This Application Note describes the functionality, board layout and applications instructions of the SKY77344-21 Power Amplifier Module. The SKY77344-21 Power Amplifier Module (PAM) is designed for quad-band cellular handsets comprising GSM850/900, DCS1800/ PCS1900, and supports Class 12 General Packet Radio Service (GPRS) multi-slot operation, and Enhanced Data GSM Environment (EDGE) (8PSK) linear modulation. A single analog control voltage is used at the VRAMP port for both GMSK and EDGE modes. The active logic level at the MODE terminal determines the function of the VRAMP signal. The EDGE mode is supported with a linear open loop configuration where amplifier gain is held constant with VRAMP and output power is determined by input power. GMSK mode is supported by operating the SKY77344-21 as a variable gain amplifier where VRAMP controls gain and resultant output power. The SKY77344-21 PAM consists of an Indium Gallium Phosphide (InGaP) PA block, a BiCMOS multi-function controller (MFC) block, and impedance-matching circuitry. The new BiCMOS collector voltage amplitude controller (COVAC) provides envelope amplitude control and bias optimization for each mode of operation, thus reducing sensitivity to input drive, temperature, power supply, and process variations. Embedded within a single Gallium Arsenide (GaAs) die using InGaP technology, one Heterojunction Bipolar Transistor (HBT) PA lineup supports the GSM850/900 bands and another supports the DCS1800 and PCS1900 bands. The module also contains band select switching circuitry to select GSM (logic 0) and DCS/PCS (logic 1) as determined from the Band Select (BS) signal. As determined by the MODE control, VRAMP controls the level of output power for GMSK modulation or optimizes the performance for EDGE modulation. The Enable input signal allows initial turn-on of the PAC circuitry to minimize battery drain

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