Edge/Gprs/Gsm Rf Block - LG GU280 Service Manual

3.3. EDGE/GPRS/GSM RF block

The EDGE/GPRS/GSM transceiver use a digital interface that is shared between receive and transmit data.
The receive interface is based on I and Q data and the transmitter interface is based on envelop and frequency data.
The quad band EDGE/GSM/GPRS transceiver has the following general features:
Power class
GMSK low bands: Class 4 (33 dBm)
GMSK high bands: Class 1 (30 dBm)
8PSK low bands: Class E2 (27 dBm)
8PSK high bands: Class E2 (26 dBm)
Multi slot class 12 (4+4=5)
Dual Transfer Mode (DTM) class 9 (3+2=5)
Zero-IF receiver
-Polar modulation transmitter
3.3.1. Transmitter Part
GSM/EDGE Transmitter Block
The QSC62x0 device supports quad-band GSM transmissions with two separate dual-band driver amplifier outputs; in
fact, most Tx active circuits are contained within the device. Both GSM transmit paths (Figure 1.3.1.1) begin with a
single, shared analog baseband signal from the device's baseband circuits — the same interface and baseband
circuits used by the UMTS transmitters. The GSM transmitters use the same quadrature upconverters as well — one
for low band signals and one for high band — with just one active at a time. The transmitter LO signals are generated
by circuits described in next section and delivered to the upconverter circuits at the correct frequency, with the
proper phase relationship, and with an adequate drive level.
The SPDT switches at each driver amplifier input allow selection of the output signal: either the actual GSM signal
from the upconverter or a test signal generated by the Tx LO synthesizer. The Tx output chain is functionally identical
for both the low band and the high band: the power amplifier is driven by the QSC device through a matching
network and a resistive attenuator; the PA output is routed to the antenna switch module whose output is connected
to the antenna.
In addition to the through signal path, the QSC device also provides the PA ramp control signal that ensures smooth
transitions while the transmitter is turned on and off for GSM's burst transmissions.
The ramp signal is generated by one of the baseband circuit's Tx DACs. A switch after the baseband amplifier selects
whether the DAC output signal is routed to GSM PA module for ramping the PA up or down, or to the transmitter
signal path for data transmission.
Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
- 19 -
3. Technical Brief
LGE Internal Use Only