As the use of Internet-of-Things (IoT) devices in medical treatment and health moni toring continues to expand, traditional battery-powered sensors are becoming increas ingly inadequateduetothechallengesassociatedwithbatteryreplacement,whichoften necessitates additional surgeries and medical care. In contrast, thermoelectric energy harvesting (TEH) systems, which convert ambient thermal energy into electrical energy, offer a sustainable solution for wearable devices. TEH systems, known for their high energy density and flexibility, have the potential to make IoT devices self-powered by utilizing ambient thermalenergy. However,itisdifficulttoefficiently extract powerfrom low-temperature gradients. Previous studies have only achieved high energy-harvesting efficiency within limited ranges of thermoelectric generator (TEG) voltage (VTEG) and TEG internal resistance (RTEG). This limitation arises due to the high power consump tion of control systems, which consume a significant portion of the harvested energy, particularly under low VTEG and high RTEG conditions. To address these challenges, an interface for TEH systems with ultra-low power consumption and precise control mod ules is urgently needed. This project is divided into two parts. The first part involves summarizing and com paring the state-of-the-art in TEH, with a focus on advanced techniques used in other TEH systems and the potential for ultra-low power consumption. The remainder of the thesis proposes an all-digital controlled TEH interface that incorporates SAR zero current sensing (ZCS) and digital Maximum Power Point Tracking (MPPT). Theoretical analysis, designdetails, andmeasuredperformanceofthissystem—thefirstfullydigital controlled TEHsystem—arethoroughlydiscussed. Thechiphasalreadybeenfabricated andtested