inductor using capacitors

this question was faced by one of my seniors during an interview
how do we realise a inductor using 1 op-amp and 3 capacitors

A.Anand Srinivasan said:

this question was faced by one of my seniors during an interview
how do we realise a inductor using 1 op-amp and 3 capacitors

Click to expand...

using a circuit sometimes called gyrator, it's possible to simulate an inductor.
This circuit use one op-amp, one capacitor and two resistors.

You can visit the following links:
https://en.wikipedia.org/wiki/Gyrator
**broken link removed**

stefano

gyrator...

It's (as I've seen it) an op amp whose output is fed back to the input node, so the two sum to create the proper phase shift.

If you determine the equation for the impedance of an inductor having series and parallel resitances, the op amp circuit will give you that same impedance, using R and C values as necessary, at the input node.

Note that the Q of the "inductor" is low, so don't expect much of a sharp tank. However, it works well enough to make a wider-bandwidth notch for an audio equalizer, where I came across the circuit years ago and it puzzled me into learning about it as much as I have. (There is no output! It's a coil to ground.)

It's, like most of electronics, all about math.

It is also called a "negative impedance converter," but I don't have much on that ...yet. It shows the source the negative of the impedance that's actually there?? I'm sure it's all about math.

I derived the circuit to prove it worked to create the same impedance, but the NIC thing in it still puzzles me. (There ae two NIC's in it somehow??)