Direct digital synthesizer with tunable delta sigma modulator

In direct digital synthesizer (DDS) applications, the drawback of the conventional delta sigma (ΔΣ) modulator structure is that its signal band is fixed. In the proposed architecture, the signal band of the ΔΣ modulator is tuned according to the DDS output frequency. We use a hardware efficient phase-to-sine amplitude converter in the DDS that approximates the first quadrant of the sine function with sixteen equal length piecewise cubic segments. The DDS is capable of frequency, phase, and quadrature amplitude modulation. Two DDSs with tunable 1 bit ΔΣ D/A converters (real and complex) were designed and implemented on a programmable logic device (PLD); experimental results show their desired operation and performance.