A low-distortion oscillator is necessary for testing today's ADCs (analog-to-digital converters) that have resolution higher than 20 bits. Low-distortion amplifiers with THD (total harmonic distortion) of -120 dB or less also need such an oscillator for testing. Commercially available distortion meters offer many measurement functions, but even the best have a THD measurement limit somewhere around -115 dB.
Several low-distortion oscillator designs have been published, but they have also have THD of -120 dB or slightly better. At JanasCard, we've developed an oscillator with THD below -140 dB that we use for in-house testing.
This detailed article gives schematics, explains design subtleties, shows performance graphs, and also provides references to other related design articles.
Click on "Low distortion oscillator tests measurement circuits" to read the entire article, which originally appeared in our sibling publication Test & Measurement World.
About the author
Vojtech Janásek has more than 20 years experience in high performance analog and mixed signal design. He holds a degree in Electrical engineering from the Czech Technical University in Prague and PhD degree from the same university. He is a founder of JanasCard . E-mail: firstname.lastname@example.org.