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.