LG KT520 Service Manual page 73

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
Figure 3-7-2. WCDMA RF structure
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 quadraturephase
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 50Ω 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
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