This work shows a novel, fully digital technique to automatically estimate distortion compensation coefficients for ADC post-correction. A synchronous phase-and-amplitude-locked loop is used to obtain a clean replica of the sinusoidal input. The estimated tone is compared to the distorted output to obtain an error signal containing information on the distortion. The technique can be synthesized, either on-chip or on a FPGA, or implemented in software, with no degradation of ADC performance. Simulations show the effectiveness of the proposed technique, that can be generalized to any distortion order thanks to the independent estimation of the correction coefficients.