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CIRCUIT DESCRIPTION
28
4. Transmitter Circuit
The output from the PLL frequency synthesizer is ap-
plied to a driver module unit, where the signal is ampli-
fied by RF amplifiers Q1. The output signal of the driver
unit is further amplified in a power hybrid module, IC1,
and ts routed to an antenna steering circuit for directing
the transmit signal to either the built-in antenna
(INT
ANT) or an external antenna terminal (EXT ANT). The
transmit signal is then routed to one of two antenna ter-
minals after going through one of two 2-pole Pi type low-
pass filters placed in each antenna circuit.
DRIVE UNIT)
IN
R2
| ais
as
LW
—
—. —
—_- —
—
—
—
The automatic power control (APC) circuit is provide
to keep transmitter output power constant, by controll-
ing the power supply current to the final module. The
APC operation is accomplished by monitoring the vol-
tage drop across a 0.10 resistor, R5, in the APC mod-
ule unit.
The voltage
across
R5
is compared
at a
comparator, IC1 (LM301AD), with a reference voltage
obtained from a 3.9V Zener diode, D1 (02CZ3.9YZ). The
output of the comparator, IC1, is fed to Q2 (2SB1182)
to control the supply voltage to the final module.
This operation limits any abnormal excess current in
the final module to a pre-determined level, and insures
stabilized transmitter output power at all time.
C12
POWER
MODEL
Lt2
LPF
to ANT. SW
WM, dre
RI4
|VR1
7
|
7
AM
=
R5
op?
ci
Rios
Tyco
alee
AN
~@-AM
Nn
GF
Fosa
201
3
ANY
C55
ae
s
1
Rg
|
an
VR2
a ag 2
8
ciom
a2
56
cay
5
iidapc
R4 | Re
ar
bd
AAA
WW,
a
Q 5
rs
|
04
|
oe
Fig. 5 APC, HI/LOW switching circuit
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