Biomedical Engineering Reference
In-Depth Information
Q
T
=
D
(3.6)
DET
1
2
2
[
T
NES
(
)]
Q
where
Q
T
is the charge capacity of a pel
NES is the noise equivalent signal
The relationship between system dynamic range and sensor dynamic range is
D
ʺ
KD
(3.7)
SYSTEM
DET
where
K
is a function related to the system transfer function. The inequality
indicates that the system dynamic range may be limited by the detector. The
NES is defined as the input exposure density,
E
(NES), which will make the
SNR equal to unity at the sensor output:
1
2
2
[
Q
(
NES
)]
⎛
⎜
μ
J
⎞
⎟
(3.8)
T
E
(
NES
)
=
2
R
m
D
Λ
where
1
2
is the rms number of photoelectrons in coulombs
2
[
Q
T
NES
(
)]
R
D
Λ
is the pel responsivity given by
Aqn
Hv
(3.9)
R
D
Λ
=
AR
=
λ
where
H
is Plank's constant
v
is the optical frequency
q
is the electronic charge
A
is the active area of a pel
n
is the total quantum efficiency
The NES is separable into two components: temporal noise and fixed pattern
noise. This separation can be expressed in terms of rms noise electrons by
the expression
1
2
1
2
2
2
2
(3.10)
[
Q
(
NES
)]
=
[
Q
+
Q
]
T
temporal
spatial
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