Differential charge transfer based accelerometer

Abstract

An integrated circuit measures a differential change between first and second mutual capacitances having receiver electrodes joined to form a common electrode of an MEMS circuit. The integrated circuit performs charge transfer measurements to transfer charge to a reference capacitor and a variable capacitor is used to change the amount of charge stored in the reference capacitor. First and second charge transfer measurements are performed, each having a number of charge transfer cycles used to transfer charge from the common electrode to the reference capacitor. In the first measurement, a transmit electrode of the first capacitance is driven high first, and in the second measurement, a transmit electrode of the second capacitance is driven high first. The circuit compensates for parasitic capacitances in the MEMS circuit with a sample-and-hold circuit selectively connected to the common electrode to maintain its voltage during a charge phase of a charge transfer cycle.