Optimized Design of the Multilevel Converter in Series-Form Switch-Linear Hybrid Envelope-Tracking Power Supply

In modern radio communications, the envelope of radio frequency (RF) signal features with large peak-to-average power ratio. This necessitates the adoption of linear power amplifiers (PAs). In order to achieve a high efficiency for linear PAs, envelope-tracking (ET) technique is employed, which provides PAs with a supply voltage that tracks the envelope of the transmitted RF signal instead of a constant voltage. This paper focuses on the series-form switch-linear hybrid ET power supply, where the switching-mode converter uses a multilevel converter. The method to select the setting voltages under the premise of ensuring the linearity of output voltage is presented. In addition, the values and number of the voltage levels of the multilevel converter are optimized using a precise loss model based on the probability density function of the envelope signal. Besides, the pulse-blank method is proposed to improve the system efficiency further. Finally, a prototype is built aiming for tracking the envelope signal of wideband code division multiple access, with 5-MHz bandwidth, 12-27 V output voltage, 4 W average, and 10 W peak output power. The experimental results show that the output voltage of the ET power supply tracks the reference accurately and the system efficiency can reach 76%.