The SKY77346 Power Amplifier
Module (PAM) is designed in a low profile (0.9 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 pads 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 SKY77346
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 PA, typical) of the dual PA module maximizes handset standby time. The SKY77346
also contains band- select switching circuitry to select GSM (logic 0) or DCS/PCS (logic 1) as determined from the Band Select (BS) signal. As shown in Figure 1 below, the BS pad selects between the GSM RF input and output pads versus the DCS/PCS RF input and output pads while the Analog Power Control (VRAMP) controls the output power level.