Low-voltage signal conditioning circuit for fluid-based inclination switch

A low-voltage signal conditioning circuit for a capacitive sensor was designed with 0.35 mum CMOS technology. A charge balanced capacitance detection circuit and summing amplifier were designed with inverter amplifier, feedback resistance and capacitance which determines the gain and frequency response of the circuit. The oscillator and hold capacitance were also integrated in the chip size of 1 mm by 0.5 mm. The chip was packaged with a fluid-based inclination switch on a ceramic substrate, and the characteristics were evaluated. A PDMS container of 4.0 mmtimes4.0 mmtimes2.0 mm was used for the inclination switch. The output voltage was changed at angles of 0, 90, 180 and 270 deg with propylene carbonate used as an electrolyte.