An approach to the design of ELIN (externally linear internally nonlinear) signal processors

In VLSI circuits used in wireless and other types of electronic communications, nonlinear signal distortion arises from the nonlinear characteristics of the active devices in the circuit such as bipolar transistors, MOSFETs, and JFETs. We present a nonintrusive method for cancellation of such distortions. Specifically, let the VLSI circuit be denoted by ψ and assume that its output consists of r ports providing r output voltage signals. We design a r-input-port/r-output-port nonlinear circuit D, called a nonlinear distortion canceller. D is such that when the r output voltage signals of ψ are applied to D, the latter generates at its outputs the distortion error components present in the output signals of ψ. These are then subtracted from the distorted output signals from ψ, to provide their desired undistorted versions. The method of design of the nonlinear circuit D is derived rigorously based on a contraction mapping formulation. The results obtained are practical. The method can also be used to cancel nonlinear channel distortion in a multi-user communication system based on nonlinear channel models.