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What is the relationship between channel width and drain current?
Wiki User
∙ 12y ago
if channel width decreases , the drain current(Id) will also decrease .
but , Id will decrease up to a certain limit , when the jfet is in pinch off condition i.e. channel width is tends to zero (Vgs is very high) the Id will be constant then.
Wiki User
∙ 12y ago
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What is Drain punchthrough in MOSFET?
punch through is a condition in which the drain and source depletion regions merge together.The current flow in this case will not be under the control of gate voltage.It is significant in short channel devices.
Explain the operation of jfet with any time?
JFET Construction and OperationA schematic representation of an n channel JFET is shown in Figure 118. An n-type channel is formed between two p-type layers which are connected to the gate. Majority carrier electrons flow from the source and exit the drain, forming the drain current. The pn junction is reverse biased during normal operation, and this widens the depletion layers which extend into the n channel only (since the doping of the pregions is much larger than that of the n channel). As the depletion layers widen, the channel narrows, restricting current flow. Figure 118: n-channel JFET structure.When , there is little voltage drop along the length of the channel, and the depletion regions are parallel, Figure 119. As vGS is increased negatively, they eventually touch reducing iD to zero. The value of vGSat which this occurs is called the pinch-off voltage, Vp (or vGS(off)).Figure: n-channel JFET structure for showing parallel depletion regions.When , there is a voltage drop along the length of the channel, and the depletion regions are no longer parallel, but are closer together towards the drain, Figure 120. As vDS is increased, they will touch (pinch-off) towards the drain, and the drain current iD can increase no longer. At the threshold of pinch-off, vGS-vDS=Vp. As vDS is further increased, iD remains constant, and the JFET is in its current saturationregion, the normal mode of operation. (This constant current region is a characteristic feature of any transistor, FET or BJT.) The channel shape remains unchanged, with a small region of touch near the drain, and further increases in vDS occurs across this small region.Figure: n-channel JFET structure for showing non-parallel depletion regions.JFETS are high input impedance devices, and so (due to the reverse bias pn junctions).
What is drain resistance?
drain resistane is basically the resistance offered by the drain terminal of the fet device.its the ratio of change in drain to source voltage to the change in drain current at a constant gate to source voltage.
Which bipolar transistor circuit carries the lowest current?
Drain is the answer
Why is the substrate in nmos connected to ground and in pmos to vdd?
we try to reverse bias not the channel and substrate but we try to maintain the source,drain junctions reversed biased with respect to the substrate so that we dont loose our current in the substrate.
How drain current is controlled in JFET?
The gate voltage controls the extent of depletion layer and thereby controls the width of the channel. As the width of the channel varies, current also varies. Width of the channel is inversly proportional to drain current.
What happens in n channel at pinch off voltage that the drain current becomes constant?
At pinch off voltage, the channel is blocked at its maximum. (depletion region blocks almost entire channel, so no charge exchange). Therefore, no drain is flown through the channel.
The transfer characteristics of a JFET with external bias?
Transfer Characteristic of JFETThe transfer characteristic for a JFET can be determined experimentally, keeping drain-source voltage, VDSconstant and determining drain current, ID for various values of gate-source voltage, VGS. The circuit diagram is shown in fig. 9.7 (a). The curve is plotted between gate-source voltage, VGS and drain current, ID, as illustrated in fig. 9.8. It is similar to the transconductance characteristic of a vacuum tube or a transistor. It is observed that (i) Drain current decreases with the increase in negative gate-source bias(ii) Drain current, ID = IDSS when VGS = 0(iii)Drain current, ID = 0 when VGS = VD The transfer characteristic follows equation (9.1)The transfer characteristic can also be derived from the drain characteristic by noting values of drain current, ID corresponding to various values of gate-source voltage, VGS for a constant drain-source voltage and plotting them.It may be noted that a P-channel JFET operates in the same way and have the similar characteristics as an N-channel JFET except that channel carriers are holes instead of electrons and the polarities of VGS and VDSare reversed.
What are depletion and enhancement mosfet?
A depletion MOSFET is a MOSFET that is normally on. It outputs maximum current when the gate-source voltage is 0V. As the gate-source voltage increases, the drain-source channel becomes more resistive and the current decreases. An enhancement MOSFET has the opposite behavior. It is normally off. It outputs no current when the gate-source voltage is 0V. As the gate-source voltage increases, the drain-source channel becomes less resistive and the current increases.
What is Drain punchthrough in MOSFET?
punch through is a condition in which the drain and source depletion regions merge together.The current flow in this case will not be under the control of gate voltage.It is significant in short channel devices.
Why is it thatFET is called a voltage operated device?
since in an FET the value of the current depends upon the value of the voltage applied at the gate and drain...so it is known as voltage controlled device.. for example..in a mosfet..the current from drain to source depends upon the width of the depletion layer..which in turn depends upon the voltage applied on the gate.. so that is the reason
What is current drain cells?
the current in the drain circuit of a field effect transistor.
What are the rating of MOSFET?
The basic ratings are:ID, the highest average current (and IDmax, the highest peak current) that you are allowed to feed through the drain and source terminals, andVD, the maximum voltage that you are allowed to apply between drain and source.
What is the use of gate in fet?
This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain.
Explain the operation of jfet with any time?
JFET Construction and OperationA schematic representation of an n channel JFET is shown in Figure 118. An n-type channel is formed between two p-type layers which are connected to the gate. Majority carrier electrons flow from the source and exit the drain, forming the drain current. The pn junction is reverse biased during normal operation, and this widens the depletion layers which extend into the n channel only (since the doping of the pregions is much larger than that of the n channel). As the depletion layers widen, the channel narrows, restricting current flow. Figure 118: n-channel JFET structure.When , there is little voltage drop along the length of the channel, and the depletion regions are parallel, Figure 119. As vGS is increased negatively, they eventually touch reducing iD to zero. The value of vGSat which this occurs is called the pinch-off voltage, Vp (or vGS(off)).Figure: n-channel JFET structure for showing parallel depletion regions.When , there is a voltage drop along the length of the channel, and the depletion regions are no longer parallel, but are closer together towards the drain, Figure 120. As vDS is increased, they will touch (pinch-off) towards the drain, and the drain current iD can increase no longer. At the threshold of pinch-off, vGS-vDS=Vp. As vDS is further increased, iD remains constant, and the JFET is in its current saturationregion, the normal mode of operation. (This constant current region is a characteristic feature of any transistor, FET or BJT.) The channel shape remains unchanged, with a small region of touch near the drain, and further increases in vDS occurs across this small region.Figure: n-channel JFET structure for showing non-parallel depletion regions.JFETS are high input impedance devices, and so (due to the reverse bias pn junctions).
Why input is voltage and output is current in fet?
The input is a Gate that is essentially infinite impedance, so no current. The output is essentially the resistance between Source and Drain, which controls the current flowing through it.
Define pinch off voltage and the gate source cut off voltage?
If negative voltage is applied to the gate of a NMOS, it repels electrons from the channel region towards the bulk of the p-substrate and attaract holes from p-substrate towards the channel. The recombination between holes and electrons causes a deplation of majority carriers in the channel. Enough nagative gate voltage can cause the channel depleted of majority carriers and cuts off the current between the source and the drain. The least negative gate voltage causing this is called gate-source cut off voltage.
