Optimization of NFC compatible transponder with respect to the nonlinear IC impedance

A very important quality factor of a transponder is its threshold field strength which is a result of the performance of the integrated circuit (IC) and the loop antenna. This is very important for near field communication (NFC) applications to ensure a fast and reliable communication between the active device and the transponder with a minimum of battery power. In this paper a new approach using a nonlinear model for the IC and an analytical description of the coil is presented to design a loop antenna with minimal threshold field strength. For comparison the IC is modeled with both a linear model and a nonlinear model. The optimization results for both cases show clearly the advantage of the procedure with a nonlinear IC model. Afterwards, the design constraints due to the input capacitance of the IC is analyzed.