# MOSFET saturation current

Discussion in 'Homework Help' started by smrams28, Mar 29, 2013.

1. ### smrams28 Thread Starter New Member

Mar 29, 2013
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Hi. Im a first year engineering student and was having trouble on a problem. I am probably overthinking it.

Q)The n-channel MOSFET threshold voltage is +2 V. The gate voltage is +4V. The drain voltage is +5V. Is the MOSFET in the current saturation mode?

I think VGS-VT = VDS for it to be in saturation but this one is not. So is it not in saturation?

2. ### tshuck Well-Known Member

Oct 18, 2012
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675
Nope. Saturation is:
$provided\ that\ \ V_{GS} \ > \ V_{TH},\ \ then\ V_{DS}\ >\ V_{GS} - V_{TH}$

See here.

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Mar 29, 2013
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4. ### Ron H AAC Fanatic!

Apr 14, 2005
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What?
4V>2V
5V>(4V-2V)

That looks like saturation to me.

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5. ### tshuck Well-Known Member

Oct 18, 2012
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Wasn't saying that it wasn't in saturation, but that the equation for whether or not it is is wrong. Your red line is the equation in the OP.

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6. ### Ron H AAC Fanatic!

Apr 14, 2005
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OK, I see. The OP thought the expression was an equation, rather than an inequality.
I saw that, but thought it was just sloppy writing by the OP.

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7. ### WBahn Moderator

Mar 31, 2012
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Notice that the OP gave the threshold voltage, the gate voltage, and the drain voltage. They didn't give any indication of the source voltage. Perhaps they mean the other voltages as voltages relative to the source. Perhaps the source is tied to ground. But perhaps niether of these is the case.

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