Siemens S55 Repair Documentation page 11

The VCO (Z850) is switched on by the EGOLD+ signal
V850 and therefore supplied with VCC2_8. The VCO guarantees by using the control
voltage at pin5 a coverage of the EGSM900, GSM1800 and GSM1900 frequency
band and frequency stability. The Bright gained control voltage passes on the way to
the VCO a discreet loop filter (typical value from 0,5 – 2,1V).
The channel programming of the PLL happens via the EGOLD+ signals RFDATA;
RFCLK; RFSTR.
(RF Control J15, J16, J17)
GSM1800 channel information, the VCO is switched to this frequency by
(Pin 3 VCO).
For GSM900 - RX= "low signal" for Channel 975-49 "high signal" for channel 50-
124
- TX= "high signal" for all channels
For GSM1800 - RX= "low signal" for all channels
- TX= "low signal" for all channels
For GSM1900 - RX= "low signal" for all channels
- TX= "low signal" for all channels
The VCO output signal passes the "Balun" transformer (Z851) with insertion losses of
~ 2dB to arrive at the Bright IC.
The required voltage VCC8_8
Circuit diagram
from EGOLD+
Balun transformer
V1.00
S55/S57
. If the Bright IC gets via the same signals a
is provided by the
Bright 4
Page 11 of 49
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PLLON
(TDMA-Timer F16)
ASIC D361
26MHz
via
Pin 42 Bright
ICM MP CCQ GRM
12/02