17:35 <bvernoux> hi

17:37 <azonenberg_work> o/ bvernoux

17:38 <azonenberg_work> So, i got really busy this week - i have a bunch of 200R resistors i wanted to try on the handheld probes

17:38 <azonenberg_work> Do you want me to hold off for that testing or just mail you the test boards now?

17:48 <bvernoux> like you prefer there is no hurry

17:48 <bvernoux> more we test better it is

17:48 <bvernoux> the idea is to fine tune the things and find root cause if there is any issue

17:53 <azonenberg_work> Yeah

17:53 <azonenberg_work> Right now it looks like we have two major known problems

17:54 <azonenberg_work> The first is the unterminated stub from the resistor to the tip of the needle, which has a resonance around 9 GHz but that might be causing weird effects lower down as well since we have sharp edges coming into it

17:55 <azonenberg_work> We cannot eliminate the stub, it's inherent in the construction of the probe, but simulation suggests that adding a different-sized stub to the probe just past the resistor will null out the peak and make it flat out to ~3 GHz which is probably fine for a handheld probe

17:56 <azonenberg_work> The second is the parasitic capacitance between pads of the resistor

17:57 <azonenberg_work> It's only 26 fF according to vishay's package model, but past ~1 GHz the shunt impedance of that capacitor is within the same OOM as the 1K ohm resistor and as you go further, the C dominates

17:57 <azonenberg_work> which causes significant peaking at higher frequencies

17:58 <azonenberg_work> however, neither of these two appear to explain the weird shapes we're seeing in the time domain plots

17:59 <azonenberg_work> Or if they do, my understanding of black magic is not sufficient to grok the cause