Improved numerically-controlled digital sinusoidal oscillator

The design of a digital sinusoidal oscillator with finite word length having excellent capability to reduce DC drift, frequency and amplitude drifts is proposed. The design utilizes the fundamental properties of a simple second order difference equation. The key element of this NCO is a ROM look-up-table (LUT) that translates the control input into a value of beta (the cosine of the desired frequency angle theta) that guarantees stability of the oscillator. The disadvantage is that the frequency of oscillation may be slightly different from that specified by the NCO input. But the result is an oscillator that has zero drift in amplitude, DC value or frequency. The proposed oscillator utilizes an LUT, a single multiplier, two input adders and two delays. Simulations confirm the no DC drift, no amplitude distortion and no frequency drift occur for long-term oscillation.