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Page
21
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53
TD_Repair_L2.5_A70_A75_R1.0.pdf Release
1.0
Transmitter: Power Amplifier
The output signals (
PCN_PA_IN ,
and
GSM_PA_IN
) from the TxVCO are led to the power
amplifier. The power amplifier is a PA-module
N901
from Hitachi. It contains two separate 3-
stage amplifier chains GSM850/EGSM900 and GSM1800 / GSM1900 operation. It is
possible to control the output-power of both bands via one VAPC-port. The appropriate
amplifier chain is activated by a logic signal
RF_BAND_SW
(TDMA Timer P10)
which is provided by
the
EGOLDLite
.
To ensure that the output power and burst-timing fulfills the GSM-specification, an internal
power control circuitry is use. The power detect circuit consists of a sensing transistor which
operates at the same current as the third RF-transistor. The current is a measure of the
output power of the PA. This signal is square-root converted and converted into a voltage by
means of a simple resistor. It is then compared with the
RF_RAMP1
(F12)
signal.
The
N901
is activated through the signal
RF_TXONPA
(TDMA Timer P3)
.
The required voltage
BATT+
is provided by the battery.
Circuit diagram
from TxVCO
to antenna
connector
