The Research And Implementation Of Doherty Radio Frequency Power Amplifier Based On Envelope Tracking Technology

With the evolution of wireless communication signals from constant envelope to high PAPR, the average power of RF PA(power amplifier)must be in the BOP(back of power) region. It means that the PA has to exchange high efficiency for good linearity. To improve the efficiency of PA, people try to change the structure of PA and change the dc power supply. Thereinto, Doherty technology is the represent of changing the structure of PA while ET(envelope tracking) technology is the represent of changing dc power supply. Doherty and ET have excellent effect in improving efficiency, so they are widely researched. This paper combines these two technology and focuses on ET power supply which is applied to Doherty PA. Finally, this paper achieves the efficiency improvement and linearity optimization of Doherty PA. The main content of this paper is as follows:1. This dissertation researches and analyzes the principle of ET technology and characteristics of different ET schemes based on the large signal nonlinear equivalent model of PA. Then an optimized ET solution is deduced and verified through simulation. The simulation shows that the optimized ET scheme improves the PAE of PA by 25% at 8dB BOP with the decrease of gain only by 1.5dB.2. This dissertation researches and designs an ET scheme applied to Doherty PA, including the ET scheme applied to the drain supply of Doherty’s carrier PA and the ET scheme applied to the gate supply of Doherty’s peak PA. The former effectively improves the efficiency of Doherty PA at high BOP region while the latter effectively compensates the linearity deterioration and gain fluction brought by drain voltage modulation with just a little drop of efficiency.3. This dissertation designs and implements a Doherty PA based on ET technology. The ET power supply can track and modulate the drain voltage of carrier PA and the gate voltage of peak PA at the same time. It can effectively improve the efficiency at high BOP region and make up for the linearity deterioration. The test results show that the ET power supply promotes the PAE of Doherty PA by 8% at lOdB BOP and by 10% at 10.7dB BOP with the linear gain falling by 3.31dB. When the system is tested by a 5MHz WCDMA signal, the ET power supply is proved to promote the average PAE of Doherty PA by 8.5% and decrease the ACPR by 4.5dBc.