Transmit Circuits; Frequency Synthesizer Circuits; Voltage Block Diagram - Icom IC-F2000 Service Manual

4-2 TRANSMIT CIRCUITS

TX AF CIRCUIT
The audio signal from the internal or external microphone
(MIC signal) is passed through the MIC gain SW (IC2) and
applied to the baseband IC (IC4).
The processed AF signal is passed through the AF
SW (IC2) and LPF (IC11), and then applied to the D/A
converter (IC10), which adjusts its level (=deviation). The
level-adjusted MIC signal is applied to the TX VCO as the
modulation signal.
• TX AF CIRCUIT
LIMIT
SPLT
HPF
EMPH
AMP
IC2
IC11
AF
SW
LPF
MOD
To the modulation circuit
IC10
MODULATION CIRCUIT
The modulation signal from the TX AF circuits is applied
to D13 of the TX VCO (Q27, D11 to D13). The frequency-
modulated signal from is amplified by two buffers (Q30 and
Q31), and then applied to the TX AMP circuit, through the
TX/RX SW (D16).
• MODULATION CIRCUIT
Q30 Q31
TX VCO
Q27,
BUFF BUFF
D11,D12
D13
FREQUENCY
MODULATION
From the TX AF circuits
TX AMP CIRCUIT
The buffer amplified signal from the TX/RX SW (D16) is
sequentially amplified by the pre-AMP (Q34), pre-drive AMP
(Q35), drive AMP (Q36) and power AMP (Q38). The power
amplified TX signal is passed through the antenna SW (D19)
and LPF (L29 to L31, C333, C348, C349 and C352), and
then applied to the antenna.
APC CIRCUITS
At the TX output power detector, the RF signal at the LPF
(L29 to L31, C333, C348, C349 and C352) is rectified by
the diodes (D22 and D23), and it is used as the TX power
sensing voltage.
The voltage is applied to the APC AMP (IC17), and the out-
put voltage controls the bias voltages of
drive AMP (Q36) and power AMP (Q38) to keep the TX out-
put power constant.
• TX AMPLIFIERS AND APC CIRCUIT
Q34 Q35
From the
TX VCO PRE PRE
AMP DRIVE
*
*:For [EUR] and [UK] versions.
IC4
IC2
MIC
AMP
COMP
GAIN
D16
To the TX AMP circuits
TX/RX
SW
the pre-drive (Q35),*
D19,D27
Q38
Q36
ANT
PWR
DRIVE
LPF
AM P
AM P SW
IC17
APC
PWR
D22,D23
AMP
DET
To the RX circuits

4-3 FREQUENCY SYNTHESIZER CIRCUITS

The RX VCO is composed of Q25, D9 and D10. The output
signal is amplified by two buffers (Q31 and Q31) and
applied to the 1st IF mixer (Q37), through the LO SW (D17)
and LPF (L20, C291 and C292).
The TX VCO is composed of Q27 and D11 to D13. The
output signal is amplified by two buffers (Q31 and Q31) and
applied to the pre-AMP (Q34), through the LO SW (D16).
A portion of oscillated VCO output signal from each VCO is
fed back to the PLL IC (IC15), through the buffer (Q32).
The applied VCO output signal is divided and phase-
compared with a 15.3 MHz reference frequency signal from
the TCXO (X3), which is also divided. The resulting signal
MC1
is output from the PLL IC (IC15), and DC-converted by the
loop filter, and then applied to the VCO as the lock voltage.
J1
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
15.3MHz
CR-794
X3
IC7
BAL
BUFF TCXO
REF
Q26
PLL
X3
IC
IC15
45.9MHz
IF IC
BPF
IC16

4-4 VOLTAGE BLOCK DIAGRAM

IC20
PWON
+5V
VCC REG
IC6
CPU5
REG
VCC
ANT
4-2
Q23 Q29
RX VCO
RIPPLE VCO R5V
FIL SW
D10
Q25
D9,D10
LV
ADJ
Q30 Q31
LOOP LV
BUFF BUFF
FIL
D11
D11,D12
LVA
LV
Q27
ADJ
TX VCO
Q32
BUFF
×2
Q17
T5C
T5 T5V
To the TX circuits
REG
Q16
R5C
R5 R5V
To the RX circuits
REG
Q15
S5 S5V
To both RX and TX circuits
S5C
REG
+5V
To both RX and TX circuits
CPU5
To the logical circuits
S5 F1
1 2
D17
D16
TX/RX
To the TX AMPs
SW
LPF
Q37
1st IF mixer