Filter equalization using magnitude measurement data

Abstract

A filter equalization technique for an analog signal path, such as in an instrument that simultaneously measures a signal over a band of frequencies, uses magnitude measurement data for high frequency bands for which phase-calibrated sources are not readily available. A sinusoidal signal source together with an accurate power meter is used to provide a stepped frequency input over a desired frequency band to the analog signal path with an accurate measured magnitude. The output of the analog signal path is digitized and the resulting frequency magnitudes are computed. Then the resulting power meter results are deducted from the frequency magnitudes measured each time by the instrument to determine the magnitude response of the analog signal path. Using a Hilbert transform the corresponding phase response is determined based on a minimum phase assumption over the desired frequency band. From the magnitude and phase responses an inverse or digital equalization filter may be designed for the analog signal path.