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FOR
WRITING
SERVOS
The circuits for the servo read amp and ftlter are shown in Figure 1-20. In this
~t
U3(NE592) amplifies the
servo read signal, which then
passes
through a differential ftlter to eliminate data write
crosstalk
at
frequen~es
greater
than
542 KHz. Next, the signal is AC coupled by Cl2, Cl3, R37, and R38. and further amplified by UIC
(NE592). Finally. Cl4 and R39 AC couple at approximately 80 KHz and R41 and CIS ron off at about 1.0 MHz to
band pass the signal.
SERVO
HEAD
CR22
.26
IK
-=
CR21
I~
1/8w
R27
1.69K
R28
1.69K
r---DIFfERENTIAl
F'LTER~
FIGURE 1-20
SERVO READ AMP AND FILTER CIRCUITS
TO
>--~-v;;..~~-+PEAK
DET.
The Servo Peak Detector (Figure 1-21) takes a 540 KHz sine wave input and finds the greatest positive voltage.
The peak voltage is amplified (3X) and held in capacitor C16. The Reset Peak Detector Gate U11 (7406) receives in-
put from the microprocessor and resets C-16.
SERVO
BURSTS
+RST PEAK
DET
+5V
TP6
7
)
R43
200K
R44
lOOK
13
-
FIGURE 1-21
SERVO PEAK DETECTOR
1-21
TO AB SWITCH
R42
2K
CI6
I
470 _
Pf
REV A (01/84)
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