Harmonic Distortion: Part I - Understanding Harmonic Distortion Vs. Frequency Measurements in Op Amps

by Jorge Vega, Characterization Engineer, and Raj Ramanathan, Analog Design Engineer, Texas Instruments

A sound understanding of harmonic distortion in amplifiers is a good starting point in choosing the right amplifier for a particular application. This understanding begins with an explanation of the measurement setup and what total harmonic distortion plus noise, THD N, means. This TechNote addresses the main contributors of distortion in amplifiers as depicted in the typical curves presented in amplifier datasheets. The two curves typically presented are THD N versus frequency and THD N versus amplitude. This TechNote covers THD N versus frequency. The regions in this curve are explained in light of the amplifier’s noise characteristic, source impedance, open-loop gain, bandwidth, and slew rate.

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