Front End - Nokia NPM-6 Series Manual

CCS Technical Documentation
by four in EGSM900. Those frequency dividers are integrated in the Helga and in addition
to the division they also provide accurate phase shifting by 90 degrees which is needed
for the modulator mixers.
At the upper band there is a dual mode buffer amplifier at the output of the IQ-modula-
tor.
The final amplification
There are two different amplifier chains in a single amplifier module, one for EGSM900
and one for GSM1800/GSM1900. The lower band power amplifier is able to deliver over
2 W of RF power, while the capability of the upper band amplifier is over 1 W.
In the GMSK mode the gain control is implemented by adjusting the bias voltages of the
first two transistor stages thereby reaching the dynamic range of over 70 dB.
After the power amplifier the signal goes through a low pass filter and a pin-diode
switch which is used to select between the reception and transmission. Finally, the two
signal paths, lower and upper band, are combined in a diplexer after which the signal is
routed through the antenna.
Power control circuitry consists of a power amplifier and an error amplifier. The power
amplifier produces a voltage level related to the value of the RF voltage. It is fed to the
negative input of the error amplifier where it is compared to the level of the reference
signal, TXC, obtained from UEM. Depending on the difference between the two signals
the biases of the power amplifier stages are either increased or decreased to get the cor-
rect power level out of the power amplifier.

Front End

The front end module includes:
- Antenna 50 ohm input
- RX GSM1900 single output, RX EGSM900 and GSM1800 balanced output
- TXs EGSM900 and GSM1800/GSM1900 single 50 ohm input
-3 control lines from the Helga
Issue 1 01/03
System Module and User Interface
is realized by a three stage power amplifier.
ãNokia Corporation.
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