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channel length modulation

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vaidhyanathan

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I read that in an n-mosfet, when drain voltage is increased above threshold (in saturation mode) the inversion channel between the source and drain is pinched-off near the drain region. so the channel length decreases and so its resistance. so larger current flows through the channel.
My doubt is, when a smaller portion is pinched off near the drain, why it is not considered as open? the substrate will be of p-type. so there is no way of electrons flowing from the source to drain na?(due to the region that is cut off between them)
 

billow

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first of all there is something that you need to understand. when you apply a positive voltage at the gate(Vgs) , it creates a positive magnetic field and that pushes down the positive holes creating the n channel at the same time it also attracts the minority electron. now, when you apply a positive voltage across the drain, the positive magnetic field attracts the negative electrons. when you apply Vds bigger than Vgs, it pinch off the channel and pushes the channel by creating some space between the pinch of point and the drain. Your question was that how can a current flow if the channel was away from the drain. if you look at it from the physical stand point it a legit point but if you look at it from the magnetic field stand point, you would understand it. the more Vds more positive magnetic field which will attract the more electron which means it produces more current.
I read that in an n-mosfet, when drain voltage is increased above threshold (in saturation mode) the inversion channel between the source and drain is pinched-off near the drain region. so the channel length decreases and so its resistance. so larger current flows through the channel.
My doubt is, when a smaller portion is pinched off near the drain, why it is not considered as open? the substrate will be of p-type. so there is no way of electrons flowing from the source to drain na?(due to the region that is cut off between them)
 

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