Energy-Efficient PRBS Impedance Spectroscopy on a Digital Versatile Platform

This article presents the digital design of a versatile and low-power broadband impedance spectroscopy (IS) system based on the pseudorandom binary sequence (PRBS) excitation. The PRBS technique allows fast and low-power estimation of the impedance spectrum over a wide bandwidth with adequate accuracy, proving to be a good candidate for portable medical devices, especially. This article covers the low-power design of the firmware algorithms and implements them on a versatile and reconfigurable digital platform that can be easily adjusted to the specific application. It will analyze the digital platform with the aim of reducing power consumption while maintaining adequate accuracy of the estimated spectrum. This article studies two main algorithms (time-domain and frequency-domain) used for PRBS-based IS and implements both of them on the ultralow- power GAP-8 digital platform. They are compared in terms of accuracy, measurement time, and power budget, while the general design tradeoffs are drawn out. The time-domain algorithm demonstrated the best accuracy, while the frequency-domain one contributes more to save power and energy. However, the analysis of the energy-per-error FOM revealed that the time-domain algorithm outperforms the frequency-domain algorithm, offering better accuracy for the same energy consumption. Numerical methods and microprocessor resources are exploited to optimize the implementation of both algorithms, achieving a 27-ms processing time, the power consumption of as low as 1.4 mW, and a minimum energy consumption per measurement of 0.5 mJ, for a dense impedance spectrum estimation of 214 points.