Transmitter Part - LG G1500 Manual

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.
GSMSEL
ANT
DCSSEL
S/W
LMSP54AA-097
GSM : 880 ~ 925MHz
DCS : 1710 ~ 1785MHz
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.
f
vco
/3
DCS
GSM
f
TX
PAM(RF3110B)
TXVCO
TXRAMP
TXPA
BANDSEL1
Fig.3-2 Transmitter Block diagram
- 19 -
CX74017
X2
f
LO
X2
f
IF
/D1
PFD
LF
/D2
3. TECHNICAL BRIEF
Block
TXIP
TXIN
0
90
TXQP
TXQN
Base
Band