LG U880 Service Manual page 29

3. TECHNICAL BRIEF
A low current (VCONT) pin provides improved operating efficiency in the low RF power range. To
further improve efficiency in this range, a separate VBIAS pin can be directly connected to the battery,
which allows reducing VCC1 and VCC2 voltages to 0.8 V to achieve very low power consumption.
The single Gallium Arsenide (GaAs) Microwave Monolithic Integrated Circuit (MMIC) contains all
active circuitry in the module. The MMIC contains on-board bias circuitry, as well as input and
interstage matching circuits. The output match is realized off-chip within the module package to
optimize efficiency and power performance into a 50 Ω load. This device is manufactured with
Skyworks' GaAs Heterojunction Bipolar Transistor (HBT) process that provides for all positive voltage
DC supply operation while maintaining high efficiency and good linearity.
Primary bias to the SKY77410 is supplied directly from a three-cell Ni-Cd, a singlecell Li-Ion, or other
suitable battery with an output in the 3.2 to 4.2 volt range.
Power down is accomplished by setting the voltage on the low current reference pin to zero volts. No
external supply side switch is needed as typical "off" leakage is a few microamperes with full primary
voltage supplied from the battery.
Figure 3.5.3-1 UMTS PA functional block diagram
An isolator between the Power Amplifier and the duplexer is highly recommended to provide constant
load and source impedances (respectively) to those devices.
This improves PA stability, ACPR performance, and harmonic suppression, as well as duplexer
isolation, insertion loss, and ripple. Transmitter performance is always improved when an isolator is
included and is well worth the added cost.
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