BPF problem microcap

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praveen450

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Hi,

I'm implementing a BPF using Opamp and the microcap circuit file is attached to this post.

My question is

1) When I change vcc from 8 to 0V, when using dual power supply (12V) the filter is having gain. And when I'm using vcc open, I'm not seeing gain

2) When I remove vcc when using dual power supply the filter is having no gain.

3)If I have single power supply and biasing vcc at 6V gives me gain.

My question is when using dual power supply,

I should be able to get gain at no bias i.e when vcc is not connected in the circuit. Then why my active filter is not giving me a gain?

Help me with that..
 

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  • Activefilter.png
    11.5 KB · Views: 64

I simulated your bandpass filter. It is extremely simple so its highpass and lowpass slopes are gradual. It peaks at about 25kHz. Its gradual slopes produce plenty of output at 2.5kHz and at 250kHz.
It is not actually an active filter. It is a simple passive RC highpass followed by an opamp integrator.

Since the opamp has a dual polarity supply then the "bias voltage vcc" should be 0V. Your R7 should connect to a series capacitor to 0V or directly to 0V.

The gain calculates to be 30 times but since the very simple highpass and lowpass filters interfere with each other the circuit has a gain at its peak frequency of 20 times.
 

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  • bandpass filter.png
    8.8 KB · Views: 57

According to your designations, Vc is + and Vee is - then you have Vcc, which should be gnd or midpoint of whatever you use for +/- supplies.

What gain do you get and need now?
 

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