ABSTRACT
The multiple-feedback (MFB) filter is also called the Deliyannis filter; it is most familiar as a bandpass filter working at a modest Q, but the basic configuration can also be used to make lowpass and highpass filters. MFB bandpass, highpass, and lowpass filters all inherently give a phase inversion. The MFB highpass filter is the multiple-feedback lowpass filter with the resistors and capacitors interchanged. For simple lowpass and highpass applications the Deliyannis-Friend filter requires more precision passive components than the Sallen & Key and is harder to design. Most biquad filters are composed of three amplifier stages in a loop. It is also possible to make biquads using just one amplifier with passive components around it, and they are unsurprisingly known as single-amplifier biquad (SAB) filters. The Akerberg-Mossberg filter uses three amplifiers. It is best suited to lowpass applications. It is a combination of an Antoniou active compensated non-inverting integrator and a leaky integrator.
