Abstract:   A new technique of mapping from phase to sine amplitudes in direct digital frequency synthesizer ( DDS) is presented in this paper. Through using parabolic approximation and linear approximation together, sine function signal is approximated with highly accuracy. The generated sine function signal with the maximum harmonic level of 56. 7 dB can be used directly in many situations. With the aid of few ROM the accuracy of the generated sine function signal can be improved even more.

Key words: direct digital frequency synthesizer ( DDS), parabolic approximation, software radio