I don't understand why channel tapering at saturation in an enhancement type MOSFET gives a constant current? As the channel closes, why doesn't the current drop even though it is at its maximum?
Adding the channel length modulation effect makes it even more strange!
The explanation given by the colleague Gurmohan Singh is short, but very accurate.
Are there any real time videos showing this effect, because it is hard to imagine!
1. As VDS increases, channel length decreases. Then, where is the path for electrons to flow from source to drain (n channel MOSFET)?
2. As channel tapers due to a reduction of positive voltage at the drain end (due to high +ve VDS, thickness of channel at drain reduces as VDS approaches VGS), in theory VGS = VDS+Vt (n-channel MOSFET) and the channel is pinched off at drain. This must not allow any current to flow as per theory. And as VDS increases, VGS is reduced and channel is continuously diminished. This has to reduce the current again as there is no path for electrons to flow!
In essence, high VDS allows a current to flow even though the channel is tapered/diminished.
But, if extremely high VDS is applied, the channel keeps on diminishing and a point will reach where no current flows or current flows without the help of VGS/no channel established!
Correct me if I am wrong.
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