A nonlinear macromodel for CMOS OTAs

A nonlinear parameterizable macromodel for CMOS Operational Transconductance Amplifiers (OTAs) is presented. The macromodel captures the DC, AC and large signal features of the transistor level original circuit, thus modeling accurately its time domain and nonlinear performance. The main contribution of this work is to account for the bias-dependent transconductance nonlinearities in the circuit, by curve-fitting the desired output characteristics with n-dimensional polynomials. The model can also account for the nonlinear dependence of the circuit's characteristics on several design parameters. The applicability of the model is demonstrated by modeling the response of an OTA-C filter.