Asymmetry measuring apparatus and method

Details Asymmetry measuring apparatus and method Asymmetry measuring apparatus and method

1999-04-15

2001-02-27

Patidar, Jay (Department: 2862)

Electricity: measuring and testing

Magnetic

Magnetic information storage element testing

C360S053000

Reexamination Certificate

active

06194895

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a testing apparatus for floppy disk drives (hereinafter often abbreviated to “FDD”), and more particularly to an apparatus for measuring the asymmetry of reproduced output.
BACKGROUND OF THE INVENTION
In a waveform of read data output from FDD, a difference in time between the time T
1
from the rise edge of read data RD
1
to the rise edge of read data RD
2
and the time T
2
from the rise edge of read data RD
2
to the rise edge of read data RD
3
, T
1
-T
2
, is called “waveform asymmetry” or “asymmetry” that is one of important characteristics in reproduction of data from floppy disks by means of FDD.
A conventional method for simply measuring the asymmetry is to directly measure time using an oscilloscope.
Another conventional method for measuring the asymmetry is disclosed in Japanese Patent Laid-Open No. 94271/1989. According to this conventional method, the time between edges of the read data pulse is measured with a clocking circuit. In this method, a reference clock pulse from a reference pulse generator is counted by means of a clocking circuit to determine the time between the read data pulses.
The above prior art methods have suffered from the following problems.
Specifically, in the measuring method using an oscilloscope, images displayed on the oscilloscope are always swung. Therefore, measuring point cannot be easily determined. This requires a lot of time and skill for the measurement. Further, large measurement errors and personal errors are created. Therefore, the conventional methods lack in reliability and are unsuitable for mass production.
Adoption of an oscilloscope having a time measuring function for mass production enables shortening of the measuring time and the measuring accuracy. This, however, poses a problem of increased cost due to necessity of investment in plant and equipment.
On the other hand, the method for measuring the time from edge to edge in read data pulses by means of a clocking circuit causes a counting error of pulses due to a correlation between two clocking circuits. Further, there is a possibility that a quantization error up to ± one period of the reference clock occurs at the time of rising to a unit/omission or rounding-off in clocking with the reference clock. In this case, the lower the frequency of the reference clock, the larger the time per period of the reference clock and the larger the error.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to solve the above problems of the prior art and to provide an asymmetry measuring apparatus which does not require a lot of time for the measurement and causes no significant measurement error and hence is suitable for mass production and, in addition, does not create a quantization error at the time of counting of the reference clock.
According to the first feature of the invention, an asymmetry measuring apparatus comprises:
dividing means for dividing read data output from a read data generator in data storing means;
a DC level converter for converting the duty ratio of a signal divided by the dividing means to a DC voltage level; and
DC voltage measuring means for measuring the output voltage of the DC level converter.
The dividing means may be flip-flop.
The data storing means may be a floppy disk drive.
According to the second feature of the invention, an asymmetry measuring method comprises the steps of:
dividing read data read and output from data storing means;
converting the duty ratio of the divided signal to a DC voltage level; and
measuring the DC voltage level.


REFERENCES:
patent: 1-94271 (1989-04-01), None

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