Understanding linearity in wireless communication amplifiers

This paper investigates the linearity of active devices and amplifiers that have modulated input signals. We describe an implementation of a mathematical technique for calculating spectral regrowth due to nonlinear amplification for modulated signals typically used in wireless communication systems. This technique requires only single-tone gain and phase data as a function of input power and can be applied to any modulated signal so long as the device or amplifier characteristics do not change significantly over the band width of the input signal and the modulation frequencies are much less than the carrier frequency. Verification of the mathematical technique is presented using examples of measured and calculated spectra for /spl pi//4-DQPSK PHS (Personal Handy Phone) and CDMA Offset-QPSK PCS (Personal Communication System) modulation schemes. Finally, this calculation technique is used to determine fundamental tradeoffs between device performance (linearity, output power, gain, and power added efficiency) and device bias conditions and load impedance.