You high impedance scope probe has a non-zero capacitance (probably 10pF with a 1M probe) which will lead to the rounding off of high frequency response.

The probe effect is often modelled as a simple RC element, but in reality is considerably more complex, and this tends to be more visible when the source circuit impedance is high.

The discontinuity you are seeing looks to me like an RCRC effect from the combination of probe and scope architecture, exposed by the very high source impedance.

If you need better results, I'd suggest you look at some of the custom probing options in Howard Johnson and Martin Graham's excellent "High Speed Digital Design: A Handbook of Black Magic.".

These show how you can tailor probe characteristics for particular applications, often trading signal amplitude for veracity.

If it works in you application, the best result might come from connecting your scope in 50R mode between the bottom of R12 and Gnd. You signal will be down to 1mV, but I suspect the waveform shape will have way fewer artefacts.

Your high impedance scope probe has a non-zero capacitance (probably 10pF with a 1M probe) which will lead to the rounding off of high frequency response.

The probe effect is often modelled as a simple RC element, but in reality is considerably more complex, and this tends to be more visible when the source circuit impedance is high.

The discontinuity you are seeing looks to me like an RCRC effect from the combination of probe and scope architecture, exposed by the very high source impedance.

If you need better results, I'd suggest you look at some of the custom probing options in Howard Johnson and Martin Graham's excellent "High Speed Digital Design: A Handbook of Black Magic.".

These show how you can tailor probe characteristics for particular applications, often trading signal amplitude for veracity.

If it works in you application, the best result might come from connecting your scope in 50R mode between the bottom of R12 and Gnd. You signal will be down to 1mV, but I suspect the waveform shape will have way fewer artefacts.

(You should also check the trimmer cap adjustment of your probe, as that not being right would definitely make the system RCRC.)

You high impedance scope probe has a definite capacitance (probably 10pF with a 1M probe) which will lead to the rounding off of high frequency response.

The probe effect is often modelled as a simple RC element, but in reality is considerably more complex, and this tends to be more visible when the source circuit impedance is high.

The discontinuity you are seeing looks to me like an RCRC effect from the combination of probe and scope architecture, exposed by the very high source impedance.

If you need better results, I'd suggest you look at some of the custom probing options in Howard Johnson and Martin Graham's excellent "High Speed Digital Design: A Handbook of Black Magic.".

These show how you can tailor probe characteristics for particular applications, often trading signal amplitude for veracity.

If it works in you application, the best result might come from connecting your scope in 50R mode between the bottom of R12 and Gnd. You signal will be down to 1mV, but I suspect the waveform shape will have way fewer artefacts.

You high impedance scope probe has a non-zero capacitance (probably 10pF with a 1M probe) which will lead to the rounding off of high frequency response.

The probe effect is often modelled as a simple RC element, but in reality is considerably more complex, and this tends to be more visible when the source circuit impedance is high.

The discontinuity you are seeing looks to me like an RCRC effect from the combination of probe and scope architecture, exposed by the very high source impedance.

If you need better results, I'd suggest you look at some of the custom probing options in Howard Johnson and Martin Graham's excellent "High Speed Digital Design: A Handbook of Black Magic.".

These show how you can tailor probe characteristics for particular applications, often trading signal amplitude for veracity.

If it works in you application, the best result might come from connecting your scope in 50R mode between the bottom of R12 and Gnd. You signal will be down to 1mV, but I suspect the waveform shape will have way fewer artefacts.