In this paper, we present a modeling approach for analog-to-digital converters (ADCs) based on modeling the static transfer function using integral nonlinearity (INL) measurements. The methodology relies on applying a Fast Fourier Transform (FFT) test to the output of a real ADC circuit and extracting the significant harmonics. These are used in a behavioral functional model to approximate the INL using a polynomial function. The resulting model is independent of the ADC type or structure, and is suitable for bottom-up system verification. We compare the performance of the new model with other models based on different modeling approaches, and show a gain in simulation speed of up to 300X.