This paper demonstrates a background timing skew calibration for the time-interleaved (TI) ADCs using a direct time-based estimation to facilitate the input-independent and fast convergence features. It suppresses the timing spurs of a 20GS/s 8× TI-ADC below ‒50dB at a Nyquist input regardless of the calibrating input condition with 24 calibration cycles. The 8b time-domain TI-ADC achieves a 91.3fJ/conv.-step FoMWalden and >16GHz bandwidth.