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3. TECHNICAL BRIEF
3.3 FEM with integrated Power Amplifier Module (SKY77531, U400)
3.3.1 Internal Block Diagram
3.3.2 General Description
The SKY77531 is a transmit and receive front-end module (FEM) with Integrated Power Amplifier Control for
quad-band cellular handsets comprising GSM850/900 and DCS1800/PCS1900 operation. Designed in a low
profile, compact form factor.
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
input and output impedances, TX harmonics filtering, high linearity and a low insertion loss
PHEMT RF switch, and a Power Amplifier Control (PAC) block with internal current sense resistor. A custom
BiCMOS integrated circuit provides the internal PAC function and decoder circuitry to control the RF switches.
The two Heterojunction Bipolar Transistor (HBT) PA blocks 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 four receive pads are connected to the antenna pad through
a PHEMT RF switch. The GaAs die, PHEMT die, Silicon (Si) die and passive components are mounted on a
multi-layer laminate substrate. The assembly is encapsulated with plastic overmold.
LGE Internal Use Only
Figure. 3-3-1 SKY77318 FUNCTIONAL BLOCK DIAGRAM
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3. TECHNICAL BRIEF
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