Disk Prml Parameters - LeCroy WaveMaster 8600A Operator's Manual

Disk PRML Parameters

These enable parameter measurements of auto-correlation signal-to-noise (ACSN) and non-linear
transition shift (NLTS). The calculation of both parameters is based on a correlation math function.
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ACSN can be applied to any periodic waveform. Since these waveforms are by definition
identical in every period, any deviation is due to uncorrelated noise sources. By performing
an auto-correlation calculation of the waveform over successive periods, the level of
less-than-perfect correlation can be measured. With this measurement, the noise level can
be derived by ACSN. (See ACSN description.)
•
NLTS offers the ability to measure all echoes in the auto-correlation calculation of a disk
waveform. This includes the NLTS (adjacent location), second adjacent location, and
overwrite (initial magnetization) echoes. The parameter performs NLTS averaging, pattern
length searching, and limit checking to reduce the effects of noise and to ensure accurate
measurements. (See NLTS description.)
Correlation Theory of Operation
The DDAs correlation function measures the correlation between one section of a waveform and
other sections of the same waveform having the same length, or between a section and sections of
equal length belonging to another waveform.
When the correlation is performed on the same waveform it is called an auto-correlation. If the
shape of two waveform sections are identical, the correlation value will be maximized.
The DDA normalizes correlation values to +/-1, with 1 indicating that the waveform sections are
identical, -1 that the sections are inverted from each other, and 0 that there is no correlation.
Noiseless periodic waveforms will have perfect correlation (a correlation value of 1) when
performing auto-correlation, and when the start of the second section is an integer number of
periods later than the start of the first section.
Correlation values can be calculated as a function of various amounts of time shift between two
waveform sections used in calculating a correlation. This calculation, as a function of the starting
point of the second section being the i
408
th
waveform sample, is determined by:
WM-OM-E Rev I