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Transmitter: Power Amplifier - Siemens C75 Service Repair Documentation

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4.8 Transmitter: Power Amplifier

The output signals
amplifier. The power amplifier is a PA-module
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
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
The
N901
is activated through the signal
The required voltage
Service Repair Documentation
Level 2.5e – C75
(PCN_PA_IN ,
and GSM_PA_IN) from the TxVCO are led to the power
RF_BAND_SW
BATT+
is provided by the battery.
N901
from Hitachi. It contains two separate 3-
which is provided by the SGOLDlite.
(TDMA Timer A10)
RF_RAMP1
RF_TXONPA
(TDMA Timer A17)
Page
of
17
37
s Com
(Analoq Interface L24)
.
Release 1.0
signal.

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