LG -P500 Service Manual page 31

3. TECHNICAL BRIEF
3.6.3 ASM + GSM PAM (U1002, SKY77544)
SKY77544 is a transmit and receive Front End Module (FEM) designed in a very low profile (0.9 mm), compact
form factor for quad-band cellular handsets comprising GSM850/900, DCS1800, and PCS1900 operation — a
complete transmit VCO-to-Antenna and Antenna-toreceive SAW filter solution. The FEM also supports Class
12 General Packet Radio Service (GPRS) multi-slot operation and EDGE Polar Modulation. WCDMA switch-
through support is provided by three dedicated high-linearity ports.
The module consists of a GSM850/900 PA and DCS1800/PCS1900 PA block, impedancematching circuitry for
50 Ω input and output impedances, Tx harmonic filtering, high linearitylow insertion loss switches, and a
CMOS Power Amplifier Control (PAC) block. A custom silicon integrated circuit contains decoder circuitry to
control the RF switch while providing a low current external control interface. An integrated temperature
sensor provides an analog voltage based on the temperature of the module.
Fabricated in InGaP/GaAs, the Heterojunction Bipolar Transistor (HBT) PA blocks support the GSM850/900
bands and DCS1800/PCS1900 bands. Both PA blocks share common power
supply pads to distribute current. The output of the PA block and the outputs to the seven
receive pads connect to the antenna pad through a highly linear antenna switch. The WCDMA
and Rx ports feature a 0 volts DC offset level, which eliminates any need for external blocking capacitors. The
InGaP/GaAs die, switch die, Silicon (Si) controller die, and passive components are mounted on a multi-layer
laminate substrate and the entire assembly is encapsulated with plastic overmold.
RF input and output ports of the SKY77544 are internally matched to a 50 Ω load to reduce the number of
external components for a quad-band design. Extremely low leakage current of the FEM maximizes handset
standby time. Band selection and control of transmit and receive RF signal flows are performed by use of four
external control pads. See
DCS, PCS, and UMTS) is controlled with 4 logic inputs: BS1, BS2, Mode, and TxEN. Proper timing of the TxEN
input and the VAPC input ensures high isolation between the antenna and Tx-VCO while the VCO is being
tuned prior to the transmit burst. The Enable input controls the initial turn-on of the PAC circuitry to
minimize battery drain.
The integrated power amplifier control (PAC) function provides envelope amplitude control by reducing
sensitivity to input drive, temperature, power supply, and process variation.
LGE Internal Use Only
Figure 1.9 shown on overleaf. Mode of operation Tx, Rx, Band (GSM850, GSM900,
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