基于优化混频器的数字下变频系统的设计与实现

Design and implementation of digital down converter system based on optimized mixer

在利用频谱分析仪对信号进行实时频谱监测过程中,针对其数字下变频模块精度不高、逻辑资源耗费大、难以对数字中频信号进行实时处理的问题,本文对传统数字下变频系统的混频器模块进行优化并提出一种高效的数字下变频(DDC)系统。首先,设置模数转换器(ADC)的采样率为载波中心频率的4倍且采样率转换比率和子ADC的数量是4的正整数倍,此时混频器可以完全合并到多相CIC抽取滤波器中。接着,基于优化的混频器构建一套DDC系统,并为每个系统节点合理分配采样率转换倍数。最后,加入CIC补偿滤波器,提高数据传输过程中的精度。实验结果表明,与传统DDC相比,优化后的DDC资源消耗减少,数据精度误差从1.7%减小到0.8%。基本满足功耗低、精度高、稳定运行等要求。

Aiming at the shortcomings of digital down-conversion(DDC)module such as low precision,expensive logic resources and difficult to process the digital intermediate frequency(IF)signals in real-time when using spectrum analyzer to monitor spectrum,this paper optimizes the mixer module of the traditional digital down conversion system and proposes an efficient one.Firstly,the sampling rate of the analog-to-digital converter(ADC)is set to 4 times the carrier center frequency,while the sampling conversion ratio and the number of sub-ADCs is set to a positive integer multiple of 4,now the mixer can be completely merged into the multiphase Cascaded Integrator Comb(CIC)decimation filter.Then,a set of DDC system is constructed based on the optimized mixer,where each node is reasonably allocated to the system down sampling rate.Finally,CIC compensation filters are added so as to improve the accuracy of data transmission.Experimental results show that compared with the traditional DDC,resource consumption is reduced and the data accuracy error is reduced from 1.7%to 0.8%in optimized DDC.It can satisfy the requirements of small power consumption,high accuracy and stable operation.