1.2.3 TX MCM (SKY74709: U1102)
The SKY74709 transmitter is a highly integrated device designed for dual-band, single-mode CDMA handsets
in the cellular CDMA and Personal Communications System (PCS) modes. The SKY74709 includes interstage
transmit Surface Acoustic Wave (SAW) filters and separate CDMA and PCS Gallium Arsenide
(GaAs) Microwave Monolithic Integrated Circuit (MMIC) Power Amplifiers (PAs). The device meets the
stringent CDMA linearity requirements up to 28 dBm output power. The incoming CDMA baseband signal is
upconverted to the desired RF frequency by the In-Phase and Quadrature (I/Q) modulator and amplified by the
appropriate PA driver stage to provide variable output power. The signal is filtered by an interstage transmit
SAW filter and sent to the respective PA to obtain the final rated power.
The only external components needed to complete a CDMA radio subsystem are supply bypass capacitors and
filtering capacitors at the I/Q inputs. The required Phase Lock Loop (PLL) filter and bias resistors have been
included on-chip. The state of the PAs is controlled by the SKY74709, which eliminates the need for
external switches to enable/disable the PAs and control their gain. The SKY74709 is designed to operate within
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