Time domain characterization of power amplifiers with memory effects

Memory effects in power amplifier nonlinearity are frequently an impediment to amplifier linearization. In this paper, memory effects in a cellular phone power amplifier are characterized via time domain measurements, with waveforms including steps, triangular waveforms and CDMA signals. Memory effects found with different waveforms are shown to be consistent, and in agreement with measurements made with sinusoids in two-tone tests. The results are analyzed by considering gain modulation by a parameter varying at the baseband frequency in response to the signal envelope. For pseudorandom input signals, such as for CDMA, cross-correlation of gain residues with the signal envelope yields an impulse response associated with the memory effects.