Radio Part Description; Introduction - Siemens A55 Repair Documentation

4 Radio Part Description

4.1 Introduction

The radio part is necessary to convert the GMSK-RF-signals from the antenna to the
baseband and vice versa.
In the receiving direction, the signals are split in the I- and Q-component and fed to the
A/D-converter of the logic part. In the transmission direction, the GMSK-signal is
generated with the Direct Modulator by modulation of the I- and Q-signals, which are
generated in the baseband section. After the modulation the RF-signals are amplified by
a buffer-limiter and, for the GSM900 path, filtered with a SAW-Filter. Finally, the power
amplifier (PA) is attached to reach the output power.
Transmitter and Receiver are never active at the same time. Simultaneous
reception in the EGSM 900 and GSM 1800 band is impossible as well as
simultaneous transmission in both bands. However the monitoring band
(monitoring timeslot) in the TDMA-frame can be chosen independently of the
receiving or transmitting band (RX- and TX timeslot of the band).
The RF-part is designed for dualband operation (EGSM 900, GSM 1800) and consists of
the following main components:
1. 26MHz reference crystal Z1500
2. TX-Filter in GSM section Z1600
3. Transmitter power amplifier RF9340 with integrated regulator Z1700
4. Front-End-Module including RX-/TX-switch and EGSM 900/GSM1800 receiver SAW-
filters D1740
5. Infineon Limiter/Buffer PMB2256 to amplify the RF signals from the modulator to
drive the PA D1600
6. Infineon Smarti DC2 PMB6256 with the following functionality D1785:
•
Integrated active part of the 26MHz crystal oscillator
•
PLL for local oscillator LO1
•
LO1-VCO
•
Direct conversion receiver with channel filtering
•
Direct Modulator
•
Active part of the reference oscillator including buffer
•
Control circuit for band switch
V 1.10
A52/A55/C55 IFX
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