Transmitter Part; If Modulator - LG G5300 Service Manual

3. TECHNICAL BRIEF

3.3 Transmitter Part

The Transmitter part contains CX74017 active parts, PAM 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.
Fig. 3-2. Transmitter Block diagram.
The peak output power and the profile of the transmitted burst are controlled by means of power
control loop. The power control function is integrated, eliminating the need for directional couplers,
detector diodes, power control IC and other power control circuitry. This allows the module to be
driven directly from the DAC output. 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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