This paper applies the proportional-integral (PI) observer in connecti
on with loop transfer recovery (LTR) design for continuous-time system
s. We show that a PI observer makes it possible to obtain time recover
y, i.e., exact recovery for t --> infinity, under mild conditions. Bas
ed on an extension of the LQG/LTR method of proportional (P) observers
, a systematic LTR design method is derived for the PI observer. Our r
ecovery design method allows time recovery and frequency (normal) reco
very to be done independently. Furthermore, we give explicit expressio
ns for the recovery error when asymptotic recovery cannot be obtained.
A design example demonstrates the advantages of time recovery in the
non-minimum phase case.