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Prefiltering in the Design of Peristaltic Envelope Detectors

IP.com Disclosure Number: IPCOM000120002D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 5 page(s) / 215K

Publishing Venue

IBM

Related People

Chung, PW: AUTHOR [+6]

Abstract

In data channels using MR sensors where thermal asperity disturbances are present, it is desirable to eliminate the effects of the thermal asperity disturbance which is the additive transient disturbance signal. The method and circuitry used to eliminate this disturbance signal has a compromise of increasing additive correlated noise, or residue, when a fast initial decay derivative exists in the falling edge of the additive transient disturbance signal. When this decay derivative is too fast for the peristaltic envelope detector needed, a pulse or glitch is present in the corrected signal output of the additive transient suppression electronics as a result of an incompletely corrected signal.

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Prefiltering in the Design of Peristaltic Envelope Detectors

      In data channels using MR sensors where thermal asperity
disturbances are present, it is desirable to eliminate the effects of
the thermal asperity disturbance which is the additive transient
disturbance signal.  The method and circuitry used to eliminate this
disturbance signal has a compromise of increasing additive correlated
noise, or residue, when a fast initial decay derivative exists in the
falling edge of the additive transient disturbance signal. When this
decay derivative is too fast for the peristaltic envelope detector
needed, a pulse or glitch is present in the corrected signal output
of the additive transient suppression electronics as a result of an
incompletely corrected signal.  When this pulse is excessively wide,
gain errors will result in the AGC circuit needed for amplitude
correction prior to data detection, and may result in lengthy data
errors.

      Because the additive transient disturbance signal may have a
faster than acceptable initial decay derivative, the use of a linear
prefilter becomes desirable.  This filter modifies the frequency
response of the additive disturbance suppression electronics in such
a way as to slow down the initial decay derivative of the additive
transient disturbance signal.  This allows the peristaltic envelope
detector to be designed with a slower decay response and therefore
less residue.  The resulting block diagram of a system which is
capable of doing the aforementioned tasks is shown in Fig. 1.  The
signal from MR element 1 on lines 1' is fed into MR preamplifier 2.
The additive transient disturbance waveform is shown as it appears on
1' with the associated characteristic decay time constant.  The MR
preamplifier output 2' has an additive transient disturbance waveform
which is modified by its low frequency roll off and shown as it
appears on 2'. This signal is then fed into the aforementioned linear
prefilter 3.  A second filter 4 can be selected only during those
times when normal data reading is required, and elimination of the
additive transient disturbance signal is not required.  A selection
means 5 selects the output of the linear prefilter 3' during a mode
of operation where the additive transient disturbance is present.
The linear prefilter output 3' modifies the decay profile of the
additive transient disturbance signal, as shown, to slow the initial
decay derivative of the signal at 2'.  After the select means 5, the
signal is processed to remove the additive transient disturbance from
the coincident data by the means in the prior art.  This method
involves feeding forward the selected signal from select means 5
through a gain (or attenuation) stage 6 and a summing means 9 to the
output 9'.  In addition, this signal is also fed forward via a
parallel path through an envelope detector 7, next through a
nonlinear filter 8, then through a second selection means 10 and
finally to the seco...