Method and apparatus for calibration of stray capacitance mismatch in a closed loop electro-mechanical accelerometer
First Claim
1. In a closed loop transducer having a micro-machined sensing element which moves between top and bottom plates and the position of said element is sensed by changes in capacitance between the top and bottom plates in response to an external force by an integrated circuit which measures the position of said sensing element and provides a feedback force to said sensor to center it between said top and bottom plates,apparatus for calibrating stray capacitance between said sensing element and said top and bottom plates comprising,means for determining a stray capacitance parameter that is representative of the difference of stray capacitance between the sensing element and the top plate and stray capacitance between the sensing element and the bottom plate, andmeans for applying calibrating capacitance across said sensing element and said top plate or across said sensing element and said bottom plate, where said calibrating capacitance is proportional to said stray capacitance parameter.
4 Assignments
0 Petitions
Accused Products
Abstract
A method and apparatus for measuring and compensating for stray capacitance of a micro-machined sensor of an accelerometer system is disclosed. Stray capacitance differences between a top plate and a sensing element and between a bottom plate and the sensing element degrade accelerometer performance if not compensated for. Measurement of stray capacitance difference is achieved by operating the accelerometer in two calibration phases and measuring the steady-state output voltage in each of the two phases. In calibration phase 1, no force is applied to the sensor during clock intervals 1-4. In calibration phase 2, a dummy force up is applied and then a dummy force down is applied during those intervals 1-4. The difference in the output voltage of the two calibration phases is representative of the difference in stray capacitance of the sensor. Capacitance is added to the top or bottom plates in an amount proportional to the measured stray capacitance. The procedure is repeated until the voltage difference of the two calibration phases is zeroed, which is indicative that the inherent stray capacitance has been zeroed.
59 Citations
12 Claims
-
1. In a closed loop transducer having a micro-machined sensing element which moves between top and bottom plates and the position of said element is sensed by changes in capacitance between the top and bottom plates in response to an external force by an integrated circuit which measures the position of said sensing element and provides a feedback force to said sensor to center it between said top and bottom plates,
apparatus for calibrating stray capacitance between said sensing element and said top and bottom plates comprising, means for determining a stray capacitance parameter that is representative of the difference of stray capacitance between the sensing element and the top plate and stray capacitance between the sensing element and the bottom plate, and means for applying calibrating capacitance across said sensing element and said top plate or across said sensing element and said bottom plate, where said calibrating capacitance is proportional to said stray capacitance parameter.
-
7. In a closed loop transducer having a micro-machined sensing element which moves between top and bottom plates and the position of said element is sensed by changes in capacitance between the top and bottom plates in response to an external force by an integrated circuit which measures the position of said sensing element and provides a feedback force to said sensor to center it between said top and bottom plates,
a method for calibrating stray capacitance between said sensing element and said top and bottom plates comprising the steps of, determining a stray capacitance parameter that is representative of the difference of stray capacitance between the sensing element and the top plate and stray capacitance between the sensing element and the bottom plate, and applying calibrating capacitance across said sensing element and said top plate or across said sensing element and said bottom plate, where said calibrating capacitance is proportional to said stray capacitance parameter.
Specification