Q value adjustable band stop filter (741) circuit diagram

As shown in the figure is a band-stop filter circuit with adjustable Q value .

This circuit is composed of an amplifier with a gain of 1, an RC double T network , and an RC single T network that determines the Q value of the circuit. Its Q value is variable, and changes in the Q value have no effect on the notch frequency. The stability of the notch frequency and Q value depends on the passive components in the T-shaped network . By selecting appropriate components, a stable filter can be made. The notch frequency ω0 and Q value in the figure are:

It can be seen from the above formula that the notch frequency is determined by the double T network . When R=1.8kΩ, C=0.02μF, the notch frequency f0=4.4kHz. In order to obtain a highly stable notch filter, in addition to using high-performance operational amplifiers, high-precision passive components must also be used . If the resistor R and the capacitor C have opposite temperature coefficients, and the temperature coefficients of R1 and R are also the same, stable ω0 and Q values ​​can be obtained.