how to know the mininum Vov(v* or Vdsat)

[carlson]

Hi!
How to know the minimun Vov(sometimes called V* or Vdsat) when designing the
amplifiers?
thank you!

 

[sunking]

I=K(Vgs-Vth)^2
Vds>=Vgs-Vth
I=KVdsat(min)^2

 

[estradasphere]

The determination of vdssat can be cumbersome for short channel FETs, because the transition from the linear region to the saturation region is not abrupt, but smooth contrary to long channel theory. that's why we need some more complicated analytical equations to derive vdssat. attached, please a find a paper which suggets a method about this issue. I tried and it works !

hope this helps.

 

[carlson]

Thanks. Can we obtain the results from the plot?

 

[wing]

In hspice simulation, use .op, then it will give you all the biasing points, include the vdsat. It is very diffcult and not accurate to use formular to calculate it, especially in short channel.

 

[Sergiu_Q]

exactly ...wing has right . use .op in your simulation , from Hspice use Edit LL button (edit a listing file) and in this file you will see all operation points you need ...something like this

subckt
element 0:m_i_1 0:m_i_2 0:m_i_3 0:m_i_8 0:m_i_5 0:m_i_6
model 0:nch.8 0ch.2 0ch.2 0ch.2 0:nch.2 0:nch.2
region Saturati Saturati Saturati Cutoff Cutoff Linear
id 481.0145n -481.0110n -481.0128n -6.1423p -995.6203a 12.7433p
ibs -8.473e-21 1.401e-21 4.1767a 1.576e-26 -116.7836a -8.687e-26
ibd -20.2645a 4.1739a 9.2777a 982.0779a -1.924e-26 -4.248e-24
vgs 973.0549m -1.0471 -1.2799 -478.6239m -2.8214 1.2000
vds 973.0549m -1.0471 -1.2799 -3.3000 -2.8214 111.2103n
vbs 0. 0. 1.0471 0. -2.8214 0.
vth 844.9315m -903.7326m -1.1359 -880.7675m 803.4797m 807.6500m
vdsat 98.1536m -121.1253m -125.9005m 0. 0. 305.2207m
beta 60.6852u 46.7744u 45.4565u 209.6135u 318.2910u 304.2494u
gam eff 836.5092m 503.9618m 487.6734m 482.3907m 754.5155m 754.5155m
gm 5.4208u 5.2860u 5.3421u 182.9708p 26.8169f 31.0466p
gds 18.3133n 39.9352n 41.1744n 447.2014f 59.5854a 119.3721u