Different drain current values in CADENCE.Which one is true?

[andich]

Hello everybody,

Firstly, I use Spectre, mmsim-72, Cadence 5.10.41.

I have an interesting problem. I want to measure the drain current of a nMOSFET; however I get different results based on what I actually look at. Here is what I mean:

1. If I simply click to the drain terminal of the NMOS and plot the transient current, I get one value.

2. If I look at the 'id' variable of"transient operating points" from Analog environment, then I get a different number. It is always smaller, I guess.

My question is where this difference arises from. Is there something not included in "id"of "transient operating points"? Which value should I trust?

I have attached image of my simple circuit. As you may see, in plot it is 11.83p and annotated id is 9.43p.

I would be really happy if one of you guys can help me.

Thanks in Advance.
**broken link removed**

 

[hqqh]

Re: Different drain current values in CADENCE.Which one is t

Hi,

what do you mean with id variable? Do you mean a value in the Result Browser?
Normally the values in the Result-Browser section tran and the values in ADE->Results->Plot transient signal should be the same. Maybe you can check the terminal mapping between Schematic Editor terminals and simulation model terminals in DFII->Tools->Edit CDF -> choose Device -> Edit simulation Properties -> Spectre

Kind regards
hqqh

 

[drabos]

Hi,

Do you aware, that you have almost no current? have you tried increasing the current and making the same comparison?

what kind of model do you use?
You should check what is inside your transistor and how the extra devices are aligned hierarchically. Usually you have also the diodes included in that model. So, let us say you have 1 MOS transistor and two diodes inside your transistor and I have the feeling this id is only for the MOS transistor.
Basically if it is the case, you can measure the diode leakage.

br