“…In [5], the Hermite-Biehler theorem is used to determine analytically the set of stabilizing gains , , and of a PID controller by replacing the time delay by a �rst-order Padé approximation. In fact, extensions of the HermiteBiehler theorem were effectively used to determine the set of all stabilizing controllers of a given order and a given structure for systems without delay, see [1,6,7].…”