An apparatus for filtering an input signal includes a first second order filter section having an output and an intermediate output, a second second order filter section having an input connected to the output of the first second order filter, and a gain stage coupling the output of the first second order filter section and the intermediate output of the first second order filter section to the output of the second second order filter section. The gain stage is coupled such that a transfer function between the output of the second second order filter section and the input of the second second order filter section is a biquadratic transfer function.