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Analyzing the DC Characteristics of the example Circuit

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B. Program Schematics Startup.
        1. For Window 95/98/NT users, go to the Start Menu and left click the mouse.
        2. Under the Start Menu, find Programs and left click the mouse again.
        3. Find the folder named either DesignLab Eval 8 or Microsim Eval 8 and again left click.
        4. Finally, left click on Schematics. The Schematics section of the PSPICE program should start up.

C. Load or Build the Example Circuit.

a. To load up the circuit.
If you have already built and saved a schematic file of example circuit, load it up by selecting File - Open in the schematics. If you have not saved the circuit, the example circuit may be downloaded.

       To download Right Click the mouse over the link and choose Save Target As... or Save Link As..., select target directory and then save.

Download Low Pass Filter Example Schematic Circuit (LPFilter.sch)

b. Build the Circuit.
If you have not yet built the circuit, follow the instructions in the section indicated below showing how to build the circuit.

How to Build Example Circuit (p-build.html)

    The example circuit should look something like this:

D. Insert Input Source.

To properly analyze a circuit, a proper input source has to be connected to the input of the circuit. In this case, we have to connect a source to the left end of Resistor R1.

1. For a DC or AC type analysis, one of possible input source is VSRC. So go to Draw - Get New Part and select VSRC. Insert the + end of the source at the input of the circuit and add a GND_ANALOG to the - end of the source.

2. Now, set up VSRC by double left clicking the mouse on it. Change the values of DC to 0 and AC to 1 remembering to click on Save Attr after each change. Finally Click on OK. What has been done here is to provide the circuit with a AC source of 1 Volt biased on a DC point of 0 Volt.

1. Setup the the desired type of analysis by going to Analysis - Setup.

a. Change Name to V3, since the name of the source inserted is V3. Of course, if the name of the source is different, change the name accordingly.
b. Enter -10 as the Start Value and +10 as the End Value with an Increment of 0.1. This means that the circuit will be analyzed with a DC input voltage from -10 Volts to 10 Volts with a voltage increment of 0.1 Volts. Remember not to enter any spaces between the characters.
c. Click on OK.

3. Back on the Analysis Setup Screen, make sure DC sweep and Bias Point Detail are Enabled (their corresponding boxes ticked). Bias Point Detail allows the user to examine the operating points (or DC points) of the circuit. Click on Close.

4. Using File-Save As Save the circuit with another name, for example LPfilter1.sch.
 

1. To Start the DC analysis, Go to Analysis - Simulate. After a brief while of calculation, P-SPICE will display the MicroSim Probe Window.
    If there are any errors, check the circuit, the values for the components.

2. To choose which plot to trace, select Plot - Add Traces. Select V(U1:OUT) which is the output voltage of the Operational Amplifier and V(3:+) which is the positive terminal of the input source. The box Trace Expression at the bottom of the window indicates the outputs that will be traced. Click on OK.

3. We should see the trace of the output and input voltage displayed. In this case, the output voltage is the Green line and the input is the Red line. The results seem to be correct as DC wise, the circuit is an inverting amplifier of a gain of 1. Therefore V(out) = - V(in)

 
4. If there is a need to examine the slopes in detail, go to Tools - Cursor - Display. PSPICE  will provide 2 cursors for value examination. One cursor is controlled by the Left Hand Mouse Button and the other one by the Right Hand Mouse Button.

a. Left-Click on the Green Square by V(V1:OUT) (at the bottom of the display), now move the mouse across the graph while Holding down the Left Button of the Mouse, the Left Cursor should move along the green line with the coordinates values displayed in the Probe Cursor window.
b. Right-Click the mouse on the Red Square by V(V3:+), now when Holding down the Right Button of the Mouse, the Right cursor will move along the Red Line with its coordinates values displayed in the Probe Cursor window.