Theoretical Analysis of Hole Punch Signal Conditioning for High Efficiency EER Power Amplifiers

Abstract

High efficiency and linearity can be achieved using Kahn's envelope elimination and restoration (EER) technique. However, when used with modulation schemes such as code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM), the resulting polar drive signals suffer from expanded bandwidth. Rudolph has shown that the bandwidth of the polar drive signals can be reduced by hole punching the signal in the phase plane (limiting the minimum envelop of the modulated signal). This paper theoretically analyses the hole punch method and quantifies adjacent channel interference (ACI) and the error vector magnitude (EVM) caused by the ensuing distortion. It also shows how the results differ using different shapes and lengths of window functions. Although the hole punch process manages to achieve spectrum improvement for polar components, its EVM will limit the data throughput in some wireless standards.