IBIS4-1300
Document Number: 38-05707 Rev. *B
Page 13 of 37
Figure 7. offset adjustment: fast offset adjustment mode
There are 2 modes of offset calibration for the output amplifier:
slow and fast adjustment. Figure 7. shows the timing and
signal waveforms for fast offset adjustment mode. Closing
both 'calib_f' and 'unitygain' operates it. After 'calib_f' is
opened again, the offset level is adjusted to the desired value
in a single cycle. The signal applied to the output amplifier
should be stable just before and during the adjustment phase.
The same is true for the DAC output.
The signal applied to the output amplifier can be either:
• The signal generated by the electrical dark reference in the
imager core itself, i.e. the pixels named "dark" inFigure 20.
• Apply the reference from outside on the pin EXTIN,
controlled by SEL_EXTIN.
If this fast offset adjustment is used, it should be done once
each frame, before the readout of the frame starts, e.g. during
the blanking time of the first line.
Figure 8. slow offset adjustment mode
Figure 8. shows the timing and signal waveforms for slow
offset adjustment mode. It is operated by pulsing 'calib_s'. The
amplifier input signal must be stable and refer to 'dark' signal
at the moment when calib_s goes low. The offset is slowly
adjusted with a time constant of about 100 of these pulses.
One pulse is then generated during each row blanking time.
The baseline is to use the fast calibration once per image. The
slow calibration is intended as alternative if, for very slow
readout, the offset drifts during the image.
calib_f
min. 500 ns
stable input
dark
signal
unitygain
>0
> 100 ns
calib_s
min. 100 ns
stable input
dark
signal
min 100 ns
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