Timing Generator
Version 1.1, December 7, 2004
Proprietary to OmniVision Technologies
13
O
mni
ision
The minimum allowable exposure value is 1 line. Exposure modes of less than 1 line may be used
in special cases. The LSB signifies the 1 line exposure time. The exposure value data is 16-bits in
length.
If the exposure increment exceeds the Exposure Gap (SXGA - 15 lines max, VGA - 11 lines max,
QVGA/QVGA - 3 lines max, CIF - 89 lines max, QCIF/QQCIF - 41 lines max), the next frame will
appear over-exposed. Setting register
[1] (0x14) to a value of "1" will eliminate this
over-exposure frame by eliminating the HREF signal output. This provision also allows for the
companion backend processor to use the VSYNC as a frame data reset to eliminate the undesired
frame by register
[2] (0x14). Refer to
for details.
Figure 3-1
Manual Exposure Frame Drop Timing Diagram
Rolling Horizontal Band Elimination in Manual Mode
The OV9650 supports a rolling shutter exposure mode and requires special exposure values when
used in 50/60 Hz lighting conditions to eliminate rolling horizontal band (flicker). The minimum
exposure value is 1/120 second for 60 Hz and 1/100 second for 50 Hz lighting conditions. The
following steps outline how to calculate the proper exposure value at 50 Hz/60 Hz light conditions:
1. Calculate the C
AMERA
C
HIP
Minimum Exposure Line (MEL):
Line period is T
line
= K
×
T
pclk
= K/f
pclk
, while K is PCLK number in one line, T
pclk
is PCLK period (sec)
and f
pclk
is PCLK frequency (Hz). T
pclk
= 1/f
pclk
. For example, for default 1280 x 1024 at 7.5 fps, K is
1520 x 2 in YUV mode and 1520 in RGB Raw Data mode. But YUV PCLK frequency is double that of RGB
Raw Data mode with same T
line
.
For 60 Hz lighting: MEL = (1/120)/T
line
= 1/(120
×
K
×
T
pclk
) = f
pclk
/(120
×
K)
For 50 Hz lighting: MEL = (1/100)/T
line
= 1/(100
×
K
×
T
pclk
) = f
pclk
/(100
×
K)
Note:
For calculating MEL, use the line period of QCIF for QQCIF
resolution. For QQVGA, use the line period of QVGA.
