Receiver; Receiver: Egsm900/Gsm1800/Gsm1900 -Filter To Demodulator - Siemens SL55 Repair Documentation

4.4 Receiver

4.4.1 Receiver: EGSM900/GSM1800/GSM1900 –Filter to Demodulator
From the antenna switch, up to the demodulator the received signal passes the following
blocks to get the demodulated baseband signals for the EGOLD+:
Filter LNA
Inside Z650 Smarti
Filter: The EGSM900, GSM1800 and GSM 1900 filters are located inside the frontend
module. The Filter are centred to a frequency of 942,5MHz for EGSM900, 1847,5MHz for
GSM1800 and 1960MHZ for GSM1900.
LNA: The LNA´s (EGSM900/GSM1800/GSM1900) are located inside the Smarti. The
LNA can be switched in HIGH (On) and LOW (Off) mode and is controlled by the Smarti
depending on EGOLD+ information.
Demodulator: The Smarti DC consists of a direct conversion receiver for GSM
900/1800/1900. The amplified RF signal is converted by a quadrature demodulator to the
final outputsignals at baseband frequency. The LO signals are generated by a divider by 4
for the GSM900 band and by a divider by 2 for GSM1800 and GSM1900 band.
The resulting in-phase and quadratursignals are fed into two baseband low pass filters
and the PGC amplifier chain. The baseband filter provide a suppression of inband-
blocking and adjacent channel interferers.
PGC: After baseband filtering the signal is fed into a PGC amplifier chain. The baseband
amplifier offers 78 dB programmable gain with 2 dB steps. Due to the high baseband gain
(58 dB), DC offsets can corrupt the signal at the baseband outputs. Differential offset
voltages are reduced by an internal offset compensation circuit. The control is realised
through the EGOLD+ signals (RFDATA; RFCLK; RFSTR.
The required voltages
V 1.0
SL55
Demodulator
Smarti
VREGRF1 and VREGRF2
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D650
Top View
(RF Control J15, J16, J17
are provided by the ASIC
PGC
Smarti
).
D361
ICM MP CCQ GRM
06/03