Instruction manual

Description of the data path
MARLIN Technical Manual
Page 40
8.2.1 IBIS5A multiple slope
The MF-131 sensor has a high dynamic range of about 60 dB. This can be further extended to
almost 100 dB by switching to a special mode..
This is called dual (in the case of rolling shutter) or multiple slope mode (in the case of global
shutter).
The following diagram taken from FillFactory’s application note, explains the functionality.
Figure 26: Multiple slope (high dynamic range)
The colored lines represent the analogue signal on the photodiode which decrease as a resultof
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 analogue signal
will no longer change despite further exposure. As shown in the diagram, without any dual or
multiple slope pulse, pixels P3’ and P4’ reach saturation before the sample moment of the
analogue values.
When dual slope is enabled, a second reset pulse will be given (blue line) at a certain time before
the end of the integration time.
This dual slope reset pulse resets the analogue signal of the pixels below the dual slope reset
level to this level. After the reset, the analogue signal starts to decrease with the same slope as
before (pink P3 and yellow P4 lines).
This introduces a knee-point in the exposure function.
If the dual slope reset pulse is placed at the end of the integration time (90% for instance), the
analogue signal that would have reached the saturation levels is no longer saturated (which
increases the optical dynamic range) at read out.