numerically controllable oscillator (DDS) (NCO)

Numerically Controlled Oscillators (NCO) or Digitally Controlled Oscillators(DCO) are digital generators that derive synchronized sinusoidal signals from a highly accurate time reference. Compared to other oscillators, they have high accuracy, stability and reliability.

NCO oscillators consist of a phase accumulator that adds a frequency-controlled value to its output value for each time reference sample. The digital output value of the phase accumulator is fed to a phase-to- amplitude converter( PAC), which is used to convert the phase into an amplitude. The converted output value is used as an index for a table of values( LUT) and produces a corresponding amplitude at each sample point. To produce higher accuracy and lower phase noise, in some circuits the output value is interpolated with the values of the value table. Other Numerically Controlled Oscillators use mathematical algorithms for phase-to-amplitude conversion.

The frequency accuracy is limited in relation to the clock frequency only by the arithmetic precision of the phase calculation. NCO oscillators are phase and frequency agile and can be easily modified to generate phase and frequency modulated signals.

Numerically Controlled Oscillators are used in communication systems, synthesizers, high precision function generators, RF generators, radar systems, Software Defined Radios( SDR), in drivers for optical or acoustic transmission media and in modulators and demodulators.