A digital predistortion assisted hybrid supply modulator for envelope tracking power amplifiers

• The proposed architecture uses a parallel combination of class D and linear stage topology for the modulator.
• The presented architecture incorporates digital controller for the linear stage.
• The proposed digital modulator output inductor is lower than other reported supply modulator at the same output power.
• The given approach improves static efficiency up to 9% in comparison to conventional one-phase and two-phase modulators at the same condition in terms of output inductor due to lower switching frequency.
• The presented method is able to reduce output switching noise ripples up to 10 MHz input signal bandwidth, at the condition of low inductor size.
• The low inductance property of the presented architecture will improve large signal behavior and reduce the ripples at transition points, which results in better linearity.

In this paper, a novel digital predistortion assisted supply modulator is presented. The proposed modulator is suitable for envelope tracking power amplifiers. In this topology, a digitally controlled linear power amplifier is used to compensate the switching noise ripples of the switching modulator. The proposed structure is evaluated with a 0.18 µm CMOS process technology. The results show up to 9% static efficiency improvement in comparison with previous one-phase and two-phase architectures. It is shown that for a 5 MHz WiMAX signal with a 6.7 dB PAPR at 26.8 dBm output power, a maximum average efficiency of 73.5% is achieved in the proposed design.