A CMOS RF-Powered Tag with Sensing and Localization Capabilities

This paper presents a battery-less CMOS integrated RF tag with sensing and localization capabilities. In order to allow tag addressing, communication, and localization by external readers, the IC performs a back-scattering modulation of a sequence of received UWB pulses according to specific spreading codes. For this purpose a UWB RF switch is designed and connected to the UWB antenna. The adoption of backscattering is integral to achieve ultra-low power wireless communication. The use of quasi-orthogonal spreading codes allows communication and localization with multiple tags at the same time. The IC includes a low-power sensing interface suitable for internal temperature sensing or external capacitive sensors. The power required for operation is scavenged from an UHF signal and converted by means of an internal RF rectifier and of a dynamically reconfigurable charge pump circuit. An on-chip micropower oscillator clocks a digital control circuit. The circuit is implemented in a 0.18 μm CMOS process. The architecture of the IC and preliminary test results are disclosed.