New universal biquad filters using only two unity-gain cells

New current-mode and voltage-mode universal biquad filters are presented using only two unity-gain cells (one current follower and one voltage follower) in each configuration. The proposed filters employ one less follower than in the literature to date. The filters can realize highpass, bandpass, lowpass, notch and allpass responses without any changes in the circuit topology. The circuits enjoy the following advantages: minimum number of active elements, no component-matching condition and low active and passive sensitivities.