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C3683-01 View Datasheet(PDF) - Unspecified

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Characteristic and use
7. Saturation photocurrent
Photocurrent saturation must be taken into account when a
PSD is used outdoors, in locations where the background
light level is high, or the signal light amount is extremely
large. Figure 7-1 shows typical photocurrent output of a
PSD in a non-saturated state. This PSD is operating nor-
mally with good output linearity over the entire active area.
If the background light level is excessively high or the sig-
nal light amount is extremely large, the PSD photocurrent
will saturate. A typical output from a saturated PSD is
shown in Figure 7-2. The output linearity of the PSD is im-
paired so the correct position cannot be detected in this
case.
Photocurrent saturation of a PSD depends on the interelec-
trode resistance and reverse voltage, as shown in Figure 7-
3. The saturated photocurrent is measured as the total
photocurrent of a PSD when the entire active area is illumi-
nated. If a small spot light is focused on the active area, the
photocurrent that is generated is concentrated only on a lo-
calized portion, so saturation occurs at a lower level.
To avoid the saturation effect, use the following methods.
· Reduce the background light level by using an optical filter.
· Use a PSD with a small active area.
· Increase the reverse voltage.
· Decrease the interelectrode resistance.
· Avoid concentrating the light beam on a small area.
Figure 7-1 Photocurrent output example of PSD in
normal operation (S5629)
(Ta=25 ˚C)
120
IX1 + IX2
100
IX1
IX2
80
60
CENTER OF
ELECTRICITY
40
20
0
-4 -3 -2 -1 0 1 2 3 4
INCIDENT POSITION (mm)
KPSDB0087EA
Figure 7-2 Photocurrent output example of saturated
PSD (S5629)
(Ta=25 ˚C)
120
IX2
100
80
IX1
IX2
IX1 + IX2
60
40
CENTER OF
ELECTRICITY
20
0
-4 -3 -2 -1 0 1 2 3 4
INCIDENT POSITION (mm)
11
KPSDB0086EA
Figure 7-3 Saturation photocurrent vs. interelectrode resistance
(entire active area fully illuminated)
(Typ. Ta=25 ˚C)
10
VR=5 V
1
VR=2 V
0.1
VR=1 V
VR=0 V
0.01
10
100
1000
INTERELECTRODE RESISTANCE (k)
KPSDB0085EA
 

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