Pll Circuits - Icom IC-R8500 Service Manual

and
consists of
a
PLL
1C,
VCO-B and
loop
filter circuits,
etc.
The
output signal
is
applied to the
2nd mixer
circuit In
the
RF-A
or
RF-B
unit
as a 2nd
LO
signal via the
multiplier
circuit.
The
generated
signal
from the
VCO-B
(VCO-B
board, Q1,
03)
is
amplified
at
the
buffer-amplifier (IC12)
and
is
then
applied to
the prescaler section
In
the
PLL
1C (IC10, pin
11).
The
reference
signal
from
the
divider circuit
(IC11; 15.1
MHz)
is
divided
at
the
programmable
divider section
in
the
PLL
1C.
The
output signals from these
section are
phase
detected
at
the
phase detector
section,
and
then output
from
pin
6
of
the
PLL
1C via the
charge
pump
section.
The
output signals are applied
to
the loop
filter
circuit
(Q14,
Q15)
to
converted
into
DC.
The
DC
voltage
is
then applied
to the
VCO-B
circuit.
•
VCO-B
output frequency
Receive
freq.
[MHz]
VCO-B
output
Ireq.
{MHz]
VCO
Multiplier
action
0.1- 29.99998 304.8 Q1
i;e
30.0- 489.99999 768.0
Q3
-
500.0-1199.99989
256.0
Q1
-
1200.0-1499.99999 768.0
Q3
-
1500.0-1999.99999
256.0
Q1
-
4-2-3
CONVERTOR
PLL CIRCUIT
(CONV
UNIT)
The generated
signal
from the convertor
VCO
circuit
(IC6)
is
amplified
at
the
buffer-amplifier
circuit
(IC7)
and
then
applied
to
the
PLL
IC (IC4) via the
low-pass
filter
circuit
(L29, L30.
C78-C78).
The
filtered
signal
is
applied to the
prescaler section
to
produce an
approx.
100 kHz phase
signal.
The
reference
signal
from the
PLL
unit
(15.1
MHz)
is
divided
at
the
programmable
divider
section
in
the
PLL
IC,
and
the
phase
signals are applied
to the
phase
detector
section.
The
output signals from
the
phase
detector section are
applied to
the convertor
VCO
circuit (1C6).
•
Convertor
VCO
output frequency
Receive
freq.
[MHz]
Convertor
VCO
output
freq.
[MHz]
Divider
action
1025.0-1199.99999
1000.0
1/2
1200.0-1889.99989 1000.0 bypassed
1990.0-1999.99989
1010.0 bypassed
•
PLL
circuits
DOSIC
IC3
PLLIC
ICS
4-7