abuelmaatti
Newbie level 2
transistor vt
Folks, have got a very simple yet very difficult question.
How do I identify (accurately) the threshold voltage of a small-scale (l=180nm, w=100um) NMOS transistor from DC simulation? We all know that the threshold voltage is the voltage which if Vgs was higher than, current will start following in the channel and the transistor will be considered ON. The question is though, at what point do we say, current is now following? (This is like when somebody says large but doesn’t specify how large is large) because even at very small gate voltages there is still current in the channel but it is very small. So what is the ACCURATE point at which we say now current is following in the channel, so that is VT?
I carried out a VG sweep at a fixed VDD on the transistor and plotted the current against my swept gate voltage. We all know how this will look like, the current will be zero at very small gate voltages then when the gate voltage exceeds VT the current will start increasing in a square-law (I think?!) manner. Now, if I zoom into the graph near where the current starts (visibly) increasing I would notice that at these small voltages the current is not actually zero but has a small value and is increasing gradually, so it all depends on how much you zoom in. So how can I identify that ACURATE point where I would say this is a small current and this is a large current so that must be VT?
Thanks in advance for your help
Ali
Folks, have got a very simple yet very difficult question.
How do I identify (accurately) the threshold voltage of a small-scale (l=180nm, w=100um) NMOS transistor from DC simulation? We all know that the threshold voltage is the voltage which if Vgs was higher than, current will start following in the channel and the transistor will be considered ON. The question is though, at what point do we say, current is now following? (This is like when somebody says large but doesn’t specify how large is large) because even at very small gate voltages there is still current in the channel but it is very small. So what is the ACCURATE point at which we say now current is following in the channel, so that is VT?
I carried out a VG sweep at a fixed VDD on the transistor and plotted the current against my swept gate voltage. We all know how this will look like, the current will be zero at very small gate voltages then when the gate voltage exceeds VT the current will start increasing in a square-law (I think?!) manner. Now, if I zoom into the graph near where the current starts (visibly) increasing I would notice that at these small voltages the current is not actually zero but has a small value and is increasing gradually, so it all depends on how much you zoom in. So how can I identify that ACURATE point where I would say this is a small current and this is a large current so that must be VT?
Thanks in advance for your help
Ali