As MOSFET current depends on the channel length and due to channel length modulation drain current increases .
What will be the impact on the device?
Pinch off occurs
DIBL , Threshold gets affected
Again, other than stand -alone metrics , the impact is on operating frequency .
Dear Biswajit,
welcome,
Adding to Aparna, At the on set of channel pinch off the triode region ends and the saturation region starts. The drain current in this point is called the saturation point drain current IDsat. This occurs at specific VDS called VDSsat. Increasing VDS beyond VDSsat, the channel length decreases leading to the decrease of its resistance and slight increase of IDS with the VDS. The current in this region of VDS>VDSsat can be expressed then by:
IDS= IDsat( 1+ lambda VDS) where lambda is the channel length modulation factor. It is related to the Early voltage VA= 1/lambda
The impact on the device is to make its output resistance in saturation region not infinity but limited to VA/ IDsat= rDS and the transistor is no longer an ideal current source in the saturation region VDS>VDSsat.
For more information please follow this subject in chapter 5 of the text book: Book Electronic Devices
Best wishes
thanks to both Abdelhalim Zekry sir and Aparna Sathya Murthy .
could you please throw some light on this
"Due to channel length modulation current in mosfet increases but is this current less than triode region current?"
As per my understanding in triode region MOSFET is fully on and due to channel length Drain current increases but again there will be several other effect will be present like short channel effect ,velocity saturation so the drain current will be limited by these effect.
From the above can we conclude that Due to channel length modulation current in mosfet less than triode region current?
Dear Biswajit,
Welcome again
It is so that for constant VGS as one increases VDS from zero value, ID the drain current increases until it reaches it saturation value IDsat at VDSsat. This point is the end of the triode region. Increasing the drain voltage beyond VDSsat the transistor enter the saturation region where ID begins to further weak increase above ID sat. So, the current in the saturation region is greater than the current in the triode region.
Best wishes
TRIODE region is a fancy name for linear region . When applied voltage increases (or rather field ) , it proportionally increases drain current . What happens next after TRIODE is saturation where current stabilizes. Now , say current reduces , that is when pinch off happens that is when current is being sourced by 'SOURCE' side of the device (or like how you have stated velocity saturation ) . The situation when carrier is toooooo tired to go yet the channel is not cut short but reverse happens that is 'SOURCE' tries to bridge maintaining the channel . Effect is DIBL too and overall resistance of the channel .
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