<s>
Transistor	B-General_Concept
–	I-General_Concept
transistor	I-General_Concept
logic	I-General_Concept
(	O
TTL	B-General_Concept
)	O
is	O
a	O
logic	B-General_Concept
family	I-General_Concept
built	O
from	O
bipolar	O
junction	O
transistors	O
.	O
</s>
<s>
Its	O
name	O
signifies	O
that	O
transistors	O
perform	O
both	O
the	O
logic	O
function	O
(	O
the	O
first	O
"	O
transistor	O
"	O
)	O
and	O
the	O
amplifying	O
function	O
(	O
the	O
second	O
"	O
transistor	O
"	O
)	O
,	O
as	O
opposed	O
to	O
earlier	O
resistor	O
–	O
transistor	O
logic	O
(	O
RTL	O
)	O
and	O
diode	B-General_Concept
–	I-General_Concept
transistor	I-General_Concept
logic	I-General_Concept
(	O
DTL	B-General_Concept
)	O
.	O
</s>
<s>
TTL	B-General_Concept
integrated	O
circuits	O
(	O
ICs	O
)	O
were	O
widely	O
used	O
in	O
applications	O
such	O
as	O
computers	O
,	O
industrial	O
controls	O
,	O
test	O
equipment	O
and	O
instrumentation	O
,	O
consumer	O
electronics	O
,	O
and	O
synthesizers	O
.	O
</s>
<s>
After	O
their	O
introduction	O
in	O
integrated	O
circuit	O
form	O
in	O
1963	O
by	O
Sylvania	O
Electric	O
Products	O
,	O
TTL	B-General_Concept
integrated	O
circuits	O
were	O
manufactured	O
by	O
several	O
semiconductor	O
companies	O
.	O
</s>
<s>
TTL	B-General_Concept
manufacturers	O
offered	O
a	O
wide	O
range	O
of	O
logic	O
gates	O
,	O
flip-flops	B-General_Concept
,	O
counters	O
,	O
and	O
other	O
circuits	O
.	O
</s>
<s>
Variations	O
of	O
the	O
original	O
TTL	B-General_Concept
circuit	O
design	O
offered	O
higher	O
speed	O
or	O
lower	O
power	O
dissipation	O
to	O
allow	O
design	O
optimization	O
.	O
</s>
<s>
TTL	B-General_Concept
devices	O
were	O
originally	O
made	O
in	O
ceramic	O
and	O
plastic	O
dual	O
in-line	O
package(s )	O
and	O
in	O
flat-pack	O
form	O
.	O
</s>
<s>
Some	O
TTL	B-General_Concept
chips	O
are	O
now	O
also	O
made	O
in	O
surface-mount	O
technology	O
packages	O
.	O
</s>
<s>
TTL	B-General_Concept
became	O
the	O
foundation	O
of	O
computers	O
and	O
other	O
digital	O
electronics	O
.	O
</s>
<s>
Even	O
after	O
Very-Large-Scale	O
Integration	O
(	O
VLSI	O
)	O
CMOS	B-Device
integrated	O
circuit	O
microprocessors	B-Architecture
made	O
multiple-chip	O
processors	O
obsolete	O
,	O
TTL	B-General_Concept
devices	O
still	O
found	O
extensive	O
use	O
as	O
glue	O
logic	O
interfacing	O
between	O
more	O
densely	O
integrated	O
components	O
.	O
</s>
<s>
TTL	B-General_Concept
was	O
invented	O
in	O
1961	O
by	O
James	O
L	O
.	O
Buie	O
of	O
TRW	O
,	O
which	O
declared	O
it	O
,	O
"	O
particularly	O
suited	O
to	O
the	O
newly	O
developing	O
integrated	O
circuit	O
design	O
technology.	O
"	O
</s>
<s>
The	O
original	O
name	O
for	O
TTL	B-General_Concept
was	O
transistor-coupled	B-General_Concept
transistor	I-General_Concept
logic	I-General_Concept
(	O
TCTL	B-General_Concept
)	O
.	O
</s>
<s>
The	O
first	O
commercial	O
integrated-circuit	O
TTL	B-General_Concept
devices	O
were	O
manufactured	O
by	O
Sylvania	O
in	O
1963	O
,	O
called	O
the	O
Sylvania	O
Universal	O
High-Level	O
Logic	B-General_Concept
family	I-General_Concept
(	O
SUHL	O
)	O
.	O
</s>
<s>
TTL	B-General_Concept
became	O
popular	O
with	O
electronic	O
systems	O
designers	O
after	O
Texas	O
Instruments	O
introduced	O
the	O
5400	O
series	O
of	O
ICs	O
,	O
with	O
military	O
temperature	O
range	O
,	O
in	O
1964	O
and	O
the	O
later	O
7400	O
series	O
,	O
specified	O
over	O
a	O
narrower	O
range	O
and	O
with	O
inexpensive	O
plastic	O
packages	O
,	O
in	O
1966	O
.	O
</s>
<s>
Not	O
only	O
did	O
others	O
make	O
compatible	O
TTL	B-General_Concept
parts	O
,	O
but	O
compatible	O
parts	O
were	O
made	O
using	O
many	O
other	O
circuit	O
technologies	O
as	O
well	O
.	O
</s>
<s>
At	O
least	O
one	O
manufacturer	O
,	O
IBM	O
,	O
produced	O
non-compatible	O
TTL	B-General_Concept
circuits	O
for	O
its	O
own	O
use	O
;	O
IBM	O
used	O
the	O
technology	O
in	O
the	O
IBM	B-Device
System/38	I-Device
,	O
IBM	B-Device
4300	I-Device
,	O
and	O
IBM	B-Device
3081	I-Device
.	O
</s>
<s>
The	O
term	O
"	O
TTL	B-General_Concept
"	O
is	O
applied	O
to	O
many	O
successive	O
generations	O
of	O
bipolar	O
logic	O
,	O
with	O
gradual	O
improvements	O
in	O
speed	O
and	O
power	O
consumption	O
over	O
about	O
two	O
decades	O
.	O
</s>
<s>
Typically	O
,	O
TTL	B-General_Concept
chips	O
integrate	O
no	O
more	O
than	O
a	O
few	O
hundred	O
transistors	O
each	O
.	O
</s>
<s>
Functions	O
within	O
a	O
single	O
package	O
generally	O
range	O
from	O
a	O
few	O
logic	O
gates	O
to	O
a	O
microprocessor	B-Architecture
bit-slice	B-General_Concept
.	O
</s>
<s>
TTL	B-General_Concept
also	O
became	O
important	O
because	O
its	O
low	O
cost	O
made	O
digital	O
techniques	O
economically	O
practical	O
for	O
tasks	O
previously	O
done	O
by	O
analog	O
methods	O
.	O
</s>
<s>
The	O
Kenbak-1	B-Device
,	O
ancestor	O
of	O
the	O
first	O
personal	B-Device
computers	I-Device
,	O
used	O
TTL	B-General_Concept
for	O
its	O
CPU	B-General_Concept
instead	O
of	O
a	O
microprocessor	B-Architecture
chip	O
,	O
which	O
was	O
not	O
available	O
in	O
1971	O
.	O
</s>
<s>
The	O
Datapoint	B-Device
2200	I-Device
from	O
1970	O
used	O
TTL	B-General_Concept
components	O
for	O
its	O
CPU	B-General_Concept
and	O
was	O
the	O
basis	O
for	O
the	O
8008	B-General_Concept
and	O
later	O
the	O
x86	B-Operating_System
instruction	O
set	O
.	O
</s>
<s>
The	O
1973	O
Xerox	B-Device
Alto	I-Device
and	O
1981	O
Star	B-Operating_System
workstations	O
,	O
which	O
introduced	O
the	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
used	O
TTL	B-General_Concept
circuits	O
integrated	O
at	O
the	O
level	O
of	O
arithmetic	B-General_Concept
logic	I-General_Concept
units	I-General_Concept
(	O
ALUs	O
)	O
and	O
bitslices	B-General_Concept
,	O
respectively	O
.	O
</s>
<s>
Most	O
computers	O
used	O
TTL-compatible	O
"	O
glue	O
logic	O
"	O
between	O
larger	O
chips	O
well	O
into	O
the	O
1990s	O
.	O
</s>
<s>
Until	O
the	O
advent	O
of	O
programmable	O
logic	O
,	O
discrete	O
bipolar	O
logic	O
was	O
used	O
to	O
prototype	O
and	O
emulate	O
microarchitectures	B-General_Concept
under	O
development	O
.	O
</s>
<s>
TTL	B-General_Concept
inputs	O
are	O
the	O
emitters	O
of	O
bipolar	O
transistors	O
.	O
</s>
<s>
Unlike	O
DTL	B-General_Concept
,	O
a	O
small	O
“	O
collector	O
”	O
current	O
(	O
approximately	O
10	O
µA	O
)	O
is	O
drawn	O
by	O
each	O
of	O
the	O
inputs	O
.	O
</s>
<s>
This	O
is	O
a	O
critical	O
advantage	O
of	O
TTL	B-General_Concept
over	O
DTL	B-General_Concept
that	O
speeds	O
up	O
the	O
transition	O
over	O
a	O
diode	O
input	O
structure	O
.	O
</s>
<s>
The	O
main	O
disadvantage	O
of	O
TTL	B-General_Concept
with	O
a	O
simple	O
output	O
stage	O
is	O
the	O
relatively	O
high	O
output	O
resistance	O
at	O
output	O
logical	O
"	O
1	O
"	O
that	O
is	O
completely	O
determined	O
by	O
the	O
output	O
collector	O
resistor	O
.	O
</s>
<s>
Open-collector	O
outputs	O
of	O
some	O
gates	O
have	O
a	O
higher	O
maximum	O
voltage	O
,	O
such	O
as	O
15	O
V	O
for	O
the	O
7426	O
,	O
useful	O
when	O
driving	O
non-TTL	O
loads	O
.	O
</s>
<s>
The	O
main	O
advantage	O
of	O
TTL	B-General_Concept
with	O
a	O
"	O
totem-pole	O
"	O
output	O
stage	O
is	O
the	O
low	O
output	O
resistance	O
at	O
output	O
logical	O
"	O
1	O
"	O
.	O
</s>
<s>
Like	O
DTL	B-General_Concept
,	O
TTL	B-General_Concept
is	O
a	O
current-sinking	O
logic	O
since	O
a	O
current	O
must	O
be	O
drawn	O
from	O
inputs	O
to	O
bring	O
them	O
to	O
a	O
logic	O
0	O
voltage	O
level	O
.	O
</s>
<s>
The	O
driving	O
stage	O
must	O
absorb	O
up	O
to	O
1.6	O
mA	O
from	O
a	O
standard	O
TTL	B-General_Concept
input	O
while	O
not	O
allowing	O
the	O
voltage	O
to	O
rise	O
to	O
more	O
than	O
0.4	O
volts	O
.	O
</s>
<s>
The	O
output	O
stage	O
of	O
the	O
most	O
common	O
TTL	B-General_Concept
gates	O
is	O
specified	O
to	O
function	O
correctly	O
when	O
driving	O
up	O
to	O
10	O
standard	O
input	O
stages	O
(	O
a	O
fanout	O
of	O
10	O
)	O
.	O
</s>
<s>
TTL	B-General_Concept
inputs	O
are	O
sometimes	O
simply	O
left	O
floating	O
to	O
provide	O
a	O
logical	O
"	O
1	O
"	O
,	O
though	O
this	O
usage	O
is	O
not	O
recommended	O
.	O
</s>
<s>
Standard	O
TTL	B-General_Concept
circuits	O
operate	O
with	O
a	O
5-volt	O
power	O
supply	O
.	O
</s>
<s>
A	O
TTL	B-General_Concept
input	O
signal	O
is	O
defined	O
as	O
"	O
low	O
"	O
when	O
between	O
0V	O
and	O
0.8V	O
with	O
respect	O
to	O
the	O
ground	O
terminal	O
,	O
and	O
"	O
high	O
"	O
when	O
between	O
2V	O
and	O
VCC	O
(	O
5V	O
)	O
,	O
and	O
if	O
a	O
voltage	O
signal	O
ranging	O
between	O
0.8V	O
and	O
2.0V	O
is	O
sent	O
into	O
the	O
input	O
of	O
a	O
TTL	B-General_Concept
gate	O
,	O
there	O
is	O
no	O
certain	O
response	O
from	O
the	O
gate	O
and	O
therefore	O
it	O
is	O
considered	O
"	O
uncertain	O
"	O
(	O
precise	O
logic	O
levels	O
vary	O
slightly	O
between	O
sub-types	O
and	O
by	O
temperature	O
)	O
.	O
</s>
<s>
TTL	B-General_Concept
outputs	O
are	O
typically	O
restricted	O
to	O
narrower	O
limits	O
of	O
between	O
0.0V	O
and	O
0.4V	O
for	O
a	O
"	O
low	O
"	O
and	O
between	O
2.4V	O
and	O
VCC	O
for	O
a	O
"	O
high	O
"	O
,	O
providing	O
at	O
least	O
0.4V	O
of	O
noise	O
immunity	O
.	O
</s>
<s>
Standardization	O
of	O
the	O
TTL	B-General_Concept
levels	O
is	O
so	O
ubiquitous	O
that	O
complex	O
circuit	O
boards	O
often	O
contain	O
TTL	B-General_Concept
chips	O
made	O
by	O
many	O
different	O
manufacturers	O
selected	O
for	O
availability	O
and	O
cost	O
,	O
compatibility	O
being	O
assured	O
.	O
</s>
<s>
In	O
some	O
cases	O
(	O
e.g.	O
,	O
when	O
the	O
output	O
of	O
a	O
TTL	B-General_Concept
logic	I-General_Concept
gate	O
needs	O
to	O
be	O
used	O
for	O
driving	O
the	O
input	O
of	O
a	O
CMOS	B-Device
gate	O
)	O
,	O
the	O
voltage	O
level	O
of	O
the	O
"	O
totem-pole	O
"	O
output	O
stage	O
at	O
output	O
logical	O
"	O
1	O
"	O
can	O
be	O
increased	O
closer	O
to	O
VCC	O
by	O
connecting	O
an	O
external	O
resistor	O
between	O
the	O
V4	O
collector	O
and	O
the	O
positive	O
rail	O
.	O
</s>
<s>
Like	O
most	O
integrated	O
circuits	O
of	O
the	O
period	O
1963	O
–	O
1990	O
,	O
commercial	O
TTL	B-General_Concept
devices	O
are	O
usually	O
packaged	O
in	O
dual	B-Algorithm
in-line	I-Algorithm
packages	I-Algorithm
(	O
DIPs	B-Algorithm
)	O
,	O
usually	O
with	O
14	O
to	O
24	O
pins	O
,	O
for	O
through-hole	B-Algorithm
or	O
socket	O
mounting	O
.	O
</s>
<s>
Epoxy	O
plastic	O
(	O
PDIP	B-Algorithm
)	O
packages	O
were	O
often	O
used	O
for	O
commercial	O
temperature	O
range	O
components	O
,	O
while	O
ceramic	O
packages	O
(	O
CDIP	O
)	O
were	O
used	O
for	O
military	O
temperature	O
range	O
parts	O
.	O
</s>
<s>
Beam-lead	B-Algorithm
chip	O
dies	O
without	O
packages	O
were	O
made	O
for	O
assembly	O
into	O
larger	O
arrays	O
as	O
hybrid	O
integrated	O
circuits	O
.	O
</s>
<s>
Parts	O
for	O
military	O
and	O
aerospace	O
applications	O
were	O
packaged	O
in	O
flatpacks	B-Algorithm
,	O
a	O
form	O
of	O
surface-mount	O
package	O
,	O
with	O
leads	O
suitable	O
for	O
welding	O
or	O
soldering	O
to	O
printed	O
circuit	O
boards	O
.	O
</s>
<s>
Today	O
,	O
many	O
TTL-compatible	O
devices	O
are	O
available	O
in	O
surface-mount	O
packages	O
,	O
which	O
are	O
available	O
in	O
a	O
wider	O
array	O
of	O
types	O
than	O
through-hole	B-Algorithm
packages	O
.	O
</s>
<s>
TTL	B-General_Concept
is	O
particularly	O
well	O
suited	O
to	O
bipolar	O
integrated	O
circuits	O
because	O
additional	O
inputs	O
to	O
a	O
gate	O
merely	O
required	O
additional	O
emitters	O
on	O
a	O
shared	O
base	O
region	O
of	O
the	O
input	O
transistor	O
.	O
</s>
<s>
At	O
least	O
one	O
computer	O
manufacturer	O
,	O
IBM	O
,	O
built	O
its	O
own	O
flip	B-Device
chip	I-Device
integrated	O
circuits	O
with	O
TTL	B-General_Concept
;	O
these	O
chips	O
were	O
mounted	O
on	O
ceramic	O
multi-chip	O
modules	O
.	O
</s>
<s>
TTL	B-General_Concept
devices	O
consume	O
substantially	O
more	O
power	O
than	O
equivalent	O
CMOS	B-Device
devices	O
at	O
rest	O
,	O
but	O
power	O
consumption	O
does	O
not	O
increase	O
with	O
clock	O
speed	O
as	O
rapidly	O
as	O
for	O
CMOS	B-Device
devices	O
.	O
</s>
<s>
Compared	O
to	O
contemporary	O
ECL	B-General_Concept
circuits	O
,	O
TTL	B-General_Concept
uses	O
less	O
power	O
and	O
has	O
easier	O
design	O
rules	O
but	O
is	O
substantially	O
slower	O
.	O
</s>
<s>
Designers	O
can	O
combine	O
ECL	B-General_Concept
and	O
TTL	B-General_Concept
devices	O
in	O
the	O
same	O
system	O
to	O
achieve	O
best	O
overall	O
performance	O
and	O
economy	O
,	O
but	O
level-shifting	O
devices	O
are	O
required	O
between	O
the	O
two	O
logic	B-General_Concept
families	I-General_Concept
.	O
</s>
<s>
TTL	B-General_Concept
is	O
less	O
sensitive	O
to	O
damage	O
from	O
electrostatic	O
discharge	O
than	O
early	O
CMOS	B-Device
devices	O
.	O
</s>
<s>
Due	O
to	O
the	O
output	O
structure	O
of	O
TTL	B-General_Concept
devices	O
,	O
the	O
output	O
impedance	O
is	O
asymmetrical	O
between	O
the	O
high	O
and	O
low	O
state	O
,	O
making	O
them	O
unsuitable	O
for	O
driving	O
transmission	O
lines	O
.	O
</s>
<s>
ECL	B-General_Concept
,	O
by	O
virtue	O
of	O
its	O
symmetric	O
low-impedance	O
output	O
structure	O
,	O
does	O
not	O
have	O
this	O
drawback	O
.	O
</s>
<s>
The	O
TTL	B-General_Concept
"	O
totem-pole	O
"	O
output	O
structure	O
often	O
has	O
a	O
momentary	O
overlap	O
when	O
both	O
the	O
upper	O
and	O
lower	O
transistors	O
are	O
conducting	O
,	O
resulting	O
in	O
a	O
substantial	O
pulse	O
of	O
current	O
drawn	O
from	O
the	O
power	O
supply	O
.	O
</s>
<s>
TTL	B-General_Concept
systems	O
usually	O
have	O
a	O
decoupling	O
capacitor	O
for	O
every	O
one	O
or	O
two	O
IC	O
packages	O
,	O
so	O
that	O
a	O
current	O
pulse	O
from	O
one	O
TTL	B-General_Concept
chip	O
does	O
not	O
momentarily	O
reduce	O
the	O
supply	O
voltage	O
to	O
another	O
.	O
</s>
<s>
Since	O
the	O
mid	O
1980s	O
,	O
several	O
manufacturers	O
supply	O
CMOS	B-Device
logic	O
equivalents	O
with	O
TTL-compatible	O
input	O
and	O
output	O
levels	O
,	O
usually	O
bearing	O
part	O
numbers	O
similar	O
to	O
the	O
equivalent	O
TTL	B-General_Concept
component	O
and	O
with	O
the	O
same	O
pinouts	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
the	O
74HCT00	O
series	O
provides	O
many	O
drop-in	O
replacements	O
for	O
bipolar	O
7400	O
series	O
parts	O
,	O
but	O
uses	O
CMOS	B-Device
technology	O
.	O
</s>
<s>
Although	O
vendors	O
uniformly	O
marketed	O
these	O
various	O
product	O
lines	O
as	O
TTL	B-General_Concept
with	O
Schottky	O
diodes	O
,	O
some	O
of	O
the	O
underlying	O
circuits	O
,	O
such	O
as	O
used	O
in	O
the	O
LS	O
family	O
,	O
could	O
rather	O
be	O
considered	O
DTL	B-General_Concept
.	O
</s>
<s>
Variations	O
of	O
and	O
successors	O
to	O
the	O
basic	O
TTL	B-General_Concept
family	O
,	O
which	O
has	O
a	O
typical	O
gate	O
propagation	O
delay	O
of	O
10ns	O
and	O
a	O
power	O
dissipation	O
of	O
10mW	O
per	O
gate	O
,	O
for	O
a	O
power	O
–	O
delay	O
product	O
(	O
PDP	O
)	O
or	O
switching	O
energy	O
of	O
about	O
100	O
pJ	B-Language
,	O
include	O
:	O
</s>
<s>
Schottky	O
TTL	B-General_Concept
(	O
S	O
)	O
,	O
introduced	O
in	O
1969	O
,	O
which	O
used	O
Schottky	O
diode	O
clamps	O
at	O
gate	O
inputs	O
to	O
prevent	O
charge	O
storage	O
and	O
improve	O
switching	O
time	O
.	O
</s>
<s>
Low-power	O
Schottky	O
TTL	B-General_Concept
(	O
LS	O
)	O
–	O
used	O
the	O
higher	O
resistance	O
values	O
of	O
low-power	O
TTL	B-General_Concept
and	O
the	O
Schottky	O
diodes	O
to	O
provide	O
a	O
good	O
combination	O
of	O
speed	O
(	O
9.5	O
ns	O
)	O
and	O
reduced	O
power	O
consumption	O
(	O
2mW	O
)	O
,	O
and	O
PDP	O
of	O
about	O
20	O
pJ	B-Language
.	O
</s>
<s>
Probably	O
the	O
most	O
common	O
type	O
of	O
TTL	B-General_Concept
,	O
these	O
were	O
used	O
as	O
glue	O
logic	O
in	O
microcomputers	O
,	O
essentially	O
replacing	O
the	O
former	O
H	O
,	O
L	O
,	O
and	O
S	O
sub-families	O
.	O
</s>
<s>
These	O
families	O
achieved	O
PDPs	O
of	O
10	O
pJ	B-Language
and	O
4	O
pJ	B-Language
,	O
respectively	O
,	O
the	O
lowest	O
of	O
all	O
the	O
TTL	B-General_Concept
families	O
.	O
</s>
<s>
Low-voltage	O
TTL	B-General_Concept
(	O
LVTTL	B-General_Concept
)	O
for	O
3.3-volt	O
power	O
supplies	O
and	O
memory	O
interfacing	O
.	O
</s>
<s>
Before	O
the	O
advent	O
of	O
VLSI	O
devices	O
,	O
TTL	B-General_Concept
integrated	O
circuits	O
were	O
a	O
standard	O
method	O
of	O
construction	O
for	O
the	O
processors	O
of	O
minicomputer	B-Architecture
and	O
midrange	O
mainframe	B-Architecture
computers	I-Architecture
,	O
such	O
as	O
the	O
DEC	B-Device
VAX	I-Device
and	O
Data	B-Device
General	I-Device
Eclipse	I-Device
;	O
however	O
some	O
computer	O
families	O
were	O
based	O
on	O
proprietary	O
components	O
(	O
e.g.	O
</s>
<s>
Fairchild	O
CTL	O
)	O
while	O
supercomputers	O
and	O
high-end	O
mainframes	B-Architecture
used	O
Emitter-coupled	B-General_Concept
logic	I-General_Concept
.	O
</s>
<s>
They	O
were	O
also	O
used	O
for	O
equipment	O
such	O
as	O
machine	O
tool	O
numerical	O
controls	O
,	O
printers	O
and	O
video	O
display	O
terminals	O
,	O
and	O
as	O
microprocessors	B-Architecture
became	O
more	O
functional	O
for	O
"	O
glue	O
logic	O
"	O
applications	O
,	O
such	O
as	O
address	O
decoders	O
and	O
bus	O
drivers	O
,	O
which	O
tie	O
together	O
the	O
function	O
blocks	O
realized	O
in	O
VLSI	O
elements	O
.	O
</s>
<s>
The	O
Gigatron	O
TTL	B-General_Concept
is	O
a	O
more	O
recent	O
(	O
2018	O
)	O
example	O
of	O
a	O
processor	O
built	O
entirely	O
with	O
TTL	B-General_Concept
integrated	O
circuits	O
.	O
</s>
<s>
While	O
originally	O
designed	O
to	O
handle	O
logic-level	O
digital	O
signals	O
,	O
a	O
TTL	B-General_Concept
inverter	O
can	O
be	O
biased	O
as	O
an	O
analog	O
amplifier	O
.	O
</s>
<s>
Connecting	O
a	O
resistor	O
between	O
the	O
output	O
and	O
the	O
input	O
biases	O
the	O
TTL	B-General_Concept
element	O
as	O
a	O
negative	O
feedback	O
amplifier	O
.	O
</s>
<s>
TTL	B-General_Concept
inverters	O
can	O
also	O
be	O
used	O
in	O
crystal	O
oscillators	O
where	O
their	O
analog	O
amplification	O
ability	O
is	O
significant	O
.	O
</s>
<s>
A	O
TTL	B-General_Concept
gate	O
may	O
operate	O
inadvertently	O
as	O
an	O
analog	O
amplifier	O
if	O
the	O
input	O
is	O
connected	O
to	O
a	O
slowly	O
changing	O
input	O
signal	O
that	O
traverses	O
the	O
unspecified	O
region	O
from	O
0.8V	O
to	O
2V	O
.	O
</s>
<s>
If	O
such	O
an	O
analog	O
input	O
must	O
be	O
used	O
,	O
there	O
are	O
specialized	O
TTL	B-General_Concept
parts	O
with	O
Schmitt	O
trigger	O
inputs	O
available	O
that	O
will	O
reliably	O
convert	O
the	O
analog	O
input	O
to	O
a	O
digital	O
value	O
,	O
effectively	O
operating	O
as	O
a	O
one	O
bit	O
A	O
to	O
D	O
converter	O
.	O
</s>
