User Guide

CCS Technical Documentation 7 - System Module & UI
Company Confidential NMM-3
Issue 1 (11/2003) Copyright  2003 Nokia Corporation Page 7-45
Company Confidential
After the SAW filter the signal is fed back to REX to the demodulator. After the preampli-
fier stage there are demodulator mixers which convert the RF signal to analog baseband
I- and Q-signals. The LO signal for the mixers is generated by the external RX VCO at
twice the RF frequency. The frequency division and 90 deg phase shift is made in REX.
I- and Q-signals are then amplified and filtered by the BB stage. The 3dB bandwidth of
the BB stage is from 10kHz…2MHz. The low pass 2MHz cut off frequency is tuned on the
production line. The tunable channel filter is an active 4
th
order RC filter. The large
ceramic capacitors (33nF) of the filter are external to REX. The high pass pole at 10kHz
can be controlled by the value of capacitor used. The BB AGC is a bipolar AGC with max-
imum gain of 54 dB with a step size of 3 dB. The AGC is made up of three 18dB gain
stages cascaded in series. The gain is controlled by RFBus.
The differential analog I-/Q-signals are then fed to the AD converters in TIKU.
AGC strategy
The AGC-amplifier is used to maintain the voltage swing at the RF-BB interface at the
wanted level. The nominal differential signal level is 400 mV
pprms
. The total gain of REX
is 100 dB (min) with a typical dynamic range of 80 dB. The BB gain is divided into steps
of 3 dBs with the LNA having 3 gain steps. The RX AGC is controlled via RFBus.
The Rx AGC system has to be aligned from -99dBm to -25dBm (74dB).
The production calibration is done with one RF-level. The calibrated parameters are
receiver gain offset, LNA gain steps, LNA gain with 2
nd
bias current value and BB AGC-
stage slope error.
Figure 9: Rx Gain control in WCDMA