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Chapter 5
Measurement Definition
Parametric Sweep Measurement Definitions
Write Current Sweep Measurement
Write current sweep is a measurement of the TAA, narrow band TAA, PW, Overwrite and
NLTS by 5th Harmonic method. The typical shape of this curve is a flat part at low
currents, i.e. nothing is happening then a rising part as more DC bias causes better
operation, then another flat part where there is saturation.
Typical values of write current are set at the left portion of the region just before it reaches
the saturation level. Typical value of write current is 30 - 40 [mA] for modern MR and
GMR heads.
There are important factors that need to be considered in determining the appropriate value
of the write current. These are the following:
1. The write current should be large enough to saturate the media during write process.
2. As erasure of previously written data is necessary to reduce error rates. The write
current should be large enough to achieve an acceptable overwrite.
3. The write current influences the erase bands on the sides of the track width. An
increase in the write current will increase the fringe field, this increases the width of the
erase band and the interference between adjacent tracks.
The detailed measurement sequence is described in Chapter 3 of the programming manual.
Figure 5-43
Write Current Saturation
Analyzing the illustration of Figure 5-43 for small currents the medium does not saturate
and voltage output is low. At some value the signal voltage is at maximum and any further
increase in current beyond this point will not add to voltage. At voltage maximum the write
current is saturated Iw(sat).
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