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PULSE .IOTH LIMITE II
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FIGURE 1-34
READ DATA PULSE GENERATION
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.M'MIIOOAT/I.
_II'MIIO DATA
Up to this point, flux changes on the media that have been detected, amplified, and filtered are in the form of
voltage peaks. Since the precise bit timing required by the data separator is not easily achievable by peak detection,
the data is differentiated to accurately convert the peaks into zero voltage crossings. Figure 1-34 illustrates the re-
mainder of the read channel. Amplifier U2e is configured as a differentiator with the differentiated outputs appear-
ing at the input to the comparator. The zero crossings are detected by the comparator, whose output is the D input of
flip-flop U2F, part of the droop ignore circuit. The zero crossings also trigger a one-shot whose period is set shorter
than the expected bit time. When the one-shot times out, the flip-flop latches the state of the comparator. The one-
shot time is long enough that any change in the comparator output due to noise in the differentiated signal will be
filtered by the flip-flop and will not be detected as data bits. The output of the droop ignore flip-flop then passes
through a pulse width limiter comprised of a series of gates with added delays. The resulting narrow positive pulses
represent the detection of flux reversals in the media. These pulses are input to a differential line driver and are out-
put as ± MFM READ DATA to the controller via the 20 conductor data cable.
1-31
REV A (01/84)
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