Research And Design Simulation Predistortion Power Amplifier Based LTE System

LTE uses a more efficient modulation mode, such as QAM (Quadrature Amplitude Modulation), to make full use of the limited spectrum resources. The signal is non-constant envelope and high peak-average power ratio, and it is sensitive to the nonlinearity. When it amplified by the nonlinear amplifier,then produced the intermodulation distortion, spread spectrum, interfere with the adjacent channel, error rate and so on. Especially the the intermodulation distortion is too near with the carrier, it can’t be filtered simply. In order to increase efficiency, the amplifier usually work in the saturation area. This will produce more distortion. So in order to meet the linearity and the efficiency, the amplifier must use linearization techniques.This paper mainly design a LTE power amplifier with an analog predistortion.The power amplifier includes a balanced amplifier and an analog predistortion circuit. In order to testing the power amplifier the driving amplifier is designed.The third-order intermodulation of the analog predistortion balanced power amplifier is lower than the traditional balanced power amplifier. Design the PCB and produced it. This paper main work is:1.Designed a balanced power amplifier worked between700MHz to800MHZ for LTE system. The amplifier uses the Freescale transistor MRF8P9040NR1, the matching circuit is microstrip and capacitance mixed. the coupler is Yantel HC0650A03. Simulation results show that P1dB is43.8dBm,the gain is24dB. The input two-tone signal that is between5MHz,when the output power is38dBm, the IMD3is26.8dBc at the frequency750MHz and is less than-20dBc in the entire frequency band.2. Designed a analog predistortion circuit to improve the balanced amplifier linearity. The analog predistortion circuit is two branches, there are a diode and matching circuit in each branch, and the two diode reverse placed. Diodes are Avago’s HSMS-282Y, the bias current is10mA, matching circuit use three-stage transmission line. Simulation results show that the insertion loss of analog predistortion circuit is1.8dB between700MHz and800MHz.3. Designed the analog predistortion balanced amplifier which work at between700MHz and800MHz. The designed analog predistortion circuit is before the balanced amplifier,when the output power is38dBm, compared with the balanced amplifier, IMD3have19dbc improvement at750MHz, the entire band, IMD3can be improved by7dBc.4. Designed a driving amplifier which work between700MHz and800MHz. The driving amplifier used a Freescale transistor MW7IC915NT1, the matching circuit is mixed matching network. After simulation, the P1dB is38dBm,the gain is36dB, the gain flatness is ldB.5. Designing the PCB,using FR-4base board to proces of the PCB board,testing the power amplifier.