This brief presents an overview of recent background timing mismatch calibration techniques in time-interleaved ADCs. Regarding the methods of detecting timing skew, the brief divides the existing methods into two categories: a) strategies based on deterministic equalization and b) techniques based on the statistical information of the input signal. Similarly, we can also divide timing skew correction into analog tuning and digital processing. The brief reviews previous works comparatively with these different methods and summarizes their pros and cons.