Rf Description; Introduction To Receiver Functionality; Wcdma Receiver Functionality; Gsm Receiver Functionality - Nokia 6233 Service Manual

RM-123; RM-145
System Module Nokia Customer Care
The radio has an automatic band search function, which can search for a strong write/read signal from a
certain frequency. When this is found, data is transmitted to the radio. When the signal strength is low, the
RETU can read data, which is available until the signal is strong again.

RF description

Introduction to receiver functionality

Receiver functions are implemented in an RF ASIC.
The receiver is a linear direct conversion receiver consisting of separate front ends (LNA (Low Noise Amplifier)
and demodulator) for each supported system. After the demodulators, the signal paths are combined to one
common BB path.

WCDMA receiver functionality

In the WCDMA mode, the received signal is fed from the antenna to a duplex filter. After the duplex filter the
signal goes via a balun to an LNA (Low Noise Amplifier) residing in N7500. From the LNA, the signal goes
trough a band pass filter.
After filtering, the signal goes to the down conversion mixer, which converts the signal to baseband I and Q
signals. At the BB frequency the signal is amplified, and fed to a low pass filter. The Rx channel filter must be
calibrated with an automatic routine whenever the Rx ASIC IC is changed to a phone.
In the WCDMA mode, the corner frequency of the filter is set to approximately 2.1 MHz. The filter is followed
by an AGC (Automatic Gain Control) amplifier with an adjustable gain. The signal is further amplified before
it is fed to balanced analogue IQ output pins. The analogue output pins are accompanied by reference voltage
output, which sets the DC level for the AD converter in the BB ASIC RAP.
The last stage of the RF Rx chain is an output buffer which feeds the signal and a reference voltage (VREFCM)
to the BB ASIC.

GSM receiver functionality

As GSM Rx branches are functionally identical, the following description is applicable to all of them.
The received signal goes from the GSM antenna to the antenna switch module.
The antenna switch module is followed by integrated LNAs residing in the Rx ASIC.
The LNAs are followed by demodulators which downconvert the signal to baseband I and Q signals.
After the down conversion mixer, the Rx chain is similar to the WCDMA Rx. The channel select filter is set to
115 kHz in the GSM mode.

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.
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