User Guide

Introduction to transmitter functionality

Transmitter functions are implemented in an RF ASIC. The ASIC contains a BB frequency low pass filter, which

is tunable according to the signal bandwidth of the system in use.

In addition, the ASIC contains separate RF paths comprising a final frequency IQ modulator and VGA amplifiers.

WCDMA transmitter functionality

In the transmitter side, an analogue I/Q modulated signal is received from digital baseband into an RF ASIC

and fed through a low pass filter. After the filter the signal is fed to the IQ modulator, which converts the

signal to final Tx frequency. There are two separate I/Q modulators: one for WCDMA and another for GSM

signals. The signal then exits the RF ASIC via a balanced line. Next, the signal is band pass filtered by a SAW

filter before it is fed to the WCDMA PA module. After the PA, the transmitted WCDMA signal is fed through an

isolator and a duplex filter to the antenna.

WCDMA power control

WCDMA Tx power control is accomplished by the two VGA amplifier stages in the Tx ASIC.

The VGAs have a common temperature compensation circuit and one voltage mode analogue input for gain

control (TXC).

Another function of the detector voltage is to steer the DC/DC converter, which is providing a variable supply

voltage for the WCDMA PA.

WCDMA PA module

The WCDMA PA is housed in a separate module having:

• a variable supply voltage input for the amplifier stages (Vcc11),

• a battery supply voltage for the bias circuits (Vcc12),

• and two bias current inputs.

Bias currents are generated by 5-bit DA converters in the RF ASIC.

If a different manufacturer's PA is changed to the phone, this setting must be set again.

PA DC/DC converter

The control of the DC/DC converter is fed back from the power detector circuit.

GSM transmitter functionality

An RF ASIC receives an analogue IQ modulated signal from digital BB, which is first low pass filtered with

filter corner frequency set to approximately 200 kHz. After the filter, the signal is routed to the GSM modulator.

After the VGA stage the signal exits the RF ASIC. In case of GSM1800/1900 the signal goes directly to the GSM

PA module. In case of EGSM900 (and GSM850), the PA module is preceded by a SAW filter. After the filter, the

signal is fed to the GSM PA module. Finally, the signal is routed via the antenna switch to the antenna.

RM-10;RM-24

Nokia Customer Care System Module

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