# ADS Spiral Inductor on Silicon Example - Inductance Calculation Problem

1. ## ADS Spiral Inductor on Silicon Example - Inductance Calculation Problem

Hi all,

I have been looking for one of the ADS example workspaces, namely 'Spiral Inductor on Silicon'. There is a bunch of equations which also calculate the effective inductance and those equations are also mentioned in the thread, given below;

My problem is, whenever I run an EM simulation of the inductor in this example workspace I loose effective inductance. It becomes zero after simulation for every frequencies. I delete and unzip the workspace, again, to bring the graph showing the inductance back to life.

I checked the equations. They start with converting S matrix to Z matrix. Is it because I loose S matrix when I do EM simulation? Or what else could be the reason?  Reply With Quote

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2. ## Re: ADS Spiral Inductor on Silicon Example - Inductance Calculation Problem

From your description, it is not clear what goes wrong.
Have you checked the values/variables?

What is special for EM is that there is no "freq" variable, so we use indep(S) to get the frequency vector.  Reply With Quote

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3. ## Re: ADS Spiral Inductor on Silicon Example - Inductance Calculation Problem

There is an example workspace in ADS. It is called 'Spiral Inductor on Silicon'. When you just open this workspace, there are graphs showing effective inductance value of the spiral inductor in .dds file.

When I implement the stack up file provided by the foundry and then run the EM simulation, I start seeing 'zero' effective inductance. That was the problem and I was searching for its reason.

Now, while writing this post, one of my colleague showed me that there seems no via between the conductors of inductor. I checked the substrate file and indeed the last two up metals are not connected with each other through any via. So I defined that via in the substrate file and checked from the 3D view of inductor that the last two conductors are connected and run the EM simulation again. Thank God, a reasonable inductance value is obtained with this configuration.  Reply With Quote

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4. ## Re: ADS Spiral Inductor on Silicon Example - Inductance Calculation Problem

Ok, that is a VERY basic simple example with a single ended spiral. I thought you referred to equations and silicon type circuit models from the thread that you linked to.

If you are looking for differential (symmetric) inductors, you can also have a look at my RFIC Inductor Toolkit for ADS. The free demo version includes some useful shapes, and provides automated inductor synthesis.  Reply With Quote