Error feedback loop linearizes direct digital synthesizers

The fidelity of a signal formed by recalling samples of a sinusoid from a look-up table and converting these sample amplitudes to a waveform in a digital-to-analog converter (DAC) is affected by both the phase and amplitude quantization of the process. The length and width of the look-up table affect the signal's phase angle resolution and the signal's amplitude resolution respectively. These resolution limits are equivalent to time base jitter and to amplitude quantization of the signal and add spectral modulation lines and a white broad-band noise floor to the signal's spectrum. These undesired spectral terms can be controlled by the use of noise shaping to spectrally alter the structure of the quantization noise related to limited table length and width.