An adaptive controller used in a photoplethysmography sensing system, comprises a plurality of hardware circuits which are configured to: receive a photoplethysmography signal (hereinafter, “PPG signal”) processed； determine whether the PPG signal processed satisfies with a requirement； output the PPG signal processed if the PPG signal processed satisfies with a requirement； and adjust a gain of an amplifier for amplifying the PPG signal and/or a driving signal of a light source if the PPG signal processed does not satisfy with a requirement.
