As per advice in this thread
https://www.eevblog.com/forum/projects/cheap-source-of-8mhz-square-wave/msg565436/#msg565436 I've built an inverter oscillator using SN74HC04 inverter and 12 Mhz ZTT ceramic resonator
http://www.ecsxtal.com/store/pdf/zttr.pdf It's a standard minimal oscillator setup as in ZTT datasheet, with one inverter in oscillator and one for buffering, no dampening resistor.
At first I've built everything on a breadboard, the waveform was terrible, I thought, all the stray capacitance is affecting and 12MHz is a bit too much for it, so I've soldered everything on a piece of copper board.
The waveform was a lot better, but still with quite significant overshoot and undershoot. I've tried adding a dampening resistor, but that didn't work, I've tried adding a resistor between output of the first inverter and input of the second one, but that didn't affect the waveform anyhow.
Then I thought that maybe the problem is in my probing setup, I was already using probe in x10 mode, so I tried to get rid of ground lead, I've used a spring on a probe. The waveform is somewhat better, but still overshoots are there.
Then I've tried adding a 330 Ohm resistor at the output and scoping after this resistor. Whaoa.. overshoots are gone.
Another pecularity - since I have a resistor at the input of the second buffering inverter, I can see that the waveform entering the second inverter is without overshoots, but I can see overshoots at the output.
My question is - how do I interpret what I see here? Are the edges of the oscillator too steep for my scope to display? Or is the oscillator really producing the waveform with those overshoots and scope probe 15pF capacitance in conjunction with 330 Ohm resistor filtering those out?