Receiver; Receiver: Egsm900/Gsm1800 - Filter To Demodulator - Siemens A55 Repair Documentation

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4.6 Receiver

4.6.1 Receiver: EGSM900/GSM1800 – 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 filters are located inside the frontend module. The Filter
are centred to a frequency of 942,5MHz for EGSM900, 1847,5MHz for GSM1800.
LNA: The LNA´s (EGSM900/GSM1800) 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.
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 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.
V 1.10
A52/A55/C55 IFX
to Demodulator
Demodulator
Smarti
Page 11of 45
Company Confidential © Copyright Siemens AG
to Antenna
PGC
Smarti
(RF Control J15, J16, J17
).
ICM MP CCQ GRM
08/03