Total Harmonic Distortion Measurement System of Electronic Devices up to 100 MHz With Remarkable Sensitivity

This paper describes a system for measuring total harmonic distortion (THD) signal components between 1 and 100 MHz at levels down to 130 dBc, which has not been previously achieved. This system consists of mechanically sturdy passive bandpass (BPF) and passive band-elimination (BEF) filters with carefully selected parts. The BPF is used to create a pure sinusoidal signal input to the device under test, whereas the BEF removes the fundamental frequency component of the output signal to overcome dynamic range limitations of a spectrum analyzer that is used to measure the output. We describe design concepts and implementation of these filters, as well as measurement results that show the performance achieved. We also propose to use our BPF to provide a pure sine wave output from signal generators that use analog-to-digital converters (ADCs) as the signal source. A high-precision THD measuring system can be used to measure the ac linearity of electronic devices (such as operational amplifiers, ADCs, and digital-to-analog converters) that operate at frequencies up to several tens of megahertz.