MOSFET Characteristics

This lab has two parts; first a simulation part and next a practical portion.

Simulation:

ORCAD is to be used to investigate the characteristics of an N-channel MOSFET.

Draw the following circuit in ORCAD:

MOSFET Circuit
Figure 1 - MOSFET Circuit

The version of ORCAD on lab computers is a limited version and does not include many models. IRF150 has been chosen because its model is available. Notice that there is a current marker at the Drain of the MOSFET. This facilitates the curves that this lab is looking for. Now create a new simulation profile and set the Analysis type to "DC Sweep". Follow the settings shown in figure 2.

New Simulation Profile
Figure 2 - Simulation Profile Settings

Run the simulation at this point. You should get a graph of drain current vs. VGS.

Next step is to find the effect of temperature on the drain current. Follow the steps in figure 3 to set up the temperature sweep. The list of temperatures to use are 0, 27, 50, 75 and 100 degrees C.

Temperature Sweep Settings
Figure 3 - Temperature Sweep Settings

The resulting graph from running the simulation would have 5 curves of drain current for each temperature again vs. VGS.

The next step is to do a parameter sweep. The parameter to sweep is VGS. The following figures show the process to achieve this goal. First is to set VDS as the primary sweep.

V<sub>DS</sub> as the Primary Sweep
Figure 4 - VDS as the Primary Sweep

Next is to set VGS as the sweep parameter.

Add VGS and its Nominal Value
Figure 5 - Add VGS and its Nominal Value
Circuit with PARAM Added
Figure 6 - Circuit with PARAM Added.

Note that VGS has to be in brackets for its values. Modify the simulation profile to include parameter sweep.

Parameter Sweep Settings
Figure 7 - Parameter Sweep Settings

If you run the simulation, you should see a graph with several curves for each value of VGS.

Lab:

Assemble the circuit shown in Figure 8. Apply a signal as indicated in the figure. Vary the input frequency up to 10 MHz by 10 points per decade and for each frequency measure the amplifier gain. Create an Excel sheet with the range of frequencies, Vout/Vin and 20*log(Vout/Vin). Graph the log ratio versus frequency. Repeat the same procedure for C3=22nF. Explain your findings.

Circuit to use as an amplifier
Figure 8 - An Amplifier Circuit