EE331LE3rev6 - Experiment-3 Experiment-3 JFET and MOSFET...

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Experiment-3 R. B. Darling EE-331 Laboratory Handbook Page E3.1 Experiment-3 JFET and MOSFET Characterization Introduction The objectives of this experiment are to observe the operating characteristics of junction field-effect transistors (JFET's) and metal-oxide-semiconductor field-effect transistors (MOSFET's). Some basic methods for extracting device parameters for circuit design and simulation purposes are also examined. Precautions Junction field-effect transistors (JFET's) involve only an internal pn-junction and are thus relatively static insensitive and may be handled freely. However, MOSFET's involve a very thin gate oxide layer which may not have any static protection diodes included as part of the device. As a result, MOSFET's can be very static sensitive and must be treated properly to avoid having to buy replacements. To avoid static discharge damage to MOSFET's, keep their leads inserted into black conductive foam whenever possible. Always touch a grounded object, such as the frame of the lab bench, to discharge any built-up static charges from your body before handling the MOSFET. After this, carefully remove the MOSFET from the black foam and insert it into either the curve tracer or the solderless breadboard. Pay particular attention to correctly identifying the leads on the devices. Improper connection of the device is another means in which they can be destroyed. Once the MOSFET is correctly connected into its test circuit, it is reasonably well protected from static, since there now exist resistors or power supply terminals which allow current to flow from lead to lead. As a basic rule, remember that static electricity affects only floating terminals on a device or circuit. Simply connecting these floating terminals to ground with a large value resistor, say 1 M or so, is often sufficient to provide a discharge path for any built-up charges. If you are still having difficulty in keeping the MOSFET's from being destroyed by static, you may wish to try another trick which works well for very senstive parts. While the MOSFET is still plugged into the conductive black foam, take a 1-2 inch long piece of very fine bare copper wire and wrap it around all of the leads, just below the lip of the case, so that it shorts all of the leads together. (Some discrete MOSFET's even come with a piece of wire around the leads for this purpose.) Twist the free ends of the wire together so that it will not fall off. After the leads have all been shorted together by the wire, remove the MOSFET from the black foam and re-insert it into either the curve tracer or the solderless breadboard. Finish all of the rest of the circuit connections and instrument set-ups, and then only before you test the circuit, remove the bare copper shorting wire. Re-wrap the MOSFET leads with the
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Experiment-3 R. B. Darling EE-331 Laboratory Handbook Page E3.2 bare copper shorting wire before removing it from the breadboard or test fixture.
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EE331LE3rev6 - Experiment-3 Experiment-3 JFET and MOSFET...

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