  A simplified approach is proposed to investigate the continuous-time and
discrete-time complementary sensitivity Bode integrals (CSBIs) in this note.
For continuous-time feedback systems with unbounded frequency domain, the CSBI
weighted by $1/\omega^2$ is considered, where this simplified method reveals a
more explicit relationship between the value of CSBI and the structure of the
open-loop transfer function. With a minor modification of this method, the CSBI
of discrete-time system is derived, and illustrative examples are provided.
Compared with the existing results on CSBI, neither Cauchy integral theorem nor
Poisson integral formula are used throughout the analysis, and the analytic
constraint on the integrand is removed.
