The Research And Circuit Design Of Doherty Technology

2014 is known as the first year of 4G era.The 4G mobile communication system,for example,TD-LTE,FDD-LTE,uses some complicated modulation technique when processing signal typically.In order to transmit large amounts of data within a limited time,changes rapidly and exhibit high peak-to-average power ratio become a feature of modulated signal.After amplified by nonlinear system,these modulated signal with large magnitude dynamic range will produce nonlinear distortion more easily,for example.harmonic distortion and inter modulation distortion.In a wireless communication base station,the power amplifier is a key module.Good linearity is the prerequisite to ensure that no distortion of the amplified signal system.Because if the signal amplified by communication system has nonlinear distortion seriously,it would be meaningless to transfer the signal.How to improve power amplifier’s nonlinear distortion is urgent in practice.In this context,the paper takes the structure of Doherty amplifier with analog pre-distortion technology design.And choose ADS(Advanced Design System) software as a platform for circuit design and simulation.Third-order inter-modulation in PA remained in the vicinity of-39dBc and ensuring the added efficiency is greater than 35%at the same time.Meet the goal of design.Research results are as follows:(l)Through designing of Doherty amplifier,this paper met the goal of an efficient structure.LDMOS field effect transistor using Freescale MW6S004N studied to design the whole Doherty,MWS004N models can be imported into ADS via DesignKit,Doherty power amplifier gain can reach 12.9dB when the core frequency of working is 900MHz,bandwidth is about 40MHz,in-band gain flatness can be controlled in ldB or less,power added efficiency is 41%,in the case of equal power output in normal power power amplifier efficiency based on the 18%,so as to meet the design goals for efficient implementations.(2)The paper uses the linearity of power amplifier for analog predistortion structure to ensure the overall requirement.This study used a Freescale LDMOS field effect transistors MRF6V4300,MRF6V2010 and MMG3014NT1 to complete the analog pre-distortion system design and emulation,we can get the conclusion through PA system on the ADS,when the input signal is a dual-tone signal that it’s interval frequency between 900MHz and 9505MHz,the system’s third-order inter-modulation is less than -40dBc,it improve 12dB than the system without pre-distortion structure.The paper reached the goal that improve the linearity of system while guaranteeing amplifier’s high efficiency.