A 0.13 um CMOS Operational Schmitt Trigger R-to-F Converter for Nanogap-Based Nanosensors Read-Out

We report design and measurements on a 0.13 um CMOS Schmitt Trigger-based quasi-digital resistance-to-fre- quency 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%  measurement accuracy and a dynamic range between 50 kOhm and 3 GOhm. The flexible R-to-F converter occupies 0.005 mm2 silicon area and has a simulated power consumption of 142 uW at 1.2 V supply.