NOIV1SN5000A Datasheet, PDF (33/71 Pages) ON Semiconductor – VITA 5000 5.3 Megapixel 75 FPS Global Shutter CMOS Image Sensor

NOIV1SN5000A
exposure time and gain are reconfigured together, as an
exposure time update always has one frame latency.
Table 22. SIGNAL PATH GAIN STAGES
(Analog Gain Stages)
gain_stage1 Gain gain_stage2 Gain
Stage 1
Stage 2
0x2
1.00
0xF
1.00
0x2
1.00
0x7
1.14
0x2
1.00
0x3
1.33
0x2
1.00
0x5
1.60
0x2
1.00
0x1
2.00
0x1
2.00
0x7
1.14
GAIN
total
1.00
1.14
1.33
1.60
2.00
2.29
0x1
2.00
0x3
1.33
2.67
0x1
2.00
0x5
1.60
3.20
0x1
2.00
0x1
2.00
4.00
0x1
2.00
0x6
2.67
5.33
0x1
2.00
0x2
4.00
8.00
Digital Gain Stage
The digital gain stage allows fine gain adjustments on the
digitized samples. The gain configuration is an absolute 5.7
unsigned number (5 digits before and 7 digits after the
decimal point).
Requested Illumination Level
(Target)
AEC
Statistics
AEC
Filter
Image Capture
AEC
Enforcer
Integration Time
Analog Gain (Coarse Steps)
Digital Gain (Fine Steps)
Figure 27. Automatic Exposure Control Loop
Automatic Exposure Control
The exposure control mechanism has the shape of a
general feedback control system. Figure 27 shows the high
level block diagram of the exposure control loop.
Three main blocks can be distinguished:
• The statistics block compares the average of the current
image’s samples to the configured target value for the
average illumination of all pixels
• The relative gain change request from the statistics
block is filtered in the time domain (low pass filter)
before being integrated. The output of the filter is the
total requested gain in the complete signal path.
• The enforcer block accepts the total requested gain and
distributes this gain over the integration time and gain
stages (both analog and digital)
The automatic exposure control loop is enabled by
asserting the aec_enable configuration in register 160.
NOTE: Dual and Triple slope integration is not
supported in conjunction with the AEC.
AEC Statistics Block
The statistics block calculates the average illumination of
the current image. Based on the difference between the
calculated illumination and the target illumination the
statistics block requests a relative gain change.
Statistics Subsampling and Windowing
For average calculation, the statistics block will
sub-sample the current image or windows by taking every
fourth sample into account. Note that only the pixels read out
through the active windows are visible for the AEC. In the
case where multiple windows are active, the samples will be
selected from the total samples. Samples contained in a
region covered by multiple (overlapping) window will be
taking into account only once.
It is possible to define an AEC specific sub-window on
which the AEC will calculate it’s average. For instance, the
sensor can be configured to read out a larger frame, while the
illumination is measured on a smaller region of interest, e.g.
center weighted.
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