This application note provides design formulas and a circuit example for a Dual-T notch filter using precision operational amplifiers.
This application note discusses a design example for a Dual-T notch filter, which is part of a series of small guides introducing discrete circuits for precision operational amplifiers. The document covers the structure of the Dual-T notch filter, design formulas, adjustment methods, and related parameter explanations. It highlights that while the passive implementation has a fixed Q of 0.25, applying positive feedback to the reference node allows for adjustable Q values and deeper notch depths. The note explains that using standard 1% components can achieve up to 60 dB of notch depth, with typical values ranging from 40 to 50 dB. It also notes that achieving maximum notch depth involves removing resistors R4 and R5 and the corresponding operational amplifier, directly connecting the C3 and R3 node to the output. This manual is written in Chinese.
The Q value is fixed at 0.25.
Up to 60 dB of notch depth can be achieved.