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Only for training and service purposes
3. TECHNICAL BRIEF
- 35 -
3.5.4 Dual band GSM Power amplifier (U102: SKY77318)
Product Description: The SKY77318 Power Amplifier Module (PAM) is designed in a low profile (1.2
mm), compact form factor for tri-band cellular handsets comprising EGSM (includes standard GSM900
band), DCS1800, and PCS1900 operation.
The PAM also upports Class 12 General Packet Radio Service (GPRS) multislot operation. The
module consists of separate EGSM PA and DCS1800/PCS1900 PA blocks, impedance-matching
circuitry for 50 ߟ 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 EGSM 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 ߟ load to reduce the number of external components for a
tri-band design. Extremely low leakage current (2.5
µ
A, typical) of the dual PA module maximizes
handset standby time.
The SKY77318 also contains band-select switching circuitry to select EGSM (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 EGSM_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
TM
) 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.
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