Of course, it does on the screen. At t = -200 ps, we cannot yet be sure that the rising edge
will come at all, there still could be a dropping clock enable, but the trace is already
shivering in anticipation of the things to happen. That is simply wrong. We do not want
a brick wall filter, it is only there so that marketing can advertize more -3dB bandwidth than is really
usable. When I see that step response: Is that pre-edge ringing the ground bounce of my driver
chip, or capacitive feedtrough trough the driver, or is it just an artefact?
If it is an artefact, is the ringing after the edge also an artefact, or do I have a little resonator
somewhere? It looks so identical to the time when we could not know if the pulse would fire at all.
If you read the book of Hollister on wideband amplifier design or that of Staric, you can see
what amount of work they used to put at Tektronix into their Y amplifiers, just to get a clean
step response. That has been replaced by marketing in the mean time.
Is there any pre-ringing in the screen dumps of that old 68030-based sampling scope?
Which scope should I trust when I tune the bias tee?
<
https://www.flickr.com/photos/137684711@N07/46284720054/in/album-72157706443876665/ >
(54751A 20 GHz plug in & 54754A 18 GHz differential TDR, and the pics left/right).
I have made these pictures this week for a discussion of bias tees on usenet sci.electronics.design.
regards,
Gerhard