Comments on "a technique for optimal digital redesign of analog controllers"

A `lifting'-based method for the digital redesign of analog controllers was proposed in `A technique for optimal digital redesign of analog controllers'. The weighted sum of energies of continuous-time signals is presented as follows: J = ∫0∞ [(y(t)-yd(t))2+ρ2(u(t)-ud(t))2]dt, ρ2 = const. It was used as a cost functional, where y(t) and u(t) are the output and the control signal in the continuous system, while yd(t) and ud(t) denote the associated signals in the redesigned digital system. Some comments regarding the redesign of the analog computers are discussed.