# EEsof EDA

3 Posts authored by: Vandana Duff

# Make a Bee Line to Keysight ADS' Linear Simulations

Posted by Vandana Duff Jun 1, 2017

Today we are going to talk about the different types of linear simulation tools ADS provides.  ADS sets up its linear simulations into three different categories:  DC, AC, and S-parameter simulation.  Let’s go over each of these simulations, and how easy they are to run in ADS.

1.  DC Simulation:

Per Ohm’s law(V=IR), you get steady-state DC voltages and currents.  Capacitors are treated as ideal open circuits, and inductors are treated as ideal short circuits.  DC convergence occurs when 2 conditions are met:  Voltage change at each iteration is zero and Kirchoff’s Law is satisfied, meaning the sum of the node currents equal 0.

DC Simulation controller & sweep VAR

The DC Simulation icon translates to the following blue image in your workspace.

Once you double-click the VAR eqn icon, you can select the option to sweep, which allows you to sweep a parameter, but it must be declared as a variable.  To declare a variable, or a variable equation, select the following icon:

2.  AC Simulation:

An AC Simulation is performed in the frequency domain.  You can simulate a single frequency point, or across a frequency span in a linear or logarithmic sweep.

AC Simulation Controller

The following is what the default settings look like in your workspace.

AC simulation is either a linear or small signal simulation and the frequency is defined in the controller, not the source.  On-screen parameters can be set in the Display tab.  AC sources are identified as:  V_AC, I_AC, and P_AC.

3.  S-Parameter Simulation:

S-parameters describe the response of an N-port network to signals to any of the ports you want measurements from in terms of power ratios.  For example, an S12 measurement is the response at port 1 given the input power wave at port 2.

Results of an S-Parameter Simulation in ADS include:

• S-matrix with the complex values at each frequency point
• Gamma value (complex reflection value)

• Marker readout for Zo (characteristic impedance)
• Smith chart plots for impedance matching

These results are similar to Network Analyzer measurements, so if you don’t have one, you can simply simulate what you are looking for in ADS.

If you don’t have ADS get a free 30-day trial here.

S-Parameter Simulation Controller

The link below guides you through examples of an AC and S-Parameter simulation, as a visual walk through experience.

You made a bee line for understanding linear simulations!  The best way to learn is by doing, so check out the attached PDF that will walk you through an amplifier design.  This gives you the chance to see applications of the different types of linear simulations when designing.

Posted by Vandana Duff May 15, 2017

You successfully created a Low Pass Filter in ADS by following my example in the last blog post.  Let’s build off what you know from the Low Pass Filter exercise and learn how to add flexibility to your design, including PDKS and compare an ideal schematic to a schematic with external vendor’s components.

What’s a PDK?

You now want to design a low noise amplifier and need to select what type of process the device needs to be fabricated, whether it’s Si, SiGe, GaAs, or other high frequency manufacturing processes.  A Process Design Kit (PDK) contains active and passive device components with symbols, parameterized layouts, simulations models, and much more for IC design.   A PDK provides both the opportunity to shorten the product design-cycle for high frequency chip design, and the capability to simulate your chip exactly as you expect it before the chip is manufactured.  Some features of a PDK may include:

Schematic Example

Parametric Layout Cells

Design Rule Checks

Simulation Results

Layout Options

Vendor supplied models provide more realistic results, that may include parasitics.  Once your LNA has been created with the PDK of your choice, you can now compare your data to an ideal design by adding your PDK design, and ideal when setting up your plots.  The data can be viewed in several plots, including rectangular and smith chart plots. When setting up your plot, you can plot several traces, which can include any S-parameter measurement, in dB or log.

The lab attached at the bottom shows you how.

What are Cell Views?

Another capability is cell view, which is a way of capturing a design.  It has multiple views and can define a design in that cell using a schematic.  Another way to think about it is within a hierarchy type setting for coding, like pointers in the programming language C.  This capability simplifies what can be viewed in your workspace.

Check out the attached lab with step-by-step instructions that walk you through the topics we covered:

• What is a PDK?
• Data Comparison
• What is Cell View?

For other getting started topics, check out our video playlist:

# Design a Low Pass Filter in 3 Steps

Posted by Vandana Duff Apr 27, 2017

I was excited and intimidated when I took the opportunity to write this blog post for Keysight EEsof EDA.  I had some exposure to what Keysight ADS is and what you can use it for in college – but to write tutorial blogs to assist engineers who design the next satellite that will be launched into space?  That seemed like a daunting task.

I participated in a training session that walked me through designing a Low Pass Filter and I wanted to share it with you.

I was able to design this low pass filter in 3 easy steps.

If you don’t have ADS get a free 30-day trial here.

Select only the Analog/RF library, and uncheck all others if needed.  This means that the components from the RF/Analog library will be available for later.

Name your library, and select the Standard ADS Layers .0001 mil layout resolution.  Make sure everything looks correct, and click “Finish”.

By expanding to cell view, you can now see that your schematic pops up in your workspace.

Select the components you need by clicking on the component and dropping it on the schematic page.  You can rotate parts by using the toolbar icon or cursor on or use the cursor to drag the handle on the component.  Connect up the components with the wire button, and don’t forget to ground your circuit!

To change the values, units, or even the name of your component, double-click the component and make changes as needed.

Step 3:  Set up an S-Parameter Simulation.

Select the “Simulation-S_Param” on the palette and drop it on your schematic area.  Insert the port terminations, and make sure to ground them.

To set up the simulation, double-click the gear on the schematic. Change the step size and frequency range.  I used a step size of .5 going from 1 GHz to 10 GHz.  Click OK, and now you are ready to simulate!

Click the gear (alternatively, use F7), select simulate, and fix any errors that may have shown up.

ADS has a variety of different plots.  I’m going to create a rectangular plot.

Select the rectangular plot and select which S-parameter measurement you want to use, select your units (S-parameters are usually measured in dB), and click ok. You can zoom in and out with your mouse, and view all with this icon:

Put a marker on the trace, and you can move them around with the red arrows.

Now I’ve created a low pass filter and plotted an S-parameter measurement.

That wasn’t so bad, was it?

I skipped a few steps. For a complete set of instructions check out the attached PDF at the bottom of this blog post.

For other getting started topics, check out our video playlist: