A Low-Cost, Low-Power, 10MHz Multifrequency Impedance Analyzer

In this paper we present a low-cost low-power multifrequency impedance analyzer based on a monolithic mixed-signal (analog/digital) microchip that performs all the tasks necessary to perform impedance measurements in the frequency range from 10kHz to 10MHz. In contrast to a full analog lock-in approach, this mixed-signal solution combines the lock-in approach with the dual step super-heterodyne demodulation scheme. The circuit ensures a CMRR of 81dB@10kHz, which increases to 84dB@10MHz. The measured equivalent input noise power spectral density is e(n)=2.57nV/root Hz at 10kHz in the worst case, close to the 1/f corner frequency. It decreases to e(n)=1.8nV/root Hz at 1MHz and e(n)=1.9nV/root Hz at 10MHz. Measurements of a reference RC network performed with the proposed low-cost low-power multifrequency impedance analyzer are compared with a Keysight E4980A Precision LCR Meter showing a maximal relative error of 0.8% over the whole operating frequency range.