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average New Member Offline Posts: 9	A basic question? Aug 08^th, 2006, 2:23am Does the mosfet have the channel_length modulation effect when it operates in the triode region? Green
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jeffyan Community Member Offline Posts: 47	Re: A basic question? Reply #1 - Aug 8^th, 2006, 2:47am average wrote on Aug 8^th, 2006, 2:23am: Does the mosfet have the channel_length modulation effect when it operates in the triode region? Green hi, as i know, the channel_length modulation effect is defined in mosfet's saturation region. jeff.yan
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loose-electron Senior Fellow Offline Best Design Tool = Capable Designers Posts: 1638 San Diego California	Re: A basic question? Reply #2 - Aug 8^th, 2006, 10:23am Channel length modulation is applicible only in saturation region. You need to have a pinch off scenario in place, so that the pinch off location changes. When you are in triode region the entire channel is inverted (drain to source fully) so length modulation is not applicable. hope that helps Jerry
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ACWWong

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Re: A basic question?
Reply #3 - Aug 8^th, 2006, 10:56am

loose-electron wrote on Aug 8^th, 2006, 10:23am:

Channel length modulation is applicible only in saturation region. You need to have a pinch off scenario in place, so that the pinch off location changes.

When you are in triode region the entire channel is inverted (drain to source fully) so length modulation is not applicable.

hope that helps

Jerry

When you are in triode region, the entire channel is indeed inverted, but you can still have pinch-off due to velocity satuation (short channel effect). Although this is not "channel length modulation" in the traditional sense, the velocity saturation point is dependant on Vds, so the effects are similar to channel length modulation (ie, you see the knee in the Ids vs vds graph within the triode region).
This effect only occurs (as the name depicts) on short channel devices/high field strength situations.

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loose-electron

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Re: A basic question?
Reply #4 - Aug 8^th, 2006, 11:18am

Well yes, agreed -
But there is a lot of bad information in textbooks on velocity saturation

Pinchoff Region � Electron carriers in the pinched-off region are velocity saturated,

Many texts use the illustration: "velocity saturation is similar to a gas under pressure traveling through a very small tube�

I still don't know who the originator of that one is. It is a nice illustration, but not valid.

Carrier velocity saturation is caused by horizontal electric fields to the channel. end. �

For an in depth discussion see:
"Carrier Mobility and Current Saturation in the MOS transistor"
IEEE Transactions on Electron Devices, March 1965.

I wish I had an e-copy of the above, but it predates most computers.

- Jerry

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Jerry Twomey
www.effectiveelectrons.com
Read My Electronic Design Column Here
Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical

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average New Member Offline Posts: 9	Re: A basic question? Reply #5 - Aug 8^th, 2006, 5:57pm I think your replies are very helpful for me, thanks all.
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qiushidaren Community Member Offline I am a lovely MOSFET! Posts: 86 Chengdu	Re: A basic question? Reply #6 - Aug 21^st, 2006, 1:46am jeffyan wrote on Aug 8^th, 2006, 2:47am: average wrote on Aug 8^th, 2006, 2:23am: � Does the mosfet have the channel_length modulation effect when it operates in the triode region? Green hi, as i know, the channel_length modulation effect is defined in mosfet's saturation region. jeff.yan I agree with you, jeff.
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