IBIS4-6600_09 Datasheet, PDF (16/35 Pages) Cypress Semiconductor – 6.6 MP CMOS Image Sensor

IBIS4-6600 CYII4SM6600AB
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" (patents pending). This is
obtained by adding charge packets from a long and a short
integration time in the pixel during the same exposure time.
Figure 18 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 2.0V to 2.5V).
Note that for normal (single slope) operation, VDD_RESET_DS
must have the same value as 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.
Figure 18. Double Slope Response
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0%
20%
40%
Dual slope operation
Long integration time
Short integration time
Relative exposure (arbitrary scale)
60%
80%
100%
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 9 on page 17 summarizes the advantages and disadvantages of
nondestructive readout.
Figure 19. Principle of NonDestructive Readout
Document Number: 001-02366 Rev. *E
time
Page 16 of 35
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