Since for each
, a nonminimum phase
zero contributes an additional phase lag and imposes limitations on the rolloff rate of the
open-loop gain. For example, suppose L has a zero at z>0; then
Since the slope Lof near the
crossover frequency is, in general, no greater than -1, which means that the phase due to the minimum phase part, Lmp, of L will, in general, be no greater than -90o, the crossover frequency(or the closed-loop bandwidth) must satisfy
wc< z/2