Transmit Section; A Noverview Of Transmit Section - Pantech PG-3210 Service Manual

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PG-3210 Service Manual

4.2.4 Transmit Section

4.2.4.1 An Overview of Transmit Section

The transmit section consists of an I/Q baseband upconverter, an offset phase-locked loop (OPLL),

and two 50 Ω output buffers that can drive an external power amplifier (PA). One output is for the

GSM 850 (824–849 MHz) and E-GSM 900 (880–915 MHz) bands and one output is for the DCS 1800

(1710–1785 MHz) and PCS 1900 (1850–1910 MHz) bands.

The OPLL requires no external filtering to attenuate transmitter noise and spurious signals in the

receive band, saving both cost and power. 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. Additionally, the TXVCO benefits from isolation provided by the transmit output buffers. This

significantly minimizes any load pull effects and eliminates the need for off-chip isolation networks.

A quadrature mixer upconverts the differential in-phase (BIP, BIN) and quadrature (BQP, BQN)

baseband signals to an intermediate frequency (IF) that is filtered and which is used as the reference

input to the OPLL. The OPLL consists of a feedback mixer, a phase detector, a loop filter, and a fully

integrated TXVCO.

Low-pass filters before the OPLL phase detector reduce the harmonic content of the quadrature

modulator and feedback mixer outputs.

The transmit I/Q interface must have a non-zero input no later than 94 quarter bits after PDN is

asserted for proper operation. If the baseband is unable to provide a sufficient TX I/Q non-zero input

preamble, then the CWDUR bits can be used to provide a preamble extension.

The receive and transmit baseband I/Q pins are multiplexed together in a 4-wire interface (BIP, BIN,

BQP, and BQN). In transmit mode, the BIP, BIN, BQP, and BQN pins provide the analog I/Q input

from the baseband subsystem. The full-scale level at the baseband input pins is programmable with

the BBG[1:0] bits. The I and Q signals are automatically swapped within the Aero II transceiver when

switching bands. The transmit output path is automatically selected by the ARFCN bits and the

BANDIND bits.

Fig.4-8. Transmitter block diagram

PANTECH

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