Hi there. The enclosed schematic shows an 'Active Twin T Resonant Peak Filter.' The filter which is fed with a square wave, produces a sine wave output and peaks perfectly at the desired frequency of 250Hz. However being a resonant circuit with a rather high 'Q', the output is very slow to decay. This effect is even more pronounced if I choose a lower frequency. (say 150Hz and changing the components accordingly) It can be up to about 1 second before the output collapses completely. The application that I'm using this circuit for requires a fast decay of the output signal. If I try to reduce the value of the feedback resistor, it starts to impact on the frequency that the filter peaks at. Is there a modification I can make to this circuit, or additional circuitry that I can add, to improve the decay of the output signal without impacting too much on the Q of the circuit or the resonant frequency it's tuned to? Thanks for any help.

 

If you want the output to rapidly stop, you could add an analog switch on the output that opens, as soon as there's no input signal.

If you wanted a slower decay, you could using a variable gain element, such as an analog multiplier to reduce the output amplitude.

 

If you want the output to rapidly stop, you could add an analog switch on the output that opens, as soon as there's no input signal.

If you wanted a slower decay, you could using a variable gain element, such as an analog multiplier to reduce the output amplitude.

Thank you so much. Both very good ideas!