<s>
In	O
digital	O
circuits	O
,	O
the	O
contamination	B-Device
delay	I-Device
(	O
denoted	O
as	O
tcd	O
)	O
is	O
the	O
minimum	O
amount	O
of	O
time	O
from	O
when	O
an	O
input	O
changes	O
until	O
any	O
output	O
starts	O
to	O
change	O
its	O
value	O
.	O
</s>
<s>
The	O
contamination	B-Device
delay	I-Device
only	O
specifies	O
that	O
the	O
output	O
rises	O
(	O
or	O
falls	O
)	O
to	O
50%	O
of	O
the	O
voltage	O
level	O
for	O
a	O
logic	O
high	O
.	O
</s>
<s>
The	O
determination	O
of	O
the	O
contamination	B-Device
delay	I-Device
of	O
a	O
combined	O
circuit	O
requires	O
identifying	O
the	O
shortest	O
path	O
of	O
contamination	B-Device
delays	I-Device
from	O
input	O
to	O
output	O
and	O
by	O
adding	O
each	O
tcd	O
time	O
along	O
this	O
path	O
.	O
</s>
<s>
For	O
a	O
sequential	O
circuit	O
such	O
as	O
two	O
D-flip	O
flops	O
connected	O
in	O
series	O
,	O
the	O
contamination	B-Device
delay	I-Device
of	O
the	O
first	O
flip-flop	B-General_Concept
must	O
be	O
factored	O
in	O
to	O
avoid	O
violating	O
the	O
hold-time	O
constraint	O
of	O
the	O
second	O
flip-flop	B-General_Concept
receiving	O
the	O
output	O
from	O
the	O
first	O
flip	B-General_Concept
flop	I-General_Concept
.	O
</s>
<s>
Here	O
,	O
the	O
contamination	B-Device
delay	I-Device
is	O
the	O
amount	O
of	O
time	O
needed	O
for	O
a	O
change	O
in	O
the	O
flip-flop	B-General_Concept
clock	O
input	O
to	O
result	O
in	O
the	O
initial	O
change	O
at	O
the	O
flip-flop	B-General_Concept
output	O
(	O
Q	O
)	O
.	O
</s>
<s>
If	O
there	O
is	O
insufficient	O
delay	O
from	O
the	O
output	O
of	O
the	O
first	O
flip-flop	B-General_Concept
to	O
the	O
input	O
of	O
the	O
second	O
,	O
the	O
input	O
may	O
change	O
before	O
the	O
hold	O
time	O
has	O
passed	O
.	O
</s>
<s>
Because	O
the	O
second	O
flip-flop	B-General_Concept
is	O
still	O
unstable	O
,	O
its	O
data	O
would	O
then	O
be	O
"	O
contaminated.	O
"	O
</s>
<s>
Every	O
path	O
from	O
an	O
input	O
to	O
an	O
output	O
can	O
be	O
characterized	O
with	O
a	O
particular	O
contamination	B-Device
delay	I-Device
.	O
</s>
<s>
The	O
condition	O
of	O
data	O
being	O
contaminated	O
is	O
called	O
a	O
race	B-Operating_System
.	O
</s>
