Implicit energy cost of feedback in noisy channels

We investigate the energy cost of negative feedback in first and second order linear systems. Previous work demonstrated that, in noisy physical channels, tradeoffs between information and power lead to an energy cost for information. We show that, for a fixed signal power and output noise, the introduction of negative feedback reduces capacity for first and second order lowpass linear systems. This capacity reduction constitutes a fundamental energy cost associated with the use of feedback in linear systems.