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Synthesizer: Lo1 - Siemens A55 Repair Documentation

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Circuit diagram
to EGOLD+
from EGOLD
4.3.2

Synthesizer: LO1

The local oscillator (LO1) consists of a PLL inside the Smarti DC (D720), an external loop
filter. The VCO is build in.
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. The
LO1/PLL part is switched on with
PLLON
(
) from the
EGOLD+ (D171
pin 5
(GSM TDMA Timer
). The PLL settings are programmed by the 3 wire bus
RFCLK
(
),
RFDATA
(
)
F16)
pin 1
pin2
and
RFSTR
(
). The LO frequency is 4 times the RX/TX frequency for EGSM 900 and 2
pin3
times for GSM1800.
This LO1 frequency range
The required voltage
VCC_SYN
is provided by the
ASIC D361
V 1.10
Page 8of 45
ICM MP CCQ GRM
A52/A55/C55 IFX
Company Confidential © Copyright Siemens AG
08/03

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A52C55 ifx

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