Gyrator circuit that simulates an inductance

[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 can't 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?

 

[berkeman]

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?

 

[ravenprp]

Hi there,

It sounds like you are on the right track with your calculations for the values of the resistors and capacitor in the Gyrator circuit. However, there are a few other conditions that need to be met in order for the circuit to accurately simulate an inductance.

First, the input signal needs to be connected between the Vin and Vout pins, as this is where the simulated inductance will be present. The input signal should also be a sinusoidal waveform with a frequency within the range of the circuit's bandwidth.

Second, the op-amps in the circuit need to be configured in a specific way in order for the Gyrator to work. One op-amp should be configured as a non-inverting amplifier, and the other should be configured as an inverting amplifier. The output of the non-inverting amplifier should be connected to the input of the inverting amplifier, and the output of the inverting amplifier should be connected to the input of the non-inverting amplifier. This creates a feedback loop that allows the circuit to simulate an inductance.

Lastly, it's important to make sure that the values of the resistors and capacitor fall within the appropriate ranges for the circuit to function properly. It's also a good idea to double check your calculations and make sure you are using the correct equations for the circuit.

I hope this helps and good luck with your assignment!