## DC Sweep Result of Schmitt Trigger Inverter? ##

[june]

If I do a DC SWEEP of -0.5v~0.5v to a Schmitt Trigger Inverter,
Why do I see

Y:VOUT
-----------------------------------
\
\
\

----------------------------------- x: VIN
a b

(a=-0.2v, b=-0.19v)

If I dida TRANSIENT Simulation of an Inverter of question.

Y:VIN
-------------------------
/ \
/ \
/ \
/ \
/ \
-----------------------------
----------------------------- x:time


Y:VOUT
-------------------------------
------------------------------- x:time

\ /
\ /
\ /
\ /
-------------------------


What I want say is that the Inverter above has Hysteresis
Characteristic of a Schmitt Trigger Inverter.

However, if I do a DC simulation of the same Inverter of question,
(i.e. when the inverter is dc swept)

Y:VOUT
-----------------------------------
\
\
\

----------------------------------- x: VIN

It seems to be just a normal Inverter.

Why does this Inverter shows an Schmitt Trigger Characteristics in
TRANSIENT sim, and a normal Inverter Characteristic in DC simulation?


Is this Inverter a Schmitt Trigger Inverter or a Normal Inverter?

Regards,
June

 

[Jamie]

june wrote:

If I do a DC SWEEP of -0.5v~0.5v to a Schmitt Trigger Inverter,
Why do I see

Y:VOUT
-----------------------------------
\
\
\

----------------------------------- x: VIN
a b

(a=-0.2v, b=-0.19v)

If I dida TRANSIENT Simulation of an Inverter of question.

Y:VIN
-------------------------
/ \
/ \
/ \
/ \
/ \
-----------------------------
----------------------------- x:time


Y:VOUT
-------------------------------
------------------------------- x:time

\ /
\ /
\ /
\ /
-------------------------


What I want say is that the Inverter above has Hysteresis
Characteristic of a Schmitt Trigger Inverter.

However, if I do a DC simulation of the same Inverter of question,
(i.e. when the inverter is dc swept)

Y:VOUT
-----------------------------------
\
\
\

----------------------------------- x: VIN

It seems to be just a normal Inverter.

Why does this Inverter shows an Schmitt Trigger Characteristics in
TRANSIENT sim, and a normal Inverter Characteristic in DC simulation?


Is this Inverter a Schmitt Trigger Inverter or a Normal Inverter?

Regards,
June
Hard to follow your description but I would say that in a DC model, you

are supplying a low and high input signal with no middle range. This
would make it look like a generic inverter, because you have quickly
gone past the hysteresis region and thus, no effect will be visible.

with a TRANSIENT simulation, you are supplying a ramp up and ramp down
and this will give enough time to see the hysteresis effect.

DC modeling most likely is to assume an ideal signal of 0 or fully on
with no ramp visible (slew/Skew times = 0.0) etc...

Of course, there is no such thing as an ideal condition. Simulators
must be forgiven for their bad insight!


http://webpages.charter.net/jamie_5"