Low Distortion Oscillators

To measure harmonic distortion, and other related measures such as THD+N, a sinusoidal oscillator is required. It should have very low distortion and noise, such that it does not limit the measurement resolution. Achieving this is a very demanding task, particularly if fast settling after a frequency change is also required. Below some findings from my studies of this topic.

Low Distortion Oscillator Design Master Thesis

This thesis is available for download: low_distortion_oscillator_design.pdf and low_distortion_oscillator_design_schematics.pdf.

Low Distortion Oscillator Comparison

The following file contains some comparative measurement for the Tektronix SG 505 and the Audio Precision System One, SYS-2722 and APx555: low_distortion_oscillator_comparison.pdf

Passive Notch Filter

passive_notch_filter_r1.pdf
passive_notch_filter_r1_notes.pdf

A fixed frequency passive notch to measure distortion at very low levels.

Gerber files for this design can be downloaded here: passive_notch_filter_r1.zip