Nokia 2650 Manual Do Serviço

 RH-53/54

Nokia Customer Care

8-System Module

38

COMPANY CONFIDENTIAL

ISSUE 1 09/2004

Copyright © 2004 Nokia. All Rights Reserved.

The AGC keeps the BB level form the receiver within a certain range in order to stay within the 
dynamic range for the BB, even during fading.

■ 

The transmitter chain consists of two direct frequency I/Q-modulators, one for the GSM850/E-
GSM900 and one for GSM1800/1900, and a dual-band power amplifier.

The I/Q-signals, generated in BB, are fed to the individual I/Q-modulators in the RF-ASIC. The 
frequency and phasing parameters for the individual modulators/bands is generated by the LO 
dividers, division is by 2 in GSM1800/1900 and by four in GSM900/E-GSM900. Each modulator 
has a separate output.

In GSM850/E-GSM900 the modulator is terminated in a balanced input SAW filter.  

The GSM1800/1900 modulator is using a balun instead of a SAW filter.

The dual-band FEM contains two separate gain chains, with separate inputs and outputs, 
where the GSM850/E-GSM900 part is able to produce over 33 dBm and the GSM1800/
PCS1900 part over 30 dBm, both in 50 

Ω. The two gain chains shares a common control line 

to set the gain of amplifiers.

The output from the individual gain chains is feed to the internal RX/TX switch in the FEM.

The detected voltage is compared in the error-amplifier in Mjoelner to TXC- voltage, which is 
generated by a DA-converter in BB. 

High band

input

Low band

input

R620

12K

C642

100pF

Ffbl

Cfbl

Rfb

R655
330R

C644

100pF

Lowband

Highband

R623

6K8

Vpc

Detect