How to measure amplitude MHz sine wave with 50 volts common mode
The proper way to measure ripple in a 1MHz SMPS is to use a 100nF ~ 1uF low ESR DC blocking cap and  50 Ohm coax with 50 Ohm termination .  0.1uF*50R =...30kHz HPF

This may reject low frequency noise and pass the ripple you are trying to measure. 

The causes of Ripple are mainly the ESR of the caps, chokes and switches with some possibilities of resonance and harmonics stimulated by std step load tests like 20% to 100%, 100~20% or just steady state.

The reasons for the measurement should be shared.

There are many ways to detect the peak or pk-pk voltage with 500 MHz GBW Op Amps and diodes but with 2V ripple , you don't need any gain just a fast diode and unity gain precision peak detector.  

The load &lt; 1K is critical to prevent measurement errors from stray capacitance and inductance and for cable distance , must use 50 ohm terminated coax.

You could also compress it and use an RF power detector (cheap ) LTC5507.

You can also get within 50~75 mV of 2Vpk-pk and 100kHzBW @ 10kOhm using a Schottky diode. By reducing Cap load of 100pF to near 0, improves slightly.



specs: source = 50Vdc + Slider ripple 0 to 2Vp 1MHz @ 0.1 OHm ESR
Ac couple with 100nF = 2 Ohm @ 1MHz = 150kHz HPF
rectify with 1N5712 model into 10k + 100 pf = 200kHz LPF

SIMulation

The other way to measure it  is 0.1UF coupled to a 50 Ohm Spectrum Analyzer but with diode clamps to protect the input.