User Guide

CCS Technical Documentation System Module
RH-10
Issue 1 09/2002 Nokia Corporation Confidential Page 29
Transmitter
Figure 2: TX block diagram
The transmit chain up to the RF driver stage is integrated into one transmit-integrated
circuit called Robin, with external power amplifiers (PA). The channel bandwidth is
50 kHz.
All data transmitted on the channel is convolutionally encoded and block-interleaved.
Modulation is 64-ary orthogonal (RC1 and RC2) and direct sequence spread by a quadra-
ture pair of PN sequences at a fixed chip rate. The data is filtered, O-QPSK modulated
and up-converted to the appropriate transmission frequency. RC3 and RC4 use HPSK
modulation at data rates up to 153.6 kBPS (RC3) and 115.2 kBPS (RC4).
The baseband I/Q signals are converted to IF frequency in the I/Q modulator by Quadra-
ture mixing. The modulated IF signals go through a variable gain amplifier (IF AGC). The
IF signal is converted up to RF with a differential output upconverter and then fed to the
RF amplifier. The RF amplifier has variable gain capability (RF AGC) with up to 25 dB of
dynamic gain control.
The outputs of the RF amplifiers are differential. The differential outputs from Robin are
combined into single-ended output by an external balun and fed into an external driver
amplifier module (Tomcat). There are two outputs from this module that feed a split-
band filter. The split-band filter output is connected to a SPDT RF switch that results in a
single output.
The output of the SPDT RF switch then is connected to the PA (Snapper). Out of the PA is
an isolator, then antenna.
The PA modules contain all the necessary matching networks and reference current cir-
cuitry for variable gain control and biasing ON/OFF. A variable reference current is used