JPS60251521A - Inspecting device of magnetic disk board - Google Patents

Abstract

PURPOSE:To make an input change to correspond to an output change, by providing BPFs for low and high of read signals from a head and supplying outputs of the BPFs to the non-inversional input of a comparator by switching, and then, connecting the output signal of the LPF to an AD converter through a logarithmic amplifier. CONSTITUTION:A control section 8 first connects a change-over switch 3 to a terminal 103 side by using a signal (f) and, when signals of a quantity equal to the one turn of a disk are supplied, reads the output value of HF signals by using a conversion starting signal (g) after converting the output value into digital signals (h), and then, sets the value to X. Then the control section 8 switches the changeover switch 3 and sets another value obtained by performing the same process to Y. The X and Y thus obtained respectively represent HF frequency components and LF frequency components contained in read signals in decibel and (Y-X) decibel becomes a value indicating an overwriting characteristic. Therefore, the overwriting characteristic can be obtained in a short time without using any man power.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a magnetic disk plate inspection apparatus, and more particularly to a magnetic disk plate inspection apparatus for inspecting override characteristics.

[Common technology]

Generally, the surface of a magnetic disk plate is coated or plated with a magnetic medium, and the state of residual magnetization in the thickness direction of the medium varies depending on the write current value and frequency applied to the head, and the Therefore, even if a high-frequency pattern is written on top of a low-frequency pattern with the same current value, the low-frequency pattern will be In deep areas, the pattern cannot be rewritten to a higher frequency pattern and remains.

It is said that the smaller the residual component is, the better the characteristics of a magnetic disk plate are, and this value is expressed in decibels, called override customization, and used to evaluate the characteristics of the disk plate.

[Prior art]

In conventional magnetic disk plate inspection equipment, in order to inspect override characteristics, a first specified frequency (hereinafter referred to as L) is placed on the disk plate.
F), then overwrite the second specified frequency (hereinafter abbreviated as HF), which is higher in frequency than LF, and measure the HF decibel output value and the LP residual decibel output value with a full spectrum analyzer. The override characteristic value was determined by taking the difference between the values, but the disadvantage was that the measurement was time-consuming because it was measured manually, and the spectrum analyzer used for the measurement was very expensive.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic disk plate inspection apparatus that can inspect override characteristics at high speed and at low cost without requiring manual intervention.

[Structure of the invention]

The magnetic disk board inspection apparatus of the present invention includes a first bandpass filter that passes only the LP frequency component of the amplified read signal from the head, and a second bandpass filter that passes only the HP frequency component of the read signal. filter and
a changeover switch that selects only one of the output signals of the first and second bandpass filters; the signal selected by the changeover switch is used as a non-inverting input signal; the output signal is fed back to the inverting input via a low-pass filter; It is configured to include a comparator, a logarithmic amplifier that logarithmically amplifies the output signal of the low-pass filter, and an analog-digital converter that converts the output of the logarithmic amplifier into a digital signal.

[Explanation of Examples]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

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

The amplified read signal a from the head supplied to the input terminal 101 is input to the LP bandpass filter 1 and the HF bandpass filter 2.

The output signal C of the LF bandpass filter 1 and the output signal C of the TF bandpass filter 2 are connected to terminals 102 and 103 of the changeover switch 3, respectively.

The output signals S and C input to the changeover switch 3 are output to the control section 8.
Either one is selected by the switching signal fK from the selector switch 3, and enters the non-inverting input terminal 105 of the comparator 4 via the common terminal 104 of the changeover switch 3.

The output signal d of the comparator 4 is fed back to the inverting input terminal 106 of the comparator 4, and is also sent to the logarithmic amplifier 6, together with the output signal e from which high frequency components have been removed by the low-pass filter 5.

The output signal of the logarithmic amplifier 6 is sent to the AD converter 7, converted into a sidigital signal by the conversion start signal g from the control section 8, and then sent to the control section 8.

In this embodiment, the LP band-pass filter 1 has a center frequency of LP and has an attenuation characteristic of O decibels for LP and 50 dB or more for HF, and the HF band-pass filter 2 has a center frequency of HP and θ decibel,
The LP is designed to have an attenuation characteristic of 50 decibels or more, and after passing through a band pass filter (designed so as not to include any important frequency components), the cutoff frequency of the low pass filter 5 is determined by the Set the frequency to completely remove the modulation signal included in the lead signal.

The output voltage of the logarithmic amplifier 6 changes linearly in response to a logarithmic change in the input voltage. For example, if the input signal is one digit (1
0 times or 1/10) Every time the output signal changes
If it is designed to change, a 1 dB change in the input will result in a 0.0 dB change in the output. This will correspond to changes in IV.

Comparator 4 generates a high-level output signal when the signal voltage at non-inverting input terminal 105 is greater than the signal voltage at inverting input terminal 106.

The operation will be explained below. LP to terminal 101.

When a signal containing both HF and the same frequency components is input, the LF bandpass filter 1 selects only the LP acid component, and the HF bandpass filter 2 selects only the HP acid component.

If the changeover switch 3 is now connected to the terminal 103 side, the output signal C is supplied to the non-inverting input terminal 105 of the comparator 4. Here, if the output signal C has a waveform as shown in FIG. Since the output signal d of the comparator 4 is at a high level while the voltage at the voltage terminal 105 is high, when the input signal oscillates around 0, like the signal C, the output d
has a pulse waveform as shown in FIG. 2(b).

This output signal d becomes an output signal e from which high frequencies are removed by a low-pass filter 5. At first, the output signal e gradually rises because the output pulses of the comparator 4 occur frequently.
Eventually, the voltage of the comparator 4, which is higher than the peak voltage of the signal C, no longer generates an output pulse, and the voltage begins to fall. However, when the voltage drops a little, the voltage becomes lower than the peak voltage of the output signal C, and an output pulse is generated again, causing the voltage to rise and turn around. Thus the signal e
becomes an envelope signal that follows the peak voltage of the input signal C, as shown in FIG. 2(C), and can be used as a signal representing the magnitude of the output signal C.

This signal e is sent to the logarithmic amplifier 6, where it is converted into a signal that changes logarithmically as described above, and then supplied to the AD converter 7, where it is converted into a digital signal by the conversion start signal g from the control section 8. converted. The control unit 8 can know the magnitude of the output signal C in decibels by reading the digital signal.

Further, when the changeover switch 3 is connected to the terminal 102 side, the same operation is performed, and the control unit 18 can know the magnitude of the output signal in decibels.

In order to test the override characteristic using this circuit, the HF signal is overwritten after the LP signal is written on the disk board.

At this time, the read signal from the head is H as mentioned above.
The F signal includes a residual LP multiplied signal.

The control unit 81 connects the changeover switch 3 to the terminal 103 side using the signal V and the signal f, waits for the disk plate to make one rotation and a signal outside the one rotation is supplied to the circuit, and then outputs the conversion start signal g. After converting the output value of the I-HF signal into a digital signal using Next, the control section 8 connects the changeover switch 3 to the terminal 102 side using the output signal f, performs similar processing, and sets the obtained value as Y.

The obtained X and Y are each included in the read signal)
The magnitude of the TF frequency component and the LF frequency component is expressed by a defbel value, and (y-x) decibel is a value indicating the override characteristic.

〔Effect of the invention〕

The magnetic disk plate inspection device of the present invention can easily obtain override characteristics in a short time without using expensive measuring equipment or human intervention. Can be configured at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention. FIGS. 2(a), 2(b), and 2(c) are waveform diagrams of each part of FIG. 1. 1...LP band pass filter, 2...
・HF band pass filter, 3... Selector switch, 4... Comparator, 5... Low pass filter, 6... Logarithmic amplifier, 7... ...A
D converter, 8...Control unit, a...Read signal, b-f...Output signal, g...
Conversion start signal, h...Digital signal. Agent Patent Attorney Hara Uchi - Figure 2″′

Claims (1)

[Claims] a first bandpass filter that passes only the first frequency component of the amplified read signal from the head; a second bandpass filter that passes only the second frequency component of the nJ read signal; and the IEI , a changeover switch that selects only one of the output signals of the second bandpass filter, and a comparator that uses the signal selected by the changeover switch as a non-inverting input signal and feeds the output signal back to the inverting input via the low-pass filter; A magnetic disk board inspection apparatus comprising: a logarithmic amplifier that logarithmically amplifies the output signal of the low-pass filter; and an analog-to-digital converter that converts the output of the logarithm amplifier into a digital signal.