LG G5500 Manual page 16

FL501
Antenna Switch
D
D
I
I
PAM
P
U504
P
RF3133
DCS
EGSM
3.2.6. 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. 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 Si4133T[U706] generates the IFLO frequency. The IFLO is divided by two to
generate the quadrature LO signals for the quadrature modulator.
3.2.7. 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 GSM 850 and E-GSM 900 bands. The Si4133T 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
GSM 850 and 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.
Figure 3. RF Transmit Block
RF_Lo(Tx)
÷1
÷1
÷2
÷2
PA_BAND
GATE_VC1
GATE_VC2
-17-
IF_Lo(Tx)
÷2
÷2
Φ
Φ
DET
DET
Baseband
Baseband
(TI)
(TI)
U102
U102
IOTA
Q IOTA
+
+
U101
U101
Calypso
Calypso
(CO35)
(CO35)
I