A Low-Power Sensing System of VEGF Concentration with Monolithic Electrodes and An All-Digital Sub-Sampling Delay-Locked Loop

The CMOS MEMS capacitive transducer is integrated on the same chip for the point-of-care (PoC) applications. A low-noise sensing system using the sub-sampling technique to suppress the interface noise is presented. The biomarker is vascular endothelial growth factor (VEGF). The proposed sensing system converts the capacitance variations caused by the VEGF concentration at the transducer into digital codes with a low-power SAR-assisted time-to-digital converter (TDC). CMOS MEMS interdigitated electrodes are adopted as the transducer. Post-process etching and Au plating are applied on the surface of the electrodes. Experimental results show that a capacitive resolution of 28.3 fF and a sensing range of VEGF concentration from 1 to 1000 pg/ml are achieved. The power consumption of the sensing front-end is 18 μW and overall sensing system is merely 60.65 μW. The FOM of the proposed low-power VEGF sensing system is 587.8 pJ/conv.-step.