If Modulator; Opll - LG T5100 Service Manual

2. TECHNICAL BRIEF

2.4.1 IF Modulator

The Baseband Converter (BBC) within the Analog Baseband Chipset [TWL3014, U101] generates I/Q
baseband signals for the transmit vector modulator. The Tx-modulator implements a quadrature
modulator. A quadrature mixer up-converts the differential baseband I/Q signals with the IFLO to
generate a IF signal, which signal is filtered and used as the reference input to the OPLL. The IFLO is
divided by two to generate the quadrature LO signals for the quadrature modulator.
Figure 4. Block Diagram of IF Modultaor

2.4.2 OPLL

The OPLL consists of a feedback mixer, a phase detector, a loop filter, and two fully integrated Tx-
VCOs, one is a low band VCO for GSM band and another is a high band VCO for DCS band. The RF
Main Chipset generates the RFLO signal with Main VCOs. The MAINVCO1 is used for GSM900,
DCS1800900.
Low-pass filters before the OPLL phase detect or reduce the harmonic content of the quadrature
modulator and feedback mixer outputs. The cutoff frequency of the filters is programmable with
register setting, which register is contained in the RF main chipset and set with a serial communication
port of the RF main chipset.
The OPLL requires no external duplexer to attenuate transmitter noise and spurious signals in the
receive band.
Additionally, the output of the transmit VCO (TXVCO) is a constant-envelope signal which reduces the
problem of spectral spreading caused by non-linearity in the PA.
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