The maximally flat response is obtained when Q = 0.707, which results when K = 1.586. In this case
the poles are at 45° angles, as indicated in Fig. 10.40(c). The poles cross the jω axis into the right half of
the s plane at the value of K that results in Q = ∞, that is, K = 3. Thus for K ≥ 3 this circuit becomes unstable