Frequency Accuracy Improvement in the Direct Digital Synthesis for the Wave Form Generators

This work presents a method which limits the frequency error in analog signal digital synthesis. Two basic DDS (direct digital synthesizer) structures are studied and their dynamic characteristics are analyzed: frequency error, amplitude error and the SNR. A new structure that adds a variation to the basic DDS is proposed. Results from the three structures are compared by means of Matlab simulation. A compromise is found between the number of points per period of the generated signal and the frequency error. In order to vary the number of points, the proposed structure provides a control register of the phase-amplitude converter length. The frequency error, its variation with the synthesized signal frequency and the amplitude error has been significantly reduced in the DDS proposed and the SNR has been improved. The proposed solution improves the low frequency function generators performances which are commonly based on a microprocessor, and then, they have a capability of obtain and write the phase-amplitude converter values or lookup table (LUT) when the generated signal frequency is changed