IBIS4-1300_09 Datasheet, PDF (26/37 Pages) Cypress Semiconductor – 1.3 MPxl Rolling Shutter CMOS Image Sensor

IBIS4-1300
Example: timing used on the IBIS4 breadboard
The next figure is the timing as used in the IBIS4 breadboard
version 12 jan 2000. In this baseline only CALIB_F is used
(pulsing once per frame). CALIB_S (pulse every line) is shown
as reference, but is actually not used in the baseline. The
UNITY_GAIN pulse is identical to CALIB_F.
Figure 22. pulse sequence used in IBIS4 breadboard v. jan 2000
1 usec
CLCK_Y
SIN
CALIB_S
Is calib_s is used, calib_f&unity are 0
Or CALIB_F&UNITY GAIN
Is calib_f&unity are used, calib_s is 0
RESET
SYNC_X
CLCK_X
SYNCY_L and SYNCY_R; once per frame per register (for electronic shutter L and R at different moments)
L/R
SHY
Illumination control
There are two means of controlling the illumination level
electrically. For high light levels, there is an electronic shutter.
For low light levels, the output signal can be amplified by
controlling the output amplifier gain. The offset level of the
signal can also be controlled digitally.
“Rolling curtain" electronic shutter
The electronic shutter can reduce the integration time (=
exposure time). This is achieved by an additional reset pulse
every frame. In this way, the integration time is reduced to a
fraction of the frame readout time.
There are two Y shift registers. One of them points at the row
that is currently being read out. The other shift register points
at the row that is currently being reset. Both pointers are
shifted by the same Y-clock and move over the focal plane.
The integration time is set by the delay between both pointers.
Figure 23. Schematic representation of the curtain type
electronic shutter
Readout
pointer
Reset
pointer
This is a so-called 'rolling curtain'-type shutter. It 'rolls' over the
focal plane.
The left and right shift registers can be used both for pointing
to the row that is readout or the row that is reset. The shift
register that is active for readout or reset is selected by the
signal on L/R. In the above timing diagrams, we use the R shift
register for readout, and the L shift register for electronic
shutter reset. We call them the readout shift register and reset
shift register.
The integration time is controlled by the delay between the
SYNCY_L and SYNCY_R pulse. The shorter this delay, the
shorter the integration time and the smaller the output signal
will be.
If the electronic shutter is not used, the L/R signal is not pulsed.
The integration time is then equal to the frame readout time.
For proper operation of the ES, the CLOCK_Y must come as
an uninterrupted pulse train. Also during the dead time
between frames the CLOCK_Y must be clocked. The reason
is that each line should see the same elapsed time between
the "ES-reset" and the reset of the line being read-out. If the
CLOCK_Y is halted, the lines between the two pointers will
have a longer effective integration time, and appear brighter.
Gain control
For low illumination levels, the electronic shutter is not used -
or set to its maximal value. Longer integration times can only
be obtained by decreasing the frame rate. As an alternative or
in complement, one can increase the output amplifier gain.
The gain is controlled by a 4-bit word. Gain values vary
between 1.2 and 16, and on an exponential scale, as the
F-stops of a lens.
Of course, increasing the signal amplitude by increasing the
gain, will also increase the noise level. The apparent increase
of sensitivity is at the cost of a lower dynamic range.
Document Number: 38-05707 Rev. *B
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