| With the rapid development of modern wireless communication technology,millimeter wave(MMW)communication system featuring broadband and high-speed is getting extensive attention.However,due to the limitation of semiconductor process,power amplifiers(PAs)normally exhibit low efficiency and output power,which cannot satisfy the requirements of MMW communication system excited by complicated modulation type and high peak-to-average power ratio(PAPR)signals.Digital pre-distortion(DPD)technique is adopted to enhance the linearity of the PA,meanwhile to improve the efficiency of the PA at back-off point.This thesis focuses on the design and implementation of the RF front-end in DPD platform.The RF front-end covers a frequency band from 40.5GHz to 43.5GHz and adopts super-heterodyne architecture.Maximum bandwidth is up to 1GHz.Transmit link,feedback link and local oscillator(LO)doubler are the three primary modules of the RF front-end.IF signals corrected according to pre-distortion model of the PA is up converted by the transmit link,while distorted RF signals can be down converted by the feedback link.LO doubler is used to provide transmit link and feedback link with LO signals.Transmit link is measured with 16 QAM and 64 QAM signals.Data rate of these two signals are both 500 Msps.Error vector magnitude(EVM)of the RF output signals are 4.94 % and 4.55% respectively,both less than 5%.As for the feedback link,output spectrum includes little weak(lower than-60dBm)out-of-band spurious except IF signals,which indicates excellent performance of the RF front-end.To validate the effectiveness of the DPD platform,an experiment is carried out with a balanced power amplifier.The power amplifier is driven by a 240MHz(4 carriers,each 60MHz)orthogonal frequency division multiplexing(OFDM)signal.Measured results show that the adjacent channel leakage ratio(ACLR)before DPD is-33 dBc while ACLR after DPD is-41 dBc.The linearity of the balanced power amplifier is obviously improved. |
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