Pressure sensor with differential capacitive output
A MEMS pressure sensor device is provided that can provide both a linear output with regard to external pressure, and a differential capacitance output so as to improve the signal amplitude level. These benefits are provided through use of a rotating proof mass that generates capacitive output from electrodes configured at both ends of the rotating proof mass. Sensor output can then be generated using a difference between the capacitances generated from the ends of the rotating proof mass. An additional benefit of such a configuration is that the differential capacitance output changes in a more linear fashion with respect to external pressure changes than does a capacitive output from traditional MEMS pressure sensors.
1. A micro electro-mechanical system (MEMS) pressure sensor comprising:
a rotating proof mass, wherein the rotating proof mass comprises
a moveable element adapted for motion relative to first and second rotational axes offset between first and second ends and from the other rotational axis,
a first section of the moveable element is formed between the first rotational axis and the first end and comprises an extended portion spaced away from the first rotational axis and the second rotational axis,
a second section of the moveable element is formed between the second rotational axis and the second end and comprises an extended portion spaced away from the second rotational axis and the first rotational axis,
a length of the extended portion of the second section is approximately equal to a length of the extended portion of the first section, and
a third section is formed between the first rotational axis and the second rotational axis;
a first diaphragm configured to deform in response to a first fluid pressure applied to a first side of the first diaphragm;
a second diaphragm configured to deform in response to a second fluid pressure applied to a first side of the second diaphragm;
a first linkage configured to couple a second surface of the first diaphragm to a first pivot point at the first rotational axis, wherein the second surface of the first diaphragm is opposite to the first surface of the first diaphragm; and
a second linkage configured to couple a second surface of the second diaphragm to a second pivot point at the second rotational axis, wherein the second surface of the second diaphragm is opposite to the first surface of the second diaphragm.
2. The MEMS pressure sensor of claim 1 further comprising:
the rotating proof mass further comprising a first major surface and a second major surface;
a first moveable element electrode placed on the first major surface of the first section of the moveable element at a first distance from the first rotational axis;
a second moveable element electrode placed on the first major surface of the second section of the moveable element at a second distance from the second rotational axis;
a first fixed electrode placed on a fixed surface in a location opposing the first moveable element electrode;
a second fixed electrode placed on the fixed surface in a location opposing the second moveable element electrode, wherein
the first moveable element electrode is electrically isolated from the second moveable element electrode,
the first fixed electrode is electrically isolated from the second fixed electrode,
the first moveable element electrode and the first fixed electrode form a first variable capacitor, and
the second moveable element electrode and the second fixed electrode form a second variable capacitor.
3. The MEMS pressure sensor of claim 2 further comprising:
a processor, coupled to the first and second variable capacitors, and configured to measure a difference between a first capacitance of the first variable capacitor and a second capacitance of the second variable capacitor, wherein the first and second capacitances are responsive to the first fluid pressure as applied to the first diaphragm and the second fluid pressure as applied to the second diaphragm.