Inertial sensor
In an inertial sensor that includes an angular rate detection circuit having a structure synchronized with a resonant frequency of an angular rate detection element, an object thereof is to realize an angle output having high accuracy with less integration error in an integration circuit for detecting an angle. The inertial sensor includes an angular rate detection element chip C 1 that has a mechanical structure for angular rate detection; and a signal processing LSI chip C 2 that is angular rate detection circuit for detecting an angular rate from the angular rate detection element chip C 1 . The signal processing LSI chip C 2 calculates an angle by sampling a signal obtained from the angular rate detection element chip C 1 at a discrete time synchronized with a drive frequency of the angular rate detection element chip C 1.
1. An inertial sensor comprising:
an angular rate detection element that has a mechanical structure configured to detect angular rate; and
an angular rate detection circuit configured to detect an angular rate from the angular rate detection element, wherein
the angular rate detection circuit is configured to calculate an angle by sampling a signal obtained from the angular rate detection element at a discrete time synchronized with a drive frequency of the angular rate detection element,
the signal obtained from the angular rate detection element by the angular rate detection circuit is an angular rate,
an operation clock of the angular rate detection circuit is synchronized with the drive frequency of the angular rate detection element,
a calculation in which the angular rate detection circuit calculates the angle is a time integration,
the drive frequency of the angular rate detection element is a resonant frequency of the angular rate detection element,
the drive frequency of the angular rate detection element or a value obtained from multiplication or division thereof is stored in advance in a storage region in the angular rate detection circuit, and
the angular rate detection circuit calculates the angle by using the drive frequency or the value stored in the storage region.
2. The inertial sensor according to claim 1 ,
wherein an angular rate used for integration calculation by the angular rate detection circuit is a signal before passing through an LPF that outputs as the angular rate.
3. The inertial sensor according to claim 1 ,
wherein in the integration calculation of the angular rate detection circuit, correction is performed by a temperature sensor.
4. The inertial sensor according to claim 1 ,
wherein in the integration calculation of the angular rate detection circuit, an integration value is reset by an external resent signal.
5. The inertial sensor according to claim 1 ,
wherein the integration calculation of the angular rate detection circuit detects that a movement of a measurement object does not occur or acceleration other than gravity is not applied to the measurement object, from an external signal indicating a motion state of the measurement object, and resets the integration value at a timing of the detection.
6. The inertial sensor according to claim 1 , further comprising:
an acceleration detection element that has a mechanical structure for acceleration detection; and
an acceleration detection circuit for detecting an acceleration from the acceleration detection element,
wherein the acceleration detection circuit determines that at least one sensor has failed in a case where a difference between a result of an angle obtained from an inverse trigonometric function of the acceleration and a result of an angle obtained from a time integration of the angular rate exceeds a certain value.
7. The inertial sensor according to claim 1 , further comprising:
a plurality of the angular rate detection elements that have a mechanical structure for detecting the angular rate of at least two axes or more; and
the angular rate detection circuit for detecting an angle from the plurality of angular rate detection elements,
wherein the angular rate detection circuit is synchronized with a drive frequency of the plurality of angular rate detection elements,
wherein the drive frequency of the angular rate detection element synchronized with the drive frequency or the value obtained from multiplication or division thereof is stored in advance in the storage region, and
wherein the angular rate detection circuit calculates angles of all axes using a value stored in the storage region.
8. The inertial sensor according to claim 1 , further comprising:
a plurality of the angular rate detection elements that have a mechanical structure for detecting the angular rate of at least two axes or more; and
the angular rate detection circuit for detecting an angle from the plurality of angular rate detection elements,
wherein the angular rate detection circuit calculates a value which is obtained from a calculation result of a plurality of angles and by which a property of a measurement object is uniquely obtained, and outputs the calculated value.
9. The inertial sensor according to claim 1 ,
wherein the angular rate detection circuit has
a storage region that stores in advance the drive frequency of the angular rate detection element or the value obtained from multiplication or division thereof, and
a calculation circuit that calculates an angle by sampling a signal obtained from the angular rate detection element at the discrete time synchronized with the drive frequency of the angular rate detection element, and calculates the angle by using the value stored in the storage region when calculating the angle.