$5\mathrm{.}4-3$ Use small$-$error PLLanalysis to show that a first$-$order loop $H(s)=1$ cannot track an incoming signal whose instantaneous frequency is varying linearly with time ${}_i(t)=k{t}^2.$ This signal can be tracked within a constant phase if $H(s)=\frac{s+a}{s}.$ It can be tracked with a zero phase error if $H(s)=\frac{s^2+as+b}{s^2}.$