Smoothing filter for digital to analog conversion

An electronic filter comprised of three active filter sections to smooth the stepped signal from a digital to analog converter is described. The first section has a noninverting low pass filter transfer function, and the second has an inverting transfer function designed to pass a narrow frequency band centered at the step frequency of the stepped output signal with sharp cutoff of either side of that narrow band. The third section adds the noninverted output of the first section to the inverted output of the second section. This third section has a lead-lag transfer function designed to reduce the phase angle between the signal at its output terminal and the stepped signal at the input of the first section.