Differential amplification for micro-electro-mechanical ultra-sensitive accelerometer
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorsRichard L. Waters, Chris Hutchens, Monti E. Aklufi
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Abstract
An improvement to an optical accelerometer based upon the monolithic integration of a Fabry-Perot interferometer and a p+n silicon photosensor includes using one or more pairs of optical accelerometers wherein each pair provides for greater accelerometer sensitivity than a single independent accelerometer, and allows for a reduction in common mode noise due to amplitude and phase difference variations of the utilized light source as well as supply voltage. The differential approach of the invention provides for the biasing of the optical accelerometers such that their output signals are 180 degrees out of phase with each other.
Claims17
A high sensitivity micro-electro-mechanical optical accelerometer system comprising:
- first and second substantially identical optical accelerometers each including,
- an interferometer, including a pair of partially transmissive, partially reflective, surfaces wherein a first of said surfaces is flexibly suspended adjacent and parallel to a second of said surfaces so that a gap exists therebetween;
- a proof mass attached to said flexibly suspended first surface;
- and
- a photosensor attached to one of said surfaces outside of said gap, said photosensor for receiving light through said first and second surfaces wherein said light is also partially reflected between said surfaces;
- whereby a change in said gap due to an acceleration force is sensed by a change in said light as detected by said photosensor;
- a source of monochromatic light for irradiating said photosensors of said first and second optical accelerometers;
- a power supply for biasing said photosensors with a substantially equal amount of current and for providing a common supply voltage to said accelerometer system;
- wherein said gap of said first optical accelerometer is set so that said first optical accelerometer provides an increase in light transmission upon initially sensing said acceleration force and said gap of said second optical accelerometers is set so that said second optical accelerometer provides a decrease in light transmission upon initially sensing said acceleration force;
- and
- a differential circuit for subtracting a photosensor output of one of said optical accelerometers from a photosensor output of the other of said optical accelerometers.
A high sensitivity micro-electromechanical optical accelerometer system comprising:
- first and second substantially identical optical accelerometers each including,
- a Fabry-Perot interferometer, including a pair of partially transmissive, partially reflective, surfaces wherein a first of said surfaces is flexibly suspended adjacent and parallel to a second of said surfaces so that a gap exists therebetween;
- a proof mass attached to said flexibly suspended first surface;
- a photodiode attached to said second surface outside of said gap, said photodiode for receiving light through said first and second surfaces wherein said light is also partially reflected between said surfaces;
- whereby a change in said gap due to an acceleration force is sensed by a change in said light as detected by said photodiode;
- a source of monochromatic light for irradiating said photodiodes of said first and second optical accelerometers;
- a power supply for biasing said photodiodes with a substantially equal amount of current and for providing a common supply voltage to said accelerometer system;
- a source of variable electrostatic potential for providing a separate selected electrostatic potential between said first and second surfaces of said interferometers so that said gaps are adjustable;
- wherein said gap of said first optical accelerometer is set so that said first optical accelerometer provides an increase in light transmission upon initially sensing said acceleration force and said gap of said second optical accelerometers is set so that said second optical accelerometer provides a decrease in light transmission upon initially sensing said acceleration force;
- and
- a differential circuit for subtracting a photodiode output of one of said optical accelerometers from a photodiode output of the other of said optical accelerometers.
Dependencies are inferred from the claim text.