Direct digital frequency synthesizer based on curve approximation

Phase to amplitude conversion is an essential part in the technique of direct digital frequency synthesis. A novel theory of phase to amplitude conversion named curve approximation is proposed in this paper to solve the existing problems of present digital frequency synthesizers. It has more advantages over traditional phase to amplitude conversion methods, such as simple hardware circuit, fast conversion speed, low loss and high precision. A mathematical function approximating normalized waveforms is presented in the paper and then is corrected by a small ROM lookup table containing the difference between normalized waveform and curve approximation. It can be seen from MATLAB simulation that the given curve is essentially coincident with the normalized waveform. Frequency synthesizer based on DSP and MCU verifies the feasibility of curve approximation in direct digital frequency synthesis. Experimental result shows that this method has excellent performance.