Gsm Receiver; Transmitter; Introduction To Transmitter Functionality - Nokia n80 User Manual

RM-91; RM-92
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The filter is followed by an AGC amplifier with adjustable gain. The signal is further amplified before it is fed
to balanced analog IQ output pins. Analog output pins are accompanied by reference voltage output, which
sets the DC level for the AD converter in BB ASIC.
Figure 114 WCDMA receiver after duplexer, LNA and SAW filter

GSM receiver

As GSM850, GSM900, GSM1800 and GSM1900 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 switch module contains
PIN diode switches for band and RX/TX. The antenna switch module is followed by integrated LNA stages in
the RF ASIC. The LNAs are followed by demodulators which downconvert the signal to baseband I and Q
signals.
In the BB-chain there are two adjustable gain stages and one mode specific gain. The first one called BB-gain
is just after the demodulator. It has a 12 dB gain range with 6dB steps. After the BB-gain there is the channel
select filter.
Main AGC amplifier proceeds the channel selection filter. It has 30 dB of gain control range with 3 dB steps.
Final amplifier stage is used as an output buffer for IQ signals. This stage is set to 0 dB gain in GSM mode.
Figure 115 GSM receiver after the antenna switch

Transmitter

Introduction to transmitter functionality

In RM-92, transmitter functions are implemented in the RF ASIC N7500, in RM-91, in RF ASIC N7505.
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