Monte Carlo Simulations Experiments 8 and 9

Monte Carlo Simulation Monte Carlo simulations in PSpice can be run as either: a worst case analysis where the maximum deviation from the nominal values of each component are used in the calculations a statistically-driven variation from the nominal values of the components using a bell shaped curve for the distribution of deviations.

Prior to Monte Carlo Set up a Simulation Run using Analysis Setup You must select one of the other types of analysis first Click on DC Sweep Pick either of the voltage sources to sweep Make both the start and end values equal to the nominal value of the voltage source Pick any value for the increment. Click OK.

Analysis Setup Select Monte Carlo/Worst Case In the pop-up window, enter the number of runs in MC Run At least 500 is recommended for statically reasons Not more than 2000 due to run time issues Do not unselect the Bias Point Detail

Monte Carlo or Worst Case In Output Var: box, enter V(node name) or V(component:node) This is the advantage of labeling the nodes. So, you will enter V(X) and V(Y) for the two Monte Carlo simulations that are required. Note that you will also have to put a voltage marker on to the circuit schematic no matter what you put as the output variable If you have selected a DC Sweep, select DC as the Analysis Type.

Monte Carlo or Worst Case Select All on the MC Options. Then, click OK. Once the schematic is saved, you are ready to run the simulation.

Open the Plot Window Click OK.

Output Plot is a Histogram

Histogram The shape of the histogram and the values of the mean, maximum, and minimum voltages at node X will differ every time you run the simulation because a random number generator is used to determine the values of each of the five resistors in every one of the runs. The differences in the mean, maximum, and minimum values are negligible if sufficient number of runs are entered in the MC Run box when you set up the simulation. The shape of the histogram becomes more symmetrical as the number of runs approaches 2000.

Your Experimental Results If your voltage supplies are exactly +5 V and +9 V, then the voltages that you measure at nodes X and Y should fall somewhere within the range from the minimum to maximum values of the voltages calculated during the Monte Carlo simulation. If you measure the actual values of the +5 V and +9 V supplies and enter them into the simulation, then there is a 100% likelihood that your measurements will fall within this range.