A direct-digital synthesizer with improved spectral performance

The authors present a modified direct-digital synthesizer which uses noise shaping to reduce the effects of phase-accumulator truncation on the output spectrum. The discrete spectral disturbances associated with this truncation error are strongly reduced with the proposed method, making the synthesizer suitable for high-performance signal processing. The proposed architecture uses first-order noise shaping. Higher order noise shaping can also be used if required. The modified circuit offers considerable improvement in the synthesizer performance when the generated frequency is low with respect to the clock frequency