Frequency Synthesizer Circuits - Icom IC-M23 Service Manual

4-3 FREQUENCY SYNTHESIZER CIRCUITS

VCO
While transmitting, the oscillatinon frequency of VCO (Q21,
Q22, D22) is determined by the value of D22, L22, C26 and
C27, and the frequency modulation is carried out by adding
modulation signal to D20.
The generated signal is passed through the buffers (Q23
and Q24), and then applied to the pre-drive AMP (Q53),
through the LO SW (D50) and buffer (Q50).
While receiving, D21 is turned ON and C28 is connected to
the GND to shift the oscillation frequency lower.
The generated signal is passed through the buffers (Q23
and Q24), and then applied to the 1st mixer (Q150), through
the LO SW (D51).
• FREQUENCY SYNTHESIZER CIRCUITS
IC1
PLL IC
PLLO
X1
21.25MHz
2ND LO
CPU
IC360
4-4 VOLTAGE BLOCK DIAGRAM
CHASSIS
Battery
HV
pack
Q 21,Q22
Q23
D22
LOOP
BUFF
FIL
Q25
BUFF
I C170
IF IC
IC220
regulator
Q224, Q225
Q353
POWER
VCC
regulator
CTRL
PLL
IC1 is a PLL IC which contains the prescaler, programmable
counter, phase comparator and charge pump in its package.
The 21.25 MHz reference frequency signal is fed from X1.
The loop fi lter for the VCO is composed by R8, R10, R22,
C11, C13 and C24.
D 50,D51
Q24
LO
BUFF
SW
BPF
VCO
Q150
1st mixer
3V
: To CPU and EEPROM
CPU3V
3V
Q221
R3V
SW
Q222
T3V
SW
4 - 3
TX AMPs
MAIN UNIT
M3V : To the TX/RX common circuits
: To the RX circuits
R3V
T3V : To the TX circuits