Technics ST-9038 User Manual

t
PART
II
PLL SYNTHESIZER
,{rü
of
C
to be
dischar:ged
thus
incr"easing
the output
voltage
of the
LPF
and raising the VCO frequency.
As these
operations
are
repeated,
the outputs
become identical
in
phase,
and
both Dr and
Ur
become
"1".
Consequently,
Or and
Oz
turn
OFF, causing
charge
and discharge to
stop. These
operations
result
in a response
as
illustrated
below.
,f,,)
1-7-2
Circuit to
prevent
shock noise
The lS
(lnstant
stop)
terminal
is
employed to
prevent
shock
noise during the
OFF mode. The level
of
this
terminal is
usually
"l"
when
the PLL
is
being
locked.
lt becomes
"0"
immediately after the
power
source turns
OFF.
(Reference:
square
wave
form
with
PLL
unlocked).
As
shown
in the
afore-mentioned
circuit
diagram,
a diode
is
connected to
lS
to
discharge the
capacitor
at the
base of
Oz
during the
OFF
mode,
thus accellerating the rise
of the collector voltage
of
Oo.
e
1-g
VCO
(Voltage
control
oscillator)
s
l¿
l/
4.5V
14V
VD
_B
VD
=
4.5
-approx.
14V
(from
LPF
output
voltage)
TO INTERFACE To MIX
Fis. 1
Flg.2
This
VCO is a Colpitts
oscillator
circuit in which
a variable capacitor
(variable
capacitance diode)
and an inductance are
combined
as
shown
in Fig.
1. The frequency ranges
from
98.3
(98.8)
MHz
to 118.6
MHz.
lf inverse
voltage VD is applied
to
the variable
capacitor, it causesthe
capacitor
to
have
capacity
C
as the
space-charge
layer spreads.
The relation
is in
inverse
proport¡on
as
shown
in Fig.
2.
Therefore,
the frequency
is
proportional
to VD. The
MA320G1-N
(MEC
make) employed for
this
circu it varies
with
in
2
-
12pF
,
and
VD
used
ranges
f rom
4.5V
to 1
4V.
Also, the
ANT
circuit uses two
double
tuned
circuits
with variable
capacitors, which
serves to
apply
DC
bias
VD
the same
as
VCO.
This
method,
however,
causes
tracking erior
problem
to arise.
So,
five
variable
capacitors
whose
variation
in
capacity at
3, 10,
17 and 25 is less than3%
areemployed
for
the ANT
and
OSC circuits.
-
ll
-
c
;
Buffer

Technics ST-9038 Specifications

General

Brand	Technics
Model	ST-9038
Category	Tuner
Language	English