Thw all,
I do realize, that my post was kind of misleading.
I need a well calibrated square pulse generator to inject a charge sensitive amplifier through a capacitor.
Amplitude x Capacitance gives the injected charge.
I need to ram up the injected charge from 5 mV to a couple of volts to check the spectroscopic chain linearity.
If the injection signal (the square pulse) is not linear, I'm screwed.
The ripple/noise is not really an issue here since the charge preamp output will go to a spectroscopic amplifier, which is basically a band pass filter. (300Khz typical central frequency) and a ADC to get the peak amplitude.
I'll look at the average amplitude over , says thousands of triggers, washing out further the uncertainty linked to rippls/noise.