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3. TECHNICAL BRIEF
3.1 Power Amplifier (SKY77517, U500)
The SKY77517 is a transmit and receive front-end module (FEM) with Integrated Power Amplifier
Control (iPAC¢‚) for dual-band cellular handsets comprising GSM850 and PCS1900 operation.
Designed in a low profile, compact form factor, the SKY77517 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 PA block and a
PCS1900 PA block, impedance-matching circuitry for 50 Ω 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 GSM850 band and the other PA block supports the PCS1900
band. 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 PHEMT RF
switches and a diplexer. 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.
Band selection and control of transmit and receive modes are performed using two external control
pads. Refer to the functional block diagram in Figure 1 below. The band select pad (BS) selects
between GSM and PCS modes of operation. The transmit enable (TX_EN) pad controls receive or
transmit mode of the espective RF switch (TX = logic 1). Proper timing between transmit enable
(TX_EN) and Analog Power Control VRAMP) allows for high isolation between the antenna and
TXVCO while the VCO is being tuned prior to the transmit burst. The SKY77517 is compatible with
logic levels from 1.2 V to VCC for BS and TX_EN pads, depending on the level applied to the VLOGIC
pad. This feature provides additional flexibility for the designer in the selection of FEM interface control
logic.
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
Figure 3.1 Functional Block Diagram
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3. TECHNICAL BRIEF
LGE Internal Use Only
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