and Fig. 4 is a circuit diagram of the present invention. FIGS. 5 and 6 are circuit diagrams showing the second embodiment in blocks, and are time charts of voltage waveforms at various parts of the circuit shown in FIG. 4. DESCRIPTION OF SYMBOLS 1...Magnetic head, 2...Amplifier, 3...Low pass filter, 4...Signal detector, 5...Data discriminator, 6...Threshold setter, 7...Magnetic head, 8...Amplifier, 9...Low pass filter, 10...Full wave rectifier, 11...Signal detector, 12...Low pass filter, 13...Logic gate circuit,
14...Threshold value setter.

Claims (1)

[Claims] 1. Signal detection means that compares the peak amplitude of a signal with a threshold voltage and generates a pulse train in accordance with the magnitude of both; noise detection means that detects the presence or absence of noise in the pulse train; and threshold setting means for changing the threshold voltage when the noise is detected, and in the case of normal readout, the signal is detected at the first threshold voltage, and when the noise is detected, the signal is detected at the first threshold voltage. A signal detection method using a variable threshold for a magnetic recording device, characterized in that the signal of the portion where the noise is detected is read again at a second threshold voltage different from the threshold voltage of .