PI627MC-A4 / PI628MC-A4 / PI629MC-A4 Engineering Data Sheet

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Reset Level and Video Sampling Time

Figure 3. Reset Level and Sample Time

Figure 3 shows the video signal waveform and details a single pixel. The signal output waveform is shown

referenced to the input clock waveform. Also shown is the terminology used to define the dark and bright

output levels and the recommended pixels sampling times.

The dark level is defined by using the module imaging on a black target or with the light source turned off.

The dark level is then measured from ground or 0 volts. The reset level is a reference level of the reset

switch, which is not necessarily at ground. The reason for this is that after the reset operation, the video

signal is passed through an amplifier, which may have some offsets. The difference between the dark level

and reset level is called the pedestal, PED. Hence, the reset level will sit below the dark level.

The video pixels, demonstrated in this graph, are ideal waveforms from a CIS module using a

phototransistor imaging structure. The video output at high speeds, such as 5.0 MHz, does not instantly rise

to its final value, although, if it is given enough time it would eventually approach its steady state value (in

order of milliseconds). However, at high speeds it is impractical to wait until a final stable value is reached.

The suggested sampling point is therefore a few nanoseconds prior to the signal falling edge.

Page 10 of 13, Revised 2-23-04