IBIS4-1300
Document Number: 38-05707 Rev. *B
Page 5 of 37
Image sensor core - focal plane array
Figure 1. shows the architecture of the image sensor core.
The core of the sensor is the pixel array with 1280 x 1024
(SXGA) active pixels.
The name 'active pixels' refers to the amplifying element in
each pixel. This type of pixels offer a high light sensitivity
combined with low temporal noise. The actual array size is
1286 x 1030 including the 6 dummy pixels in X and Y. Although
the dummy pixels fall outside the SXGA format, their
information can be used e.g. for color filter array interpolation.
Figure 2. Pixel selection - principle
Next to the pixel array there are two Y shift registers, and one
X shift register with the column amplifiers. The shift registers
act as pointers to a certain row or column. The Y readout shift
register accesses the row (line) of pixels that is currently
readout. The X shift register selects a particular pixel of this
row. The second Y shift register is used to point at the row of
pixels that is reset. The delay between both Y row pointers
determines the integration time -thus realizing the electronic
shutter.
A clock and a synchronization pulse control the shift registers.
On every clock pulse, the pointer shifts one row/column
further. A sync pulse is used to reset and initialize the shift
registers to their first position.
The smart column amplifiers compensate the offset variations
between individual pixels. To do so, they need a specific pulse
pattern on specific control signals before the start of the row
readout.
Table 1. summarizes the optical and electrical characteristics
of the image sensor. Some specifications are influenced by the
output amplifier gain setting (e.g. temporal noise, conversion
factor,...). Therefore, all specifications are referred to an output
amplifier gain equal to 1.
Xshift register
Table 1. optical & electrical characteristics
Pixel characteristics
Pixel structure
3-transistor active pixel
Photodiode
High fill factor photodiode
Pixel size
7 x 7
µm2
Resolution
1286 x 1030 pixels
SXGA plus 6 dummy rows & columns
Pixel rate with on-chip ADC
Nominal 10 MHz (note 1) (note 2)
Frame rate with on-chip ADC
About 7 full frames/s at nominal speed
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