The significance of envelope peak-to-average ratio for estimating the spectral regrowth of an RF/microwave power amplifier

The peak-to-average ratio (PAR) of a signal is commonly used for estimating the backoff required for an radio-frequency/microwave puffer amplifier to exhibit acceptable intermodulation distortion. In this paper, it is shown t hat the PAR is an inaccurate metric for predicting the backoff and can lead to improper choices for modulation with respect to the linearity-efficienc y tradeoff A specific ease is presented, based on the IS-94 code-division m ultiple-access communication (CDMA) reverse-link and IS-95 CDMA forward-lin k wireless standards. Using simulation and load-pull measurements, it is il lustrated that although quaternary phase-shift keying has a higher PAR than offset QPSK (O-QPSK), it has lower adjacent-channel power, for constant av erage power. This observation, contrary to what is expected, is explained b y introducing the envelope distribution function, which characterizes the s aturation of an amplifier based on the time-domain statistics of the applie d signal.