一种基于多项式拟合的VCO开环线性校正法

压控振荡器VCO(Voltage Controlled Oscillator)是输入控制电压影响输出频率的振荡电路,可用于产生调频信号。应用于安检成像时,其输出信号的线性度通过影响副瓣电平和距离分辨率,从而决定了安检成像的效果。为了提高安检成像效果,提出了一种基于多项式拟合的VCO开环线性校正法,使VCO的输出频率通过分频器,并对分频后的信号进行滤波和AD采集,通过在FPGA中进行数字信号处理获得VCO输出射频信号的非线性信息,并通过修正DA输出的电压信号实现对VCO的校正。该方法与系统发射线性调频连续波FMCW(Frequency Modulated Continuous Wave)脉冲同时进行,具有较好的实时性,能够解决VCO的温度漂移问题,在长时间合成孔径成像中具备优势。实验结果进一步验证了方法的可行性和有效性。

A VCO open-loop linearity correction method based on polynomial fitting

Voltage Controlled Oscillator (VCO) is an oscillating circuit whose input control voltage affects the output frequency and can be used to generate frequency modulation signals. VCO can be applied in security imaging, and the linearity of its output frequency determines the side lobe level and distance resolution of the imaging result. Therefore, a VCO open-loop linearity correction method based on polynomial fitting is proposed to improve the imaging effect of security inspection. The output frequency of VCO passes through a frequency divider, and the divided signal is filtered and then collected by AD. The nonlinear information of the VCO output is obtained through digital signal process in FPGA. Finally, VCO is corrected by the output voltage signal of DA. When the system transmits linear frequency modulated continuous wave (FMCW) pulse, this method is applied at the same time. So it has good real-time performance and it can solve the temperature drift problem of VCO so as to be applied for long-term synthetic aperture imaging. The feasibility and effectiveness of this method are verified by experimental results.