Synthesizer: Lo2 - Siemens C45 Repair Documentation

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
nd
2 LO freq. = 360...368 MHz
The LO2 PLL and power-up of the VCO is controlled via the tree-wire-bus of
Bright IV+.(EGOLD+ signals
The required voltage VCC_SYN
Circuit diagram
V1.0
C45, M50 AND MT50
divided by 8 = 45...46 MHz,
divided by 4 = 90...92 MHz
SYGCCL, SYGCDT, SYNSTR
is provided by the
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(RF Control K14, K15, M15)
N840
)
Loop-filter LO2
ICM MP CCQ ST
05/02