ENGR325 Electronics II

Lab #3 MOSFET Characteristics

 

Objectives:

                      To get acquainted with the characteristics of a typical MOSFET.

                      To get practice designing the dc bias for a MOSFET to achieve the desired Q point.

 

Procedures:

1. Use the same setup we used to measure the JFET I-V characteristics in Electronics I to obtain the I-V characteristics for either the 2N7000 or the BS170 N-Channel MOSFET. Carefully determine the threshold voltage at which drain current just begins to flow. Save the I-V curves for a number of values of VGS and include a copy of these characteristics in your report.

 

2. From the characteristics determine the value of the transconductance gain gm = ΔID/ΔVGS. Compare your value with the data sheet for your transistor. Also, you should be able to calculate a value for Kn for your transistor in the vicinity of the Q point (ID@5mA and VDS @5V)

 

3. Compare the shape of the I-V characteristics with those for the 2N5458 JFET and comment on any differences you see. Also, compare the value of gm for your MOSFET with the JFET.

 

4. Design a dc bias circuit to meet these specifications (similar to problem 3.28).

IDQ @5 mA

VDSQ @5V

VDD = 10V

VTN = your measured value

Kn = your computed value from measurements

Voltage across RS is approximately equal to VGS

 

5. Build the bias circuit that you designed using standard values of 5% resistors, and take measurements to determine how close you are to the above specifications.

 

6. Clearly present your findings for the MOSFET and discuss their meaning/application in your report.