Frequency Synthesizers; Regulators - Nokia 6233 Service Manual

RM-123; RM-145
System Module Nokia Customer Care
GSM power control
A closed control loop comprise an integrated power detector (in PA module) and an error amplifier. The error
amplifier resides in N7500, and it controls the transmitter power of GSM.
GSM PA module
A single GSM/EDGE PA module contains two separate amplifier chains, one for GSM900 and another for
GSM1800/1900. Both amplifiers have a battery supply connection and two bias current inputs.

Frequency synthesizers

RF has separate synthesizers for Rx and Tx. Both synthesizers consist of:
• PLL (Phase-Locked Loop)
• loop filter
• VCO (Voltage Controlled Oscillator)
• balun
The VCO frequencies are locked by PLLs into a reference oscillator, VCTCXO (Voltage Controlled Temperature
Compensated Crystal Oscillator).
The PLLs are located in RF ASICs and controlled via RFBus.
Reference oscillators
A 38.4MHz VCTCXO is used as a reference oscillator for the frequency synthesizers.

Regulators

RF ASIC contain integrated regulators to supply regulated voltages for their internal circuitry and other RF
parts. Rx VCO supply is got via a switch from an RF ASIC VR1 regulator. VCO can be switched on and off by
controlling the switch via RFBus.
Supply voltage for the VCTCXO is provided by a BB mixed mode ASIC. The same supply is used for reference
clock input buffers, output buffers and for the digital control blocks of both RF ASICs.
Other supplies, like 4.7 V supply for PLL charge pumps and bias reference (VREFRF01) are also provided by
the BB mixed mode ASIC.
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