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 the n onlinear amplification of modulated signals typically used in wireless communication systems, This technique only requires knowledge of the single-tone gain and phase data as a function of input power and can b e applied to any modulated signal given a) the device or amplifier cha racteristics do not change significantly over the bandwidth of the inp ut signal and b) the modulation frequencies are much less than the car rier frequency, Verification of the mathematical technique is presente d using examples of measured and calculated spectra for pi/4-different ial quadrature phase shift keying (DQPSK) personal handy phone system (PHS) and code division multiple access (CDMA) Offset-QPSK personal co mmunication system (PCS) modulation schemes, This calculation techniqu e is essential in determining fundamental tradeoffs between device per formance (linearity, output power, gain, and power-added efficiency) a nd device bias conditions and load impedance.