Comments on "Further improvements in digitizing continuous-time filters"

This correspondence points out that an algorithm proposed by C. Wan and A.M. Schneider (see ibid., vol.45, no.3, p.533-42, March 1997) as a new digitizing method is, in fact, an extension of the linear interpolation design. Unlike previously published extensions, which incorporate the interpolation step into the s- to z-domain mapping step, this algorithm cascades the interpolator and the analog filter. Original design formulas derived for a rigorous comparison support the assertion that the above algorithm yields less accurate results than the other interpolation designs.