Reseach On Envelope Tracking Technology Of Rf Power Amplifier

With contemporary communication technology developing, multi-carrier modulation signal with high peak-to-average ratio is widely utilized. Generally we use power back-off technique which can retract the output power to low-efficiency area to meet the linearity requirements of high peak-to-average ratio input signal. In that case, the efficiency of RF power amplifier declines heavily. Envelope tracking technology(ET)is a hot research topic of power amplifier in recent years because it is possible to improve the efficiency of power amplifier in case that the linearity of power amplifier dos not decline. This paper mainly studies envelope tracking technology in terms of envelope of signal processing made detailed analysis and simulation, Focusing on envelope tracker, which is the core of envelope tracking technology. Also, related principles and design methods are discussed.First of all, the forming process of envelope signal is the first step on the envelope tracking technology. In this paper, peak clipping technology, envelope forming technology and envelope bandwidth-reduction technology have carried on the discussion and analysis starting from the principle. Three kinds of technology are proved effective in simulation.Next, this paper analyzes the principle and design method of envelope tracker. Firstly, for buck converter topology of envelope tracker, this paper puts forward to four order Bessel low-pass filter transfer function as a whole mathematical model from mathematics principle to suppress the phase distortion. We also carry on the optimization design of linear control part to improve tolerance of circuit parameters. Simulation shows that the efficiency of buck envelope tracker with linear control can reach 77%. For the slow transient response and large delay of linear control, the article discusses the sliding mode variable structure control of buck envelope tracker. mathematical principles and the selection of circuit parameters of Second-order sliding mode variable structure control and interleaving buck structure are emphatically analyzed. Simulation shows that the sliding mode variable structure control of buck envelope tracker has fast response and high efficiency. If only use switch converter topology to design envelope tracker, the tracking bandwidth is always difficult to expand. Based on tracking bandwidth extension, this paper studies the linear part and buck part parallel hybrid envelope tracking topology with the simulation verification. A low power envelope tracker with 9W peak power has been designed and carried on the experiment with a bias voltage sine signal as input envelope signal. The result shows that the efficiency can reach 74%. A medium power envelope tracker with 112 W peak power has been designed and carried on the experiment with a bias voltage sine signal as input envelope signal. Result shows that the average efficiency can reach 70.8%.Finally, in this paper, the envelope tracking system is verified on simulation. A class AB power amplifier is designed with BLP7G22-10 LDMOS. The simulation model is established in ADS. Simulation is carried on with 8 times oversampling WCDMA single carrier signal as input signal to compare the efficiency and linearity with envelope tracking power supply and constant 28 V power supply. Such comparisons are needed in the case of equal output power. Simulation results show that the PAE increased about 8% with envelope tracking power supply, and linearity deterioration can be controlled in a smaller range.