LG MG810c, Руководство по обслуживанию

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3. H/W Circuit Description
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3.4.1. 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
sideband. 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. A quadrature mixer upconverts the
differential I/Q signals with the IFLO to generate a SSB IF signal, which is filtered and used as the
reference input to the OPLL. The SI4210[U401] generates the IFLO frequency. The IFLO is divided by
two to generate the quadrature LO signals for the quadrature modulator.
3.4.2. OPLL
The OPLL consists of a feedback mixer, a phase detector, a loop filter, and a fully integrated
TXVCO.The TXVCO is centered between the DCS 1800 and PCS 1900 bands, and its output is
divided by 2 for the E-GSM 900 bands. The Si4206 generates the RFLO frequency between 1327 and
1402 MHz. To allow a single VCO to be used for the RFLO, high-side injection is used for the E-GSM
900 bands, and low-side injection is used for the DCS 1800 and PCS 1900 bands. Low-pass filters
before the OPLL phase detector reduce the harmonic content of the quadrature modulator and
feedback mixer outputs. The cutoff frequency of the filters is programmable with the FIF[3:0] bits in
register 04h. 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
3.4.3. Power Ampifier Module
The RF3166[U400] is a triple-band GSM/DCS/PCS power amplifier module that incorporates an
indirect closed loop method of power control. The indirect closed loop is fully self-contained and it does
not require loop optimization. It can be driven directly from the DAC output in the baseband circuit. On-
board power control provides typical 50 dB of control range with an analog voltage input (Vapc).
Efficiency is 53% at GSM, DCS and PCS.