Comparison of direct digitization current sensing circuits for EIS

Abstract

In this work, a qualitative comparison between state of the art current recorders for biomedical applications is presented. Prior work showed that direct digitizing frontends outweight their analog counterparts. This work performs a comparison between the direct digitization frontends, namely time-based and current-input CTSDM frontends. It is shown that time-based converters - due to usage of current conveyors to generate a low impedance node - suffer from inferior linearity. Also the trade-off between SNR versus conversion time limits their achievable SNR and the maximum input signal frequency. On the other hand, with the usage of a FIR-DAC within a current input CTSDM, the requirements of the critical first amplifier are highly relaxed. In addition, the FIR-DAC reduces the influence of clock jitter and allows the current-input CTSDM to achieve a higher SNR and linearity compared to the time-based converters.