Development Of Envelope Tracking Power Supply For Mobile Communication System

For high data transmission rate and efficient utilization of the increasingly crowded spectrum,non-constant-envelope modulation methods have been widely used in modern mobile communicationsystem. In order to avoid considerable power loss of power amplifier (PA) in mobile base stationpowered by a constant voltage, envelope tracking (ET) technique is adopted, which provides a variablepower supply voltage tracking the envelope of the radio frequency (RF) input signal, so that the PA canalways operate in its theoretical high efficiency region, and the system efficiency can be improvedaccordingly. This dissertation is dedicated to the ET power supply configuration, control andexperimental verifications.The switch-linear hybrid configuration for constructing the ET power supply can achieve bothhigh efficiency and high linearity. This dissertation discusses the possible combinations of switchingconverter and linear amplifier, and it is pointed out that the series-connected and parallel-connectedswitch-linear hybrid schemes with voltage-controlled output are preferred to construct the ET powersupply. By analyzing the sideband frequencies of the pulse-width modulation (PWM) based switchingconverters and the multi-frequency small signal model, it is indicated that achieving a high bandwidthof the switching converter often requires too high switching frequency, which is very difficult to obtainsuitable power switches. The possible control methods and new configurations are discussed to reducethe required switching frequency while retaining a high tracking bandwidth. The multilevel converterwith block diodes scheme and the multi-phase current sources scheme are proposed forseries-connected and parallel-connected hybrid configuration, respectively. Additionally, the topologyselection of the linear amplifier is discussed for the two hybrid schemes.A voltage-controlled Class AB linear amplifier in parallel with a current-controlled synchronousrectification buck converter is employed to construct the parallel-connected hybrid ET power supply,where the linear amplifier controls the output voltage while the buck converter provides the most partof the load power. The expression of the linear amplifier output current is derived, and from which, it isfound that when the loop gain magnitude at the tracking frequency is not sufficiently high, the linearamplifier is forced to output a fundamental-wave current by the influence of the output voltage, whichgreatly degrades the system efficiency. This dissertation proposes a full feed-forward of the outputvoltage scheme, which can substantially reduce the linear amplifier output current. A prototype for100kHz sine wave tracking, with5V~15V output voltage, and75W peak output power is fabricated and tested in the lab. The experimental results verify the effectiveness of the proposed full feed-forward ofthe output voltage scheme.A multilevel converter in series with a Class A linear amplifier is employed to construct theseries-connected hybrid ET power supply, where the multilevel converter fits the output voltage with astep-wave, and the linear amplifier provides the voltage difference between the step-wave voltage andthe final output voltage. Due to the abundant harmonics, the influence from the step-wave voltage onthe output voltage cannot be suppressed effectively by the loop gain, which leads to high spikesappearing at the ET power supply output voltage. This dissertation proposes a feed-forward of thestep-wave voltage scheme to eliminate this influence, and it is verified effectively by the simulationresults. However, in practical implementation, the operational amplifiers suffer bandwidth limitation inrelatively high-frequency range, thus better output voltage linearity cannot be achieved as expected. Toimprove the tracking performance, the frequency compensation scheme is proposed to extend theeffective bandwidth of the operational amplifier cascade path, and the output voltage high-frequencyspike elimination scheme is proposed to further eliminate the influence from the high frequencyharmonics of the step-wave voltage on the final output voltage. A prototype for300-kHz sine wavetracking, with10V~32V output voltage, and50W peak output power is fabricated and tested in thelab. The experimental results validate the proposed schemes.