Question: Can the MAX2235 RF amplifier be used for quadrature amplitude modulation (QAM) schemes?
Answer: Because the gain rolls off nonlinearly near the top of its output range, the MAX2235 is mainly recommended for constant envelope modulation schemes, in which the amplitude is not modulated at all. For applications where the amplitude of the signal carries information, it would be necessary to operate the PA in backoff, where it is more linear, or use a power amplifier linearizer in order to achieve acceptable linearity. Alternately, the MAX2265 is optimized for CDMA transmission, which uses a QAM modulation scheme, and provides a more linear gain across the operating range of the amplifier.