Tech Briefs Magazine - September 2022 - PIT-5

lar to the difference between rolling and
global shutters in 2D vision. Motion blur
can slightly warp the objects, which are
moving fast but it does not provide false
information, while motion artifacts can
drastically change the appearance of the
objects and provide false measurement,
which can have major consequences in
some applications.
Reliable Measurement with High
Dynamic Range
Another crucial matter in ToF is dynamic
range. ToF is intrinsically a very
high dynamic range application, due
to the combined contribution of the reflectivity
of the objects and the distance
range required. To illustrate this point,
assume an original application targeting
the detection of objects with reflectivity
between 15 percent and 85 percent and
a distance from 0.5m to 6m that needs
to be improved to detect objects with
reflectivity between 1.8 percent and 95
percent reflectivity and up to 10m distance.
In these conditions, the new case
requires more than 25-times more dynamic
range than the original one. This
is large enough to need much more than
a good Full Well Capacity in the pixel.
Teledyne e2v's Hydra3D ToF CMOS
image sensor embeds specific techniques
to manage this huge dynamic
range, such as non-destructive readouts
based on multiple captures combined
with a high frame rate, making it suitable
for most application cases.
Reliable Measurement in All
Conditions with High Flexibility
Having said that, brute force is normally
not a good idea in ToF. Having
high flexibility to adapt to a very wide
range of situations in terms of distance
range, reflectivity, dynamics, etc., is
clearly a significant asset. In Hydra3D, a
single trigger initiates a sequence of acquisitions
and readouts and is very easy
to program, resulting in a tool that can
adapt to the conditions of each application.
This illustrated in Figure 5.
The first blue outlined rectangle is
the exposure and readout of the three
phases, resulting in one 3D image. Multiple
acquisitions (blue outline rectangles)
can be done in each measurement
sequence (green outline rectangles),
either to increase the dynamic range or
to improve the precision. Also, having
multiple measuring sequences allows
measurement at different distance ranges,
or with different levels of precision,
Example in ToF
Analogy in 2D
Figure 3. Motion Blur/Motion Artifact - two different phenomena.
* HDR due to the distance
∆DR =
d
2d
4d
* HDR due to significant differences in reflectivity
* Example
*
*
∆DR =
(
Distance from 0.5m to 6m and
reflectivity range from 15% to 85%
=> ∆DR > 800
Distance from 0.5m to 10m and
reflectivity range from 1.8% to 95%
=> ∆DR > 21000
It implies more than 26 times more Dynamic Range
Figure 4. ToF is intrinsically a very high dynamic range application, and the sensor must manage it.
∆
or to perform 2D captures. This happens
all with a single trigger. On top of that,
the sequence is changeable from frameto-frame,
live, without halting the sensor.
This high configurability can be used
to find the best trade-off for every application
between distance range, reflectivity
range, precision, frame rate, light
power, etc.
Examples of Flexibility
For an application where the distance
range and the reflectivity range are
small, a configuration with a single 3D
Photonics & Imaging Technology, September 2022
acquisition (only the first blue outline
rectangle) will be enough. In this case,
the dynamic range won't be the largest,
but it is possible to reach a 100 fps frame
rate, with a total lack of motion blur.
For an application where it is required
to use the HDR capabilities due to the
large distance range and/or reflectivity
range, several acquisitions and readouts
can be performed (several blue outline
rectangles) to increase the dynamic range.
With such an application, around 25 fps
can be achieved with a 10m range and targets
between 15 percent and 85 percent.
5
Rmax
Rmin
)
*
*
*
*
(
dmax
dmin
)
2
Hydra3D technology
High flexibility combined
with high frame rate
HDR based on multiple
captures
Non-destructive
readouts
Highest exposure before
saturation
Motion artifact
Motion blur

Tech Briefs Magazine - September 2022

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