Frequency Generation; Synthesizer: The Discrete Vcxo (26Mhz) - Siemens S55 Repair Documentation

4.2 Frequency generation

4.2.1 Synthesizer: The discrete VCXO (26MHz)

The S55/S57 mobile is using a reference frequency of 26MHz for the Hitachi chip set.
The generation of the 26MHz signal is done via a discrete "Colpitts" VCXO. This
oscillator consists mainly of:
A 26MHz crystal
An oscillator switch
A capacity diode
TP (test point) of the 26MHz signal is the TP 1501
The oscillator output signal 26MHz_RF is directly connected to the BRIGHT IC
38) to be used as reference frequency inside the Bright (PLL). The signal leaves the
Bright IC as BB_SIN26M at
the EGOLD+ (D100
(functional T3))
Bright 4
To compensate frequency drifts (e.g. caused by temperature) the oscillator frequency
is controlled by the (AFC) signal, generated through the internal EGOLD+
) PLL via the capacity diode V951. Reference for the "EGOLD-PLL" is the
(functional U5)
base station frequency. To compensate a temperature caused frequency drift, the
temperature-depending resistor
temperature. The measurement result
via R138 as the signal TENV.
Interface P3)
The required voltage VCC_SYN
V1.00
S55/S57
Z950
V950
V951
(pin 36) to be further used from
.
R959 is placed near the VCXO to measure the
TVCXO
is provided by the ASCI
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is reported to the EGOLD+
D361
(pin
(D100
(Analog
ICM MP CCQ GRM
12/02