Orcad 10.3 Tutorial

 

Introduction

This tutorial is designed for the beginning student interested in simulating and designing circuits using Orcad 10.3.  PSpice circuit simulation packages are tremendously useful for verifying designs, refining designs and teaching us how circuits work. While they can never replace an initial hand design or actual hardware, they can be used to test different design configurations, various component values and signal inputs and other parameter variations.

 

OrCad 10.3: This is a professional version of the software. There are over 2 million (!) parts in the library and there is no node limitations (except as imposed by computer memory of course.) It has the disadvantage that you must be at a lab computer to use it.

 

Getting Started

To start OrCad Capture, go to the start menu highlight OrCad Release Edition 10.3 and then OrCad Capture. Under the File pull down highlight New and then click on Project.... Give your project a name, click on the circle next to Analog or Mixed A/D and type in a location in your file space. Click ok and a pop up window will appear. Click the circle next to Create a blank project then ok. On the left you should see an icon with filename.dsn. Click on this and then click on SCHEMATIC1 folder and then PAGE1.

Now you should be on a schematic with a toolbar which is quite similar to the one to which you might be accustomed from PSpice.

In order to ensure that you have all the PSpice parts available to simulate circuits go to the Place pull down menu and highlight Part. In the pop up window click Add Library and go into the PSpice folder and add all the libraries in that folder.

 

 

Basic DC Analysis, DC Bias

 

The toolbar on the right-hand side of the screen is the one associated with building the circuits.  The description of each of the significant buttons for analog simulations is shown below

 

  This is the Place Part Button.  You can place resistors, capacitances, inductance and source on the screen through this button.

 

  This is the Place Wire Button.  You will use this to connect up the parts with virtual wires.

 

  This is the Net Alias Button.  It is useful for renaming nodes when using probe.

 

  This is the Place Ground Button.  This button is very important.  Forgetting to place a ground in your circuit is a common mistake among all users.

 

For example, to place a source on your schematic screen, click on the Add Library button and add the library called source.  This library includes all of the sources you will use in simulations.  After you have added the library (the default path to it is Program Files/OrCad Lite/Capture/Library/Pspice if you couldn’t find it), scroll down to the bottom of the list and select VSRC.  Since we know that VSRC is in the source library, we can look at just the elements within the source library by clicking on it in the lower left window. 

 

  Go ahead and place one VSRC anywhere on the schematic.  You will notice that your mouse still has the outline of VSRC under it.  If you had to place multiple voltage sources in the circuit, you only have to get the part once and you can place as many as you want to onto the schematic.  Right-click and select End Mode.  The outline of VSRC disappears.

 

Name nodes: there are three ways to name nodes. Here we will introduce two.

 

1.        Use the power symbols. Go to the Place menu and select Power, you can choose any part that starts with VCC. Connect this part to your circuit at the node and name it as you would.

2.        Go to the Place menu and select Net Alias, name the net alias and press ok. A small box will appear on the cursor. Move the box to where you want and place it.

 

Before you do simulation, put markers on your circuit, which is going to be your simulation results. To put a marker, go to the PSpice and select Marker.., choose the marker type you prefer and place it to the node you want to monitor.

To simulate a circuit, go to the Pspice menu and select (about the only thing you can select) New Simulation Profile.  You get a window with a lot of tabs on top.  Select Analysis (if it isn’t selected already) and change the Analysis Type to Bias Point. Now click OK.  We have now told Pspice what it will do to simulate the circuit.  We now have to run the simulation.    is the button that runs Pspice.  Click it.  A new window opens up.  In the lower-left corner of that window you may or may not have gotten any errors.  If the last line says Simulation Complete, you had no errors.  Close this window and go back to OrCad Capture.  Your circuit should now have voltages on it which tells you the bias for different nodes.

 

FYI:  Sometimes you have a small circuit to simulate and Pspice gives you such a large area to work with that you have a hard time seeing the circuit.  Go to the View menu, select zoom, and you can zoom in and out of the schematic.  The Zoom Area is the most useful because you can construct your circuit and then zoom in to print out a nice picture for your professor.

 

 

Parametric DC Sweep

 

A parametric DC sweep means varying the parameter or value of a component.

 

In order to do a sweep of the values of a component, let’s say resistor value, you need to change its value from a fixed number to a variable text. The following is an example procedure:

 

1.      Click on the resistor value and change it to {RVAL}.

 

2.      Now go to the Place Part menu, under the SPECIAL library, select a “part” called PARAM. If this library is not on your list, you will have to add it using the Add Library… button. Place it anywhere near your schematic. Double left-click on it, bringing up the [Property Editor].

 

3.      Left-click on the New Column button give the variable a name, in this case our variable name RVAL, and a value (one that is reasonable for your design). This value will be used as the default condition if you choose to do another type of simulation on this design. Apply it.

 

4.      Highlight this new column. Left-click Display… and then activate the button labeled Name and Value. Close out the property editor.

 

5.      To start the simulation process, open the PSpice menu. The first choice available is New Simulation Profile. Left-click on it and give the new simulation a Name. Left-click Create and the next screen will appear.

 

6.      Choose the analysis type as DC sweep. Activate the Global parameter button and add the name of your parameter that you are sweeping. In this example it is RVAL. The sweep type will be Linear. Put in the Start value, End value and Increment you want. Apply it and hit OK.

 

7.      Go try it, run PSpice and see the results. If everything was entered correctly, the simulation will run without any errors and return a plot about V vs. resistor value.

 

8.      Add a trace by left-clicking on the Trace menu and Add trace… 

 

 

Sensitivity analysis

 

Sensitivity causes a DC sensitivity analysis to be performed in which one or more output variables may be specified. You would use the sensitivity setting for discovering the maximum range of circuit performance and the causes of extreme operation. The sensitivity analysis is performed under Bias Point analysis type. Following is an example procedure:

 

1.      To start the simulation process, open the PSpice menu. The first choice available is New Simulation Profile. Left-click on it and give the new simulation a Name (can be corresponding to your simulation). Left-click Create and the next screen will appear.

 

2.      Select Analysis and change the Analysis Type to Bias Point. Check Performance Sensitivity analysis (.SENs). Type in the Output Variable (for example: V). Apply it and hit OK.

 

3.      Run PSpice and see the results by click PSpice ŕ View Output File. In the output file, you can see the DC sensitivities of the output V with the resistances.

 

 

Monte Carlo /Worst case Analysis

 

We can expect circuit parameters to vary. For example a 5% 1K resistor can be expected to have values between 950 ohms and 1050 ohms depending on the probability distribution of values. In a Monte Carlo simulation a circuit is simulated a number of times. Each time a parameter value is changed. PSpice produces charts showing distributions of circuit performance measures derived from the simulations.

 

Worst case analysis helps you to find out the worst situation in the circuits with the tolerance of components.

 

To performance the Monte Carlo/Worst case analysis, the tolerance of the circuit components need to be defined first.

 

1.      Double left-click the component and bring up the [Property Edit].

 

2.      Find Tolerance and input the tolerance you want. Highlight the Tolerance column and left-click Display… and then activate the button labeled Name and Value. Close out the property editor.

 

3.      To run the Monte Carlo analysis, go to menu PSpice, select Analysis tab and change the Analysis Type to DC Sweep and Primary Sweep. Put in source and range.

 

4.      Choose Monte Carlo/Worst case, select Monte Carlo. Put in output variable, number of runs for Monte Carlo. Apply it and hit OK.

 

5.      In last step, you could also edit More settings.

 

6.      Run PSpice and choose plots to be displayed.

 

7.      To run the Worst case/Sensitivity analysis, repeat step 3.

 

8.      Choose Monte Carlo/Worst case, select Worst case/Sensitivity analysis. Put in output variable and tolerances you want to vary. Apply it and hit OK.

 

9.      Run PSpice and see the results.