Feed-Forward Scheme Considering Bandwidth Limitation of Operational Amplifiers for Envelope Tracking Power Supply Using Series-Connected Composite Configuration

Wireless communication transmitters have a low efficiency because of the utilization of linear radio frequency (RF) power amplifiers (PAs) while the RF input signal is with a variant envelope. The envelope tracking (ET) technique is a very promising approach to improve the PA efficiency. For this application, this paper proposes an ET power supply consisting of a multilevel converter in series with a linear amplifier, where the multilevel converter provides the most load power with its essential high efficiency, and the linear amplifier, features of high bandwidth, improves the linearity of the output voltage. A feed-forward scheme is proposed to cancel the spikes in the output voltage caused by the step-wave voltage of the multilevel converter. In practical implementation, due to the bandwidth limitation of the operational amplifiers, a frequency-compensation scheme by adding a zero and a stability pole is proposed to extend the effective bandwidth. Furthermore, the output voltage high-frequency spike-elimination scheme using the transfer function matching concept is also proposed, removing the additional spikes at the output side of the ET power supply. A prototype for 300-kHz sine-wave tracking, with a 10-32-V output voltage and 50-W peak output power, is fabricated and tested. The experimental results validate the proposed schemes.