零中频发射机设计与实现

零中频发射机电路实现上只有DAC和IQ调制器两部分,电路结构简单,与二次变频方案相比,省去中频信号发生器、中频合成器(PLL/VCO)、中频－射频混频器以及 SAW 滤波器等,不仅降低了发射机系统的复杂度,也大幅减小了系统体积、重量、功耗和成本,但是零中频方案存在无用边带和本振泄漏。文中分析了零中频发射机的原理和存在的问题,找到了一种抑制无用边带和本振泄漏的方法,给出了一种零中频发射机实现方案。经工程验证,文中的零中频发射机64QAM调制方式EVM＜4%,ACPR＞53 dB,各项关键指标优于3GPP规范。

Design and Implementation of Zero Intermediate Frequency Transmitters

The circuit structure of Zero Intermediate Frequency （ZIF） transmitter consists only of DAC and IQ modulator without the need for the intermediate frequency signal generator, frequency synthesizer （PLLlVCO）, intennediate frequency RF mixer or a SAW filter and so on. It reduces the complexity and the system size, weight, power consumption and the cost compared with the two times frequency conversion scheme. However, ZIF scheme leads to severe sideband and local oscillator leakage. In this paper, we analyses the principle of ZIF transmitter and the existing problems, and find a method for suppressing unwanted sideband and local oscillator leakage. An implementing scheme for ZIF transmitter is presented. The engineering testing shows that the 64QAM modulation mode has better key index than the 3GPP specification with EVM 〈4% and ACPR 〉53 dB.