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Insulated Gate Field-Effect Transistors
39 questions By Tony R. Kuphaldt
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Question 7 of 39
Field effect transistors are classified as majority carrier devices. Explain why.
Reveal answerConduction through a field-effect transistor depends on charge carriers present in the channel due to doping (the “majority” type of charge carrier).
Review question: in contrast, why are bipolar junction transistors considered minority carrier devices?
Notes:Ask your students what type of transistor operates on a minority carrier principle, as opposed to field-effect transistors.
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Question 8 of 39
Bipolar junction transistors (BJTs) are considered “normally-off” devices, because their natural state with no signal applied to the base is no conduction between emitter and collector, like an open switch. Are insulate-gate field-effect transistors (IGFETs) considered the same? Why or why not?
Reveal answerIGFETs may be manufactured either as “normally-on” or “normally-off” devices.
Notes:Ask your students to elaborate on the answer given. Do not accept a mindless recitation of the answer, that “it depends on how they’re manufactured,” but rather demand that some sort of explanation be given as to why an IGFET would be normally-on versus normally-off.
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Question 9 of 39
The typical amount of current through a MOSFET gate terminal is far less than the typical amount of current through a BJT base terminal, for similar controlled currents (drain or collector, respectively). Explain what it is about the construction and/or use of the MOSFET that limits the input current to almost nothing during normal operation.
Reveal answerThe gate is electrically insulated from the channel.
Notes:If need be, refer back to a “cut-away” diagram of a MOSFET to help your students understand why the input impedance of a MOSFET is what it is.
