V1.0 Page 13 of 46 ICM MP CCQ ST
C45, M50 AND MT50 Company Confidential © Copyright Siemens AG 05/02
4.2.3 Synthesizer: LO2
The second local oscillator (LO2) consists of a PLL and a VCO which are
integrated in Bright IV and a second order loopfilter which is realized external.
Due to the direct conversion receiver architecture, the LO2 is only used for
transmit-operation. To avoid inband-spurious in the transmit-signal, the
LO2-frequency assignment is not fixed for the whole band.
Before the LO2-signal gets to the modulator it is divided by 8 for GSM900 and by 4
for GSM1800. So the resulting
TX-IF frequencies are 45…46 MHz. GSM900
TX-IF frequencies are 90…92 MHz. GSM1800
2
nd
LO freq. = 360…368 MHz divided by 8 = 45…46 MHz,
divided by 4 = 90…92 MHz
The LO2 PLL and power-up of the VCO is controlled via the tree-wire-bus of
Bright IV+.(EGOLD+ signals SYGCCL, SYGCDT, SYNSTR (RF Control K14, K15, M15))
The required voltage VCC_SYN is provided by the N840
Circuit diagram
Loop-filter LO2
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