A $0.13~\mu{\rm m}$ CMOS Operational Schmitt Trigger R-to-F Converter for Nanogap-Based Nanosensors Read-Out

We report design and measurements on a $0.13~\mu{\rm m}$ CMOS Schmitt Trigger-based quasi-digital resistance-to-frequency converter prototype that can be effectively used as a read-out circuit for nanodevice-based sensors. The readout circuit comprises an operational amplifier and an inverting Schmitt Trigger, achieving an hysteresis scaled to 1 mV-order, hence, increasing frequency compared to a standard Schmitt Trigger RC oscillator. Experimental results obtained through an opto-isolated PCB set-up show maximum 0.8% $R_{L}$ measurement accuracy and a dynamic range between $50~{\rm k}\Omega$ and $3~{\rm G}\Omega$ . The flexible R-to-F converter occupies $\sim 0.005~{\rm mm}^{2}$ silicon area and has a simulated power consumption of $142~\mu{\rm W}$ at 1.2 V supply.