User Guide

The antenna switch module is followed by integrated LNAs residing in N7501.

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

After the down conversion mixer, the Rx chain is similar to WCDMA Rx. Channel select filter is set to 115 kHz in

the GSM mode.

In the GSM mode, the DC compensation is carried out before the reception slot.

During an operation called DCN1 a sample of the DC level of the signal is stored in sufficiently large off chip

capacitors. During reception, information is in turn used for subtracting the DC information from the input signal

of the AGC amplifier.

DCN0 operation is carried out to discharge any charge from the capacitors before DCN1. This guarantees that

the starting point for the DC compensation is always the same.

See Also

• WCDMA receiver (Page 9–40)

Introduction to transmitter functionality

Transmitter functions are implemented in the RF ASIC N7501. It contains a BB frequency low pass filter, which

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

In addition, N7501 contains three separate RF paths (GSM900, GSM1800/1900 and WCDMA) comprising a final

frequency IQ modulator and VGA amplifiers.

In order to eliminate the effect of process variations on the low pass filter characteristics, a tuning procedure

is carried out in production. The same tunings must be performed if the RF ASIC N7501 is changed.

WCDMA transmitter

In the transmitter side, an analogue I/Q modulated signal is received from the digital baseband into N7501 and

fed through the low pass filter.

The corner frequency of the filter is set to approximately 3 MHz.

After the filter the signal is fed to the IQ modulator, which converts the signal to final Tx frequency. There are

two separate I/Q modulators. One for WCDMA and another for EGSM900 and GSM1800/1900 signals.

The modulator is followed by two VGA stages giving 85 dB of gain control range. The signal then exits N7501

via a balanced line. In order to attenuate the out of band noise of the transmitter the signal is band pass filtered

by a SAW filter before it is fed to the WCDMA PA module.

After the PA the transmitted WCDMA signal is fed through an isolator and a duplex filter to the antenna.

RM-1

System Module Nokia Customer Care

Issue 1 Company Confidential Page 9–41