Low Cost Autonomous Lock-In Amplifier for Resistance/Capacitance Sensor Measurements

This paper presents the design and experimental characterization of a portable high-precision single-phase lock-in instrument with phase adjustment. The core consists of an analog lock-in amplifier IC prototype, integrated in 0.18 mu m CMOS technology with 1.8 V supply, which features programmable gain and operating frequency, resulting in a versatile on-chip solution with power consumption below 834 mu W. It incorporates automatic phase alignment of the input and reference signals, performed through both a fixed -90 degrees and a 4-bit digitally programmable phase shifter, specifically designed using commercially available components to operate at 1 kHz frequency. The system is driven by an Arduino YUN board, thus overall conforming a low-cost autonomous signal recovery instrument to determine, in real time, the electrical equivalent of resistive and capacitive sensors with a sensitivity of 16.3 mu V/ohm @ epsilon(rS) < 3% and 37 kV/F @ epsilon(rS) < 5%, respectively.