Issue 2 06/2005 COMPANY CONFIDENTIAL 37
Copyright © 2005 Nokia. All Rights Reserved.
RH-53/54
8-System Module Nokia Customer Care
■ Transmitter
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.
Dual band FEM
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.
Power control scheme
The detected voltage is compared in the error-amplifier in Mjoelner to TXC- voltage, which is
generated by a DA-converter in BB.
Figure 15:Power loop
TXC
High band
input
Low band
input
R620
12K
C642
100pF
Ffbl
Cfbl
Rfb
R655
330R
C644
100pF
Front End Module
Lowband
Highband
R623
6K8
Vpc
Detect
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