基于DDS的宽带线性调频源中椭圆低通滤波器设计

The Design of Elliptic Low-Pass Filter in Wide Band Chirp Source Based on DDS

对宽带线性调频源中基带信号产生时所用的低通滤波器进行了设计。在设计过程中,考虑DDS的结构特点及其杂散信号的分布,采用了截止特性陡峭的9阶椭圆函数低通滤波器。该滤波器的3dB截止频率为125MHz,在146MHz处的衰减为70dB,并且通带内纹波小于0.2dB。通过Pspice仿真研究表明在采用了幅度均衡技术后,滤波器的幅频特性良好;实际制作电路时,应按照“选定电感,微调电容”的原则,适当调整元件值。

This article has designed an elliptic low pass filter for the generation of base band signals in a wideband chirp source. In the process of design, the structure feature of DDS and the distribution of spurious signal are considered. A 9th-order elliptic low-pass filter with cliffy cut-off character is adopted. Its 3 dB cut-off frequency is 125 MHz; Its attenuation is 70 dB in 146 MHz; and its pass band ripple is less than 0.2 dB. The study of Pspice simulation shows that amplitude-frequency characteristic of the filter is good when amplitude equalizer is used. It also can be concluded that according to the principle of ＂fixed induct- ance and changed capacitance＂, the component values are adjusted appropriately.