This paper presents a methodology that approximates the continuous non-linear differential equations describing the complex nonlinear dynamic behavior of the analog, mixed-signal I/O buffers using hybrid automaton. This modelling approach investigates the quantization of the NRZ input signal to analyze the I/O buffer's circuit dynamic and reduce its behavioral model order. This input/state decomposition consists of capturing the pre-driver's switching characteristics by a bank of discrete-controlled finite impulse response filters and integrating it with the driver's last stage output admittance nonlinear dynamics.