A novel architecture for ROM-less sine-output direct digital frequency synthesizers by using the 2nd-order parabolic approximation

An extended form of the parabolic approximation, which was previously introduced by the authors, is proposed. The proposed form of the approximation is so close to the sine function that satisfies the accuracy requirements for a typical sine-output DDFS. Then, the approximation is used to develop a novel ROM-less architecture for sine-output direct digital frequency synthesizers. Based on the optimized architecture, an experimental test system is developed. Experimental results for the implemented ROM-less sine-output parabolic DDFS show that the approximation error will cause harmonic levels below the spurious level associated with the output quantization.