The circuit shown in figure rejects the frequencies around the value for which it was calculated. The formulas that allow determining the frequency as a function of the components are given next to the diagram. The high input impedance of the operational amplifier allows the use of resistors of high values and with this it is possible to obtain a high Q factor. The power supply must be symmetrical and other operational amplifiers of the same characteristics must be used. Note that the components of the twin T must maintain the ratio of values indicated by the formulas.
