In pixel VCO-based 5V 58.5μW Capacitance Sensing for Large Area Electrowetting Arrays

Abstract

This work presents a VCO-based capacitance sensing circuit aimed at large area electrowetting on dielectric (EWOD) arrays in thin-film transistor (TFT) technology. The proposed solution can detect three levels of electrode capacitance (20fF/330fF/655fF) corresponding to three levels of droplet detection and can be implemented in-pixel (confined to the electrode’s area) or shared amongst several electrodes to enable higher resolution arrays. A method to perform calibrated measurements based on this circuit is demonstrated. Additionally, the pulsed nature of the proposed VCO’s output makes it resilient to large array parasitic elements during readout. An additional column-wise readout stage far from the electrode/pixel area is also proposed. This circuit’s total power consumption is 58.5μW and the area occupied is 418.2μm x 198.6μm including an EWOD electrode modeling capacitor.