Frequency Synthesizer Circuits; Voltage Block Diagram - Icom IC-M25 Service Manual

5-3 FREQUENCY SYNTHESIZER CIRCUITS

VCO
While transmitting, the oscillation frequency of the VCO
(Q21, Q22, D22 and D23) is determined by the value of
D22, D23, L22, C26 and C27, adding modulation signal to
D20 modulates the oscillating signal.
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, 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
X1
21.25 MHz
2ND LO
IC360
CPU
IC****
*V
+***V
regulator

5-4 VOLTAGE BLOCK DIAGRAM

MAIN UNIT
CHASSIS
Battery
HV
pack
IC601
DC-IN
5.0 V DC
(USB)
Q 21,Q22
Q23
D22,D23
LOOP
BUFF
FIL
Q25
PLLO
BUFF
I C170
IF IC
Q353
PWR
CTRL
CHARGE
CTRL
PLL
IC1 is a PLL IC which contains the pre-scaler, programmable
counter, phase comparator and charge pump in its package.
The 21.25 MHz reference frequency signal is fed from X1.
The loop filter is composed by R10, R22, C11, C13 and C24.
D 50,D51
Q24
LO
BUFF
SW
VCO
Q150
1st mixer
IC220
3V
CPU3V
regulator
Q224, Q225
3V
VCC
regulator
Q221
R3V
SW
Q222
T3V
SW
5-3
TX AMPs
: To CPU and EEPROM
M3V : To the TX/RX common circuits
: To the RX circuits
R3V
T3V : To the TX circuits