Stable-operation design and fabrication results of a battery-less wireless-sensor interface IC with a switched-capacitor frequency-locked-loop circuit

This paper describes a method of designing a wireless-sensor interface integrated circuit that operates without a battery. Stable operation at low power is realized by integrating three kinds of circuit techniques: (i) a radio-frequency backscatter circuit for wireless sensing without power consumption, (ii) a sensor interface circuit with a frequency-locked loop for stable operation, (iii) and an energy harvester circuit with a power management function for battery-less operation. The circuit was fabricated using 0.13 mu m CMOS process technology for design verification. We realized battery-less wireless sensing with intermittent operation and achieved high stability against process, voltage and temperature variations. The sensor information was obtained from the frequency variation of the radio-frequency backscatter signal. The integrated circuit was operated with radio-frequency signal power input exceeding -5 dBm. The integrated circuit dissipated less than 107.5 mu A. The communication distance was 0.8 m at 920 MHz for 250 mW equivalent isotopically radiated power.