高精度标准源中低频信号源的设计与分析

Design and analysis of low frequency signal source in high precision standard source

针对直接数字合成的高精度信号源在低频段容易产生杂波干扰,难以适应我国公共电网频率的问题,采用锁相合成频率技术来产生范围在40 Hz^65 Hz、分辨率为0.01 Hz的低频信号作为高分辨率信号源合成的时钟频率。采用数模转换器外接基准可调电压技术产生了调节细度优于满量程的0.000 1%的可调幅值;同时利用相位计数器区分相位,设计出了频率、幅值、相位都可调的正弦波信号;建立了信号源失真度与数模转换器位数的关系和取样点数的关系,找到了影响信号源输出稳定性的原因;在理论分析和实践的基础上提出了减小信号源失真度的方法。研究结果表明,该低频信号源可以在误差接受范围内减小差频影响和公共阻抗的影响,输出40 Hz^65 Hz频率范围内标准正弦波信号的失真度小于0.03%。

Aiming at the problem that clutter and interferer were likely generated in low frequency band for high-precision signal source by direct digital synthesizer,which was difficult to adapt to the frequency of public grid in China,the low frequency signal with the range from 40 Hz to 65 Hz was generated as clock frequency for high-precision signal source by the phase-locked synthesis frequency technology,meanwhile,the adjustable amplitude and phase were generated,respectively,by digital to analog converter with standard adjustable voltage and phase counter. The adjustable precision was better than 0. 000 1% of full scale for adjustable amplitude. Based on the above technology,the sine wave signal was generated with the adjustable frequency,amplitude and phase. The relationship between signal distortion and digital to analog converter digit and the number of sampling was established,the reason for output stability of the signal was investigated,and the method for decreasing the signal distortion was presented based on theory and practice. The results indicate that low frequency signal can decrease the effect of the difference frequency and public impedance under acceptable error range,which outputs the standard sine wave signal with frequency range from 40 Hz to 65 Hz,and the degree of distortion is less than 0. 03%.