AR0238
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12
Lens
Pixel (0,0)
Row
Readout
Order
Column Readout Order
Scene
Sensor (Rear View)
Figure 9. Imaging a Scene
FEATURES OVERVIEW
For a complete description, recommendations, and usage
guidelines for product features, refer to the AR0238
Developer Guide.
3.0 mm Dual Conversion Gain Pixel
To improve the low light performance and keep the high
dynamic range, a large (3.0 um) dual conversion gain pixel
is implemented for better image optimization. With a dual
conversion gain pixel, the conversion gain of the pixel may
be dynamically changed to better adapt the pixel response
based on dynamic range of the scene. This gain can be
switched manually or automatically by an auto exposure
control module.
HDR
By default, the sensor powers up in Linear Mode. One can
change to HDR Mode. The HDR scheme used is
multi−exposure HDR. This allows the sensor to handle up to
96 dB of dynamic range. In HDR mode, the sensor
sequentially captures two exposures by maintaining two
separate read and reset pointers that are interleaved within
the rolling shutter readout. The exposure ratio may be set to
4x, 8x, 16x, or 32x. Sensor also provides flexibility to
choose any exposure ratio by setting number of t2 exposure
rows indepen− dent of the t1 exposure. The data will be
output as line interleaved data as described in the T1/T2 Line
Interleaved Mode section. There is also an option to output
either T1 only or T2 only.
RESOLUTION
The active array supports a maximum of 1928x1088
pixels to support 1080p resolution. Utilizing a 3.0 um pixel
will result in an optical format of 1/2.7−inch (approximately
6.6 mm diagonal).
FRAME RATE
At full (1080p) resolution, the AR0238 is capable of
running up to 60 fps in linear mode and 30 fps in line
interleaved mode.
IMAGE ACQUISITION MODE
The AR0238 supports two image acquisition modes:
• Electronic rolling shutter (ERS) mode
This is the normal mode of operation. When the AR0238
is streaming, it generates frames at a fixed rate, and each
frame is integrated (exposed) using the ERS. When ERS
mode is in use, timing and control logic within the sensor
sequences through the rows of the array, resetting and then
reading each row in turn. In the time interval between reset−
ting a row and subsequently reading that row, the pixels in
the row integrate incident light. The integration (exposure)
time is controlled by varying the time between row reset and
row readout. For each row in a frame, the time between row
reset and row readout is the same, leading to a uniform
integration time across the frame. When the integration time
is changed (by using the two−wire serial interface to change
register settings), the timing and control logic controls the
transition from old to new integration time in such a way that
the stream of output frames from the AR0238 switches
cleanly from the old integration time to the new while only
generating frames with uniform integration. See “Changes
to Integration Time” in the AR0238 Register Reference.
• Global reset mode.
This mode can be used to acquire a single image at the
current resolution. In this mode, the end point of the pixel
integration time is controlled by an external
electromechanical shutter, and the AR0238 provides control
signals to interface to that shutter. The benefit of using an
external electromechanical shutter is that it eliminates the
visual artifacts associated with ERS operation. Visual
artifacts arise in ERS operation, particularly at low frame
rates, because an ERS image effectively integrates each row
of the pixel array at a different point in time.
EMBEDDED DATA AND STATISTICS
The AR0238 has the capability to output image data and
statistics embedded within the frame timing. There are two
types of information embedded within the frame readout.
