Very Low Power Supply Dependence ROIC for Capacitive Sensing Platforms

This paper presents a very low power consumption read out integrated circuit (ROIC) for conditioning and acquiring capacitive sensor signals for a frequency based converter platform with programmable resolution. The platform consists of a temperature compensated voltage reference circuit (bandgap) coupled to a low power capacitance to frequency converter (CtoF). It interfaces to a frequency processing architecture with high efficient frequency-to-code converters. A controlled compensation of the channel length modulation effect and the suppression of mobility dependence reduce the consumption of the ROIC down to 26 μA at half power supply. Furthermore, the temperature dependent coefficient achieved is only 16 ppm/^°C. In addition, the coupled compensated bandgap reference circuit compensates the power supply dependence of the CtoF, ensuring an output frequency completely independent of the power supply.