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Transmitter; Transmitter: Modulator And Limited Amplifier - Siemens A55 Repair Documentation

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4.7 Transmitter

4.7.1 Transmitter: Modulator and Limited Amplifier

The GMSK modulated signal is generated in the direct modulator. That means, that the
modulators are working directly on the final output frequency. The LO frequency is divided
by 2 or 4, depending on the GSM band. There are two modulators, one for the two higher
bands and the other for the two lower bands..
The required voltages
from EGOLD+
The actual signal is fed into a limiting amplifier which also provides a signal path for the
high band and one for the low band
Mode Selection
EGSM900 limiter enable
GSM1800 limiter enable
Top View
The next stage in the low band line-up is a TX saw filter.
In the high band no SAW filter is required.
V 1.10
A52/A55/C55 IFX
VCC_SYN
and
VCC2_8
Pin9 / EN (TXON1/D171_J14))
HIGH
HIGH
Page 15of 45
Company Confidential © Copyright Siemens AG
are provided by the ASIC
Pin10 / BS (OSW1/D720_25)
IC Overview
D361
to PA
LOW
HIGH
ICM MP CCQ GRM
08/03

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