Siemens C75 - Receiver

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Copyright 2005© Siemens AG
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Service Repair Documentation
Level 2.5e – C75
Release 1.0
4.4 Receiver
Receiver: Filter to Demodulator
The band filters are located inside the frontend module (D902). The filters are centred to the
band frequencies. The symmetrical filter output is matched to the LNA input of the Bright .The
Bright 6E incorporates three RF LNAs for GSM850/EGSM900, GSM1800 and GSM1900
operation. The LNA/mixer can be switched in High- and Low-mode to perform an
amplification of ~ 20dB. For the “High Gain“ state the mixers are optimised to conversion gain
and noise figure, in the “Low Gain“ state the mixers are optimised to large-signal behavior for
operation at a high input level. The Bright performs a direct conversion mixers which are IQ-
demodulators. For the demodulation of the received GSM signals the LO1 is required. The
channel depending LO1 frequencies for 1800MHz/1900MHz bands are divided by 2 and by 4
for 850MHG/900MHz band. Furthermore the IC includes a programmable gain baseband
amplifier PGA (90 dB range, 2dB steps) with automatic DC-offset calibration. LNA and PGA
are controlled via SGOLDlite signals RF_DAT; RF_CLK; RF_STR
(RF CTRL B10, C8, B12). The
channel-filtering is realized inside the chip with a three stage baseband filter for both IQ
chains. Only two capacitors which are part of the first passive RC-filters are external. The
second and third filters are active filters and are fully integrated. The IQ receive signals are
fed into the A/D converters in the EGAIM part of SGOLDlite. The post-switched logic
measures the level of the demodulated baseband signal and regulates the level to a defined
value by varying the PGA amplification and switching the appropriate LNA gains.
From the antenna switch, up to the demodulator the received signal passes the following
blocks to get the demodulated baseband signals for the SGOLDlite:
Demodulator
PGC
LNA
Filter
D903 Bright(D903)
The required voltage VDD_BRIGHT is provided by the ASIC D1300