# Make a Bee Line to Keysight ADS' Linear Simulations

Blog Post created by Vandana Duff on 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.