V1.00 Page 8 of 49 ICM MP CCQ GRM
S55/S57 Company Confidential © Copyright Siemens AG 12/02
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 Z950
An oscillator switch V950
A capacity diode V951
TP (test point) of the 26MHz signal is the TP 1501
The oscillator output signal 26MHz_RF is directly connected to the BRIGHT IC (pin
38) to be used as reference frequency inside the Bright (PLL). The signal leaves the
Bright IC as BB_SIN26M at (pin 36) to be further used from
the EGOLD+ (D100
(functional T3)).
To compensate frequency drifts (e.g. caused by temperature) the oscillator frequency
is controlled by the (AFC) signal, generated through the internal EGOLD+ (D100
(functional U5)) PLL via the capacity diode V951. Reference for the “EGOLD-PLL” is the
base station frequency. To compensate a temperature caused frequency drift, the
temperature-depending resistor R959 is placed near the VCXO to measure the
temperature. The measurement result TVCXO is reported to the EGOLD+
(Analog
Interface P3)
via R138 as the signal TENV.
The required voltage VCC_SYN is provided by the ASCI D361
Bright 4
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