Electronics - Operational Amplifiers - Discussion

LPF-Integrator (R1C1) is in series with HPF-Differentiator (R3C2).

LPF allows low frequencies & HPF allows high frequencies. Intermediate frequency bands are blocked. Hence it is a band-stop filter.

The given answer is correct because of a parallel combination of low pass filter and high pass filter. So the entire spectrum is given to both the filters. If there is an overlapping (upper cut off frequcy of lpf is greater than lower cutoff frequency of hpf) then it acts as a band stop filter.

It's not a bandpass filter because in a bandpass filter the low pass filter is followed by high pass filter (i.e, if they are cascaded or series combination) Before identifying a filter characteristics once check whether they are cascaded or in sires along with there characteristics and order.

By observing the capacitor actions at lower frequency and higher frequency the given circuit is band pass filter.

Thanks all for the explanation.

If you will calculate using KCL on the junction where R1, C2 and C1 are connected you will find a equation then replace the Vn=Vp=R4/ (R2+R4).

A band stop filter is like (C1+C2) and band pass filter is like (C1-C2).

By this you will get to know that the circuit is band stop, as the equation contains (C1+C2), if we use C1=C2, we will get Notch filter.

I have solved this, if I am wrong, correct me.

Thank you.

At angular frequency = 0 capacitor behaves like open circuit but shows some output values. So low pass filter and at angular frequency = infinite capacitor acts as short cut and shows some output value i.e. high pass.

Conclusion: A range of frequency is rejected (band stop).

At infinity all capacitors are open so it will give output and at 0 all capacitors are short circuited so then also it will give output so we call it that it is bandstop filter.

This is narrow band pass filter.

I too agree with @Madhavi. It seems to be band pass filter by analyising the circuit at f=0 and f=infinity.

Low pass filter succeeded by high pass filter in the above figure if we observe and hence according to their responses we get band stop filter's response..so ans is d