Noise Analysis of CMOS Ring Oscillator-based Capacitance Measurement for Lab-on-Chip Application

CMOS-Capacitance sensor based integrated test interface for Lab-on-Chip applications has shown promising results for dielectric constant measurement of organic solvents, biological fluids or cell growth in laboratory environment. The process leverages the direct correlation between cell health (and/or dielectric constant) and the measured capacitance. The small changes in the electrode capacitance is monitored to measure the frequency change of a capacitance controlled ring oscillator containing a sensing electrode, that acts as a variable capacitor. In this work, the impact of the environment and systemic noise on the sensor interface read-out is presented. The resolution of this sensor is limited by the amount of read time given to each pixel, while the offsets in the outputs are calibrated out using differential measurement. The sensor has been incorporated into a 3x4 array prototype in 130 nm CMOS process.