A high‐frequency compensation of sallen‐key circuits based on pole sensitivity

Abstract

AbstractThe Sallen‐Key circuit is one of the most practical circuits for active RC filter. As is well known, it is composed of the amplifier with a finite gain, for which an operational amplifier has been employed from the viewpoint of the cost and the easiness of the design. On the other hand, due to the finite gain‐bandwidth (GB) product of the operational amplifier, the cutoff frequency of the realized filter is restricted to below 10 kHz. This paper proposes a design method where a passive element is added to the Sallen‐Key circuit. By this scheme, the effect of the finite GB product is compensated, and a high‐frequency circuit is realized. the pole‐sensitivity of the transfer function with respect to GB product is also reduced. By employing the proposed method, not only the effect of the first‐order pole on the transfer characteristic due to the change of GB product, but also the effect of the second‐ order pole can be minimized. Finally, as a design example, a bandpass filter with fO = 100 kHz and Q = 1 is constructed. Its operation was verified by experiment.