Passive integrators are often used for B-dot and E-dot probes where the signal you want to see is the integral of the probe signal.
	Integrators come in a range of RC times, which you usually pick to be ~10X the width of the signal you are interested in.  For a signal that is a square pulse after integrating, the flat top will have a droop that drops ~10% in this case (worst case).
	There are two main varieties of integrators:  50 Ohm and high impedance.