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4 - 2
4-2 TRANSMITTER CIRCUITS
TX AF CIRCUITS
AF signal from the microphone (MIC signals) is passed
through the MIC mute SW (IC260A), amplifi ed by MIC AMP
(IC200B), and then applied to the D/A converter (IC190),
through another MIC mute SW (IC260C).
The level-adjusted MIC signal is pre-emphasized by R201
and C385 to 6 dB/oct of frequency response, and
then passed through the limiter (IC200A) to prevent over
deviation. The amplitude-limited MIC signal is fi ltered by the
splatter fi lter (IC200D) to remove 3 kHz and higher signals,
and then applied to the VCO (Q21, Q22, D22) for frequency
modulation.
TX AMPLIFIERS
The frequency-modulated signal from the VCO (Q21, Q22,
D22) is passed through the buffers (Q23 and Q24) and LO
SW (D50), and then sequentially amplified by the buffer
AMP (Q50) and pre-drive AMP (Q53).
The amplifi ed signal is splitted by the power splitter (L100,
L101, R463, C445, C446) and applied to the power AMPs
(Q54 and Q55). The amplifi ed signals are combined at the
power combiner (L107, L108, R465, C457, C458) to obtain
the TX output power.
The amplified TX signal is passed through the ANT SW
(D52) and LPF, and then applied to the antenna.
APC CIRCUIT
A portion of TX output signal is rectifi ed by D91 to produce
the DC voltage which corresponds to the TX power level.
The APC AMP (IC50) compares the voltage and TX power
setting voltage from the D/A converter (IC190). The resulting
voltage from the APC AMP controls the gain of both driver
AMP (Q53) and power AMPs (Q54 and Q55), to keep the TX
output power stable.
• TX AF AND MODULATION CIRCUITS
To LO switch
BUFF
BUFF
LPF
LIMIT
AM P
MIC
AMP
MIC
MUTE
MIC
MUT E
Q24
Q23
Q 21,Q22
MOD
MUT E
PRE
ENPHA
D/A
VCO
Q20
IC190
IC200A
IC200D
IC200B
MIC
D 20
D21
D22
INMIC
MOD
IC260A
IC260C
MC250
LPF
ANT
SW
ANTENNA
J1
PWR
AMP
DRIVE
PRE
LO
SW
BUFF
From VCO
APC
CTRL
Receive circuits
D52
Q53
Q54
PWR
AMP
Q55
D50
Q50
PWR
DET
D91
IC50
D90
PWR
SPLITTER
PWR
COMBINER
Q357
PCON
• TX AMPLIFIERS AND APC CIRCUIT