NOII4SM6600A Datasheet, PDF (16/34 Pages) ON Semiconductor – 6.6 Megapixel CMOS Image Sensor

NOII4SM6600A
High Dynamic Range Modes
Double Slope Integration
The IBIS4-6600 has a feature called double slope
integration to increase the optical dynamic range of the
sensor. The pixel response can be extended over a larger
range of light intensities by using a ”dual slope integration”.
This is obtained by adding charge packets from a long and
a short integration time in the pixel during the same exposure
time. Figure 14 shows the response curve of a pixel in dual
slope integration mode. The curve also shows the response
of the same pixel in linear integration mode at the same light
levels, with a long and short integration time.
Dual slope integration is obtained by feeding a lower
supply voltage to VDD_RESET_DS (for example, apply
2.0 V). Note that for normal (single slope) operation,
VDD_RESET_DS must have the same value as
1.8
VDD_RESET. The difference between VDD_RESET_DS
and VDD_RESET determines the range of the high
sensitivity, and as a result the output signal level at which the
transition between high and low sensitivity occurs.
Put the amplifier gain to the lowest value where the analog
output swing covers digital input swing of the ADC.
Increasing the amplification too much may boost the high
sensitivity part over the whole ADC range.
The electronic shutter determines the ratio of integration
times of the two slopes. The high sensitivity ramp
corresponds to “no electronic shutter”, thus maximal
integration time (frame read out time). The low sensitivity
ramp corresponds to the electronic shutter value that is
obtained in normal operation.
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0%       20%      
Dual s lope operation
Long integration time
Short integration time
Relative exposure (arbitrary scale)
40%       60%       80%       100%
Figure 14. Double Slope Response
NonDestructive Read Out (NDR)
The default mode of operation of the sensor is with FPN
correction (double sampling). However, the sensor can also
be read out in a nondestructive method. After a pixel is
initially reset, it can be read multiple times, without being
reset. The initial reset level and all intermediate signals can
be recorded. High light levels saturate the pixels quickly, but
a useful signal is obtained from the early samples. For low
light levels, use the later or latest samples. Essentially an
active pixel array is read multiple times, and reset only once.
The external system intelligence interprets the data. Table 10
on page 17 summarizes the advantages and disadvantages of
nondestructive readout.
time
Figure 15. Principle of NonDestructive Read Out
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