Power Amplifier Module; Sky77318 ) - LG KM330 Service Manual

3.2 Power Amplifier Module(SKY77318)
Figure.3-2-1 SKY77318 FUNCTIONAL BLOCK DIAGRAM
The SKY77318 Power Amplifier Module (PAM) is designed in a low profile (1.2 mm),
compact form factor for quad-band cellular handsets comprising GSM850/900, DCS1800, and
PCS1900 operation. The PAM also supports Class 12 General Packet Radio Service (GPRS)
multi-slot operation.
The module consists of separate GSM PA and DCS1800/PCS1900 PA blocks,
impedance-matching circuitry for 50 . input and output impedances and a Power Amplifier
Control (PAC) block with an internal current-sense resistor. The custom BiCMOS integrated
circuit provides the internal PAC function and interface circuitry. Fabricated onto a single
Gallium Arsenide (GaAs) die, one Heterojunction Bipolar Transistor (HBT) PA block supports
the GSM bands and the other supports the DCS1800 and PCS1900 bands. Both PA blocks
share common power supply pins to distribute current.The GaAs die, the Silicon (Si) die, and
the passive components are mounted on a multi-layer laminate substrate. The assembly is
encapsulated with plastic overmold.
RF input and output ports of the SKY77318 are internally matched to a 50 . load to reduce
the number of external components for a quad-band design. Extremely low leakage current
(2.5 µA, typical) of the dual PA module maximizes handset standby time. The SKY77318 also
contains bandselect switching circuitry to select GSM (logic 0) or DCS/PCS (logic 1) as
determined from the Band Select (BS) signal. In
output (DCS/PCS_OUT or GSM_OUT) and the Analog Power Control (VAPC) controls the
level of output power.
The VBATT pin connects to an internal current-sense resistor and interfaces to an
integrated power amplifier control (iPAC.) function, which is insensitive to variations in
temperature, power supply, process, and input power. The ENABLE input allows initial turn-on
of PAM circuitry to minimize battery drain.
Figure 1 below, the BS pin selects the PA
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