IBIS5-B-1300 CYII5FM1300AB
Figure 10. ADC Timing
Due to these delays, it is advisable that a variable phase
difference is foreseen between the ADC_CLOCK and the
SYS_CLOCK to tune the optimal sample moment of the ADC.
Non-linear and Linear Conversion Mode—’gamma’ Correction
Figure 12 on page 11 shows the ADC transfer characteristic. The
non-linear (exponential) ADC conversion is intended for
gamma-correction of the images. It increases contrast in dark
areas and reduces contrast in bright areas. The non-linear
transfer function is given by:
Setting of the ADC Reference Voltages
Figure 11. In- and External ADC Connections
2
a*x + b*x
Vin = ADC_VHIGH + (ADC_VHIGH – ADC_VLOW) * -----------------------------------------------
2
a*1023 + b*1023
With:
a = 5
RADC_VHIGH
b = 0.027
ADC_VHIGH ~ 2.7V
external
x = digital output code
internal
Electronic Shutter Types
RADC
The IBIS5-B-1300 has two different shutter types: a rolling
(curtain) shutter and a snapshot (synchronous) shutter.
external
Rolling (Curtain) Shutter
ADC_VLOW ~ 1.8V
The name is due to the fact that the effect is similar to a curtain
shutter of a SLR film camera. Although it is a pure electronic
operation, the shutter seems to slide over the image. A rolling
shutter is easy and elegant to implement in a CMOS sensor.
Notice that in Figure 13 on page 11, there are two Y-shift
registers. One of them points to the row that is currently being
read out. The other shift register points to 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.
RADC_VLOW
The internal resistor R
has a value of approximately 585Ω.
This results in the following values for the external resistors:
ADC
Resistor
Value (O)
360
Figure 13 on page 11 graphically displays the relative shift of the
integration times for different lines during the rolling shutter
operation. Each line is read and reset in a sequential way. The
integration time is the same for all lines, but is shifted in time. You
can vary the integration time through the INT_TIME register (in
number of lines).
R
R
R
ADC_VHIGH
ADC
585
1200
ADC_VLOW
Note that the recommended ADC resistor values yield in a
conversion of the full analog output swing at unity gain
This indicates that all pixels are light sensitive at another period
of time, and can cause some blurring if a fast moving object is
captured.
(V
<
ADC_VHIGH and
V
>
DARK_ANALOG
LIGHT_ANALOG
ADC_VLOW).
When the sensor is set to rolling shutter mode, make certain to
hold the input SS_START and SS_STOP low.
The values of the resistors depend on the value of R
. To
ADC
assure proper working of the ADC, make certain the voltage
difference between ADC_VLOW and ADC_VHIGH is at least
1.0V.
Document #: 38-05710 Rev. *E
Page 10 of 41
[+] Feedback