LG -A258 Service Manual page 34

3. TECHNICAL BRIEF
Figure. 3.4.1 SKY77550 FUNCTIONAL BLOCK DIAGRAM
3.4.2 General Description
SKY77550 is a transmit and receive Front-End Module (FEM) with Integrated Power Amplifier Control(iPAC™)
for Dual-band cellular handsets comprising GSM850/900 and DCS1800/ PCS1900 operation.
Designed in a low profile, compact form factor, the SKY77550 offers a complete Transmit VCO-to-Antenna
and Antenna-to-Receive SAW filter solution. The FEM also supports Class 12 General Packet Radio Service
(GPRS) multi-slot operation.
The module consists of a GSM850/900 PA block and a DCS1800/PCS1900 PA block, Impedance matching
circuitry for 50 ohm input and output impedances, Tx harmonics filtering, high linearity / low insertion loss RF
switch, and a Power Amplifier Control (PAC) block with internal current sense resistor. The two Hetero
junction Bipolar Transistor (HBT) PA blocks, a BiFET PAC and switch control circuit are fabricated onto a single
Gallium Arsenide (GaAs) die. One PA block supports the GSM850/900 bands and the other PA block supports
the DCS1800/PCS1900 bands.
Both PA blocks share common power supply pads to distribute current. The output of each PA block and the
outputs to the two receive pads are connected to the antenna pad through an RF switch. The GaAs die,
Switch die and passive components are mounted on a multi-layer laminate substrate.
The assembly is encapsulated with plastic overmold.
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