# Gyrator circuit that simulates an inductance

1. Apr 30, 2006

### infirmus

Hi,

I'm working on an assigment where i'm given an circuit which contains two op-amps and I am told it is a Gyrator circuit that simulates an inductance.

I am required to calculate the values of the resistances and the capacitor in the circuit so that the gyrator has an inductance of 11.11mH and then simulate the circuit (in Electronics Workbench) and show a demonstrator the results..

Only problem is when I simulate the circuit I cant get it to act like an inductor.

I'm not sure if the inductance is between the Vin and Vout (floating?) or between Vin and ground.

The circuit diagram I have posted below shows values for the capacitor and resistors that I calculated from finding an expression for Zin (input impedence). Zin=(R1*R3*R5)/(Zc*R4)

The expression for the inductance that I found was L=(C*R1*R3*R5)/R4
The resistances had to be between 0.1k ohm and 10k ohm and the capacitance between 10pF and 500pF. I just arbitarily chose the values of the resistors and capacitance so the inductance was 11.11mH. Is this OK or is there some other condition which should have been met?

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2. May 1, 2006

### Staff: Mentor

Pretty funny -- I googled gyrator tutorial, and got lots of hits....for washing machines! LOL.

But here's a link into wikipedia for a simple gyrator circuit in case you haven't already seen it:

http://en.wikipedia.org/wiki/Gyrator

There are also other links on that page to more complicated gyrator circuits. The typical gyrator inductor circuit is not floating like yours is -- it looks like an inductor with one side grounded. But a floating inductor gyrator circuit makes sense for a general element. To answer your question, yes, it looks like that circuit is meant to simulate an inductor's two end points between Vin and Vout. In your SPICE simulation, how are you trying to see if this circuit behaves like an inductor? Are you connecting Vout to a load resistor and driving a square wave voltage source into Vin, for example?