Graphics Programs Reference
In-Depth Information
Example:
An amplifier has a 4dB noise figure; the bandwidth is . Cal-
culate the input signal power that yields a unity SNR at the output. Assume
degrees Kelvin and an input resistance of one ohm.
B
=
500
KHz
T
o
=
290
Solution:
The input noise power is
23
10
3
15
kT
o
B
=
1.38
×
10
×
290
×
500
×
=
2.0
×
10
w
Assuming a voltage signal, then the input noise mean squared voltage is
n
i
〈〉
kT
o
B
15
v
2
=
=
2.0
×
10
10
0.4
F
=
=
2.51
From the noise figure definition we get
S
o
N
o
S
i
N
i
-----
F
-----
=
F
=
and
s
i
〈〉
Fn
i
〈〉 2.51
15
15
v
2
=
=
×
2.0
×
10
=
5.02
×
10
Finally,
s
i
〈〉 70.852
nv
=
Consider a cascaded system as in Fig. 1B.3. Network 1 is defined by noise
figure
, power gain
, bandwidth
, and temperature
. Similarly, net-
F
1
G
1
B
T
e
1
work 2 is defined by
,
,
, and
. Assume the input noise has temper-
F
2
G
2
B
T
e
2
ature
.
T
0
network 1
network 2
S
i
S
o
T
e
1
;
G
1
;
F
1
T
e
2
;
G
2
;
F
2
N
i
N
o
Figure 1B.3. Cascaded linear system.
Search WWH ::
Custom Search