Real-Time Impedance Characterization Method for RFID-Type Backscatter Communication Devices

This paper presents a radio frequency (RF) measurement method that allows to determine electrical characteristics such as scattering parameters or impedance of contactless passive chips, using common measurement devices such as oscilloscope, personal computer, and directional coupler. The measurements obtained using this method are as accurate as those obtained with vector network analyzer (VNA) measurements, while providing several improvements. First, the method makes it possible to measure a chip's impedance in activation state, which requires large input power, not compatible with VNA measurements. Second, this method realizes a real-time measurement, which consists in impedance measurement as a function of time. Therefore, this real-time measurement makes it possible to detect and measure the impedance changes of an actual contactless smart card's integrated circuit during a load modulation communication at different powers. Finally, this real-time impedance measurement gives important information on chips' electrical characteristics that can be used to optimize near-field communication devices design in order to reduce the power losses within an RF identification tag.