The effects of timing skew in envelope tracking and EER type transmitters

Two supply modulated transmitter techniques, envelope tracking (ET) and envelope elimination and restoration (EER) are studied when timing skew between the RF carrier and supply signal is introduced. Measurements with digital modulations show that the spectrum asymmetry is mostly affected by the V_DD/PM distortion of the amplifier and it can be reduced by careful timing. Higher timing accuracy is needed to optimize EER, but in return the V_DD/PM distortion is smaller in average and linearity can be achieved with less effort. ACPR of 50 dB is reached with V_DD/AM, V_DD/PM, timing and IQ-modulator error corrections.