A low-ripple diode charge-pump type AC-DC converter based on the Cockcroft-Walton diode multiplier is proposed for coil-coupled passive IC tags in this paper. This circuit is developed as a power supply for passive RFID tags with smart functions such as heart rate detection and/or body temperature measurement. The proposed circuit converts wirelessly induced power to a low-ripple DC voltage suitable for a 13.56 MHz RFID tag. The proposed circuit topology and the principle of operation are explained and treated theoretically by using quasi-equivalent small-signal models. The proposed circuit was implemented on a PCB. And it was confirmed that the proposed circuit provides 3.3 V DC with a ripple of less than 20 mV when a 4 Vp-p sinusoidal input is applied. Under this condition, the maximum output power is about 310 µW. The measured results were in good agreement with theoretical and HSPICE simulation results.

A circuit design of a CMOS integrable heartbeat spike-pulse detection circuit is proposed in this paper. This circuit is developed to be implemented on a small-sized RFID sensor tag (which we call a smart RFID tag throughout this paper) implanted in a transgenic mouse. This circuit can detect only spike pulses with magnitude higher than the prescribed level from a mouse's heartbeat signal, which is sensed by a small microphone sensor and/or an electrocardiogram (ECG) microsensor attached to the RFID tag. The proposed circuit features robustness to the device tolerances and temperature variations thanks to its auto-bias technique based on good device matching and its switched-capacitor auto offset-canceling technique. The circuit was fabricated by a standard 0.35 µm CMOS process and works at a supply voltage of 3 V and dissipates less than 800 µW.

A simple CMOS Vth-adjustment method for a common-source floating-gate MOSFET(FG-MOSFET) is proposed. The apparent threshold voltage Vtha of an FG-MOSFET can be defined by a reference voltage Vref and/or a reference current Iref being almost irrelevant to the pre-stored charge on the floating gate.

To facilitate the reuse of environmental waste heat in our society, we have developed high-efficiency flexible thermoelectric power generators (TEPGs). In this study, we investigated the thermoelectromotive force (TEMF) and output power of a prototype device with 50 pairs of Π-type structures using a homemade measurement system for flexible TEPGs in order to evaluate their characteristics along the thickness direction. The prototype device consisted of C fabrics (CAFs) used as p-type materials, NiCu fabrics (NCFs) used as n-type materials, and Ag fabrics (AGFs) used as metal electrodes. Applying a temperature difference of 5K, we obtained a TEMF of 150μV and maximum output power of 6.4pW. The obtained TEMF was smaller than that expected from the Seebeck coefficients of each fabric, which is considered to be mainly because of the influence of contact thermal resistance at the semiconductor-fabric/AGF interfaces.