V1.00 Page 10 of 49 ICM MP CCQ GRM
S55/S57 Company Confidential © Copyright Siemens AG 12/02
4.2.2 Synthesizer: LO1
The first local oscillator is needed to generate frequencies which enables the
transceiver IC to demodulate the receiver signal and to perform the channel selection
in the TX part. To do so, a control voltage for the LO1 is used. Gained by a
comparator. (located inside the Transceiver (Bright -IC)). This control voltage is a
result of the comparison of the divided LO1 and the 26MHz reference Signal. The
division ratio of the dividers is programmed by the EGOLD+, according to the network
channel requirements.
The first local oscillator (LO1) consists of the PLL inside the Bright (D800), an
external loop filter and the VCO (Z850) module. This LO1 circuit generates
frequencies from
3700-3980 MHz for EGSM900
3580-3760 MHz for GSM1800
3860-3980 MHz for GSM1900
Formula to calculate the TX frequencies:
EGSM900
Channel: 975...1023/76...92 = (Channel freq. + 82MHz) * 4
Channel: 0…75/93…124 = (Channel freq. + 80MHz) * 4
GSM1800
Channel: 512...661 = (Channel freq. - 80MHz) * 2
Channel: 662…885 = (Channel freq. - 82MHz) * 2
GSM1900
Channel: 512...810 = (Channel freq. – 80MHz) * 2
Formula to calculate the RX frequencies:
EGSM900 = Channel freq. * 4
GSM1800 = Channel freq. * 2
GSM1900 = Channel freq. * 2
26MHz
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