Impedance Measurement Integrated Circuit for Wireless Sensor Readout

Abstract

This chip detects the resonant frequency of an inductor-capacitor (LC) wireless sensor by analyzing its impedance characteristics. When wireless coupling occurs between the transmitter (TX) resonator and the receiver (RX) sensor, the impedance of the TX coil varies with the RX sensor’s frequency response. By analyzing the voltage variation across the TX resonator, the TX coil’s impedance can be determined, achieving resonant frequency detection of the RX sensor. Existing portable sensor readout systems using commercial ICs suffer from high complexity and power consumption. To address these issues, an impedance measurement IC is designed. The proposed IC extracts voltage characteristics at both ends of the TX resonator using a single-to-differential converter, mixer, level shifter, and low-pass filter. Therefore, the impedance of the TX coil is derived by dividing the two output DC voltages. Post-layout simulations with varying the TX coil resistance confirm that the measured values match the initial set values. The IC is designed using the TSMC 180nm RF CMOS process.