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NLTS Measurement
Agilent E5022/E5023 has three methods of measuring Non Linear Transition Shift
(NLTS). Ideally the location of the transitions when the track is read is where they were
written. But in actual case the location of the transitions changes since it is influenced by
its neighboring transitions i.e. how close they are to previous and following transitions.
•
5th Harmonic (Harmonic Elimination) Method
•
Dipulse Extraction Method
•
Time Correlation Method
5th Harmonic NLTS is measured using a spectrum analyzer while Dipulse Extraction and
Time Correlation NLTS are done with an oscilloscope.
5th Harmonic Method
This is a popular way of measuring NLTS. The Agilent E5022/E5023 writes the 30 bit data
pattern (110000001000000110000001000000), then measures the amplitude of the 5th
harmonic of this pattern E(5f
consisting of isolated transitions separated by 15T (repetition period of this sequence is
30T) and measures the amplitude of the same harmonics of this new pattern X(5f
NLTS is defined as:
Equation 5-16
NLTS 5th Harmonic method Definition
Where f
Dipulse Extraction Method
Dipulse extraction is a method used for quantifying the amount of nonlinear distortion
present in the recording and playback process. The detailed description of this method is
given in a paper by D.Palmer, P.Ziperovich, R.Wood and Howell "Identification of
Non-linear Effects Using Pseudo Random Sequences: -IEEE Transactions on Magnetics",
vol. 23, 5, pp.2377-2379, 1987.
The detailed calculation sequence is described in Chapter 3 of the Programming Manual.
Time Correlation Method
Time correlation is a method that measures the SNR and the cross correlation coefficient of
the time domain readback voltages that result from writing a pseudo random sequence.
The algorithm for this method is given in the IDEMA Test and Measurement Committed
PRML Working Group Working Paper, "Nonlinear Distortion Measurement Techniques"
Issued on July 1995.
Chapter 5
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), where f
0
E 5f
NLTS
=
------------------------------------------ -
×
2π 5f
=1/30T
0
Measurement Definition
Measurement Parameter Definition
=1/30T. Next, it writes a reference pattern
0
(
)
0
×
(
)
X 5f
0
0
).
0
259
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