A PI circuit with Q=1 is a form of 'all pass' filter. Basically you have a
critically damped RLC circuit, thus the phase delay is very well known. If
you follow this with an active switching element (a transistor or a gate
or a *valve*) then you get a nicely reshaped delayed edge wrt. the input
edge. A coaxial delay line does the same thing at higher frequencies. A
series critically damped RLC can be used to make a single impulse from an
edge f.ex. Some of this is used in sonar, radar and sampling (S&H)
circuits. I understand that some ground penetrating radar for scientific
applications uses something like this to make the wideband pulse. The idea
scales well and some versions are used in multi-megawatt physics
experiments to make fast pulses etc.

Peter

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