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JFET Characteristics and Biasing Lab


N-Channel junction field effect transistor characteristics laboratory experiment using the 2N5457 through 2N5459 series general purpose JFET. The experiment will expand on and verify theoretical concepts presented in the lecture course Analog and Semiconductor Devices through the use of bench top device measurements, hand calculations, and PSpice simulations.


Equipment and Materials:
1. DC Power Supply, 2 each
2. Digital Multimeter, 2 each
3. Curve Tracer
4.
2N5458 FET, 2 each
5. Assorted resistors



Procedure:

1. Design and use a test circuit incorporating bench instruments to measure the output (drain) characteristics of a 2N5458 JFET when VGS = 0; e.g. ID vs. VDS for VDS = 0 to 15V. Plot the results on graph paper.


2. Use bench instruments to find VGSoff (e.g., Vp, for the 2N5458 JFET).

3. Repeat step I for VGS = -1V.

4. Use bench instruments to measure the transfer characteristic for the 2N5458 JFET.

5. Use the curve tracer to measure the output characteristics and transfer curve for a 2N5458 JFET.

6. Repeat steps 1 through 5 for a second 2N5458.

7. Plot the curve tracer measured transfer curves for both JFETs on the same set of axes. Use graph paper. (See Figure 4 for an example.)

8. For the circuits shown in Figures 1, 2, and 3, use graphical and algebraic analysis to set the Q point at ID = 1mA and VDS = midway between 2VP and VDD, Use the transistor with larger IDSS for calculations. (Ref. Figure 4).


9. Construct the circuits shown in Figures 1, 2 and 3 using values calculated in step 8. For each circuit:
a. Measure ID and VDS (transistor with larger IDSS)
b. Change FETs and measure ID and VDS



*Included to establish Zin in a practical amplifier; not required for this experiment.

10. Perform PSPICE analysis on the circuits shown in figures 1, 2, and 3. Compare the results to the measured values obtained in step 9a.

Note: VTO = VP , BETA = IDSS / VP2


Conclusion & Discoveries:

By using bench test measurements, a more accurate analyses can be numerically determined for the 2N5458 JFET.


In starting this experiment it was found that one of the 2N5458 JFET's previously used in experiment one had failed so a replacement device was introduced for this experiment.

By examining the 2N5458 JFET devices using three separate techniques provides one to better understand the characteristics of the device and will assist in design specifications for complex circuits.

In closing, the 2N5458 JFET device was examined even more closely then in experiment one with the use of specific measurements taken from bench test equipment. It was discovered that the measurements taken off the curve tracer scope were very similar to those measurements taken. Also in a final comparison, Pspice simulations were ran and when compared to the gathered data, all data agreed within acceptable error limits. Overall the characteristics of the 2N5458 JFET devices were learned and a general understanding of the outputs will provide one with a better understanding for using the device in an applied application.


Graphics and Data
Figure 1: Output Characteristics of a 2N5458 JFET
Figure 2: Transfer Characteristics of a 2N5458 JFET 1
Figure 2.1: Transfer Characteristics of a 2N5458 JFET 1
Figure 3: Transfer Characteristics of a 2N5458 JFET 2
Figure 5: Transfer Function Characteristics for 1 and 2
Notes and Computer Simulations
Lab Notes Page 1 of 6
Lab Notes Page 2 of 6
Lab Notes Page 3 of 6
Lab Notes Page 4 of 6
Lab Notes Page 5 of 6
Lab Notes Page 6 of 6
Input Parameters

Electrical Engineering lab key words: JFET, junction field effects transistor, JFET characteristics, biasing, q point, n-channel, FET, gate, source, drain, IDSS, VGS, 2 port model, frequency response, transfer function, Pspice simulation, self bias, fixed bias, combinational bias, VDD, differential amplifier stage.

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