Accelerometer with a combined self-test and ground electrode

Claim 1

A micro-machined accelerometer, operable in a first mode to detect an acceleration force, and in a second mode to test the operability of the accelerometer, comprising: a substrate; a moveable plate held at a fixed electrical potential and substantially parallel to and above said substrate, comprising, an aperture, a pedestal positioned within said aperture, and connected to said substrate; and means for connecting said pedestal to at least one edge of said aperture, to allow said moveable plate to rotate, relative to said substrate, about a flexure axis, in the presence of a force normal to said substrate; a first electrode formed upon said substrate which receives an AC voltage during said first mode and said second mode; a second electrode formed upon said substrate at a position opposite of said flexure axis from said first electrode, said second electrode receiving a voltage substantially similar to said AC voltage during said first and said second modes; and a third electrode formed upon said substrate to surround said aperture and extend on at least two opposing sides around said second electrode, said third electrode having an electrical potential substantially equal to said fixed electrical potential of said substrate during said first mode, and at a different electrical potential during said second mode to perform a self-test of the accelerometer.