How to calculate ro of a MOS?

[urian]

hi,there
I'm using IC5141 to design circuit.I want to know the ro of a MOS,but I only find ron in the DC operating point form.So where can I find the ro,or I have to calculate it through some parameters?

Regards

 

[jimito13]

Re: how to calculate ro?

You are provided with gds after the simulator calculates the DC operating point of your circuit.So take this value and using the formula ro=1/gds you have the small signal output resistance of your MOS transistor.

 

[urian]

Re: how to calculate ro?

thx,jimito13,but why it provide gds instead of ro?

 

[leo_o2]

Re: how to calculate ro?

You should ask Cadence. However, it will not be a technical problem.

 

[Braski]

because usually the simulators calculate transconductances and capacitances.

 

[urian]

so,what does the Ron be used for?

 

[jimito13]

When you operate the transistor in deep triode region (Vds<<2Veff) the drain current is approximately a linear function of Vds.The linear relationship implies that the path from source to drain can be represented by a linear resistor.This is the Ron.

 

[urian]

hi,jimito13
when the mos is working in saturation region ,I find there is also Ron in the DC operating point print,then,what does the Ron mean under this circumstance?Does it also mean the resistor from drain to source?