User Guide

Figure 84 Block diagram of DCDC converter and WCDMA PA

GSM transmitter

An analog IQ modulated signal is fed to N7500 from Digital BB in current form. It is first low pass filtered with

filter corner frequency set to ca. 200 kHz. After the filter the signal is routed to the GSM modulator. The

appropriate routing after the modulator is selected by biasing either GSM850/EGSM900 or DCS1800/PCS1900

variable gain amplifier. The amplifier gives 55 dB of power control dynamic range.

After the VGA stage the signal exits N7500. In case of DCS1800/PCS1900 the signal goes directly to the GSM

PA module. In case of GSM850/EGSM900 the PA module is preceded by a switch able SAW filter. After the filter,

the signal is fed to GSM TX front-end module (TXFEM), which also contains antenna switch.

GSM power control

A closed control loop comprising of an integrated power detector (in PA module) and an error amplifier,

which is integrated in N7500, controls GSM transmitter power. Detector output from the PA gives a DC level

proportional to the output power.

Note: Timings are not shown accurately in the previous figure.

GSM PA module

TXFEM module contains two separate amplifier chains, one for GSM850/EGSM900 and another for DCS1800/

PCS1900. Both amplifiers have a battery supply connection and two bias current inputs.

Frequency synthesizers

RF have separate synthesizers for WCDMA RX and WCDMA TX / one for GSM TX / RX.

RM-208

System Module Nokia Customer Care

Issue 1 COMPANY CONFIDENTIAL Page 9 –31