Harman Kardon HD7725 - Page 22

2-5. Tracking servo control operation
When
a
tracking
error
signal
is
detected
by
photodiodes
E
and
F,
it
is
fed
to
pins
11
and
10
of
IC101
respectively
as
shown
in
Fig.
6.
In
1C101,
the
signal
is
converted
into
voltage
by
the
E
!-V
amplifier
and
F
|-V
amplifier,
transmitted
to
the
tracking
error
amplifier
and
output
through
pin
20.
While
it
passes
through
IC
102,
in
from
pin
3
and
out
from
pin
28,
and
1C103,
in
from
pin
6
and
out
from
4,
it is amplified in each IC and sent to the tracking coil to adjust pickup so that the amount of track shift is reduced as closely to
none as possible,
Pick-up 1C101 iC102 1G103
Fig. 6
TRACKING
COIL
TRACHING
ERROR
AMP
3. REGENERATIVE CIRCUIT
3-1. RF circuit
The
currents
from
photo-diodes
(a,
b,
c
and
d)
are
fed
to
IC101
through
pins
7
and
8
and
converted
to
voltage
by
RF
!-V
amplifiers
(1)
and
(2)
respectively
there,
added
by
the
RF
summing amplifier
and
output
from
pin
2
as
a
signal.
As
it
is
sent to
pin
17
of
C201,
it
can
be
checked
at
the
test
point
(TP202)
provided
on
its
way
by
means
of
the
eye
pattern
check
(as
shown
by
Fig.
7).
Pick-up
A i 1101
Fig. 7
A
Js
c
1
TP202
1
B I 2
Eye Pattern (TP202)
T
D RF
! SUMMING
I RF i-V AMP. (2) AMP
I
Photo diode |
3-2, EFM demodulation, error correction, seriai/parallel conversion =~
EFM demodulation, error correction, and serial/paralle! conversion are performed by the internal circuitry of C201. The eye-pattern
signals
from
pin
2
of
1C101
are
sent
to
pin
17
of
IC201,
then
demodulated
from
14
bits
to
8
bits
by
EFM
readjustment.
At
the
same
time
any
error,
if
found,
is
corrected
(CIRC)
and
the
signais
are
sent
to
the
D/A
converter
interface.
After
that,
they
are
output
from
pins
1,
15,
70,
72,
74
and
75
of
IC201
and
fed
to
the
RLS
(Real
-Time
Linear
Smoothing
)
module
(as
shown
by
Fig.
8).
1¢201
REAL-TIME
@ LINEAR
Fig. 8 SMOOTHING
21