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r - - -
-
-
-
-
-
-
- -
-1
TO OTHER
I
TYPICAL
R53
DATA HEADS
_----.1W'TY'1 .....
~wt
DATA HEAD
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U.S
".....,._~
t-SVt-
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1
of
7
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+WRITE.
.....1::;..O_Nv-......
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HEAD
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SEL
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1(07
LINE
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-
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RI7
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ENCODER BOARD
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FIGURE 1-33
+5
VI-
READ CHANNEL FRONT END
L"
2.7
LIO
12
RSO
Z.71<
. -WRITE
Figure 1-33 illustrates the read channel up to the differentiator input. When
+
WRITE is HI, -WRITE is -3V.
This reverse biases CR8 and CR16 and blocks the AC signal from the data heads at Q2 and Q3. When
+
WRITE is
LO, -WRITE is
+
5V, which forward biases CR8 and CR16 (and the head diodes). The READ signal then flows dif-
ferentially to QA2 and Q3, which have Q4 and Q5 as current sources. The current source provides DC bias for Q2
and Q3. U2A (NE592) is set up CASCODE (common emitter, common base amp) with Q2 and Q3. The NE592, a
high frequency differential amp, amplifies the READ signal (gain approximately 400). Then the amplified differen-
tial output flows through a low pass filter. Differential processing of the READ signals up to the comparator reduces
common mode noise. The low pass filter is comprised of R47, R48, L9, Lll,C26, LtO, Lt2, C27, R56, R54, and
R57. The filtered signal is coupled to another filter by emitter followers Q8 and Q9.
REV A
(01/84)
1-30
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