Originally Posted by

**Mechatron**
I couldn't possibly have been more clear when I said that there is a voltage buffer with a high impedance input with a low impedance output. This output is the input to the bandpass filter.

I fully understood that. No problem there. However, you then say this:

The bandpass filter MUST have a low impedance input.

That makes no sense. At all. That's why I asked the specific questions I did, which you did not appreciate. So I can only offer general guidance that may or may not serve your (unstated) purpose.

The bandwidth should be 10 000 Hz, so the center frequency is then 5000 Hz.

Again, the second part of your sentence is not in any way a consequence of the first. The bandwidth is a function of Q, which may be specified independently of the center frequency. Stated another way, this is a second-order dynamical system, so there are two degrees of freedom. You are assuming away one of the degrees of freedom. That, and other statements/assertions like it, have conveyed your level of understanding. But you find my didactic style unpalatable, so we are stuck.

But if you still feel stuck about what would be the lowest resistor and capacitor value, then let's move on to something else;

We are stuck only because you lack the understanding of circuit theory to understand why answering my questions precisely is important.

What is the Q factor of the active bandpass filter (inverting band pass filter)?

Link to the filter in the link below:

http://www.electronics-tutorials.ws/filter/fil51.gif
The transfer function of the band pass filter in the link provided, is it only useful for plotting the frequency response?

And I wonder, at what point is an impedance high or low? At which values are they high or low?

Don't ask me why they didn't teach my about impedance, to the level I require at my University.

I recommend looking at a wiki article (e.g.) on impedance.

You may also benefit from studying the relevant sections in Horowitz and Hill, The Art of Electronics. There are also many handbooks on active filters that would give you useful background.

As to the transfer function, that's just a fancy name for "complete amplification factor" in this case. It will give you the gain and phase as a function of frequency. As such, it is a complex number at each frequency. The magnitude of that complex number is the magnitude of the amplification factor. The phase of that complex number is the phase of the output relative to the input.

There is no absolute "high" or "low" impedance (except, maybe, zero and infinity). The relevant issue is whether it's (much) higher or lower than some other impedance. That's what matters.