VV5801B001 Ver la hoja de datos (PDF) - Vision
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VV5801B001 Datasheet PDF : 23 Pages
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VISION VV6801/5801 PRELIMINARY CUSTOMER DATASHEET Rev 1.1
CR[18:17]
Vertical
Subsampling
Effect
Final viewfinder resolution
Max. frame
readout rate
@10MHz PCK
11
1/8
Skip 7 line pairs in
every 8
160 x 128 (With Horizontal
Cine Mode and external pixel
subsampling)
84/sec
Table 5.1 : Vertical Cine Mode
When 1/2 vertical subsampling is used in conjunction with Horizontal Cine mode, a viewfinder image of 640
x 512 pixels will be produced with the correct aspect ratio. When 1/4 or 1/8 vertical subsampling is used, an
incorrect aspect ratio will be read out from the sensor, since Horizontal Cine Mode only permits 1/2
subsampling, however pixel pairs can be skipped in software/post processing to regain the correct aspect
ratio.
y Although additional external horizontal subsampling is still required to regain the correct aspect ratio for a 1/
r 4 or 1/8 subsampled viewfinder, enabling Horizontal Cine mode is still advantageous, since it will speed up
sensor readout: one line period will require 740 PCK cycles rather than 1252 (see Section 7.5.2).
a Note: Line skipping schemes other than the those available may be desirable for certain applications where
the vertical subsampling ratio is a non integer power of two (e.g. 1/3 vertical subsampling). In these cases,
line skipping can be generated in external timing, as would be required when vertically subsampling the
in VV6850/5850, where no vertical Cine mode is available.
5.5 Parallel Integration
In this mode all of the pixels in the array are released from reset at the same time. This is achieved using the
lim VCLRB and VSETB signals for the vertical shift registers. (VSETB only effects the reset shift register). This
can be used to give a quick but crude estimate of correct exposure by, for example, counting lines until a line
is reached where all pixels in the line are saturated, then setting exposure to, say, 50% of the integration time
taken to reach that line.
e The sequence of operations is as follows:
1. Pulse VCLRB low to reset the Read and Reset vertical shift registers to all zeros; this forces all pixels
r into reset
P 2. Pulse VSETB low, this loads the Reset shift register with all ones, which starts all of the pixels integrat-
ing.
3. Then FR should be pulsed high for 2 lines to start the array readout.
LCK
EVEN
FI
FR
VCLRB
VSETB
AVO
AVO Not Valid
Black Ref Line
Valid Video Line
Figure 5.5 : Relative timing for Parallel Integration Mode
Note: VCLRB and VSETB must NEVER be taken low at the same time.
Since all pixels start to integrate at the same time and readout is sequential (line by line), each line of pixels
represents a different exposure value. If the FR pulse occurs on the next video line after VSETB goes high
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then the first valid video line readout will have been exposed for 6 lines (the black reference lines), and the
last line of valid video will have been exposed for 1306 lines.
5.6 Accumulate
In ‘Accumulate’ mode the pixel array is repeatedly re-read without resetting the pixels. This mode is intended
for exposure monitoring in conjunction with a flash when light levels are low, and more than one frame time
is required to obtain sufficient integration.
The array is released from reset by taking FI high. At the same time FR is pulsed high for 2 lines to read out
the pixel reset values. Then at the required intervals (of not less than 1306 line periods) FR is pulsed high for
2 lines to re-read the array. While the array is being repeatedly re-read FI must stay high. Effectively, the
successive reads of the array are monitoring the rate of charge accumulation in the pixels.
When sufficient integration has occurred to produce, say 50% average saturation, reading can be terminated.
The number of frames of exposure required to achieve this can then be used to calculate the flash energy
required to correctly expose the scene. On the falling edge of FR for the final array read, FI should go low, to
y return the pixel array into reset.
r LCK
a EVEN
FI
in FR
lim AVO
1306 Lines
Valid Video Line
1306 Lines
Black Ref Line
1306 Lines
AVO Not Valid
Figure 5.6 : Relative timing for Accumulate mode
e 5.7 Multiple Dark Current Periods
r This is a suggested modification to the noise cancellation sequence described in Section 5.1, to suit particular
application requirements, by extending the post image exposure ‘dark image’ capture period to some integral
P multiple of the image exposure period, in order to obtain a more accurate assessment of the dark current
FPN:
1. With the shutter closed, release the sensor from reset and immediately read a frame into buffer ‘A’
memory; this captures the array threshold FPN and reset noise (‘VReset’)
2. Open the shutter and expose the sensor to the required scene
3. Close the shutter and immediately read the array; as each pixel is read, subtract the value for that posi-
tion stored in the frame buffer to obtain the image plus dark current FPN (Vim+VDark1) value; store this
value in second frame buffer, ‘B’
4. After a further (say) four frame periods, read the array again; as each pixel is read, subtract the reset
value for that position as stored in the ‘A’ frame buffer, and overwrite the position, leaving the Vim +
VDark1 + VDark2 value in the buffer
5. For each pixel, subtract the value in ‘B’ from that in ‘A’ to give VDark2 dark current value, which is equiv-
alent to four times the VDark1 value
6. Divide the VDark2 values in ‘A’ by 4, then subtract them from the (Vim + VDark1) values in ‘B’ and store
the result, which is the Vim image data
The frame buffer now contains the corrected image values, which can be transferred to image storage
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