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參數(shù)資料
| 型號(hào)： | S3932 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | POSITION SENSITIVE DETECTOR |
| 中文描述： | 位置靈敏探測(cè)器 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大小： | 1289K |
| 代理商： | S3932 |
9
Noise currents are calculated below, assuming that the
feedback resistance Rf of the current-to-voltage conversion
circuit is sufficiently greater than the PSD interelectrode
resistance Rie. In this case, 1/Rf can be ignored since it is
sufficiently small compared to 1/Rie. Position resolution as
listed in our PSD data sheets is calculated by this method.
1) Shot noise current Is originating from photocurrent and
dark current
2)
Thermal noise current (Johnson noise current) Ij generated
from interelectrode resistance (This can be ignored as Rsh
>> Rie.)
3) Noise current Ien by equivalent noise input voltage of
operational amplifier
en
Rie
By taking the sum of equations (5-4), (5-5) and (5-6), the
PSD noise current can be expressed as an RMS value
as follows:
If Rf cannot be ignored versus Rie (as a guide, Rie/Rf >
0.1), then the equivalent noise output voltage must be
taken into account. In this case, equations (5-4), (5-5)
and (5-6) are converted into output voltages as follows:
The thermal noise from the feedback resistance and the
equivalent noise input current of the operational amplifier
are also added as follows:
The equivalent noise input voltage of the operational am-
plifier is then expressed as an RMS value by the following
equation.
Figure 5-3 shows the shot noise current plotted along the
signal photocurrent value when Rf >>Rie. Figure 5-4
shows the thermal noise current and the noise current by
the equivalent noise input voltage of the operational
amplifier, plotted along the interelectrode resistance value.
When using a PSD with an interelectrode resistance of
about 10 k
W
, the operational amplifier becomes a crucial
factor in determining the noise current, so a low-noise-
current operational amplifier must be used. When using a
PSD with an interelectrode resistance exceeding 100 k
W
,
the thermal noise generated from the interelectrode
resistance of the PSD itself will be predominant.
As explained above, PSD position resolution is determined
by interelectrode resistance and light intensity. This is the
point in which the PSD greatly differs from discrete type
position detectors.
The following methods are effective for increasing the PSD
position resolution.
·
Increase the signal photocurrent Io.
·
Increase the interelectrode resistance Rie.
·
Shorten the resistance length L.
·
Use a low noise operational amplifier.
The position resolution listed in our PSD data sheets is
measured under the following conditions.
·
Photocurrent: 1 μA
·
Circuit input noise: 1 μV (31.6 nV/Hz
1/2
)
·
Frequency bandwidth: 1 kHz
Is
=
2q
.
(Io
+
I
D
)
.
B
[A] ............ (5-4)
q : Electron charge (1.60
×
10
-19
C)
Io: Signal photocurrent (A)
I
D
: Dark current (A)
B : Bandwidth (Hz)
k : Boltzmann constant (1.38
×
10
-23
J/K)
T : Absolute temperature (K)
Rie: Interelectrode resistance (
W
)
en: Equivalent noise input voltage of operational amplifier
(V/Hz
1/2
)
Ij
=
[A] ............ (5-5)
4 kTB
Rie
Ien
=
B [A] ............ (5-6)
In =
Is
2
+ Ij
2
+ Ien
2
[A] ............ (5-7)
Vs =
Rf
.
2q
.
(Io
+
I
D
)
.
B
[V] ............ (5-8)
Vj =
Rf
.
[V] .............................. (5-9)
4 kTB
Rie
B
Ve
n
= 1 + .
en
.
[V] .............. (5-10)
Rie
B
V
R
f
=
Rf
.
[V] ............................ (5-11)
4 kTB
Rf
Vi
n
=
Rf
.
in
.
[V] ............................ (5-12)
Vn =
Vs
2
+ Vj
2
+ Ve
n2
+ V
R
f
2
+ Vi
n2
[V] ............ (5-13)
Characteristic and use
Figure 5-3 Shot noise vs. signal photocurrent
Figure 5-4 Noise current vs. interelectrode resistance
KPSDB0083EA
KPSDB0084EA
SIGNAL PHOTOCURRENT (μA)
(Typ. Ta=25 C)
0.1
0.01
0.01
0.1
10
1
1
10
S
1
)
INTERELECTRODE RESISTANCE (k
)
(Typ. Ta=25 C)
100
10
0.01
0.1
10
1
1000
N
1
)
Thermal noise current Ij generated from
Noise current (en=10 nV) by equivalent
Noise current (en=30 nV) by equivalent
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