  A multi-pole, multi-zero design allowed realizing a "true" phase-shifter (not
time-delayer) of flat frequency-response over more than 3 decades
(30Hz-100kHz), which can be extended to higher frequencies or broader bands
thanks to a modular design. Frequency-dependent optimization of a single
resistance made also the gain flat to within few percents. The
frequency-independent phase-shifter presented can find application in any
experiment in which an action needs to be taken (e.g. a measurement needs to be
performed) at a fixed phase-delay relative to an event, regardless of how
rapidly the system rotates or oscillates.
