Transmitter Circuits; Frequency Synthesizer Circuits; Voltage Block Diagram - Icom IC-V80E Service Manual Addendum

4-2 TRANSMITTER CIRCUITS

TX AF CIRCUITS
The audio signal from the internal or external microphone
(MIC signal) is applied to the MIC AMP (IC13B). The
amplified MIC signal is passed through the HPF (R266,
C132, C304) and the MIC AMP with pre-emphasis circuitry
(IC3A). The pre-emphasized MIC signal is passed through
the MIC line SW (IC4), and applied to the D/A converter
(IC10).
The level-adjusted MIC signal is applied to the modulation
circuits as the modulation signal.
• TX AF CIRCUITS
MC1
OPT
HPF
IC13B
[MIC]
MIC MIC
AMP
HPF
D31
VOX
VOX DET
MODULATION CIRCUITS
The modulation signal from the TX AF circuits are applied to
the VCO to frequency modulate it.
The frequency modulated VCO output is amplified by the
buffer (Q6), amplified by the LO AMP (Q4), then applied to
the TX amplifier circuits via the LO SW (D3 and D4) as the
TX signal.
• MODULATION CIRCUITS
X1
IC1
CP
REF. REF PLL LOOP
IC FILTER
ADJ. OSC
(21.25MHz)
IC10
DTC
D/A
TX AMPLIFIER CIRCUITS
The TX signal from the VCO is amplified by the pre-
drive AMP (Q3), drive AMP (Q2) and power AMP (Q1) in
sequence, to obtain the TX output power.
The power-amplified TX signal is fed to the antenna through
the LPFs and antenna SW (D1 and D2).
• TX AMP CIRCUITS
D3,D4
Q2
Q3
LO PRE
DRIVE
DRIVE
SW AMP
From
the VCO
IC3B,Q37
IC3A
MIC
AMP
(PRE-ENPHA)
MOD1 MODIN
IC4
MIC line
SW
IC13A
AMP
VCO
Q6 Q4
Q76,D59-D61
To the TX AMP
LO
BUFF
AMP
DEV
ANT
(TX power detector) D1,D2
Q1
PWR ANT
LPF LPF
AMP SW
APC
PWR
CTRL
DET
D32,D33
T3 TXC
To the RX circuits

4-3 FREQUENCY SYNTHESIZER CIRCUITS

The oscillation frequency of the VCO is determined by the
variable capacitors (D59 and D60). While transmitting, D58
is ON, and C461 and C462 provide the RF path to GND.
This shifts the oscillating frequency range higher. Adding
modulation signal to D61 provides frequency modulation.
The output signal of the VCO is passed through the buffer
AMP (Q6), and applied to the buffer AMP (Q5: for PLL
feedback) or the buffer AMP (Q4: LO AMP).
The output signal of the buffer AMP (Q5: for PLL feedback)
is applied to the PLL IC (IC1). The applied signal is phase-
compared with the reference frequency signal from the
TCXO (X1), and the resulting signal is output from the PLL
IC via the charge pump, and then applied to the VCO as the
lock voltage, after being passed through the loop filter.
Q58 shifts the characteristic of the loop filter for shorter PLL
lockup time when the transceiver needs to lock the PLL up
immediately.
The VCO's power supply circuit (Q11), which works as a
ripple filter, has the capability of fast ON/OFF switching
operation that works even when the transceiver is in the
power save mode.
• FREQUENCY SYNTHESIZER CIRCUITS
X1
IC1
CP
Ref.freq.
PLL
LOOP
oscillator
IC
OUT FILTER
Q58
LOOP
REF.
SW
ADJ.
FC
Q7 2nd LO
signal
BUFF

4-4 VOLTAGE BLOCK DIAGRAM

AF power AMP
TX AMP, Backlight
AF6V
AF
Q15,Q16
REG
AFON
VCC
BATT+
From the battery
Q55,Q56,
Q78,D39
BATT-
IC12,D10
CPU5
REG
4 - 2
D3,D4
Q6
Q4
VCO
Lock
LO
voltage
BUFF
AMP
Q76,D59-61
VCO SHIFT
SHIFT
Q77
Q5
BUFF
IC2
1st IF mixer
IF DET-IC
TX circuits RX circuits RX/TX circuits
PS5
T5 R5
VCC
Q22 Q21
SW 5 T5 R5
REG REG REG
T5C R5C
PCON
CPU5V
CPU, EEPROM
TX/RX
TX AMP
SW
LPF
Q13
VCO
VCO5
Q11
VCO5
REG
PSVCO