I am trying to use LMH6642MAX op amplifier in the inverting closed loop configuration (gain 3.5) for a periodic square input signal 20 kHz (2 Volts High, 0 Volts Low). The problem comes when I checked the ouput and I find that the output signal rings. When the input is low the output swings around 0 V and when is high it oscillates around 7 Volts.
My first thought was that the problem was coming from the power supply but I have added two decoupling capacitors in the positive rail of the op-amp, but it didn't fix the problem. The datasheet doesn't say the magnitude of the decoupling capacitor but I have used 0.01uF and 2.2uF because they have worked very well for similar op-amps.
My second thought was that the op-amp was unstable working at that frequency. That's is, the gain is 1 and the phase between the input and output is 180 degrees. However, after inspecting the datasheet, it seems that the open-loop gain reaches 0 dB when the frequency of the signal is of the order 100 Mhz.
I am running out of ideas about what could be the root cause of this ringing.