Fem With Integrated Power Amplifier Module; (Sky7754/Sky77543, U401); General Description - LG A175 Service Manual

3. TECHNICAL BRIEF
3. TECHNICAL BRIEF

3.3 FEM with integrated Power Amplifier Module

(SKY77542/SKY77543, U401)
3.3.1 Internal Block Diagram
Figure. 3.3.1 SKY77542 FUNCTIONAL BLOCK DIAGRAM

3.3.2 General Description

The SKY77542 is a transmit and receive front-end module (FEM) with Integrated Power Amplifier Control
(iPAC™) for dual-band cellular handsets comprising GSM900 and DCS1800 operation.Designed in a low
profile, compact form factor, the SKY77542 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 GSM900 PA block and a DCS1800 PA block, impedance-matching circuitry for 50
input and output impedances, Tx harmonics filtering, high linearity and low insertion loss PHEMT RF
switches, diplexer 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 GSM900 band and the other PA block supports
the DCS1800 band. Both PA blocks share common power supply pads to distribute current.
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