A 2.2 fA/√Hz, 120 dB Dynamic Range, 12 GΩ Hybrid Readout Interface for Various Ionic Spectroscopy Applications

This paper introduces an ultra-low noise continuous-time (CT) analog front-end (AFE) interface for ionic spectroscopy applications. The proposed readout technique combines magnitude/phase and lock-in architectures over a relatively wide frequency range, from 10 Hz to 100 kHz. This hybrid architecture enables the extension of the overall dynamic range (DR) to 120 dB. The presented AFE has a programmable transimpedance gain of 12 G$\Omega$ to cover various kinds of electrochemical impedance sensors. Moreover, the input-referred current noise reaches 2.2 fA/$\sqrt{}$Hz. This ensures a resolution of 125 fArms in a bandwidth of 2.5 kHz, which corresponds to the desired sensitivity of ionic sensing applications. The proposed readout architecture is implemented in 180 nm CMOS technology. It occupies an area of 0.7 $\mathrm{m}\mathrm{m}^{2}$ with a total power consumption equals 3.9 mW from a 1.8 V supply voltage.