2/18/2023 0 Comments Fet electronicsWe have another mode called enhancement mode of operation, which will be discussed in the operation of MOSFETs. Depletion Mode of OperationĪs the width of depletion layer plays an important role in the operation of FET, the name depletion mode of operation implies. Now that we have understood the behavior of FET, let us go through the real operation of FET. This is why the depletion layer tends to penetrate more into the channel at point A than at point B, when both V GG and V DD are applied. So, the reverse biasing effect is stronger at drain terminal than at the source terminal. Hence the voltage drop is being progressive through the length of the channel. Suppose the point at source terminal is B and the point at drain terminal is A, then the resistance of the channel will be such that the voltage drop at the terminal A is greater than the voltage drop at the terminal B. The supply at gate terminal makes the depletion layer grow and the voltage at drain terminal allows the drain current from source to drain terminal. Let us now consider the following figure, to understand what happens when both the supplies are given. In case 2, When V DD is applied (positive terminal to drain and negative terminal to source) and V GG is not applied, the electrons flow from source to drain which constitute the drain current I D. This happens as the negative voltage applied, attracts the holes from the p-type layer towards the gate terminal. In case 1, When V GG is reverse biased and V DD is not applied, the depletion regions between P and N layers tend to expand. For this, let us suppose that the voltage at gate terminal say V GG is reverse biased while the voltage at drain terminal say V DD is not applied. Operation of N-channel FETīefore going into the operation of the FET one should understand how the depletion layers are formed. The source and the drain terminals may be interchanged. Ohmic contacts are made at the two ends of the n-type semiconductor bar, which form the source and the drain. Hence the cross sectional form of the FET is understood as the following figure. The majority carriers pass through this channel. The area between gates is called as a channel. These two gate depositions (p-type materials) form two PN diodes. This can be understood from the following figure. These two sides are joined to draw a single connection for gate terminal. For the fabrication of Nchannel FET, a narrow bar of N-type semiconductor is taken on which P-type material is formed by diffusion on the opposite sides. The N-channel FET is the mostly used Field Effect Transistor. Hence it is enough to discuss one type of FET to understand both. A p-type material is added to the n-type substrate in n-channel FET, whereas an n-type material is added to the ptype substrate in p-channel FET. The types of JFET are n-channel FET and P-channel FET. The JFET is abbreviated as Junction Field Effect Transistor.
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