How obtain transfer function for nonlinear Lipschitz system in form

x(k+1) = Ax(k) + Bu(k) + g(x(k))

where function g(x(k)) is nonlinear and is assumed to be differentiable with respect to x and this function is the class of differentiable Lipschitz nonlinear systems. Be precise, the function g(x(k)) is describe by convex set where this convex set is obtain form Jacobian matrix of function g(x(k)) where each elements in this Jacobian is bunded. (Has minimum and maximum value). In below paper is described nonlinear systems for which I want to obtain transfer function but for this nonlinear function  -> g(x(k))

"Observers for a class of Lipschitz systems with extension to Hinf performance analysis"

http://www.sciencedirect.com/science/article/pii/S0167691107000795

Best,

Mariusz