Research and Design of Envelope Tracking Amplifier for WLAN 802.11g

A “split-band” envelope tracking amplifier for WLAN 802.11g was proposed. The proposed envelope tracking amplifier consists of a wide-band linear amplifier and a high-efficiency switch amplifier, which can take the advantages of both linear amplifier and switch amplifier. Linear amplifier was a two-stage structure composed of a folded-cascode amplifier stage and a class AB output stage; switch amplifier was based on synchronous Buck DC-DC converter structure, with a driving circuit and an "anti-through" module placed before. The entire envelope tracking amplifier circuit is designed and simulated with JAZZ 0.18μm SiGe BiCMOS process. The simulation results showed that the gain bandwidth of the linear amplifier was about 50.2-MHz, phase margin was 63.9 degree under 5mA bias current. The conduction ratio and switch frequency of the switch amplifier would change dynamic by tracking the non-constant envelope signal.