Power Amplifier Module (Sky77318) - LG KP151Q Service Manual

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3. HW Circuit Description

3.2 Power Amplifier Module (SKY77318)

Figure. 3-2 SKY77318 FUNCTIONAL BLOCK DIAGRAM

The module consists of separate GSM PA and DCS1800/PCS1900 PA blocks, impedance-matching

circuitry for 50 Ω 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 Ω 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 band select switching circuitry to select GSM

(logic 0) or DCS/PCS (logic 1) as determined from the Band Select (BS) signal.

In Figure 1 below, the BS pin selects the PA 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. 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.

LGE Internal Use Only

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Only for training and service purposes

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