3. TECHNICAL BRIEF
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3.3.1 Internal Block Diagram
3.3 FEM with integrated Power Amplifier Module (SKY77550, U301)
Figure. 3.3.1 SKY77550 FUNCTIONAL BLOCK DIAGRAM
3.3.2 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,
impedancematching 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 Heterojunction 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.