output residence of transistor

[Usman Hai]

hi,
How can we find out the output resistance of a single transistor? Is is "ron" as we get the DC operating point of the transistor? or we have to do something else to extract from simulation and how?

 

[MikeR]

You mean drain and source resistance ?

 

[Usman Hai]

yes Drain source resistance as we model in small signal analysis

 

[hyy95120]

resistance or impedance ? since AC signal is complex?
measure dv/di?

 

[MikeR]

May be you search this equations

 

[rameshabng]

ouput resistance of single transistor whichis in saturation is given by
r0=1/lambda*Id

 

[Jim cage]

This is only true for Large channel length (with small channel lenght modulation).

 

[jason_class]

Dear All

Actually Ron and Rsd is the same isn't it?
Usually I notice that the Ron of mosfet is very high kohm or Mohm range.
But I do see some cmos pass transistor logic with Ron of just 5 ohm or slightly higher.

ANyone know if this 5ohm refers to the Ron of mosfer aor Rsd?
Or it is simply some other parameter?
Any diagram you can provide for reference regarding this 5ohm Ron?

Thank you to discuss

best regards
Jason

 

[walker5678]

Ron should be the resistance the MOSFET present when working in the linear region as a switch. And Rds is the small signal model when MOSFET working in the saturation region.

 

[jfyan]

Dear All

Actually Ron and Rsd is the same isn't it?
Usually I notice that the Ron of mosfet is very high kohm or Mohm range.
But I do see some cmos pass transistor logic with Ron of just 5 ohm or slightly higher.

ANyone know if this 5ohm refers to the Ron of mosfer aor Rsd?
Or it is simply some other parameter?
Any diagram you can provide for reference regarding this 5ohm Ron?

Thank you to discuss

best regards
Jason

Acctually, In linear region, Ron=Rsd,
while in sturation region Ron!=Rsd. in other words, when the transistor works in saturation region, there is no Ron definition, right? because the resistance between the terminal d and s is nonlinear, we can't define it as a linear one.
as you mentioned, there do exist very small resistance value, that is the case in regulator or dc-dc converter design, where the pass transistor have a large ratio maybe larger than 10,000. when this transistor work in its linear region, it's resistance can be as low as 5 ohm.
correct me if i'm wrong.
good luck.
jeff

 

[jason_class]

Dear Fan

I think you are absolutely correct!
That is the only possible reason to explain the low Ron
Thank you for spending time in this simple question with effort!
Xie xie


best rgds
Jason