Please
comment on the definition of *V _{OH}*
and

In
your Fig. 11.2 you define *V _{OH}*,
for example, as the
maximum inverter output

voltage
and *V _{OL}* as
the minimum inverter output voltage. However,
I've seen a few

others,
including wikipedia.org, that
define *V _{OH}* (

when
the input is at *V _{IL}*
(

Good
question. Defining *V _{OH}*
(

exact
for specifying the noise margins,
Eqs. (11.1) and (11.2). However, if you

look
at the difference in a practical
inverter the numerical difference between

the
two methods is minor. It's much
easier (and more practical) to determine

*V _{OH}*
and

For
example, looking at the short channel
inverter VTC in Fig. 11.4 the inverter's

*V _{IL}*
= 350 mV (at this voltage

= 65
mV). So

*NM _{H}*
=

*NM _{L}*
=

Now
using the book's definitions, *V _{OH}*
=

*NM _{H}*
= 486 mV (difference of 56 mV)

*NM _{L}*
= 350 mV (difference of 65 mV).

However,
let's look at how much *V _{IL}*
and

to
-1.5 instead of just looking at the
values when the slope is -1. In this range

*V _{IL}*
varies from 300 to 370 mV (70 mV) and

This
variation is comparable to the
difference seen using the two different methods.

Perhaps
this minor difference is why
most books use the engineering approximation of

*V _{OH
}*/

One
last comment; CMOS is a unique
logic family where the logic outputs can swing

from *VDD* to ground. In many logic families the
outputs don't swing all
the way to

the
power supply rails. *V _{OH}*
isn't equal to

discussed
in the book.