User Guide

Figure 85 GSM transmitter

GSM power control

A closed control loop comprise an integrated power detector (in PA module) and an error amplifier. The error

amplifier resides in N7501, and it controls the transmitter power of GSM.

GSM PA module

A single GSM/EDGE PA module contains two separate amplifier chains, one for EGSM900 (and GSM850) 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.

The VCOs operate at the channel frequency multiplied by two in the upper bands and by four in EGSM900

(and GSM850, if applicable). The required frequency dividers required for modulators and demodulators are

integrated into RF ASICs. The dividers are controlled via RFBus.

Reference oscillators

A 38.4MHz VCTCXO is used as a reference oscillator for the frequency synthesizers.

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