A hybrid envelope modulator using feedforward control for OFDM WLAN polar transmitter

This paper presents a feedforward control for hybrid envelope modulator for applications in 802.11g OFDM WLAN polar transmitter. The feedforward control is constituted by hysteresis comparator and duplicate-linear amplifier that possess low power dissipation. For achieving high speed and high efficiency, the hybrid envelope modulator combines with a linear amplifier and a switch amplifier. Operational transconductance amplifier (OTA) and class-AB output stage are designed for linear amplifier as well as the buck converter is designed for switch amplifier. The chip has been fabricated in 0.35 mum SiGe process and occupies an area of 2 mm
²
including I/O pads. The die is packaged in LQFP and measurement results show that the output voltage range is from 0 to 3 V under 3.8 V power supply and drives a 5 Omega load up to 1.8 W of maximum output power with 95% of maximum efficiency.