Shifted Source Impedance and Nonlinearity Impact on RFID Transponder Communication for Drive-Level Offsets

A measurement and analysis method to quantify the communication quality for ultrahigh-frequency radio frequency identification (RFID) transponder chips under a shifting source environment is presented. A detailed description of theory, setup, and procedure is provided. The differences in on/off impedance ( |ΔΓ|-value) of the transponder chip are critical for backscatter modulation and, therefore, the overall communication and transponder response. In the present work, a new quantity which includes the difference in on/off impedance, as well as arbitrary source impedance, is defined as an overall figure of merit. A qualitative analysis, considered as novel in the RFID community, shows the impact a source impedance shift has on the communication quality. The bare chip measurement setup enables an ASK modulated wake up signal, realized as a pulse train. The chip response consisting of modulated impedance states are measured in a pulse profile setup. Results show that different degrees of nonlinearity in a transponder chip, depending on vendor and type, will have impact on the communication performance.