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In this paper, single-bit sigma-delta modulator based digital-analog conversion (DAC) is evaluated as potential driver in multichannel electrical impedance spectroscopy (EIS) arrays. The sinusoidal excitation with typical frequency range of a few Hz to a few M Hz is a challenging task, which only very few state of the art implementations are even able to realize on chip, where the corresponding DAC consumes major amounts of area and power. Sigma-delta modulators offer signal generation with 1-bit representation, which could be advantageously multiplexed, distributed, and used on switches to generate analog output; thus its use could potentially lower the area and power consumption. This paper investigates the use of a single-bit sigma-delta DAC as direct driver for EIS experiments. Performances and limitations of the proposed system are experimentally analyzed and discussed. EIS experiments of micro-electrodes could be successfully conducted in a range from 20 Hz to 1 M Hz and matched with reference measurements to better than 95 % accuracy.

Electrical Impedance Spectroscopy (EIS) is a popular method for investigating tissue properties. Implementing the signal generator for EIS measurements with a suitable excitation signal type is thereby one of the two system components. The choice of the excitation signal defines the measurement speed, signal-to-noise ratio (SNR), total area and power consumption of the system, and many more properties. Signal types such as analog single-tone, analog multi-tone, linear feedback shift registers (LFSR), and single-tone Sigma Delta Modulated (Σ∆M) are proposed in the state of the art. In this work an EIS setup is implemented and successfully tested with all the mentioned signal types to evaluate their properties on impedance models as well as in vitro cell layers. It is proposed to combine the Σ∆M with the multi-tone excitation signal yielding a very versatile excitation generator. Multi-tone Σ∆M are as fast as analog multitones, while benefiting from a binary output and thus less system complexity. The implemented EIS setup is used to perform EIS measurement for biological samples. The results show a very good matching with the reference for all the excitation signals.

In this paper, a comparison between three different current readouts for micro-potentiostats is presented: resistive transimpedance amplifier (R-TIA), capacitive transimpedance amplifier (C-TIA), and current-mode continuous-time sigma-delta modulator (Current-CTSDM). The comparison is carried out on the signal transfer function, the required amplifier gainbandwidth (GBW), its input referred noise current, required area and power, and dynamic range. Each approach and its limitations are separately discussed. The three systems have been simulated using VerilogA models and the results are compared. It is shown that each system comes with its own limitations, however current-mode CTSDM are more beneficial due to their intrinsic digitization.

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