Datasheet

PDF: 09005aef8202ec2e/Source: 09005aef8202ebf7 Micron Technology, Inc., reserves the right to change products or specifications without notice.
MT9D111__7_REV5.fm - Rev. B 2/06 EN
167 ©2004 Micron Technology, Inc. All rights reserved.
MT9D111 - 1/3.2-Inch 2-Megapixel SOC Digital Image Sensor
General Purpose I/O
Micron Confidential and Proprietary
sums per frame. As soon as these sums or raw sharpness scores are computed, they are
put in dedicated IFP registers, as are Y averages from all the AF windows. The AF driver
reduces these data to 1 normalized sharpness score per AF window, by calculating for
each window the ratio (S1+S2)/<Y>, where <Y> is the average Y and S1 and S2 are the raw
sharpness scores from the 2 filters multiplied by 128. Programming of the filters into the
MT9D111 includes specifying their relative weights, so each ratio can be called a
weighted average of two equally normalized sharpness scores from the same AF window.
In addition to unequal weighting of the filters, the AF driver permits unequal weighting
of the windows, but window weights are not included in the normalized sharpness
scores, for a reason that will soon become clear.
There are several motion sequences through which the AF driver can bring a lens to best
focus position. An example sequence is depicted in Figure 42. All these sequences begin
with a jump to a preselected start position, e.g. the infinity focus position. This jump is
referred to as the first flyback. It is followed by a unidirectional series of steps that puts
the lens at up to 19 preselected positions different from the start position. This series of
steps is called the first scan.
Before and during this scan, the lens remains at each preselected position long enough
for the AF driver to obtain valid sharpness scores. Typically, the time needed is no longer
than 1 frame, but there is an option to skip 1 frame before the AF driver grabs the scores,
so the total time spent at each position can reach 2 frames. The timing of lens move-
ments between the preselected positions is lens-actuator-dependent and not controlled
by the AF driver. Though the AF driver gives commands to move the lens, it is the AFM
driver that takes care of their execution and determines how soon after each command
the AF driver gets a signal to proceed. All inclined sections of the lens position plot in
Figure 42 are therefore of unknown duration—unless the AF algorithm discussion is nar-
rowed to a specific use case.
Figure 42: Search for Best Focus
Figure 42 shows lens movements during dual/triple-flyback auto focusing sequence.
The depicted sequence is just an example and can be changed in a number of ways. Sec-
ond scan, as well as second and third flyback are optional—final lens positioning can be
Lens
Position
P=255
P=0
1
st
scan: the lens steps
through its motion range,
sharpness scores are acquired
after each step.
Final lens positioning
(if no 2
nd
scan)
Final lens positioning
(after 2nd scan)
1
st
flyback
2
nd
flyback
2
nd
scan
(optional)
3
rd
flyback
Time
Best
focus
position