A variable gain envelope modulator with hybrid topology for high linearity/efficiency polar transmitter application

An envelope modulator with hybrid topology for a high linearity and efficiency polar transmitter is described in this paper. The hybrid configuration exhibits a high speed and high efficiency combination by a linear amplifier and a switching amplifier, respectively, thereby improving the power added efficiency (PAE) of the polar transmitter. Moreover, to achieve wideband requirement, an operational trans-conductance amplifier with class AB output stage and variable gain function is designed in the linear amplifier. The switching amplifier adopts a buck converter design. The output dynamic range of envelope modulator shows a 5 dB variable gain with 1 dB resolution. The measured output voltage is from 0 ~ 3.5 V under the supply voltage of 3.5 V. The maximum driving power is 0.991 W for a 20 ohm loading.