[SI-LIST] Re: Switching point
- From: Bi Han <mike_bihan@xxxxxxxxxxxx>
- To: super_uvais@xxxxxxxxxxx, List` Si <si-list@xxxxxxxxxxxxx>
- Date: Thu, 21 Aug 2003 15:44:05 +0800 (CST)
I am no experts. But I wish I could answer your question.
1. You want the both transistors to be in saturation point was dangerous.The
high current will cause the nmos to Vt degrade due to hot electron.
2. If you look into your .lis file, the gm of Pch Nch device was different in
your simulation. Also, Nch was in saturation region and Pch was almost in
saturation region. So, the output node was in high-impedence state. It's
voltage was very sensitive because the current doesn't depend on the Vds of
both nmos and pmos, that's why you are not having 2.5v output voltage.
3. If you do need pmos to in satration region(actually impossible that accurate
becasue of process skew), tuning pmos's width until you got what you want. Hand
calc was no doubt helpful in understand, but for practical usage, simulation
results will show more ignored effects.
Hope it helps.
BH @emlab
super cop <super_uvais@xxxxxxxxxxx> wrote:
Hi Experts,
I am trying to model an inverter switching to 2.5v of
input , for 100u Ids .
I am convinced about the operating point information
for Nch mos which gives an exact value and the region
of operation.
However, iam not able to provide convincing evidence
for self about the region of operation of Pch mos
which according to the theory should also be in
saturation region, but shows linear region .
***** Netlist **
.OP 0N 5N 10N 15N 20N
M1 OUT IN VDD VDD PCH L=0.18U W=1.2872u
M2 OUT IN 0 0 NCH L=0.18U W=536.3023e-9
.MODEL PCH PMOS LEVEL=1
+ Cox=3.453e-4
+ KP = 8.632e-06
+ GAMMA= 0.5276
+ PHI = 0.576
+ DELVTO=0.0
+ LAMBDA=0.0
+ VTO=-0.7
.MODEL NCH NMOS LEVEL=1
+ Cox=3.453e-4
+ KP = 2.0718e-05
+ GAMMA= 0.5276
+ PHI = 0.576
+ DELVTO=0.0
+ LAMBDA=0.0
+ VTO=0.7
.PARAM VDD =5
VDD VDD 0 VDD
VIN IN 0 PWL 0 0 10N 0 20N VDD
***** operating point status is all simulation time
is 15.0000n
node =voltage node =voltage node
=voltage
+0:in = 2.5000 0:out = 3.2539 0:vdd
= 5.0000
**** mosfets
subckt
element 0:m1 0:m2
model 0:pch 0:nch
region Linear Saturati
id -99.9080u 100.0000u
ibs 0. 0.
ibd 17.4540f -32.5460f
vgs -2.5000 2.5000
vds -1.7461 3.2539
vbs 0. 0.
vth -700.0000m 700.0000m
vdsat -1.7454 1.8000
beta 61.7284u 61.7284u
gam eff 527.6000m 527.6000m
gm 107.7405u 111.1111u
gds 3.3706u 0.
gmb 37.4492u 38.6208u
cdtot 3.0944a 1.446e-19
cgtot 56.6117a 22.4615a
cstot 53.2905a 22.2223a
cbtot 2.268e-19 9.448e-20
cgs 53.2905a 22.2223a
cgd 3.0944a 1.446e-19
I had equated Width of Nch mos as: Ids = [BetaN*(
Vg-Vs-Vthn)*( Vg-Vs-Vthn)]/2 which is the exact
region of opearion as in the operation region
information.
and width of Pch mos as [BetaN*( Vg-Vs-Vthn)*(
Vg-Vs-Vthn)]/2 = [BetaP*( VDD-Vs -Vthp)*( VDD-Vs
-Vthp)] /2 . However, in this it should have been
acting in Sat region, but operating point information
shows that it is acting in Linear region.
There is a difference of 0.738U current . Also vdsat
should have been -1.8v (Pmos ) ,differece of 0.0546v
is making it to act in Linear region instead of Sat.
How to make Pmos to act in Sat region. or why is
acting in linear region rather than sat region as
the theory equation states to get 100u in both, the
Ids equation should be quated.
Am i making mistake in understanding ,
Can you pls help me understand this basic doubt .
Thanks & Regards.
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