(1.Mechanical and Electrical Engineering College, Northeast Forestry University, Harbin 150040, China；

2. Metrological Verification Test Institute of Heilongjiang Province, Harbin 150036, China)

 Abstract: 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 40Hz to 65Hz 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 40Hz to 65Hz, and the degree of distortion is less than 0.03%.

 Key words: phase locked loop; signal source; degree of distortion