A 0.2%-THD Sinusoidal Signal Generator With First-Order Analog Interpolation Over More Than Three Frequency Decades for EIS Applications

To develop miniaturized devices for electrical impedance spectroscopy (EIS), sinusoidal signal generators (SSGs) need to be fully integrated on chip. High spectral purity and wide frequency tunability are required. In this work, a novel approach to SSG design is proposed, leveraging first-order interpolation executed entirely in the analog domain. Compared to standard SSGs based on zero-order interpolation, lower distortion is obtained for the same clock frequency. Experimental testing of a 0.18-$\mu $m CMOS prototype, employing 32 samples for interpolation, yielded average total harmonic distortion (THD) equal to 0.225% across a 100 Hz–300 kHz frequency range, with 130-$\mu $A consumption. Performance is consistent across different amplitude settings and process–voltage–temperature (PVT) conditions. Such findings potentially lay the groundwork for further analog-interpolation-based waveform generation solutions.