Spurious signals in direct digital frequency synthesizers(DDFSs)are partly caused by amplitude quantization and phase truncation,which affect their application to many wireless telecommunication systems. These signals are deterministic and periodic in the time domain,so they appear as line spectra in the frequency domain.Two types of spurious signals due to amplitude quantization are exactly formulated and compared in the time and frequency domains respectively.Then the frequency spectra and power levels of the spurious signals due to amplitude quantization in the absence of phase-accumulator truncation are emphatically analyzed,and the effects of the DDFS parameter variations on the spurious signals are thoroughly studied by computer simulation.And several important conclusions are derived which can provide theoretical support for parameter choice and spurious performance evaluation in the application of DDFSs. Spurious signals in direct digital frequency synthesizers (DDFSs) are partly caused by amplitude quantization and phase truncation, which affect their application to many wireless telecommunication systems. These signals are deterministic and periodic in the time domain, so they appear as line spectra in the frequency Twenty types of spurious signals due to amplitude quantization are exactly formulated and compared in the time and frequency domains respectively. Then the frequency spectra and power levels of the spurious signals due to amplitude quantization in the absence of phase-accumulator truncation are emphatically analyzed , and the effects of the DDFS parameter variations on the spurious signals are has studied by computer simulation. And several important conclusions are derived which can provide theoretical support for parameter choice and spurious performance evaluation in the application of DDFSs.