AMIS-710227 Datasheet, PDF (9/14 Pages) AMI SEMICONDUCTOR – 200dpi CIS Module

AMIS-710227, AMIS-710228, AMIS-710229: 200dpi CIS Module Data Sheet
9.0 Reset Level and Video Sampling Time
Figure 3: Video Pixel Definition
Figure 3 graphically shows the video signal waveform and defines the single video pixel structure. The signal output waveform is shown
relative to the input clock waveform as well as the symbols and terminologies used to define the performance specifications. Figure 3
serves to explain the terminology used to characterize the dark signal levels and the recommended video pixel sampling times.
Note 6, under Table 8-D, specifies the dark level (DL). This is the level during the dark read-out, i.e., either the module sits on black
target or the light source is turned off. It is measured from ground or 0V. The reset level is a reference level for the reset switch which
is not necessarily on ground because after the reset the signal is passed through an amplifier. The difference between the dark level
and the reset level is called the pedestal (PED). In most cases, the offset control of the amplifier is used to adjust the dark level to 0V
or ground. Hence, the reset level will sit below ground.
The video pixels demonstrated in this graph emanate from an ideal CIS module with a phototransistor imaging structure. The video
output at high speeds, such as 5.0MHz, does not instantly rise to its final value. Given enough time, it would asymptotically approach its
steady state value. But, at high speeds it is impractical to wait for a final stable value. Accordingly, as Figure 3 indicates, the output
signal continues to rise towards its steady state value. Consistent with the forgoing comments, in Note 7 under Table 8-D, instead of
the conventional signal sampling time (tsst) is defined to substitute the conventional settling time definition. This definition is used
because the output signal continues to rise asymptotically to the final stable value, but not within a practical time in high speed
applications. This is true even when the video rises to its peak value (Vp) indicated on the MTF Graph, see Figure 4.
AMI Semiconductor – May 06, M-20548-001
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