I'm testing a board that is having clock issues. The design uses a 40 MHz oscillator, which outputs a clipped sine wave. The clock goes into an inverter buffer to get a 3.3V, 40 MHz sine wave. When scoping the clock, there is some distortion seen on the positive peaks (shown below). I've noticed that the sine wave is fine before going into the first inverter. The issue pops up on the other side of the inverter. My suspicion is that the inverting feedback resistor value might be the cause of the issue I am seeing, however, I can't find anything that could explain the distortion I am seeing with my clock. I've also read that add a small resistor value to the input of the inverter will help reduce ringing as well. Is that the case and can someone explain to me why/point me to a direction where I can learn more?
Any insight is greatly appreciated.