LUPA-4000 Datasheet, PDF (48/49 Pages) Cypress Semiconductor – 4M Pixel CMOS Image Sensor

LUPA-4000
Data Sheet
APPENDIX B: Frequently Asked Questions
Q: How does the dual (multiple) slope extended dynamic range mode works?
A:
Reset pulse
Read out
Double slope reset pulse
Reset level 1
p1
Reset level 2
p2
p3
p4
Saturation level
Total integration time
Double slope reset time (usually 5-
10% of the total integration time)
Figure 27: Dual slope diagram
The green lines are the analog signal on the photodiode, which decrease as a result of
exposure. The slope is determined by the amount of light at each pixel (the more light
the steeper the slope). When the pixels reach the saturation level the analog signal will
not change despite further exposure. As you can see without any double slope pulse
pixels p3 and p4 will reach saturation before the sample moment of the analog values,
no signal will be acquired without double slope. When double slope is enabled a
second reset pulse will be given (blue line) at a certain time before the end of the
integration time. This double slope reset pulse resets the analog signal of the pixels
BELOW this level to the reset level. After the reset the analog signal starts to decrease
with the same slope as before the double slope reset pulse. If the double slope reset
pulse is placed at the end of the integration time (90% for instance) the analog signal
that would have reach the saturation levels aren't saturated anymore (this increases the
optical dynamic range) at read out. It's important to notice that pixel signals above
the double slope reset level will not be influenced by this double slope reset pulse (p1
and p2).
Cypress Semiconductor Corporation
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San Jose, CA 95134
408-943-2600
Contact: [e-mail] Document #: 38-05712 Rev.**(Revision 1.2 )
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