Frequency Synthesizer Circuits - Icom IC-F3210D Service Manual

MODULATION CIRCUIT
The modulation signal from the TX AF circuit is applied to
D15 of the TX VCO (Q14, D14–D17) to modulate it (FM for
the analog mode, 4FSK for the digital mode). The modulated
signal from the TX VCO is buffer-amplified by two buffers
(Q8, Q10), and applied to the TX AMP circuit through the LO
SW (D5, D6).
• MODULATION CIRCUIT
Q10 Q8
TX VCO
Q14, BUFF BUFF
D14,D16,D17
D15
MODULATION
MOD
From the TX AF circuits
TX AMPLIFIERS
The buffer amplified signal from the TX/RX SW (D5, D6) is
sequentially amplifi ed by the pre-drive AMP (Q3), drive AMP
(Q2), and power AMP (Q1), to obtain TX power. The ampli-
fi ed TX signal is passed through the antenna SW (D1, D22,
and D23) and the LPF, which eliminates harmonics, and
then fed to the antenna.
APC CIRCUIT
D7 and D8 rectify a portion of the TX signal to direct current,
and the APC AMP (IC1) 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 CIRCUITS
Q2
Q3
From the
TX VCO
PRE
DRIVE
DRIVE
AM P
4-4 VOLTAGE DIAGRAMS
Voltage from the power supply is routed throughout the transceiver, through regulators and switches.
Q71 ,Q86
S5C
S5
REG
Q72,Q87
IC54
RXC
R5
VCC REG
+5V
REG
Q73,Q88
TXC
T5
REG
IC65
POSWH
VCC DC-DC
3.3V
Q90,Q91
+3.3V
REG
PWON
Q92,
Q93,
POWER
SW D59
LINE
FILTER
LINE
FILTER
LINE
FILTER
IC900
+3.3V
DC-DC
1.6V
CPUV
D5,D6
To the TX AMP circuits
LO
SW
D1,D22,D23
Q1
ANT
PWR
LPF
AM P
SW
IC1
APC PWR
D7,D8
AMP T1
DET
Q6
TMUT
MUTE
To the RX circuits
SW
S5V
TX/RX common circuits
R5V
Receive circuits
T5V
Transmit circuits
+5V
TX/RX common circuits
CPUV
Logic circuits
+3.3V
DVDD_3.3V
LIN E
DSP flash
FILTER
3.3V_VD D
DSP
+3.3V_A
Liner codec
CVDD_1.6 V
DSP reference voltage
4-3 FREQUENCY SYNTHESIZER CIRCUIT
The RX VCO is composed of Q13, and D11–D13. The VCO
output signal is buffer-amplifi ed by two buffers (Q8 and Q10)
and applied to the 1st IF mixer, through the LO SW (D6) and
the attenuator.
The TX VCO is composed of Q14 and D14–D17. The VCO
output signal is buffer-amplifi ed by two buffers (Q8 and Q10)
and applied to the pre-driver (Q3), through the LO SW (D5)
and the LPF.
A portion of signal generated by each VCO is fed back to
the PLL IC (IC4, pin 17) through the buffer (Q9) and the LPF
(L46, C167–C169).
The applied VCO output signal is divided and phase-com-
pared with a 15.3 MHz reference frequency signal from the
TCXO (X2), which is also divided. The resulting signal is
output from the PLL IC (IC4), and DC-converted by the loop
fi lter, and then applied to the VCO as the lock voltage.
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 fre-
quency.
• FREQUENCY SYNTHESIZER CIRCUIT
X2
15.3MHz
VCON
TCXO
Q26
IC 4
PLL
X3
IC
SO,SCL,PLST
ANT
45.9MHz
IF IC
BPF
IC3
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
D5,D6
LO
To the TX AMPs
SW
ATT
Q23
1st IF mixer