Only For Training And Service Purposes - LG GD580 Service Manual

3. Technical brief
3.7.2 WCDMA Part
The W-CDMA transceiver uses differential analog in-phase and quadrature-phase interfaces,
that is an IQ-interface, both in the receiver and transmitter information path. The transceiver has
the following general features:
. Power class : Power class 3 (+24dBm) in Band I
. Zero-IF Receiver.No IF filter needed
. Direct IQ modulation transmitter
A. Transmitter Part
The W-CDMA transmitter architecture is an on frequency linear direct up-conversion IQ-modulator.
The TX IQ modulator has differential voltage I and Q inputs. It converts input signals to RF output
frequency and is designed to achieve LO and image suppression. The in-phase and quadrature
phase reconstruction filters are fully integrated and a programmable gain amplifier implements the
gain control. The transmit output stage provides at least +5 dBm at maximum power control at the
single-ended 50 Ω output. Gain is set through the 3-wire bus. An external SAW filter between the
WCDMA circuit and the power amplifier is used to improve noise performance. Two 10-bit DACs
Are used to control the DC/DC converter and the PA gain. After the power amplifier, the signal is
Sent through an isolator and through the duplex filter, which directs the transmit signal to the
antenna connector through the antenna switch. The supply voltage and bias of the power amplifier
are adapted depending on the output power to achieve high efficiency at every transmitter power
level. A high efficiency DC/DC converter regulates the supply voltage and the bias operation point
is controlled by a D/A-converter in the W-CDMA radio circuit.
These DACs are controlled through the 3-wire-bus
LGE Internal Use Only
Figure 3-7-2. WCDMA RF structure
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Only for training and service purposes