A mixed-signal adaptive filter is proposed which can work with level-crossing ADC to maintain its energy efficiency and signal quality even under powerline interference. The adaptive filter adopts a novel phase and amplitude tracking method which does not require multibit multiplication as the conventional least mean square (LMS) adaptive filter does. It tracks the 60 Hz interference and generate an analog compensation signal to cancel it. This technique improves the powerline interference rejection at 60Hz by 28dB. From MATLAB simulation, it effectively reduces the unnecessary sampling caused by powerline interference of the LC-ADC by 94.4%.