Method and apparatus for closed loop offset cancellation
First Claim
1. A method for operating a transducer having a moveable element that displaces from an initial position to sense acceleration, the method comprising the steps of:
- producing a first signal that is responsive to a capacitance of the transducer;
applying a first filter to the first signal, wherein the first filter has a frequency range pre-selected to acquire acceleration data, resulting in a filtered first signal;
producing, based on the filtered first signal, a second signal representing the acceleration sensed by the transducer, wherein the acceleration has a signal frequency within the frequency range of the first filter;
applying a low-pass filter having a cutoff frequency lower than the signal frequency of the acceleration to the second signal to thereby produce a third signal based on the second signal, wherein the third signal represents a low frequency component having a frequency lower than the signal frequency of the acceleration such that the third signal is associated with an offset of the moveable element of the transducer from the initial position; and
actuating the transducer with the third signal representing the low-frequency component to thereby apply an electrostatic force that restores the moveable element of the transducer to the initial position in response to an output of the low-pass filter and thereby substantially cancel the offset in the transducer.
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Accused Products
Abstract
An apparatus (100, 200) and method (300) for sensing acceleration are provided. The method includes producing (305) a first signal in response to an acceleration sensed by a transducer, producing (310) a second signal based on the first signal, and actuating (315) the transducer in response to the second signal to remove offset in the transducer. The first signal represents the acceleration, and the second signal represents a low frequency component associated with an offset in the transducer. The apparatus (100) includes a transducer (102) producing a capacitance in response to the acceleration, a sensing system (104, 106, 108) producing a first signal from the capacitance representing the acceleration, and a compensation system (112, 110) coupled between the sensing system and transducer. The compensation system produces a second signal based on the first signal for substantially removing an offset of the transducer.
11 Citations
24 Claims
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1. A method for operating a transducer having a moveable element that displaces from an initial position to sense acceleration, the method comprising the steps of:
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producing a first signal that is responsive to a capacitance of the transducer; applying a first filter to the first signal, wherein the first filter has a frequency range pre-selected to acquire acceleration data, resulting in a filtered first signal; producing, based on the filtered first signal, a second signal representing the acceleration sensed by the transducer, wherein the acceleration has a signal frequency within the frequency range of the first filter; applying a low-pass filter having a cutoff frequency lower than the signal frequency of the acceleration to the second signal to thereby produce a third signal based on the second signal, wherein the third signal represents a low frequency component having a frequency lower than the signal frequency of the acceleration such that the third signal is associated with an offset of the moveable element of the transducer from the initial position; and actuating the transducer with the third signal representing the low-frequency component to thereby apply an electrostatic force that restores the moveable element of the transducer to the initial position in response to an output of the low-pass filter and thereby substantially cancel the offset in the transducer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 22)
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9. An apparatus for sensing an acceleration having a signal frequency, the apparatus comprising:
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a transducer having an input and an output and a moveable element, said transducer configured to produce a capacitance based upon displacement of the moveable element from an initial position in response to the acceleration; a sensing system having an input coupled to said output of said transducer and having an output, said sensing system configured to produce a first signal from said capacitance, wherein said first signal is proportional to the acceleration, and said first signal is produced by applying a first filter of the sensing system to a capacitance-responsive signal that is derived from the capacitance, wherein the first filter has a frequency range pre-selected to acquire acceleration data; and a compensation system having an input coupled to said output of said sensing system and having an output coupled to said input of said transducer, said compensation system configured to; filter the first signal with a low-pass filter having a cutoff frequency lower than the signal frequency of the acceleration to thereby produce a second signal based on said first signal, said second signal being output representing a low-frequency component of the first signal having a frequency lower than the signal frequency of the acceleration and indicating an offset of said transducer; and supply the low frequency component that is output from the low-pass filter to the transducer to thereby apply an electrostatic force to restore the moveable element of the transducer to the initial position in response to the output of the low-pass filter and to thereby substantially cancel the offset in the transducer. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 23)
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17. A method for operating a transducer having a moveable element that displaces from an initial position to sense an acceleration, the method comprising:
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sensing a capacitance representing an acceleration sensed by the transducer, the acceleration having a signal frequency; producing a first signal that is responsive to the capacitance; applying a first filter to the first signal, wherein the first filter has a frequency range pre-selected to acquire acceleration data, resulting in a filtered first signal; producing, based on the filtered first signal, a second signal representing the acceleration, wherein the acceleration has a signal frequency within the frequency range of the first filter; applying a low-pass filter having a cutoff frequency below the signal frequency of the acceleration to the second signal to thereby extract a low frequency component from the sensed capacitance, the low frequency component representing an offset of the moveable element from the initial position and having a frequency lower than the signal frequency of the acceleration; and supplying the low frequency component that is output from the low-pass filter to the transducer to thereby apply an electrostatic force to restore the moveable element of the transducer to the initial position in response to the output of the low-pass filter and thereby substantially cancel the offset in the transducer. - View Dependent Claims (18, 19, 20, 21, 24)
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Specification