Cisco Cisco Prisma II EDR Receiver Technical References
78-4016548-01 Rev C
7
Basic Sampling Theory
An unfortunate consequence of the Nyquist sampling criterion is that signals
applied to the input of the A/D at frequencies other than the band from DC to F
NYQUIST
will produce undesired outputs and aliases.
The figure below illustrates the consequences of undesired signals applied to the
The figure below illustrates the consequences of undesired signals applied to the
A/D input.
Frequency
A
m
p
lit
u
d
e
F
s
2
F
s
3
F
s
F
N
y
q
u
is
t
3
F
N
y
q
u
is
t
5
F
N
y
q
u
is
t
Frequency
A
m
p
lit
u
d
e
F
s
2
F
s
3
F
s
F
N
y
q
u
is
t
3
F
N
y
q
u
is
t
5
F
N
y
q
u
is
t
...
Undesired
A/D input
Input
Output
Undesired
Aliases
In this example, a band of signals between F
NYQUIST
and F
S
is applied to the A/D input.
This produces aliases as shown, including signals in the band from DC to F
NYQUIST
. If
desired signals are now applied to the A/D in the band from DC to F
NYQUIST
, they will
be corrupted at the output by the alias of the undesired signals applied to the input
in the band between F
NYQUIST
and F
S
.