PI0128WSN, PI0256WSN, PI0512WSN
Engineering Data Sheet
Figure 2. Geometry and layout of photodiode pixels.
During normal operation, the photons incident in or
near the NP photodiode junction generate free charges
that are collected and stored on the junction's depletion
capacitance. The number of collected charges is
proportional to the light exposure. Figure 3 shows the
stored signal charge as function of light exposure at a
wavelength of 575 nm. The exposure is the product of
the light intensity in nW/cm
2
and integration time in
seconds. The charge accumulates linearly until reach-
ing the saturation charge, and the corresponding
exposure is the saturation exposure.
The responsivity may be calculated as the saturation
charge divided by saturation exposure. The predicted
typical responsivity of a photodiode is 3.5´10
-4
C/J/cm
2
at 575 nm. Figure 4 shows the predicted responsivity
of the photodiodes as a function of wavelength.
80
Output Charge (pC)
70
60
50
40
30
20
10
0
0
50
100
150
200
250
Saturation
Charge
Saturation
Exposure
Exposure (nJ/cm
2
)
Figure 3. Stored signal charge as function of exposure at
a wavelength of 575 nm.
Page 2 of 8
Revised March 21, 2002
AMI [ AMI SEMICONDUCTOR ]
