Pll Circuits; Power Supply Circuits - Icom IC-2100H Service Manual

3-3
PLL CIRCUITS
3-3-1
PLL CIRCUIT
A
PLL
circuit
provides stable oscillation of
the transmit
fre-
quency and
the receive 1st
LO
frequency.
The PLL
circuit
compares
the
phase
of
the divided
VCO
frequency
to
the
ref-
erence
frequency.
The PLL
output
frequency
is
controlled
by
the divided
ratio
(N-data) of
a
programmable
divider.
An
oscillated signal
from
the
VCO
passes thorough the
buffer
amplifiers
(Q4,
Q6)
is
applied to the
PLL
IC (IC1, pin 2)
and
is
prescaled
In
the
PLL
IC
based on the divided
ratio
(N-
data).
The
reference signal
is
generated
at
the reference
oscillator
(XI)
and
is
also applied
to
the
PLL
IC.
The PLL
IC
detects the out-of-step
phase using the reference
frequency
and
outputs
it
from
pin 8.
The
output signal
is
passed
thor-
ough
the loop
filter
(R89,
R90,
Cl
05,
Cl
07)
and
is
then
applied
to
the
VCO
circuit
as the lock voltage.
The
lock voltage
is
also
used
for
the receiver tunable
band-
pass
filters
to
match
the
filter's
center
frequency
to
the
desired receive frequency.
The
lock
voltage
is
applied
to
the
bandpass
filters
(D13-D16)
via the
tune
control circuit
(IC4,
D4).
3-3-2
VCO
CIRCUIT (MAIN
unit)
The
VCO
circuit
contains
a separate
TX-VCO
(01,
Q2, D1)
and
RX-VCO
(Q33, D23),
The
oscillated signal
is
amplified at
the buffer
(Q4)
and
LO
(Q5)
amplifiers,
and
is
then applied
to
the
T/R
switching
circuit
(D5).
Then
the
Tx and
Rx
signals are
applied to
the pre-driver (013)
and
1st
mixer (Q21) respec-
tively.
A
portion of the signal
from
Q4
is
amplified at
the buffer
amplifier
(06)
and
is
then fed
back
to
the
PLL
1C
(IC1 pin 2)
as
the
comparison
signal.
3-4
POWER
SUPPLY CIRCUITS
VOLTAGE
LINES
Line
Description
HV
The
voltage
from the
connected
DC
power
sup-
ply.
13.8V
The same
voltage
as
the
HV
line
which
Is
con-
trolled
by the
power
switching circuit (Q25,
Q26,
035).
When
the
[POWER]
switch
is
pushed,
the
CPU
outputs the
"PWRON"
control signal to
the
power
switching
circuit
to turn
the
circuit
ON.
CSV
Common
5
V
for
the
CPU
converted from
the
HV
line
by the
CSV
regulator
circuit
(IC9).
The
circuit
outputs the voltage regardless of
the
power
ON/OFF
condition.
-h8V
Common
8
V
converted from the
13.8V
line
by
the
-I-8V
regulator circuit (ICS).
R8V
Receive 8
V
controlled
by the
R8V
regulator
cir-
cuit
(029,
030)
using the
"RX"
signal
from the
I/O
expander
IC (IC10).
T8V
Transmit
8
V
controlled
by
the
T8V
regulator
cir-
cuit
(Oil
,
012)
using the "TX" signal
from the
I/O
expander
IC (IC10).
+5V
Common
5
V
converted from
the
+8V
line
by
the
+5V
regulator
circuit
(031, 032).
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3-3
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