Bringing the Sallen-Key Biquad back to work

In the design of active biquads with positive feedback frequently referred to as Sallen-Key networks the assumption of a low quality- or Q-factor is recommended in order to keep the active sensitivity at a low value. In this paper it will be shown that it is possible to design and to implement the Sallen-Key biquad even in the high-Q case with reasonable sensitivities.

The method is based on the unity gain version of the biquad and as unity gain buffer amplifiers are readily manufactured in integrated circuit technology the results may be very useful in the fabrication of integrated analog filters in voltage-mode as well as current-mode technology. As an example we will choose the band-pass biquad as biquads of this type often has to be designed with high-Q values.