The PW-SAF could be extended to model more complex nonlinearities in VCO characteristics by incorporating higher-order terms in the piecewise approximation. Instead of relying solely on linear segments within each tuning voltage interval, higher-order polynomial approximations could be used to capture the nonlinearity more accurately. This would involve calculating and incorporating additional derivatives of the admittance function to account for the curvature and nonlinearity of the VCO response. By including quadratic or cubic terms in the piecewise model, the PW-SAF could better represent the intricate behavior of the VCO over a wider range of tuning voltages.