1) In this problem, we are going to explore some of the concepts of field-effect
ID: 2292361 • Letter: 1
Question
1) In this problem, we are going to explore some of the concepts of field-effect transistor. a) Define "field effect" b) Precisely what is the "channel" in J-FET terminology? c) For a p-channel J-FET (a J-FET with n'-p gate junctions and a p-region between the source and drain), does the drain current flow into or flow out of the drain contact under normal operating conditions? Explain. d) What is the "gradual channel approximation? e) In J-FET, what does the term "pinch off" mean? f) Why is the magnitude of the electric field in the channel of concern in modeling short channel MESFETs? g Wha is the mathematical definition of the drain conductance? How about the h) State concisely, what is the primary difference between the long-channel and the two-region i) The dc charge distributions (black shape region) of four ideal MOS capacitors are shown in transconductance? short-channel Ip-VD theories? Figure below. For each case, answer the following three questions: (A) Is the semiconductor n- or p-type? (B) Is the device biased in the accumulation, depletion, or inversion mode? (C) Draw the energy-band diagram in the semiconductor region 0 0Explanation / Answer
a) The basic operation of the JFET is based on an electric field to control the electrical behaviour of the device. By controlling the bias between gate and channel i.e. on the pn junction, a voltage is applied between D, drain and S, source. An electric field is developed which makes a current to flow from the terminal designated to be G, gate S, source.Again. to turn the devise off, an appropriate electric feild is applied to the gate to control the channel width.
b) G, gate terminal can turn on or off the transistor by applying an appropriate electric feild to the gate and hence controling the channel width. This gate under the effect of electric field, permits electrons as only charge carries to flow and even blocks the charge carrier passage by creating or reducing a channel between the source and drain. Electron-flow from or towards the source terminal and the drain terminal is controlled by an applied voltage.
c) p-channel JFET is formed by difussing one pair of n-type region into a slab of p-type material. If Vgs is applied positive, the drain current will flow from drain to source (p to n junction) and it will decrease if Vgs is increased continuously. When Vgs reaches a certain value called pinch-off voltage, the drain current will be zero and will be independent of drain to source voltage applied.
d)
When the pn-junction of GATE is reverse biased, The channel becomes narrower. Let the thickness of conducting channel be h?x.
where h is the distance from the metalurgical junction and x is the depletion width.
depletion width, x= sqrt(2*?r*?0*(Vb?V) /(e*ND))
and, h= sqrt(2*?r*?0*(Vp) /(e*ND))
where Vb is the built-in voltage,
Vp is the pinch-off voltage,
and
V is the forward bias voltage across the junction.
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