LUPA-4000 Datasheet, PDF (22/49 Pages) Cypress Semiconductor – 4M Pixel CMOS Image Sensor

LUPA-4000
Data Sheet
3.10 Pixel array signals
The Pixel array of the image sensor requires digital control signals and several
different power supplies. This paragraph explains the relation between the control
signals and the applied supplies and the internal generated pixel array signals.
From figure 9 one can see that the internal generated pixel array signals are Reset,
Sample, Precharge, Vmem and Row_select. These are internal generated signals
derived by on chip drivers from external applied signals. Row_select is generated by
the y addressing and will not be discussed in this paragraph.
The function of each of the signals is:
Reset: Resets the pixel and initiates the integration time. If reset is high than the
photodiode is forced to a certain voltage, depending on Vpix, which is the pixel
supply; and depending on the high level of reset signal. The higher these signals or
supplies are, the higher the voltage-swing. The limitation on the high level of Reset
and Vpix is 3.3V. Nevertheless, it has no sense increasing Vpix without increasing
the reset level. The opposite does make sense. Additionally, it is this reset pulse that
also controls the dual or multiple slope feature inside the pixel. By giving a reset
pulse during integration, but not at full reset level, the photodiode is reset to a new
value, only if his value is sufficient decreased due to light illumination.
The low level of reset is 0V, but the high level is 2.5V or higher (3.3V) for the normal
reset and a lower (<2.5V) level for the multiple slope reset.
Precharge: Precharge serves as a load for the first source follower in the pixel and is
activated to overwrite the current information on the storage node by the new
information on the photodiode. Precharge is controlled by an external digital signal
between 0 and 2.5V.
Sample: Samples the photodiode information onto the memory element. This signal
is also a standard digital level between 0 and 2.5V
Vmem: this signal increases the information on the memory element with a certain
offset. This way one can increase the output voltage variation. Vmem changes
between Vmem_l (2.5V) and Vmem_h (3.3V).
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