Circuit arrangement for evaluating an acceleration sensor signal
First Claim
1. A circuit arrangement for evaluating a capacitive signal from an acceleration sensor, said acceleration sensor comprising two fixed electrodes with an electric field between said fixed electrodes;
- a first electrode on an oscillating mass in the electric field between the two fixed electrodes, said first electrode being deflectable in the electric field by an acceleration force, said two fixed electrodes and said first electrode being electrically connected to form two capacitors (2,3) with a common center tap (c) acting together as a differential capacitor, said two capacitors (2,3) having approximately equal capacitances in a resting state of the acceleration sensor;
controllable drivers (4,5) for the two capacitors (2,3) formed by the two fixed electrodes and the first electrode, said controllable drivers (4,5) including means for charging the two capacitors (2,3) in phase opposition and means for transferring charge from one of the two capacitors to another periodically with square-wave signals in phase opposition and with a predetermined voltage amplitude; and
an evaluation circuit (20) for generating an acceleration-dependent signal, said evaluation circuit (20) including means for measuring a voltage at the common center tap (c) of said two capacitors (2,3) and means for determining a voltage change (Δ
U) after a transfer of said charge between said two capacitors (2,3).
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Accused Products
Abstract
The invention is a circuit arrangement for evaluating a capacitive signal from an acceleration sensor, in which an acceleration-dependent capacitance change is evaluated by measuring the voltage at the oscillator. After each voltage change, the charge of the two capacitor elements of a differential capacitor is neutralized by applying a predetermined voltage, preferably the operating voltage. When a new acceleration occurs, a voltage difference relative to the predetermined voltage is again determined. The voltage difference is converted into a pulse-width modulated signal and is used for supplying the two capacitor elements of the acceleration sensor. The circuit arrangement is preferably usable for activating an air bag in a motor vehicle.
18 Citations
14 Claims
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1. A circuit arrangement for evaluating a capacitive signal from an acceleration sensor, said acceleration sensor comprising two fixed electrodes with an electric field between said fixed electrodes;
- a first electrode on an oscillating mass in the electric field between the two fixed electrodes, said first electrode being deflectable in the electric field by an acceleration force, said two fixed electrodes and said first electrode being electrically connected to form two capacitors (2,3) with a common center tap (c) acting together as a differential capacitor, said two capacitors (2,3) having approximately equal capacitances in a resting state of the acceleration sensor;
controllable drivers (4,5) for the two capacitors (2,3) formed by the two fixed electrodes and the first electrode, said controllable drivers (4,5) including means for charging the two capacitors (2,3) in phase opposition and means for transferring charge from one of the two capacitors to another periodically with square-wave signals in phase opposition and with a predetermined voltage amplitude; and
an evaluation circuit (20) for generating an acceleration-dependent signal, said evaluation circuit (20) including means for measuring a voltage at the common center tap (c) of said two capacitors (2,3) and means for determining a voltage change (Δ
U) after a transfer of said charge between said two capacitors (2,3). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
- a first electrode on an oscillating mass in the electric field between the two fixed electrodes, said first electrode being deflectable in the electric field by an acceleration force, said two fixed electrodes and said first electrode being electrically connected to form two capacitors (2,3) with a common center tap (c) acting together as a differential capacitor, said two capacitors (2,3) having approximately equal capacitances in a resting state of the acceleration sensor;
Specification