All content Copyright 2022 Parallel Systems Ltd.

 

Reference Schematic:

1. Open the WC project, File>Open>Project.

This circuit uses the VDC, R, Rbreak, C, 0 and Q2N2222 parts.

Note that Rb2 is a Breakout resistor.

Name the OUT net.

 

2. Edit the PSpice model for the breakout resistor to have the following definition:

.model Rbmod RES (R=1 dev=5%)

 

3. Create a simulation profile for an AC Sweep simulation analysis as shown in the graphic that follows.

 

 

4. Configure a Worst-Case analysis as seen in the next picture.

 

 

5. Left-click>More Settings and configure the additional settings as shown in the next graphic.

 

 

6. Left-click on the “OK”s to close the dialogs.

 

7. Run the simulation.

 

8. Examine the output file to see the worst-case result.

An excerpt from the file is below.

WORST CASE SUMMARY

******************************************************************

The range is ( 9.90000E+04 to 1.01000E+05)

RUN MINIMUM VALUE

WORST CASE ALL DEVICES

15.169 at F = 100.0000E+03

( 37.653% of Nominal)

JOB CONCLUDED

This is reporting that the result for the worst-case run is 15.169 at frequency = 100k.

Make a note of this value.

 

Now, move on to take a closer look at what is being displayed. A parametric analysis is going to be run on the resistor value to see that WC analysis will sometimes give us true worst-case and sometimes not.

 

9. Keep the Probe window open and go back to the schematic.

 

10. Create a new simulation profile, the AC sweep analysis will not change (a linear sweep from 90K to 110K with three points).

 

11. Set up a parametric analysis as shown in the graphic below:

 

 

12. Left-click>OK to save the settings and close the dialog.

 

13. Run the simulation and examine the results in the Probe window. A new tab is added to the Probe window for this profile.

 

14. Left-click the Performance Analysis toolbar button.

 

15. Add the trace YatX(V(OUT),100k). You should see the results as shown.

 

16. Turn on the cursors, Trace>Cursor>Display from the top menu

 

17. Left-click the Cursor Search toolbar button

 

18. Type search forward level(15.169) in the Search Command field.

 

(To find the value from the Worst case run)

 

19. Left-click>OK to move the cursor to the specified point on the trace.

 

20. Left-click the Mark Label toolbar button to mark the point on the trace.

 

21. Looking at the trace, notice how the selected point really is the worst-case result in the + / – 5% value range.

(The 0.95 multiplier is equivalent to -5%, the minimum value from the tolerance)

 

 

End of Lab

 

 

All content Copyright 2022 Parallel Systems Ltd.