LG -P970 Service Manual page 42

3.6.3 FEM + GSM PAM (U104, SKY77529)
The SKY77529 Tx Front End Module (FEM) is designed in a compact form factor for quad-band cellular handsets
comprising GSM850/900, DCS1800, PCS1900, supporting GMSK and linear EDGE modulation. Class 12 General
Packet Radio Service (GPRS) multi-slot operation is also supported.
The module consists of a GSM850/900 PA block and a DCS1800/PCS1900 PA block, a printed directional coupler
for each block impedance-matching circuitry for 50 Ω input and output impedances, a multifunction power
amplifier control (MFC) block, low pass harmonic rejection filters, and an SP8T Antenna T/R switch. Two separate
Hetero junction Bipolar Transistor (HBT) PA blocks are fabricated onto an InGaP die; one supports the
GSM850/900 bands, the other supports the DCS1800 and PCS1900 bands. The InGaP PA die, the silicon MFC die,
PHEMT switch die, and the passive components are mounted on a multi-layer laminate substrate. The assembly
is encapsulated with plastic overmold.
The FEM incorporates full support for a Serial Peripheral Interface (SPI) bus function. The SPI controller shall
accept SPI telegrams with data fields that support PA and switchplexer-related functions. All FEM operating
modes and switch states shall be determined by the SPI telegram. The Multi-function Control (MFC) provides pin
out for interoperation with a specified transceiver that will establish a closed loop power control mechanism.
The external circuit uses the Linear Detector output to set a fixed bias point for 8PSK (EDGE) mode and a variable
bias point for GMSK (GSM) mode.
The power control loop together with the MFC will reduce sensitivity to antenna load, input drive, temperature,
power supply, and process variation. The combined circuit configures the PA for fixed gain in 8PSK mode while
providing the ability to optimize the PA bias at different power levels to maximize efficiency.
VCMOS
Tx_HB
VSPI
CLK
DRW
SS
VDET
VRAMP
Tx_LB
LGE Internal Use Only
V-Q3_HB
Match
BICMOS
SERIAL MFC
PERIPHERAL
INTERFACE
CONTROL
LINEAR RF
DETECTOR
POWER
AMP
CONTROL
Match
V-Q3_LB
Batt
[Figure 3-10] SKY77529 Block Diagram
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3. TECHNICAL BRIEF
RxTx-H
Rx-M3
Rx-M
ANTENNA
RxTx-M1
Rx-L1
RxTx-L
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