Pantech GB310, Руководство по обслуживанию

Страница: 18 / 49

GB310 Service Manual
1
PANTECH
4.2.4 Transmit Section
4.2.4.1 An Overview of Transmit Section
Fig.4-8. Transmitter block diagram
The transmit (TX) section consists of an I/Q baseband upconverter, an offset phase-locked loop
(OPLL) and two output buffers that can drive external power amplifiers (U303), one for the GSM 850
(824 to 849 MHz) and E-GSM 900 (880 to 915 MHz) bands and one for the DCS 1800 (1710 to 1785
MHz) and PCS 1900 (1850 to 1910 MHz) bands. The OPLL requires no external duplexer to
attenuate transmitter noise or spurious signals in the receive band, saving both cost and power.
Additionally, the output of the transmit VCO(TXVCO) is a constant-envelope signal that reduces the
problem of spectral spreading caused by non-linearity in the PA.
A quadrature mixer upconverts the differential in-phase (TXIP, TXIN) and quadrature (TXQP,
TXQN) signals with the IFLO to generate a SSB IF signal that is filtered and used as the reference
input to the OPLL. The IFLO frequency is generated between 766 and 896 MHz and internally
divided by 2 to generate the quadrature LO signals for the quadrature modulator, resulting in an IF
between 383 and 448 MHz. For the GSM 850 band, two different IFLO frequencies are required for
spur management. Therefore, the IF PLL must be programmed per channel in the GSM 850 band.
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 RFLO frequency is generated between
1272 and 1483 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. The I and Q signals are automatically swapped when switching bands. Additionally,
the SWAP bit in register 03h can be used to manually exchange the I and Q signals.
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.