# US 8,464,585 B2 · Combined MEMS accelerometer and gyroscope

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- Number: US 8,464,585 B2
- Document ID: US8464585B2
- Status: Granted
- Kind: B2
- Application number: 12/738,504
- Filed: 2008-10-20
- Published: 2010-12-09
- Granted: 2013-06-18
- Earliest claimed: 2007-10-18
- Assignees: Melexis Technologies SA; Universiteit Gent
- Applicants: Johan Raman; Pieter Rombouts
- Inventors: Johan Raman; Pieter Rombouts
- Web page: https://patentgrep.com/patent/US8464585B2

## CPC

- G01C 19/56: Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
- G01C 19/5755: the devices having a single sensing mass
- G01P 15/125: by capacitive pick-up
- G01P 15/14: by making use of gyroscopes (gyroscopes per se G01C19/00)
- G01P 15/18: in two or more dimensions
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})

## Abstract

A MEMS structure for a combined gyroscope and accelerometer unit (100) based on in-plane vibratory movements comprises a proof mass (101) and comb-drives (102) operable to cause the proof mass (101) to resonate in the x-direction, commonly referred to as the primary mode. Under the influence of a rotation Ωz around the z-axis, a Coriolis force acting in the y-direction results. This excites the secondary (or sense) mode. A set of parallel-plate capacitors 103 are provided to enable position readout along the secondary axis. In addition to the above, the comb-drive capacitors (102) of the primary mode can also be used for readout of position along the primary axis, and the parallel-plate capacitors (103) for actuation along the secondary axis. This can be achieved either by time-multiplexing these capacitors (102, 103) or by providing separate sets of capacitors (102, 103) for sensing and actuation along each axis. The unit can operate in separate ΣΔ force-feedback loops with respect to both axes. This force-feedback approach is already known for readout of the secondary mode of MEMS gyroscopes. It has not previously been applied to the primary mode of a gyroscope for the measurement of a component of acceleration.

## Claims

### Claim 1

A combined accelerometer and gyroscope unit comprising:
a proof mass;
primary actuating means operable to actuate the proof mass along a primary axis;
secondary actuating means operable to actuate the proof mass along a secondary axis;
secondary sensing means operable to sense a position of the proof mass along the secondary axis; and
primary sensing means operable to sense a position of the proof mass along the primary axis wherein ΣΔ force-feedback loops are set up for both the secondary axis and the primary axis wherein an input Vin is included in a primary ΣΔ force-feedback loop to force the proof mass to track a predefined movement.

### Claim 2 (depends on 1)

A combined accelerometer and gyroscope unit as claimed in claim 1 wherein the accelerometer and gyroscope unit is a MEMS accelerometer and gyroscope unit.

### Claim 3 (depends on 1)

A combined accelerometer and gyroscope unit as claimed in claim 1 wherein both the primary actuating means and the primary sensing means are comb-drive capacitors.

### Claim 4 (depends on 3)

A combined accelerometer and gyroscope unit as claimed in claim 3 wherein separate comb-drive capacitors are provided for actuating and for providing a readout signal.

### Claim 5 (depends on 3)

A combined accelerometer and gyroscope unit as claimed in claim 3 wherein time multiplexing is used to allow the same comb-drive capacitors to be utilised both for actuating and for providing a readout signal.

### Claim 6 (depends on 1)

A combined accelerometer and gyroscope unit as claimed in claim 1 wherein both the secondary actuating means and the secondary sensing means are differential parallel plate capacitors.

### Claim 7 (depends on 6)

A combined accelerometer and gyroscope unit as claimed in claim 6 wherein separate differential parallel plate capacitors are provided for actuating and for providing a readout signal.

### Claim 8 (depends on 6)

A combined accelerometer and gyroscope unit as claimed in claim 6 wherein time multiplexing is used to allow the same differential parallel plate capacitors to be utilised both for actuating and for providing a readout signal.

### Claim 9 (depends on 1)

A combined accelerometer and gyroscope unit as claimed in claim 1 wherein separate ΣΔ force-feedback loops are provided for the primary axis and the secondary axis.

### Claim 10 (depends on 9)

A combined accelerometer and gyroscope unit as claimed in claim 9 wherein a primary ΣΔ force-feedback loop has an input Vin.

### Claim 11 (depends on 9)

A combined accelerometer and gyroscope unit as claimed in claim 9 wherein each loop incorporates an electrical filter.

### Claim 12 (depends on 9)

A combined accelerometer and gyroscope unit as claimed in claim 9 wherein at the end of each loop, a quantizer is provided to deliver digital output values.

### Claim 13 (depends on 9)

A combined accelerometer and gyroscope unit as claimed in claim 9 wherein each loop contains a mechanical feedback path.

### Claim 14 (depends on 13)

A combined accelerometer and gyroscope unit as claimed in claim 13 wherein an electrical feedback path is also provided.

### Claim 15 (depends on 14)

A combined accelerometer and gyroscope unit as claimed in claim 14 wherein the feedback loops include electrical filters.

### Claim 16 (depends on 9)

A combined accelerometer and gyroscope unit as claimed in claim 9 wherein each loop includes a first filter and a second filter and wherein the second filters have the same poles as the first filters.

### Claim 17 (depends on 15)

A combined accelerometer and gyroscope unit as claimed in claim 15 wherein each loop includes a first filter and a second filter and wherein the second filters have different zeros to the first filters.

### Claim 18 (depends on 13)

A combined accelerometer and gyroscope unit as claimed in claim 13 further including a controller filter to stabilize the loop.

### Claim 19 (depends on 1)

A combined accelerometer and gyroscope unit as claimed in claim 1 wherein the unit further includes a tertiary actuating means operable to actuate the proof mass along a tertiary axis and/or tertiary sensing means operable to sense a position of the proof mass along the tertiary axis.

### Claim 20 (depends on 19)

A combined accelerometer and gyroscope unit as claimed in claim 19 wherein the tertiary axis is substantially perpendicular to the plane containing the primary and secondary axes.

### Claim 21 (depends on 19)

A combined accelerometer and gyroscope unit as claimed in claim 19 wherein both the tertiary actuating means and the tertiary sensing means are comb-drive capacitors.

### Claim 22 (depends on 21)

A combined accelerometer and gyroscope unit as claimed in claim 21 wherein separate comb-drive capacitors are provided for actuating and for providing a readout signal.

### Claim 23 (depends on 22)

A combined accelerometer and gyroscope unit as claimed in claim 22 wherein time multiplexing is used to allow the same comb-drive capacitors to be utilised both for actuating and for providing a readout signal.

### Claim 24 (depends on 23)

A combined accelerometer and gyroscope unit as claimed in claim 23 wherein two sets of fingers comprising the comb-drive capacitors are of differing dimensions along the tertiary axis.

### Claim 25 (depends on 1)

A combined accelerometer and gyroscope unit as claimed in claim 1 wherein the unit is operated in a mode wherein a ΣΔ force-feedback loop is set up for only one of the secondary axis and the primary axis.

### Claim 26 (depends on 1)

A sensor cluster comprising one or more combined accelerometer and gyroscope units according to claim 1.

### Claim 27 (depends on 26)

A sensor cluster as claimed in claim 26 wherein the cluster includes one or more dedicated single axis or multi-axis accelerometers and/or one or more dedicated single axis or multi-axis gyroscopes.

### Claim 28

A method of operating a combined accelerometer and gyroscope unit having a proof mass; primary actuating means operable to actuate the proof mass along a primary axis; secondary actuating means operable to actuate the proof mass along a secondary axis; secondary sensing means operable to sense a position of the proof mass along the secondary axis; and primary sensing means operable to sense a position of the proof mass along the primary axis, the method comprising the steps of: setting up ΣΔ force-feedback loops for the both the secondary axis and the primary axis to measure both a component of rotation and two components of acceleration wherein an input Vin is included in a primary ΣΔ force-feedback loop to force the proof mass to track a predefined movement.

### Claim 29 (depends on 28)

A method as claimed in claim 28 both the primary actuating means and the primary sensing means include comb-drive capacitors.