ACWWong wrote on Jan 4th, 2007, 2:13am:Ocsilloscope scope probes x1 are normally 10pF. ESD, pads, PCB are dependant on your design but typically around 1pF.
dandelion wrote on Jan 4th, 2007, 1:04am:In the test, I added a ~10 Ohm resistor seriesed connected with the output pin, the eye-diagram is OK again.Would you help to explain it?
I would if i could, but i can't think of why adding a 10 ohms in series with say a 10pF in parallel with 1Mohm (scope load) would improve matters so much... was the 10 ohms a leaded component with LOTS of parasitic inductance ?
Hi,AW,
Thanks for the reply. It is helpful to me.
The 10 ohm is not a leaded component. But, when we introduce a lead component like(in fact, the measurement condition is changed slightly), the eye-diagram is also OK without the 10 ohm.
As for why this happened, some guies of us think the added 10 ohms resistors improves the parasitic LCR network and hence the transient reponse. The parasitic LCR network will affect the tnasient reponse with two possibilitoies, one is the overshoot and another is over damped, which above will depend on its transfer function. The added 10 ohm res make it part away from the over damp condition.
Sound reasonable.