Frequency Synthesizer Circuits; Voltage Block Diagram - Icom IC-F4001 Service Manual

TX AMPLIFIERS
The buffer amplified signal from the LO SW (D5) is amplified
by; the pre-AMP, pre-drive AMP, drive AMP, and power AMP
in sequence, to obtain TX power. The amplified TX signal
is passed through the antenna SW and the LPF, which
eliminates harmonics, and then fed to the antenna.
APC CIRCUITS
D1 and D2 rectify a portion of the TX signal to direct current,
and the APC AMP compares the voltage and the TX power
control reference voltage, "T1." The resulting voltage controls
the gain of the power and drive AMPs to keep the TX power
constant.
• TX AMPLIFIERS AND APC CIRCUIT
Q4 Q3 Q2
From the
TX VCO
PRE
PRE
DRIVE
AM P DRIVE
AM P
Q1
D3,D22
ANT
PWR
LPF LPF
AM P
SW
IC1
APC PWR
D1,D2
AMP T1
DET
Q6
MUTE TMUT
To the RX circuits
SW

4-3 FREQUENCY SYNTHESIZER CIRCUITS

The RX VCO is composed of Q13, D11 and D12. The VCO
output signal is buffer-amplified by two buffers and applied
to the 1st IF mixer, via the LO SW (D6) and the LPF.
The TX VCO is composed of Q14 and D14–D16. The VCO
output signal is buffer-amplified by two buffers and applied
to the 1st IF mixer, via the LO SW (D6) and the LPF.
A portion of oscillated signal from each VCO is fed back to
the PLL IC via the buffer and the LPF.
The applied VCO output signal is divided and phase-
compared with a 15.3 MHz reference frequency signal from
the TCXO, which is also divided. The resulting signal is
output from the PLL IC, and DC-converted by the loop filter,
and then applied to the VCO as the lock voltage.
ANT
When the oscillation frequency drifts, its phase changes
from that of the reference frequency, causing a lock voltage
change to compensate for the drift in the VCO oscillating
frequency.
• FREQUENCY SYNTHESIZER CIRCUITS
X2
IC60
BAL
15.3MHz
BUFF
TCXO
REF
Q26
IC2
PLL
X3
IC
SO,SCL,PLST
45.9MHz
IF IC
BPF
IC3

4-4 VOLTAGE BLOCK DIAGRAM

Q74-76
PWON
VCC
S5
4 - 3
D11
RX VCO
Q13,D12
LV
ADJ
LOOP
LV
FILTER
Q10
Q8
BUFF BUFF
D14
TX VCO
LVA
LV
ADJ
Q14,D16
Q9
LPF BUFF
Q73
T5C
T5 T5V
To the TX circuits
REG
Q72
R5C
R5 R5V
To the RX circuits
+5V REG
REG
Q71
S5 S5V
To both RX and TX circuits
S5C REG
+5V
To both RX and TX circuits
IC54
CPU5 CPU5
To the logical circuits
REG
D5,D6
LO
To the TX AMPs
SW
LPF
Q23
1st IF mixer