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3. TECHNICAL BRIEF
3.3 Transmitter Part
The Transmitter part contains CX74017 active parts and PAM, APC IC, coupler and Antenna
Switch. The CX74017 active part consists of a vector modulator and offset phase-locked loop
block(OPLL) including down-converter, phase detector, loop filter and dual band transmit VCO
which can operate at either final RF output frequency. The RF GMSK outputs from the transmit
VCO are fed directly to the RF power amplifiers.
TXIP
TXIN
Figure 3-2. Transmitter Block diagram
The peak output power and the profile of the transmitted burst are controlled by means of a closed
feedback loop. A dual band directional coupler is used to sample the RF output from either PA.
The PA outputs from the directional coupler pass to the antenna connector via Antenna Switch.
A. IF Modulator
The baseband converter(BBC) within the GSM chipset generates I and Q baseband signals for the
transmit vector modulator. The modulator provides more than 40dBc of carrier and unwanted side-
band rejection and produces a GMSK modulated signal. The baseband software is able to cancel
out differential DC offsets in the I/Q baseband signals caused by imperfections in the D/A
converters.
The TX-Modulator implements a quadrature modulator. The IF-frequency input signal is split into
two precise orthogonal carriers, which are multiplied by the baseband modulation signal IT/ITX and
QT/QTX. It is used as reference signal for the OPLL.
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