Low-sensitivity, low-power active-RC allpole filters using impedance tapering

A procedure for the design of allpole filters with low sensitivity to compo nent tolerance is presented. The filters are based on resistance-capacitanc e (RC) ladder structures combined with single operational amplifiers. It is shown that by the use of impedance tapering, in which L-sections of the RC ladder are successively impedance-scaled upwards, from the driving source to the amplifier input, the sensitivity of the filter characteristics to co mponent tolerances can be significantly decreased. Impedance tapering is ac hieved by the appropriate choice of component values. The design procedure, therefore, adds nothing to the cast of conventional circuits; component co unt and topology remain unchanged, whereas the component values selected fo r impedance tapering account for the considerable decrease in component tol erance sensitivity.