The IO is a regular PMOS-PULL-up and NMOS-PULL-dn IO with series resistors on pull-up and pull-dn branches. The IO is input an clock signal around 50MHz and it experiences an approximately 2nd-order ramping up to 1.8V and then suddenly being pulled to ground. The ramping-dropping pattern is periodical.
Does anyone experiences this. How to explain it? Please help.
