Power Supply Rf-Part; Frequency Generation; Synthesizer: The Discrete Vcxo (26Mhz) - Siemens A55 Repair Documentation

4.2 Power Supply RF-Part

The voltage regulator for the RF-part is located inside the
generates the required 2,85V "RF-Voltages" named
is also named VCC2 and behind
The following components are supplied by:
VCC2_8
• Limiter amplifier
The voltage regulator RFREG 1 is controlled by the signal
RFREG2 is controlled by he signal
. Both signals are provided by the
H1)
VCXOEN_UC
(Miscellaneous R6)
Circuit diagram

4.3 Frequency generation

4.3.1 Synthesizer: The discrete VCXO (26MHz)

The reference oscillator is a 26 MHz voltage controlled crystal oscillator. It has two main
tasks:
•
It is used as reference for the synthesizer phase/frequency detector (Smarti
internal circuit)
•
It gives the clock for the processor (E-Gold)
The main block is realized as an internal transistor cell with a Colpitts structure. The 26
MHz quartz crystal is connected to a tuning circuit that allows a fine-tuning of the
frequency. A current mirror, acting as buffer and amplifier followed by a LC resonant
circuit makes the signal to fit the E-Gold clock signal requirements. ON/OFF signal
(VCC_OSC) comes from the
measurements of the VCXO a temperature resistance (R700) is used. The resistor is
placed near the VCXO. The measurement result
via R138 as the signal TENV. The frequency of the reference oscillator
(Analog Interface P3)
can be adjusted by the
The signal leaves the
EGOLD+ (D171
(functional T3))
The required voltage VCC_SYN
V 1.10
A52/A55/C55 IFX
R1451 VCC_OSC)
VCXOEN_UC
EGOLD+
).
ASIC via the resistor R1451. For temperature
EGOLD+ via a PNM- modulated AFC-signal.
SMARTI as BB_SIN26M
.
is provided by the ASCI
Page 7of 45
Company Confidential © Copyright Siemens AG
ASIC D361.(see chapter 5.2).It
VCC2_8 and VCC_SYN. (VCC_SYN
VCC_SYN
• Modulators
• RX mixers
• VCO
• PLL
• 26 MHz reference oscillator
SLEEPQ (RF_EN
connected to SLEEP1_N
(SLEEPQ
(GSM TDMA-Timer H16)
VCC2_8
VCC_SYN
TVCXO is reported to the
at pin 4 to be further used from the
D361
)
(RF REG G2) ,
(on/off Control
/
EGOLD+
ICM MP CCQ GRM
08/03