Abstract
A method in designing a function observer for linear systems with unknown inputs is presented in this paper. Some properties of the function observer are also discussed. If the system with unknown inputs is right invertible, the minimal order is uniquely determined and all poles of the observer are specified as a part of invariant zeroes. When the system is not right invertible, the minimal order can not be determined. However, the design procedure presented here is based on the usual algorithm for the system without unknown inputs, so that it gives the relatively lower order function observer even if system is not right invertible.
