2 Principle of Sine Wave Generation Using NCO Module

The output of the NCO module will be a square wave at the configured frequency. A square wave has many frequency components with the main frequency being the center frequency, as per the NCO configuration. A square wave could be generated by adding a series of pure tones (sine waves) with appropriate amplitude and phase as per the Fourier transforms.

Fourier theorem assumes that the user add sine waves of infinite duration. Therefore, a square wave is essentially composed of Fundamental frequency -1/3 of third harmonic tone +1/5 of fifth harmonic tone -1/7 of seventh harmonic tone, and so on (see Figure   1). The square wave output from the NCO can be passed through a Band Pass Filter with a high Q factor to generate a sine wave at the desired frequency.

Figure   2 illustrates the frequency spectrum of a symmetric square wave observed using an oscilloscope.