User Guide

The received signal goes from the GSM antenna to the front end module (FEM) which includes switches from

band selection. FEM is followed by dedicated SAW filters which are dual packaged so that one holds SAWs for

850 and 900 and the other for 1800 and 1900 bands. The SAW filters are followed by integrated LNAs residing

in N7505.

The LNAs are followed by demodulators which downconvert the signal to baseband I and Q signals.

The channel select filter is set to 115 kHz in the GSM mode.

During a DC1 operation, a sample of the DC level of the signal is stored in off chip capacitors. During reception,

information is in turn used for subtracting the DC information from the input signal of the AGC (Automatic

Gain Control) amplifier.

A DCN0 operation is carried out to discharge any charge from the capacitors before DCN1.

Introduction to transmitter functionality

Transmitter functions are implemented in the RF ASIC N7505. The ASIC contains a BB frequency low pass filter,

which is tunable according to the signal bandwidth of the system in use.

In addition, the N7505 contains separate RF paths comprising a final frequency IQ modulator and VGA

amplifiers.

GSM transmitter

N7505 receives an analogue IQ modulated signal from digital BB, which is first low pass filtered with filter

corner frequency set to approximately 200 kHz. After the filter, the signal is routed to the GSM modulator.

The amplifier gives 40 dB of power control dynamic range.

The appropriate routing after the modulator is selected by biasing either EGSM900 (/GSM850) or

GSM1800/1900 variable gain amplifier. The amplifier gives 40 dB of power control dynamic range.

After the VGA stage the signal exits N7505. In case of GSM1800/1900 the signal goes directly to the FEM thru

a balun, which converts single ended signal into balanced signal needed to feed the FEM. In case of GSM850

and EGSM900 the PA module is preceded by a SAW filter.

TX SAW Z7503 is also dual packaged so that the correct band is selected with control voltage coming from

N7505. SAW also performs the unbalanced to balanced signal transformation. After the filter, the signal is

fed to FEM. Finally the signal is routed to the antenna.

RM-170; RM-171

System Module Nokia Customer Care

Issue 1 COMPANY CONFIDENTIAL Page 9 –35