LUPA-4000_07 Datasheet, PDF (37/38 Pages) Cypress Semiconductor – 4M Pixel CMOS Image Sensor

APPENDIX B: Frequently Asked Questions
Q: How does the dual (multiple) slope extended dynamic range mode works?
A:
Figure 29. Dual slope diagram
LUPA-4000
Reset pulse
Double slope reset pulse
Read out
Total integration time
Reset level 1
p1
Reset level 2
p2
p3
p4
Saturation level
Double slope reset time (usually 5-
10% of the total integration time)
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).
All products and company names mentioned in this document may be the trademarks of their respective holders.
Document Number: 38-05712 Rev. *B
Page 37 of 38
© Cypress Semiconductor Corporation, 2006. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use
of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be
used for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its
products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress
products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.