Patent Description:
It is often beneficial to sense the motion of an electronic device for vehicle. For this reason, many vehicles and electronic devices include inertial sensors. Inertial sensors can include accelerometers and gyroscopes. Accelerometers can detect linear motion. Gyroscopes can detect rotational motion.

Detecting a rotation rate of a vehicle or electronic device with a gyroscope can be quite complicated. This is due, in part, to the fact that complex signals are utilized to excite a resonating mass of the gyroscope enough to sense the rotational motion of the resonating mass. It can be quite difficult to accurately extract the rotational rate from the raw output signal of the gyroscope.

One particularly complicating factor is the quadrature component of an output signal. The raw output of a gyroscope corresponds to oscillation of a resonating mass in a sense direction perpendicular to the excitation direction of the resonating mass. While rotational motion will cause oscillation of the resonating mass in the sense direction, the quadrature effect will also contribute to oscillation of the resonating mass in the sense direction. However, the quadrature component of the raw output signal is spurious and does not represent rotational motion.

Gyroscopes have leveraged the fact that the quadrature component of the raw output signal is typically in phase with the excitation or driving signal, while the rotational component of the raw output signal is typically <NUM>° out of phase with the excitation or driving signal. Accordingly, the rotational component of the raw output signal the can be obtained by extracting the component of the raw output signal that is <NUM>° out of phase with the excitation or driving signal. However, if there is phase drift associated with the raw output signal, then extracting the component of the output signal that is <NUM>° out of phase with the driving signal will not accurately represent the rotational rate.

<CIT> discloses a demodulation phase calibration unit and method based on applying DCsignal to quadrature tuning electrodes in a calibration stage or in an operations stage at appropriate times, such as during startup or when a measured rate of rotation is less than a threshold.

Thus, an aim of the present invention is to overcome the drawbacks of the prior art.

According to the invention, a method for correcting gyroscope demodulation phase drift and a sensing device are provided, as defined in the accompanying claims.

In the following description, certain specific details are set forth in order to provide a thorough understanding of the invention. For example, the terms "first," "second," and similar indicators of sequence are to be construed as interchangeable unless the context clearly dictates otherwise.

In the following a sensor unit is described including a gyroscope. The sensor unit effectively and efficiently identifies phase drift between the raw output signal of the gyroscope and the drive signal of the gyroscope. This is accomplished by applying a test voltage to quadrature compensation electrodes adjacent to the resonator mass of the gyroscope and detecting changes in a demodulated output signal of the gyroscope while applying the test voltage.

After the phase drift has been identified, the phase drift can be taken into account in generating the demodulated output signal. The demodulated signal will then accurately represent the rotational component of the raw output signal.

The demodulated signal may be generated by demodulating the raw output signal with the drive signal. The demodulation process extracts the portion of the raw output signal that is <NUM> degrees out of phase with the drive signal. When a phase drift is detected while applying the test voltage, then a delay compensation circuit inserts a delay into the drive signal before demodulation occurs. The added delay compensates for the phase drift, effectively eliminating the negative effects of the phase drift.

The test signal may include a first phase and a second phase. In the first phase the test signal has a first polarity. In the second phase, the test signal has a second polarity. The sensor unit detects the difference in the demodulated output signal between the first phase and the second phase of the test signal. The difference is indicative of the phase drift.

<FIG> is a block diagram of an electronic device <NUM>. The electronic device <NUM> includes a sensor unit <NUM>. The sensor unit <NUM> includes a gyroscope <NUM>. As will be set forth in more detail below, the sensor unit <NUM> identifies phase drift associated with an output signal of the gyroscope <NUM> and compensates for the phase drift in order to provide an accurate indication of a rotational rate applied to the electronic device <NUM>.

The electronic device <NUM> can include a vehicle, such as an automobile, an aircraft, a boat, or other types of vehicles. It is often very beneficial to know the training rate of the vehicle about one or more axes of rotation. In vehicles, these axes of rotation may correspond to yaw, roll, and pitch. The gyroscope <NUM> may be utilized to detect the rotational rate of the vehicle about one or more of these axes.

The electronic device <NUM> can include a personal electronic device such as a smart phone, a smartwatch, smart glasses, a gaming device, a gaming controller, a tablet, a laptop computer, or other types of personal electronic devices. The gyroscope <NUM> may be utilized to detect the rotational rate of the electronic device <NUM> about one or more rotational axes. The electronic device <NUM> can include industrial equipment or other types of devices that may benefit from detecting rotational rates.

The gyroscope <NUM> may correspond to a microelectromechanical systems (MEMS) gyroscope. The mems gyroscope <NUM> can include one or more movable masses defined from and coupled to a silicon substrate by one or more spring members. The mems gyroscope may also include various electrodes interleaved with the movable mass. The following description is directed primarily to electro-capacitive mems gyroscopes. Nevertheless, other types of gyroscopes can be used.

The gyroscope <NUM> includes a resonator mass <NUM>, drive electrodes <NUM>, and sense electrodes <NUM>. As shown in <FIG>, the resonator mass <NUM>, the drive electrodes <NUM>, and the sense electrodes <NUM> are shown as making up the gyroscope <NUM>, while other components associated with generating signals, sensing signals, and processing signals are shown as external to the gyroscope <NUM>. However, in practice, the gyroscope <NUM> may be considered as including the various other components of the sensor unit <NUM> that will be described in greater detail below and that are shown as being external to the gyroscope <NUM>. The sensor unit <NUM> may, as a whole, be considered as a gyroscope.

The resonator mass <NUM> may include a mass suspended above or otherwise movably coupled to a substrate. The resonator mass <NUM> is configured to oscillate in at least two directions. A first direction of oscillation is known as a drive direction and corresponds to a first axis. A second direction of oscillation is known as a sense direction and corresponds to a second axis, substantially perpendicular to the first axis. Oscillation of the resonator mass <NUM> along the sense axis or sense direction is indicative of rotation of the resonator mass <NUM> about a third axis, substantially perpendicular to the first axis and the second axis.

The resonator mass <NUM> may be coupled to a fixed substrate by spring members that allow the resonator mass to move back and forth along the drive axis. The resonator mass <NUM> may also be coupled to the fixed substrate by spring members that allow the resonator mass to move back and forth along the sense axis. While <FIG> shows the resonator mass <NUM> as a single mass, in practice, the resonator mass <NUM> may include multiple masses. For example, a first mass may be coupled to a second mass by spring members. The first mass may be driven to oscillate along the drive axis. Rotation of the electronic device <NUM> around the rotation axis (third axis) may cause the second mass to oscillate along the sense axis (second axis). Various configurations of a resonator mass <NUM> or multiple resonator masses <NUM> can be utilized.

The drive electrodes <NUM> are utilized to drive the resonator mass <NUM> in the second direction. The drive electrodes <NUM> may correspond to a conductive mass with a comb shape. The fingers of the comb-shape may be interleaved with corresponding comb fingers of the resonator mass <NUM>. If a voltage is applied to the resonator mass <NUM>, then applying a periodic voltage to the drive electrodes can drive oscillation of the resonator mass <NUM> along the drive axis. However, various other configurations of drive electrodes <NUM> can be utilized.

The sense electrodes <NUM> are utilized to sense oscillation of the resonator mass <NUM> along the sense axis. The sense electrodes <NUM> may correspond to a conductive mass of the comb shape. The fingers of the comb shape may be interleaved with corresponding comb fingers of the resonator mass <NUM>. However, various other configurations of sense electrodes <NUM> can be utilized.

As described previously, if the electronic device <NUM> and, correspondingly, the resonator mass <NUM>, are rotated around the third rotation axis while the resonator mass <NUM> is oscillating along the first axis, then the resonator mass <NUM> will be forced to oscillate along the second axis by the Coriolis force that results from the rotation around the rotation axis and the oscillation along the first axis. Accordingly, the oscillation of the resonator mass <NUM> along the sense axis is indicative of the rotation of the resonator mass <NUM> around the rotation axis.

The sensor unit <NUM> includes a drive voltage supply <NUM>. The drive voltage supply <NUM> applies a drive voltage to the drive electrodes <NUM>. The drive voltage may correspond to an AC voltage having a selected amplitude and frequency. The drive voltage may be a sinusoidal voltage, a square wave voltage, a sawtooth voltage, or other types of AC voltage waveforms.

In the example of a constant rate gyroscope, the oscillation along the sense axis resulting from the Coriolis force will have the same frequency as the oscillation of the drive signal. However, the amplitude of the oscillation along the sense direction is indicative of the magnitude of the rotational rate around the third axis. The amplitude of the oscillation is indicated by the voltage that develops at the sense electrodes <NUM> by capacitive interaction with the resonator mass <NUM>. However, as set forth previously, other sensing configurations can be utilized.

The signal output by the sense electrodes <NUM> corresponds to the raw output signal of the gyroscope <NUM>. However, the raw output signal of the gyroscope <NUM> may not, by itself, accurately indicate the rotational rate around the third axis. This is because of a quadrature effect that develops at the resonator mass <NUM>. In particular, when the resonator mass <NUM> is driven to oscillate along the first axis by the drive voltage applied to the drive electrodes <NUM>, the resonator mass <NUM> may also begin to oscillate along the sense axis even if there is no rotation around the rotational axis. Accordingly, the oscillation due to the quadrature affect may be considered a spurious oscillation, or the component of the raw output signal that is based on the quadrature affect may be considered a spurious signal. The raw output signal may be a current or may be a voltage, depending on a selected configuration of the gyroscope <NUM>.

In some cases the component of the raw output signal due to the quadrature affect may be much larger than the component of the raw output signal due to the rotation of the electronic device <NUM> around the rotational axis. In fact, the component of the raw output signal from the quadrature affect may be many times larger than the component of the raw output signal from the Coriolis force.

The sensor unit <NUM> utilizes the demodulator <NUM> in order to extract the Coriolis component from the raw output signal. As the raw output signal is made up of the quadrature component and the Coriolis component, if the Coriolis component can be extracted from the raw output signal, then a final output signal can be generated that corresponds only to the Coriolis component of the raw output signal. The demodulator <NUM> extracts the Coriolis component from the raw output signal and generates a final output signal that indicates the rotational rate around the rotation axis. As used herein, the terms "Coriolis component" and "rotational component" may be used interchangeably.

The demodulator <NUM> utilizes the fact that the Coriolis component of the raw output signal will be <NUM>° out of phase with the quadrature component of the raw output signal in order to separate the Coriolis component from the quadrature component. Furthermore, absent any collective phase drift in the raw output signal, the quadrature component will be in phase with the drive signal while the Coriolis component is <NUM>° out of phase with the drive signal. Accordingly, the demodulator <NUM> receives the drive signal and the raw output signal and performs demodulation of the raw output signal based on the drive signal. In particular, the demodulator <NUM> outputs only that portion of the raw output signal that is <NUM>° out of phase with the drive signal. If there is no phase drift between the raw output signal and the drive signal, then the output of the demodulator <NUM> will represent only the Coriolis portion of the raw output signal.

Nevertheless, in some cases, there is a phase drift between the drive signal and the raw output signal. More particularly, the phase drift may occur between the raw output signal and a demodulation signal that is based on the drive signal. The demodulation signal may have a same phase as the drive signal, or may initially have a same phase as the drive signal. The phase drift corresponds to an angle ϕ by which the quadrature component is out of phase with the demodulation signal. The Coriolis component will be out of phase by <NUM>° ± the value of ϕ, depending on the direction of the phase drift. Even a very small phase drift can result in the demodulator <NUM> generating a final output signal that is very inaccurate. Phase drift can result from variations in temperature, mechanical stress, or variations during processing of the sensor unit <NUM>. The demodulation signal is a drive reference signal. As used herein, "demodulation signal" and "drive reference signal" may be used interchangeably.

The sensor unit <NUM> utilizes quadrature compensation electrodes <NUM>, a quadrature compensation driver <NUM>, a delay calculator <NUM>, and a delay compensation circuit <NUM> in order to identify and compensate for phase drift.

In one example, the quadrature compensation electrodes <NUM> are positioned adjacent to the resonator mass <NUM>. The quadrature compensation electrodes <NUM> can be used in both cases of in-plane sense axis (yaw) or out of plane sense axis (pitch and roll) based on selected design characteristics. The quadrature compensation electrodes <NUM> can be utilized to drive motion of the resonator mass <NUM> along the sense axis in order to compensate for or cancel out the natural quadrature that develops from driving the resonator mass <NUM> along the drive axis. Nevertheless, principles of the present disclosure provide a potentially more effective way to utilize the quadrature compensation electrodes <NUM> in order to identify and compensate for phase drift in the raw output signal.

The quadrature compensation driver <NUM> is configured to apply a test signal to the quadrature compensation electrodes <NUM>. The quadrature compensation driver <NUM> applies a test signal during a testing period; the delay calculator <NUM> measures changes in the output of the demodulator <NUM> during the testing period. The delay calculator <NUM> calculates the value of phase drift between the raw output signal and the demodulation signal based on changes in the output of the demodulator <NUM> during the testing period.

The testing period may have two phases. In this case, during the first phase, the test signal has a first polarity. During the second phase, the test signal switches to a second polarity opposite the first polarity. The change in the output of the demodulator <NUM> between the two phases of the test period is indicative of the magnitude of a phase drift angle ϕ. The delay calculator <NUM> calculates the value of the phase drift angle ϕ based, in part, on the change in the output of the demodulator <NUM> between the two phases of the test. Further details regarding the calculation of the phase drift angle ϕ are provided below.

The delay calculator <NUM> passes the value of the phase delay ϕ to the delay compensation circuit <NUM>. The delay compensation circuit <NUM> also receives the demodulation signal that is based on the drive signal. The delay compensation circuit <NUM> delays the demodulation signal by the value of the phase delay ϕ, generating a delayed demodulation signal. The delay compensation circuit <NUM> passes the delayed demodulation signal to the demodulator <NUM>. As used herein, the terms "phase drift" and "phase delay" may be used interchangeably.

While <FIG> illustrates the same signal being passed from the drive voltage supply <NUM> to the delay compensation circuit <NUM> and the drive electrodes <NUM>, in practice, the drive voltage supply <NUM> may supply the drive signal to the drive electrodes <NUM> and may supply the demodulation signal that is based on the drive signal to the delay compensation circuit <NUM>.

Because the demodulation signal is now delayed by the same phase delay value ϕ as is the raw output signal, the Coriolis component of the raw output signal is <NUM>° out of phase with the delayed demodulation signal. When the demodulator <NUM> performs demodulation on the delayed demodulation signal and the raw output signal, the demodulator <NUM> outputs the true Coriolis component of the raw output signal. Accordingly, the demodulator <NUM> outputs a signal that accurately indicates the rotational rate of the electronic device <NUM> around the rotational axis.

<FIG> is a simplified representation of the resonator mass <NUM> of the gyroscope <NUM>. The resonator mass is able to oscillate in the X direction by a spring represented here by the spring Kx. Oscillation of the resonator mass <NUM> in the X direction is dampened by a resistance Rx. The resonator mass <NUM> is able to oscillate in the Y direction by a spring represented here by the spring Ky. Oscillation of the resonator mass <NUM> in the Y direction is dampened by a resistance Ry. In practice, the resonator mass <NUM> may include masses coupled together in various configurations.

The X-axis corresponds to the drive axis of the resonator mass <NUM>. The y-axis corresponds to the sense axis of the resonator mass <NUM>. The z-axis corresponds to the rotational axis. Accordingly, motion of the resonator mass <NUM> along the sense axis Y is indicative of the rotational rate of the resonator mass about the rotational axis Z.

In <FIG>, the drive electrodes (see <FIG>) drive the resonator mass <NUM> to oscillate in the X direction. In <FIG>, there is no oscillation along the y-axis. Accordingly, there is no rotational rate around the rotational axis Z and there is no quadrature motion along the y-axis. Unfortunately, in practice there is typically a quadrature component along the sense axis anytime there is motion along the drive axis.

<FIG> illustrates both motion along the drive axis and motion along the sense axis. This is indicated by the diagonal arrows that have components in both the X and Y direction. In the example <FIG>, there is no rotational motion around the z-axis. Accordingly, all of the motion on the y-axis is quadrature motion. <FIG> are provided to illustrate basic concepts of drive motion and quadrature motion.

<FIG> is a graph <NUM> illustrating various possible signals output by the gyroscope <NUM>. The graph <NUM> includes the raw output signal <NUM> of a gyroscope <NUM>. The raw output signal <NUM> is sinusoidal in nature based on the capacitive output signals generated by sinusoidal motion of the resonator mass <NUM> relative to sense electrodes <NUM>.

<FIG> also illustrates the quadrature component <NUM> of the raw output signal <NUM>. If there is no phase drift between the demodulation signal and the raw output signal, the quadrature component <NUM> of the raw output signal <NUM> will be in phase with the demodulation signal.

<FIG> also illustrates the Coriolis component <NUM> of the raw output signal <NUM> of the gyroscope <NUM>. The Coriolis component <NUM> is that portion of the raw output signal that is generated by the Coriolis force from rotation of the electronic device <NUM> about the rotational axis while the resonator mass <NUM> is driven to oscillate along the drive axis. If there is no phase drift, the Coriolis component <NUM> will be <NUM>° out of phase with the demodulation signal.

The raw output signal <NUM> is the sum of the quadrature component <NUM> and the Coriolis component <NUM>. In practice, the amplitude of the quadrature component <NUM> may be many times larger than the amplitude of the Coriolis component <NUM>. Accordingly, it is highly beneficial to effectively demodulator the Coriolis component from the quadrature component using the demodulation signal as a phase reference.

<FIG> is a possible graph of the demodulation plane <NUM> associated with the raw output signal and the demodulation signal or drive signal of a gyroscope <NUM>. The demodulation plane <NUM> has two axes. The first axis is the parallel axis extending in the horizontal direction in <FIG> and annotated with the parallel symbol "=". The second axis is the perpendicular axis extending in the vertical direction in <FIG> and annotated with the perpendicular symbol "⊥". In the demodulation plane <NUM>, the parallel (horizontal) axis is the component of the raw output signal that is in phase with the demodulation signal. The perpendicular (vertical) axis is <NUM>° out of phase with the demodulation signal.

<FIG> illustrates the quadrature component Q and the rotational component Q of the raw output signal from the gyroscope <NUM>. The quadrature component Q and the raw output signal Ω are <NUM>° out of phase with each other. As described previously, if there is no phase drift, then the quadrature component Q will align with the perpendicular axis. If there is no phase drift, then the rotational component S2 will align with the parallel axis. The demodulator <NUM> of the sensor unit <NUM> outputs the parallel (horizontal) component of the raw output signal as the final output signal of the sensor unit <NUM>. Accordingly, if there is no phase drift then the output of the demodulator will correspond entirely to the rotational component of the raw output signal.

In <FIG>, there is a phase drift angle ϕ. As can be seen in <FIG>, the quadrature component Q is offset from the perpendicular axis by the phase drift angle ϕ. The rotational component S2 is offset from the parallel axis by the phase drift angle ϕ. In this situation, when the demodulator <NUM> outputs the parallel component, the parallel component will not accurately represent the rotational component Q. While <FIG> illustrates the quadrature component Q and the rotational component S2 as being substantially equal in magnitude, in practice, the magnitude of the quadrature component Q may be many times greater than the magnitude of rotational component Q. Accordingly, even a small phase drift angle ϕ will result in a very inaccurate representation of the rotational or Coriolis component S2 of the raw output signal.

<FIG> are representations of the demodulation plane <NUM> associated with a raw output signal during application of a test signal. The description of <FIG> will begin with reference to <FIG>. <FIG> illustrates the demodulation plane during a first phase of a testing period in which the test signal is applied to quadrature compensation electrodes <NUM>. <FIG> illustrates the demodulation plane during a second phase of the testing period in which the test signal is applied to the quadrature compensation electrodes <NUM>.

During the first phase of the testing period, the quadrature compensation driver <NUM> applies a test voltage -Vt, increasing the voltage difference with respect to the rotor mass. During application of the first phase of the test voltage, the quadrature component of the raw output signal will have a natural quadrature component Qnat and a negative quadrature test component -Qtest. In practice, this results in a total quadrature component that is less than the natural quadrature component Qnat. <FIG> also illustrates the rotational component Q of the raw output signal of the gyroscope <NUM>. In <FIG> there is a phase drift angle ϕ for each of the components of the raw output signal. The output IPH1 of the demodulator <NUM> in phase <NUM> of the testing period is the sum of the parallel or horizontal components of the natural quadrature component Qnat, the negative test quadrature component Qtest, and the Coriolis component.

During the second phase of the testing period, the quadrature compensation driver <NUM> applies a test voltage Vt. , reducing the voltage difference with respect to the rotor mass. During application of the second phase of the test voltage, the quadrature component of the raw output signal will have the natural quadrature Qnat component and a positive quadrature test component. In practice, this results in a total quadrature component that is greater than the natural quadrature component Qnat. The output IPH2 of the demodulator <NUM> and the second phase of the testing period is the parallel or horizontal components of the natural quadrature component Qnat, the positive test quadrature component Qtest, and the Coriolis component.

The delay calculator <NUM> receives the output of the demodulator <NUM> during the first and second phases of the testing period and calculates the phase drift angle ϕ. The delay calculator <NUM> calculates the phase drift angle ϕ based on the change in the output of the demodulator <NUM> between the first and second phases of the testing period and based on the magnitude of the quadrature test component. IPH2 is given by the following relationship: <MAT>.

IPH1 is given by the following relationship: <MAT>.

The difference in the output of the demodulator between the first and second phases is given by the following relationship: <MAT>.

Solving for sin(ϕ) gives the following: <MAT>.

Because the phase drift angle ϕ is very small (ϕ << <NUM>°), the small angle relationship can be used: <MAT>.

Incorporating the small angle approximation into the equation above yields the following relationship for the phase drift angle ϕ: <MAT>.

As set forth above, the phase drift angle ϕ can be calculated based on the difference in the output of the demodulator <NUM> between the first and second phases of the testing period and on the magnitude of the test component of the quadrature component. The phase drift angle ϕ can change based on temperature, process, mechanical stress, and other factors. However, the delay calculator <NUM>, in connection with the quadrature compensation driver <NUM>, can quickly and accurately determine the phase drift angle ϕ at any time with little or no interruption to the operation of the gyroscope <NUM>.

Furthermore, a relatively small number of compensation electrodes <NUM> can be utilized to identify the phase drift angle ϕ. In the scheme in which compensation electrodes are utilized to largely eliminate the quadrature component of the raw sensor signal, a very large number of compensation electrodes may be utilized. However, a comparatively small number compensation electrodes <NUM> can be utilized to identify the phase drift angle ϕ. This can save an enormous amount of area in manufacturing the gyroscope <NUM>.

In another example, a more accurate estimation of the amplitude of Qtest can be obtained by using the information on the perpendicular axis. While Qtest may normally be quite stable, such an estimation may be beneficial in case of reduction of second order effects. During the first phase of the testing period, the total signal QPH1 on the perpendicular axis is given by the following formula: <MAT>.

During the second phase of the testing period, the total signal QPH2 on the perpendicular axis is given by the following formula: <MAT>.

Because ϕ is typically a very small angle, Qtest can be approximated in the following manner: <MAT>.

Qtest can then be estimated in the following manner: <MAT>.

<FIG> is a graph illustrating a test signal <NUM> applied by the quadrature compensation driver <NUM> to the quadrature compensation electrodes <NUM>. At time T0 the first phase of the testing period begins by applying the test voltage with a negative polarity -Vt to the compensation electrodes <NUM>. At time T1 the second phase of the testing period begins by switching a polarity of the test signal <NUM> to a positive polarity Vt. During the first phase, a negative quadrature test voltage -Qtest is inserted into the raw output signal of the gyroscope <NUM>. During the second phase, a positive quadrature test component Qtest is inserted into the raw output signal the gyroscope <NUM>. As set forth above, the delay calculator <NUM> is able to measure the difference in the output of the demodulator between the first and second phases of the testing and calculate the phase drift angle by dividing the difference by <NUM>*Qtest.

<FIG> is a block diagram of the portion of sensor unit <NUM> implementing the above teaching. The demodulator <NUM> receives the raw output signal from the gyroscope <NUM>. The demodulator <NUM> also receives the demodulation signal from the delay compensation circuit <NUM>. The demodulation signal can correspond to the drive signal. The demodulator <NUM> provides the demodulated signal to an output block <NUM>. The output block may perform some signal processing on the demodulated signal. The output block provides the demodulated signal to the delay calculator <NUM>. The delay calculator <NUM> calculates the phase drift angle ϕ in the manner described above. The delay calculator <NUM> provides the phase drift angle value ϕ to the delay compensation circuit <NUM>. The delay compensation circuit <NUM> receives the demodulation signal, adds in a phase delay equal to the phase drift angle value ϕ, and provides the delayed demodulation signal to the demodulator <NUM>. The output of the demodulator <NUM> now corresponds to the Coriolis component of the raw output signal.

<FIG> is an illustration of a portion of the resonator mass <NUM> of the gyroscope <NUM>. <FIG> also illustrates compensation electrodes 110a and 110b positioned in gaps in the resonator mass <NUM>. The compensation electrodes 110a and 110b are fixed in place. The resonator mass <NUM> is movable.

In the example of <FIG>, the resonator mass <NUM> is driven to oscillate along the X axis by drive electrodes <NUM> (not shown, <FIG>) adjacent to another portion of the resonator mass <NUM> not shown in <FIG>. The resonator mass <NUM> has thick portions 104a that are closer to the compensation electrodes 110a and 110b and thinner portions 104b that are further away from the quadrature compensation electrodes 110a and 110b.

As the resonator mass <NUM> moves back and forth along the X axis, the amount of area of the thick portions 104a that is directly between two quadrature compensation electrodes <NUM> and 110b changes. In particular, as the resonator mass <NUM> moves to the left along the X axis, the amount of area of the thick portions 104a facing quadrature compensation electrodes 110a and 110b decreases. As the resonator mass moves to the right along the X axis, the amount of area of the thick portions 104a facing quadrature compensation electrodes 110a and 110b increases.

By applying a voltage to the resonator mass <NUM>, and then applying a voltage between each pair of electrodes 110a and 110b, a quadrature compensation force is generated. In one example, the resonator mass <NUM> receives a voltage of <NUM> V. During the first phase of the test, the electrodes 110a receive <NUM> V and the electrodes 110b receives <NUM> V. Because there is a higher voltage difference between the resonator mass <NUM> and the electrodes 110a than between the resonator mass <NUM> and the electrodes 110b, a net electrostatic force is applied to the resonator mass <NUM> in the positive Y direction. During the second phase of the test period, the polarity between the electrodes 110a and 110b is switched so that the electrodes 110a receives <NUM> V and the electrodes 110b receive <NUM> V. The result is that a net electrostatic force is applied to the resonator mass <NUM> in the negative Y direction. It should be noted that because the quadrature test force depends on the horizontal position of the resonator mass <NUM>, the quadrature test force is in phase with the drive signal.

However, other voltage schemes can be applied to generate a quadrature test force.

<FIG> is a top view of a portion of a different resonator mass <NUM> of gyroscope <NUM>. <FIG> also illustrates compensation electrodes 110a and 110b positioned in gaps in the resonator mass <NUM>. The compensation electrodes 110a and 110b are fixed in place, here carried by semiconductor regions <NUM>. The resonator mass <NUM> is movable. <FIG> is another example of in-plane quadrature compensation electrodes 110a and 110b.

In the example of <FIG>, the resonator mass <NUM> is driven to oscillate along the drive axis by drive electrodes <NUM> (not shown here, see <FIG>) adjacent to another portion of the resonator mass <NUM> not shown in <FIG>.

By applying a voltage to the resonator mass <NUM>, and then applying a voltage between the sets of electrodes 110a and 110b, a quadrature compensation force is generated. In one example, the resonator mass <NUM> receives a voltage of <NUM> V.

During the first phase of the test, the electrodes 110a receive <NUM> V and the electrodes 110b receives <NUM> V. During the second phase of the test period, the polarity between the electrodes 110a and 110b is switched so that the electrodes 110a receives <NUM> V and the electrodes 110b receive <NUM> V. Due to the geometry of the resonator mass relative to the test electrodes, a net electrostatic force is generated in different directions during the two test phases.

Other voltage schemes can be applied to generate a quadrature test force without departing from the scope of the present disclosure.

<FIG> is a cross-sectional view a portion of a different gyroscope <NUM> having compensation electrodes 110a and 110b positioned below the resonator mass on a substrate <NUM>. The compensation electrodes 110a and 110b are fixed in place. The resonator mass <NUM> is movable. <FIG> is an example of out-of-plane quadrature compensation electrodes 110a and 110b.

In the example of <FIG>, the resonator mass <NUM> is driven to oscillate along the drive axis by drive electrodes <NUM> (not shown here, see <FIG>) adjacent to another portion of the resonator mass <NUM> not shown in <FIG>. By applying a voltage to the resonator mass <NUM>, and then applying a voltage between the sets of electrodes 110a and 110b, a quadrature compensation force is generated. In one example, the resonator mass <NUM> receives a voltage of <NUM> V. During the first phase of the test, the electrodes 110a receive <NUM> V and the electrodes 110b receives <NUM> V. During the second phase of the test period, the polarity between the electrodes 110a and 110b is switched so that the electrodes 110a receives <NUM> V and the electrodes 110b receive <NUM> V. Due to the placement of the test electrodes 110a and 110b relative to the shape of the resonator mass <NUM>, a net electrostatic force is generated in different directions during the two test phases. Other voltage schemes can be applied to generate a quadrature test force without departing from the scope of the present disclosure.

<FIG> is a more detailed diagram of sensor unit <NUM> of <FIG>, wherein the resonator mass <NUM> is shown to include a drive resonator mass <NUM> and a sense resonator mass <NUM>. Though shown as separate masses in <FIG>, in some cases, the sense resonator mass <NUM> and the drive resonator mass <NUM> may be a single mass, or may effectively act as a single spring coupled mass.

The sensor unit <NUM> includes a driving MEMS/ASIC <NUM> and a sense MEMS/ASIC <NUM>.

The MEMS/ASIC <NUM> includes the drive voltage supply <NUM>. The drive voltage supply <NUM> applies the drive signal to drive electrodes <NUM>. The drive voltage supply <NUM> may include a phase locked loop for controlling the phase of the drive signal. The drive voltage supply <NUM> may also include an adaptive gain control for controlling the amplitude of the drive signal. The drive supply voltage also supplies the demodulation signal to delay compensation circuit <NUM>. The demodulation signal is a signal with a same phase as the drive signal, unless drift has occurred.

The drive electrodes <NUM> receive the drive signal from the drive voltage supply <NUM> and apply an electrostatic drive force to the drive resonator mass <NUM>. The electrostatic drive force drives the drive resonator mass <NUM> to oscillate along the drive axis. The drive resonator mass <NUM> oscillates in accordance with a mechanical transfer function.

The drive MEMS/ASIC <NUM> includes drive sense electrodes <NUM> that convert the motion of the drive resonator mass <NUM> into a capacitive signal. The capacitive signal is passed to a converter <NUM> that converts the capacitive signal to a voltage signal. The voltage signal is fed back into the drive voltage supply <NUM> in a feedback loop configuration so that the phase locked loop and adaptive gain control loop can control the phase and amplitude of the drive signal.

The displacement in the drive direction affects the sense MEMS/ASIC <NUM>. The drive displacement and the rotational rate Q interact to generate the Coriolis force based on the drive displacement velocity of the resonator mass <NUM> and the rotational rate Q around the rotation axis. The displacement of the resonator mass <NUM> also interacts via spring couplings Kxy <NUM> to generate a quadrature force in the sense direction. The displacement of the drive resonator mass <NUM> also interacts with the quadrature compensation electrodes <NUM> in generating the quadrature compensation force. The quadrature compensation driver <NUM> applies the quadrature test signal to the quadrature compensation electrodes <NUM>.

The conceptual block <NUM> represents the summation of all of the forces acting in the sense direction on the sense resonator mass <NUM>. The Coriolis force, the quadrature force, and the quadrature compensation force all affect the motion of the sense resonator mass <NUM> along the sense axis. The sense resonator mass <NUM> may be coupled to the drive resonator mass <NUM> by springs.

The sense electrodes <NUM> sense the motion of the sense resonator mass <NUM> along the sense axis. The sense electrodes <NUM> generate a capacitive signal indicative of the motion of the sense resonator mass <NUM> along the sense axis. The capacitive signal is converted at block <NUM> to a sense voltage signal corresponding to the raw output signal of the gyroscope <NUM> (<FIG>). The raw output signals is provided to the demodulator <NUM>.

The drive voltage supply <NUM> supplies a demodulated signal to the delay compensation block <NUM>. The demodulated signal corresponds to a drive reference signal. Initially, the delay compensation block <NUM> may not add any delay into the demodulation signal. The delay compensation block <NUM> merely passes the demodulation signal to the demodulator <NUM>.

During the testing phase, the quadrature compensation driver <NUM> applies a test signal to the quadrature compensation electrodes, switching polarities between first and second phases as described previously. The demodulator <NUM> demodulates the demodulation signal and the raw output signal and generates a demodulated signal. An output block <NUM> may perform some additional processing on the demodulated signal.

The output block <NUM> provides the demodulated signal to the delay calculator <NUM>. The delay calculator <NUM> calculates the phase drift angle ϕ as described previously and provides the phase drift angle value to the delay compensation circuit <NUM>. The delay compensation circuit delays the demodulation signal by the value of cp. The demodulator <NUM> then outputs a demodulated signal that accurately corresponds to the rotational rate Q.

<FIG> is a flow diagram of a method <NUM> for operating a gyroscope. At <NUM>, the method <NUM> includes driving a resonator mass of a gyroscope in a first direction by applying a drive signal to a drive electrode. At <NUM>, the method <NUM> includes applying a test voltage to a quadrature compensation electrode adjacent to the resonator mass. At <NUM>, the method <NUM> includes determining a phase difference between a first drive reference signal and an output signal of the gyroscope based on a change in the output signal during application of the test voltage. At <NUM>, the method <NUM> includes compensating for the phase difference between the demodulation signal and the output signal of the gyroscope.

Claim 1:
A method for correcting gyroscope demodulation phase drift, comprising:
driving a resonator mass (<NUM>; <NUM>, <NUM>) of a gyroscope (<NUM>) in a first direction by applying a first drive signal to a drive electrode;
applying a test voltage to a quadrature compensation electrode (<NUM>; 110a, 110b) adjacent to the resonator mass;
determining a phase difference between a first drive reference signal and an output signal of the gyroscope based on a change in the output signal during application of the test voltage, the first drive reference signal having a same phase as the first drive signal, or initially a same phase as the first drive signal; and
compensating for the phase difference between the first drive reference signal and the output signal of the gyroscope; and
reversing a polarity of the test voltage during application of the test voltage.