LeCroy DDA 7 Zi series, Руководство оператора

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WavePro 7Zi
491
WP700Zi-OM-E-RevA
msnr Media Signal-to-Noise Ratio
Definition Provides a signal-to-noise ratio for single-frequency, sector-based waveforms.
Description
Granularity in magnetic media produces zigzag transitions. The exact location of the zigzags
changes from write to write causing media noise (also known as zigzag noise). During read
operations, the read head effectively averages across the track the location of all the zigzags. If
the recorded track width is wide, there are many zigzags and very little variability in the
averaged transition location. If the track width is narrow, there are fewer zigzags, and the
variability in the averaged transition location increases.
Head signal amplitude is approximately proportional to track width. Media noise is
approximately proportional to the square root of the track width. Therefore, the ratio of the head
signal to the media noise (msnr) is proportional to the square root of the track width. As track
widths continue to decrease, msnr will get worse. Although advanced head technology (i.e.,
MJR and GMR) can increase the head signal output for a given track width, the effect of media
noise on the head signal is also increased so there is no improvement in msnr. As track widths
decrease, msnr will continue to increase despite greatly improved head technology.
By using single-frequency data, the algorithm is able to focus on the peaks, the zero-crossings,
and the troughs. The ideal Viterbi input samples are the1, 0, and -1. Deviations from the
ideal are quantified and graphed. The squared sigma of the total noise distribution is equal to
the squared sigma of the media noise distribution. This relationship is always true:
t
2
=
m
2
+
r
2
For a large number of samples:
m
2
=
a
2
r
2
=
t
2
–
a
2
Once the distribution of the media noise has been calculated, the msnr is then calculated by:
msnr = 20 log(v
0-p
/
m
)
Parameter
Settings
After specifying the location of the “Head Signal” and the optional “Read Gate,” selection of
msnr is automatic after you touch the
Noise Analysis button. Touch the Setup for Single
Frequency button to initialize the measurement.
rsnr Residual Signal-to-Noise Ratio
Definition Provides a residual signal-to-noise ratio for single-frequency, sector-based waveforms.
Description
Residual noise is the random noise present on a disk drive signal from read to read.
By using single-frequency data, the algorithm is able to focus on the peaks, zero-crossings, and
the troughs. The ideal Viterbi input samples are the1, 0, and -1. Deviations from the
ideal are quantified and graphed. The squared sigma of the total noise distribution is equal to
the squared sigma of the media noise distribution and the squared sigma of the residual noise
distribution. This relationship is always true:
t
2
=
m
2
+
r
2
For a large number of samples:
m
2
=
a
2
r
2
=
t
2
–
a
2
Once the distribution of the media noise has been calculated, the rsnr is then calculated by:
rsnr = 20 log(v
0-p
/
r
)
Parameter
Settings
After specifying the location of the “Head Signal” and the optional “Read Gate,” selection of rsnr
is automatic after you touch the
Noise Analysis button. Touch the Setup for Single
Frequency button to initialize the measurement.