Differential charge transfer based accelerometer
First Claim
1. A method for measuring a differential change between first and second mutual capacitances of a MEMS circuit, wherein receiver electrodes of said first and second mutual capacitances are joined to form a common electrode, wherein charge transfer measurements are used to transfer charge to a reference capacitor and a plurality of current mirror structures are used to scale and control the amount of charge being transferred to said reference capacitor, and wherein a digitally controlled variable capacitor is used to change the amount of charge stored in said reference capacitor;
- with said method comprising the steps of;
performing first and second charge transfer measurements, each comprising a number of charge transfer cycles used to transfer charge from said common electrode to the reference capacitor, said first measurement characterised by driving a transmit electrode of said first capacitance high first, said second measurement characterised by driving a transmit electrode of said second capacitance high first;
compensating for parasitic capacitances in said MEMS circuit through the use of a sample-and-hold circuit selectively connected to said common electrode to maintain its voltage during a charge phase of a charge transfer cycle.
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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.
49 Citations
20 Claims
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1. A method for measuring a differential change between first and second mutual capacitances of a MEMS circuit, wherein receiver electrodes of said first and second mutual capacitances are joined to form a common electrode, wherein charge transfer measurements are used to transfer charge to a reference capacitor and a plurality of current mirror structures are used to scale and control the amount of charge being transferred to said reference capacitor, and wherein a digitally controlled variable capacitor is used to change the amount of charge stored in said reference capacitor;
- with said method comprising the steps of;
performing first and second charge transfer measurements, each comprising a number of charge transfer cycles used to transfer charge from said common electrode to the reference capacitor, said first measurement characterised by driving a transmit electrode of said first capacitance high first, said second measurement characterised by driving a transmit electrode of said second capacitance high first; compensating for parasitic capacitances in said MEMS circuit through the use of a sample-and-hold circuit selectively connected to said common electrode to maintain its voltage during a charge phase of a charge transfer cycle. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- with said method comprising the steps of;
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11. An integrated circuit for measuring a differential change between first and second mutual capacitances of a MEMS circuit, wherein receiver electrodes of said first and second mutual capacitances are joined to form a common electrode, said integrated circuit performing charge transfer measurements to transfer charge to a reference capacitor, with a plurality of current mirror structures used to scale and control the amount of charge being transferred to said reference capacitor, wherein a digitally controlled variable capacitor is used to change the amount of charge stored in said reference capacitor, with said integrated circuit performing first and second charge transfer measurements, each comprising a number of charge transfer cycles used to transfer charge from the common electrode to the reference capacitor, said first measurement characterised by driving a transmit electrode of said first capacitance high first, said second measurement characterised by driving a transmit electrode of said second capacitance high first;
- and wherein the integrated circuit compensates for parasitic capacitances in said MEMS circuit through the use of a sample-and-hold circuit selectively connected to said common electrode to maintain its voltage during a charge phase of a charge transfer cycle.
- View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
Specification