Improved EER transmitters for WLAN

The envelope elimination and restoration (EER) transmitter architecture is capable of providing high power efficiency without compromising linearity. This paper shows that for a wireless local area network (WLAN) application, the envelope reconstruction process modulates the supply voltage of the switching amplifier over a large dynamic range. This introduces sufficient nonlinearity to violate emission specifications. Fortunately, the EER architecture can be improved by applying envelope and phase feedback. The phase feedback architecture satisfies the emission specifications of IEEE 802.11a, while envelope feedback provides modest adjacent channel power ratio (ACPR) improvement. The impact of clipping on the ACPR and error vector magnitude (EVM) is also investigated. It is shown that for a WLAN application, a clipping of only 1 dB can be tolerated before the output signal is degraded significantly.