Pulse shape scans with comparators on

This scan was produced with a Helix128-2.2 mounted on an MSGC-PCB. It shows the pulse shape scanned by shifting the test pulse with respect to the sampling clock (that determines the time the current amplitued value is stored into the pipeline) and the comparator clock (which determines the time the state of the comparator is latched and sent outside the chip).

Under experiment conditions the sampling clocks sensitive edge (i. e. the falling edge) would be placed right on the signal's peak. The comparators' sensitive edge (i. e. the rising edge) a bit thereafter (e. g. 5ns) to ensure that the switching of the comparators' output does not disturb sampling the analog signal.

In the test setup the sampling clock was shifted with respect to the test pulse (and thus the pulse shape). The comparator clock's rising edge was placed at the time indicated by the vertical bars. Test signals were injected into 5 channels of different groups of 4 comparators, thus 4 comparators's outputs switched (as was observed). Thus 5 x 4mA were driven into the chip, which is a realistic situation.

A crosstalk of the comparators#s output to the analog signal can still be seen, but the peak is (of course) not seen before the comparator switch and it decays until the next sampling.


If you have questions or comments, please contact Harald Deppe.
Last updated 98/06/05 by Martin Feuerstack-Raible