Receiver; Receiver: Egsm900/Gsm1800/Gsm1900 -Filter To Demodulator - Siemens S55 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
Z880 Bright
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. The symmetrical filter output is matched
via LC-Combinations to the LNA input of the BRIGHT (D800)
LNA: The 2 LNA´s (EGSM900/GSM1800/GSM1900) are located inside the BRIGHT
and are able to perform an amplification of ~ 20dB. The LNA can be switched in HIGH
(On) and LOW (Off) mode and is controlled by the Bright depending on EGOLD+
information.
Demodulator: The Bright IC performs a direct demodulation of the received GSM
signals. To do so the LO1 is required. The channel depending LO1 frequencies for
1800MHz/1900MHz bands are divided by 2 and by 4 for 900MHz band, Bright
internally.
PGC: After demodulation the "I" and "Q" signals are amplified by the PGC-Amplifier
the "I" and the "Q" path are amplified independently from each other. The performance
of this PGC is 80dB (-26 up to 54dB), switchable in steps of 2dB. The control is
realised through the EGOLD+ signals (RFDATA; RFCLK; RFSTR.
). After passing a Bright internal switch (necessary because of the double using of
J17
RX and TX lines), the signals are ready for further processing through the EGAIM
(part of the EGOLD+) The post-switched logic measures the level of the demodulated
baseband signal an regulates the level to a defined value by varying the PGA-
Amplification and switching the appropriate LNA gains
The required voltage
V1.00
S55/S57
De-
modulator
Bright
VCC_SYN is provided by the ASIC
Page 17 of 49
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PGC
Bright
(RF Control J15, J16,
D361
ICM MP CCQ GRM
12/02