A Sub-50nW Implantable Body Temperature Sensor and Its Application to a Rat

An ultra-low-power implantable body temperature sensor with a power consumption of 40.9 nW is presented. Deep body temperature measurement can be utilized for diseases such as inflammatory response due to implantable devices, treatment of traumatic brain injury, early monitoring of rejection after kidney transplantation, and monitoring of frictional heat in artificial joints, as well as health management such as ovulation cycles. Since it is implanted in the body and operated by a battery, it is very important to minimize power consumption. For low power consumption, we propose a dynamic virtual Wheatstone bridge technology for low-power transducer driving, and the simplified architecture is designed to operate at 0.6 V. The chip fabricated in a 180 nm CMOS process meets the ASTM E1112-00 specification for medical thermometers. That is, it can measure from 34 °C to 43 °C and meets the accuracy of ±0.1 °C between 37 °C and 39 °C. The measured power consumption at 37 °C is 40.9 nW. To verify practical application, a temperature sensor was implanted in a rat and body temperature changes before and after anesthesia were observed.