A Dual-Slope Capacitance-to-Digital Converter Integrated in an Implantable Pressure-Sensing System Sechang Oh, Student Member , IEEE, Y

Abstract

A dual-slope capacitance-to-digital converter for pressure-sensing is presented and demonstrated in a complete microsystem. The design uses bas e capacitance subtraction with a configurable capacitor bank to narrow down input capacitance range and reduce conversion time . An energy-efficient iterative charge subtraction method is proposed, employing a current mirror that leverages the 3.6 V battery supply available in the system. We also propose dual-pre cision comparators to reduce comparator power while maintaining high accuracy during slope conversion, further improving en ergy efficiency. The converter occupies 0.105 mm in 180 nm CMOS and achieves 44.2 dB SNR at 6.4 ms conversion time and 110 nW of power, corresponding to 5.3 pJ/conv-step FoM. The converter is integrated with a pressure transducer, battery, processor, power management unit, and radio to form a complete 1.4 mm 2.8 mm 1.6 mm pressure sensor system aimed at implantable devi ces. The multi-layer system is implemented in 180 nm CMOS. The system was tested for reso- lution in a pressure chamber with an external 3.6 V supply and serial communication bus, and the measured resolution of 0.77 mmHg was recorded. We also demonstrated the wireless readout of the pressure data on the stack system operating completely wirelessly using an integrated battery.