# Patent

## Title
Three-mass coupled oscillation technique for mechanically robust micromachined gyroscopes

## Abstract

A micromachined gyroscope is disclosed comprising a substrate, three masses m1, m2, and m3, configured to oscillate along a first direction x or y, whereby the first mass m1 is mechanically coupled to the substrate, the second mass m2 is mechanically coupled to the first mass m1 and to substrate, and the third mass m3 is mechanically coupled to the second mass m2, whereby the weight and the spring constants k1, k2, k3 of the respective masses m1, m2, and m3 and mechanical couplings k12, k23 are selected, such that, during operation mass m2 oscillates at a frequency substantially above the resonance frequencies of mass m1 and mass m3. The resonance frequency of mass m2 may be at least 2 times, or even 2.5 times, higher than the resonance frequency of mass m1 or m3.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to U.S. Provisional Patent Application No. 61/534,146 filed on Sep. 13, 2011, the contents of which are hereby incorporated by reference.


BACKGROUND
Micromachined gyroscopes are angular rate sensors that typically operate according to a physical phenomenon called the Coriolis Effect. The Coriolis Effect is, simply, the deflection of moving objects viewed from a rotating frame. For an object mounted to a substrate, the object tends to oscillate (e.g., vibrate, move, or drive) in a perpendicular plane when the substrate rotates. Hence, in order to make use of the Coriolis Effect, micromachined gyroscopes may be composed of an oscillating part comprising at least one mass, and a sensing part which is free to move in a perpendicular plane of the oscillating part. The sensing part is affected by the rotation of the gyroscope, as the oscillating part will be deflected. Under an external rotation, the oscillating mass deflects, and that deflection is sensed via the movement of the sensing part.
The sensitivity of such an oscillating gyroscope depends on its oscillation magnitude. In order to achieve a stable and large sensitivity, stable and large oscillation amplitude is desirable.
Typically, a large oscillation is achieved by using a one-degree-of-freedom (1-DOF) oscillator that is operated at its resonant frequency. Stability is then obtained with the help of stabilization circuitry (e.g., phase lock loops (PLLs), proportional integral (PI) controllers, etc.) to keep the gyroscope operating near this resonance frequency.
In some cases, the 1-DOF oscillator may be operated at non-resonance frequency, thereby reducing the need for stabilisation circuitry. However, a magnitude of the oscillation at non-resonance frequencies will be less than a magnitude of the oscillation at the resonance frequency. When the oscillator is oscillating at non-resonance frequencies, though, changes in the frequency, as well as the quality factor, will have a lesser effect on the oscillation magnitude, as compared to when the oscillator is oscillating at the resonance frequency.
Typical gyroscopes consume 10 to 20 times more power than a typical accelerometer in commercial applications. Some of this power consumption results from the comb-drive actuation used in typical gyroscopes to obtain large oscillation magnitudes. Comb-drive actuation involves electrostatic forces being generated between two comb-like structures. One comb is fixed to the substrate while the other comb is movable. The force developed by the comb-drive actuator is proportional to the change in capacitance between the two combs. However, this capacitance increases with driving voltage difference between both combs, with the coupling area reflected by the number of comb teeth, and the gap between these teeth. As a result, achieving large oscillation magnitudes with comb-drive actuation requires large polarization voltage differences, typically 12V in commercial devices. Such high polarization voltage differences are not conducive to a low-power gyroscope. Another source of this power consumption may be stabilization circuitry, such as PLLs and/or PI controllers, used to stabilize the oscillation increase power consumption of the gyroscope, which is similarly not conducive to a low-power gyroscope. Other sources of power consumption exist as well.
One option for reducing the power consumption of a gyroscope is to use a two-degree-of-freedom (2-DOF) oscillator that includes two masses and, accordingly, has two resonance frequencies. The 2-DOF gyroscope may be operated in between the two resonance frequencies. The amplitude response typically has minimal dependency on the varying quality factor and the resonance frequencies. However, the magnitude of this response is still very small and comparable to the non-resonance response of the 1-DOF oscillator discussed above.
Accordingly, a micromachined gyroscope with reduced power consumption may be desirable. It may be desirable for such a micromachined gyroscope to have a stable oscillation frequency range with a high mechanical amplification between the actuator and the driving part.
SUMMARY
Disclosed is a gyroscope with reduced power consumption, as compared to typical gyroscopes. The disclosed gyroscope is designed without the need of stabilization circuitry, and with a reduced need for driving and controlling circuitry, thereby reducing the power consumption of the gyroscope.
In one aspect, a micromachined gyroscope is disclosed. The micromachined gyroscope comprises a substrate and at least three masses (m1, m2, m3). The first mass m1 is mechanically coupled to the substrate via a mechanical connection k1, the second mass m2 is mechanically coupled to the first mass m1 via a connection k12 and to the substrate via a mechanical connection k2, and the third mass m3 is mechanically coupled to the second mass m2 via a mechanical connection k23. The three masses are each configured to oscillate along a first direction x or y.
The following relationships exist between the masses m1, m2, m3, and the mechanical connections k1, k2, k12, k23:

[(k2+k12+k23)/m2]>>([(k1+k12)/m1] ̃[(k23)/m3])

In some embodiments, the third mass m3 is also mechanically coupled to the substrate via a mechanically connection k3.
The masses m1, m2, and m3 can be the driving masses of the gyroscope configured to oscillate along a first direction x. To this end, the gyroscope may further comprise actuators for stimulating these driving masses. These actuators may be parallel plate actuators.
In another embodiment, the micromachined gyroscope further comprises a duplicate m1′, m2′, and m3′ of these 3 mass configuration and this duplicate is configured to oscillate along the first direction x but in opposite phase with these three masses m1, m2, and m3.
The masses m1, m2, and m3 can be the sensing masses of the gyroscope, which are configured to oscillate along a first direction y when the gyroscope is rotating.
In some embodiments, the three masses m1, m2, m3 can be configured to oscillate in a linear way.
In another aspect, a micromachined gyroscope is disclosed comprising a substrate, a driving mass mechanically coupled to a sensing mass, both masses being movable in perpendicular directions and, when in operation under the influence of the Coriolis force, the driving mass causes the driving of the sensing mass, whereby at least one of the driving mass or of the sensing mass is configured as a connection of three masses m1, m2, m3, whereby the first mass m1 is mechanically coupled to the substrate, the second mass m2 is mechanically coupled to the first mass m1 and to the substrate, and the third mass m3 is mechanically coupled to the second mass m2, whereby the following relationship exist:

[(k2+k12+k23)/m2]>>([(k1+k12)/m1] ̃[(k23)/m3])

with m1, m2, m3 being the weight of respectively mass m1, m2 and m3, with k1, k2 (and k3) being the spring constant of the mechanical connection between of the respective mass m1 or m2 or m3 and the substrate, and with k12, k23 being the spring constant of the mechanical connection between mass m2 and mass m1 or mass m3 respectively.

In yet another aspect, a micromachined gyroscope is disclosed comprising a substrate, three masses m1, m2, and m3 , configured to oscillate along a first direction x or y, whereby the first mass m1 is mechanically coupled to the substrate, the second mass m2 is mechanically coupled to the first mass m1 and to substrate, and the third mass m3 is mechanically coupled to the second mass m2, whereby the weight and the spring constants k1, k2, k3 of the respective masses m1, m2 and m3 and mechanical couplings k12, k23 are selected, such that, during operation mass m2 oscillates at a frequency substantially above the resonance frequencies of mass m1 and mass m3.
In some embodiments, the resonance frequency of mass m2 is at least 2 times, or even 2.5 times, higher than the resonance frequency of mass m1 or m3.
In yet another aspect, a method for designing a micromachined gyroscope is disclosed. This micromachined gyroscope comprises a substrate, at least 3 masses m1, m2 and m3 being configured to oscillate along a first direction x or y, whereby the first mass m1 is mechanically coupled to the substrate, the second mass m2 is mechanically coupled to the first mass m1 and to substrate, and the third mass m3 is mechanically coupled to the second mass m2, whereby the following relationship exist:

[(k2+k12+k23)/m2]>>([(k1+k12)/m1] ̃[(k23)/m3])

with m1, m2, m3 being the weight of respectively mass m1, m2 and m3, with k1, k2 (and k3) being the spring constant of the mechanical connection between of the respective mass m1 or m2 or m3 and the substrate, and with k12, k23 being the spring constant of the mechanical connection between mass m2 and mass m1 or mass m3 respectively.

The method comprises: selecting m1, m3, k1 and k3 whereby [(k1+k12)/m1] ̃[(k3+k23)/m3], and selecting m2, k2 such that during operation of the gyroscope:

[(k2+k12+k23)/m2]>>([(k1+k12)/m1]>[(k3+k23)/m3]).

The method further comprises selecting a mechanical amplification between the movement of mass m1 and mass m3 and dimensioning k2 in view of this desired mechanical amplification.



BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
FIG. 1 shows a schematic mechanical equivalent of a micromachined gyroscope comprising three driving masses m1, m2, m3 and one sensing mass msense, in accordance with an embodiment.
FIG. 2 shows a schematic mechanical equivalent of a micromachined gyroscope comprising three driving masses m1, m2, m3 and one sensing mass msense, in which mass m3 is coupled to the substrate, in accordance with an embodiment.
FIG. 3 shows the resonance behavior of the gyroscope shown in FIG. 2: normalized displacement response (unitless) vs. frequency (Hz), in accordance with an embodiment.
FIG. 4 shows a schematic mechanical equivalent of a micromachined gyroscope comprising three driving masses m1, m2, m3 and one sensing mass msense whereby the sensing mass is decoupled from the driving mass m3, in accordance with an embodiment.
FIG. 5 shows a schematic mechanical equivalent of a micromachined gyroscope comprising three driving masses m1, m2, m3 and 3 sensing mass msense-2, msense-3 whereby the sensing masses are decoupled from the driving mass m3, in accordance with an embodiment.
FIG. 6 shows a schematic mechanical equivalent of a micromachined gyroscope comprising the driving masses m1, m2, m3 are arranged in a tuning fork configuration and one sensing mass msense, in accordance with an embodiment.



DETAILED DESCRIPTION
The present disclosure contains particular embodiments and with reference to certain drawings but the disclosure is not limited thereto. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the disclosure. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may refer to different embodiments. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. The terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other orientations than described or illustrated herein. It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a solution comprising components A and B” should not be limited to solution consisting only of components A and B. It means that with respect to the present disclosure, the only relevant components of the solution are A and B.
In this disclosure a micromachined gyroscope is disclosed. Such a micromachined gyroscope is an angular rate sensor that operates according to the Coriolis Effect described above. Such a micromachined gyroscope is manufactured using semiconductor process manufacturing steps.
More particularly, a micromachined gyroscope is disclosed comprising a configuration of 3 masses mechanically coupled to oscillate along a first direction y. In such a three-mass oscillation scheme, illustrated by FIG. 1, mass m1 is coupled to mass m2 and to the substrate, mass m2 is coupled to mass m3 and to the substrate, while mass m3 drives the sensing part msense. Mass m3 is only mechanically coupled to mass m1 via the second mass m2.
Mass m1 is driven by actuators, which are typically electrostatically actuated. Although comb-drive actuators, when operated at lower voltages, can be used, it may be desirable to use parallel plate actuators, as they operate at lower voltages. Such parallel-plate actuators are more power-efficient, although they cannot provide large displacements due to their non-linear behavior. However, thanks to the mechanical amplification between the movement of mass m1 and mass m3 as discussed below, the small displacement of the parallel-plate actuators can be amplified, resulting in an appropriately higher oscillation amplitude of the third mass m3. For example, the amplitude increase from peak to peak may be several micrometers.
The third mass m3 is used as the oscillating mass which creates the Coriolis force upon external rotation. The deflection of mass m3 is sensed by the mass msense moving in a direction y perpendicular to the direction x along which the driving masses m1, m2, and m3 oscillates. This mass msense is, in the configuration illustrated by FIG. 1, directly coupled to mass m3drive and as such is part of the driving mass m3.
The values of the masses m1, m2, m3, spring constants k1, k2, k3, k12, k23, and the damping levels b1 and b2 are designed to result in a large, and flat (e.g., constant) over a frequency range (e.g., 50 Hz or above), displacement response for mass m3, and a mechanical amplification between mass m1 and mass m3 at this flat frequency response of mass m3. Hence, the amplitude of the oscillation of mass m1 can be small, typically less than 200 nm, or even 100 nm. As discussed above, this small oscillation amplitude of mass m1 allows low voltage actuation of actuators (e.g., parallel-plate actuators or comb-drive actuators). Hence, the response of mass m3 to the actuators will be robust without needing of any external circuitry, and overall power consumption will drop.
Whereas in FIG. 1 mass m3 was not coupled to the substrate, FIG. 2 illustrates another embodiment where mass m3 is mechanically coupled to the substrate as well. This coupling is modeled by a spring k3 and a damping b3. Such a configuration would accommodate for the imperfections coming from the fabrication of the micromachined gyroscope. If the springs k1 and k3 are designed in a similar shape, then even, if there is a process related imperfection, all springs k1, k2, k3, k12, k23 are affected to the same degree. Moreover, anchoring all masses m1, m2 and m3 to the substrate minimizes the mechanical stress related to buckling/bending of the cantilevered masses and allows a larger and flatter device.
The mechanical system illustrated by FIG. 2 can be modeled by three equations (1):



  
    Force
    =
    
      
        
          m
          1
        
        ⁢
        
          
            
              ∂
              2
            
            ⁢
            
              x
              1
            
          
          
            ∂
            
              x
              2
            
          
        
      
      +
      
        
          b
          1
        
        ⁢
        
          
            ∂
            
              x
              1
            
          
          
            ∂
            x
          
        
      
      +
      
        
          k
          1
        
        ⁢
        
          x
          1
        
      
      +
      
        
          (
          
            
              x
              1
            
            -
            
              x
              2
            
          
          )
        
        ⁢
        
          k
          12
        
      
    
  




  
    0
    =
    
      
        
          m
          2
        
        ⁢
        
          
            
              ∂
              2
            
            ⁢
            
              x
              2
            
          
          
            ∂
            
              x
              2
            
          
        
      
      +
      
        
          b
          2
        
        ⁢
        
          
            ∂
            
              x
              2
            
          
          
            ∂
            x
          
        
      
      +
      
        
          k
          2
        
        ⁢
        
          x
          2
        
      
      +
      
        
          (
          
            
              x
              2
            
            -
            
              x
              1
            
          
          )
        
        ⁢
        
          k
          12
        
      
      +
      
        
          (
          
            
              x
              2
            
            -
            
              x
              3
            
          
          )
        
        ⁢
        
          k
          23
        
      
    
  




  
    0
    =
    
      
        
          m
          3
        
        ⁢
        
          
            
              ∂
              2
            
            ⁢
            
              x
              3
            
          
          
            ∂
            
              x
              2
            
          
        
      
      +
      
        
          b
          3
        
        ⁢
        
          
            ∂
            
              x
              3
            
          
          
            ∂
            x
          
        
      
      +
      
        
          k
          3
        
        ⁢
        
          x
          3
        
      
      +
      
        
          (
          
            
              x
              3
            
            -
            
              x
              2
            
          
          )
        
        ⁢
        
          k
          23
        
      
    
  



From these 3 equations, the displacement responses of each mass m1, m2 and m3 can be derived analytically (2):



  
    
      X
      1
    
    =
    
      Force
      
        
          k
          1
        
        +
        
          k
          12
        
        +
        
          jω
          ⁢
          
            
          
          ⁢
          
            b
            1
          
        
        -
        
          
            m
            1
          
          ⁢
          
            ω
            2
          
        
        -
        
          
            k
            
              12
              2
            
          
          
            
              
                
                  
                    k
                    12
                  
                  +
                  
                    k
                    2
                  
                  +
                  
                    k
                    23
                  
                  +
                  
                    jω
                    ⁢
                    
                      
                    
                    ⁢
                    
                      b
                      2
                    
                  
                  -
                  
                    
                      m
                      2
                    
                    ⁢
                    
                      ω
                      2
                    
                  
                  -
                
              
            
            
              
                
                  
                    k
                    23
                    2
                  
                  
                    
                      k
                      23
                    
                    +
                    
                      k
                      3
                    
                    +
                    
                      jω
                      ⁢
                      
                        
                      
                      ⁢
                      
                        b
                        3
                      
                    
                    -
                    
                      
                        m
                        3
                      
                      ⁢
                      
                        ω
                        2
                      
                    
                  
                
              
            
          
        
      
    
  




  
    
      
    
    ⁢
    
      
        X
        2
      
      =
      
        
          
            X
            1
          
          ⁢
          
            k
            12
          
        
        
          
            k
            12
          
          +
          
            k
            2
          
          +
          
            k
            23
          
          +
          
            jω
            ⁢
            
              
            
            ⁢
            
              b
              2
            
          
          -
          
            
              m
              2
            
            ⁢
            
              ω
              2
            
          
          -
          
            
              k
              23
              2
            
            
              
                k
                23
              
              +
              
                k
                3
              
              +
              
                jω
                ⁢
                
                  
                
                ⁢
                
                  b
                  3
                
              
              -
              
                
                  m
                  3
                
                ⁢
                
                  ω
                  2
                
              
            
          
        
      
    
  




  
    
      
    
    ⁢
    
      
        X
        3
      
      =
      
        
          
            X
            2
          
          ⁢
          
            k
            23
          
        
        
          
            k
            23
          
          +
          
            k
            3
          
          +
          
            jω
            ⁢
            
              
            
            ⁢
            
              b
              3
            
          
          -
          
            
              m
              3
            
            ⁢
            
              ω
              2
            
          
        
      
    
  



FIG. 3 illustrates the resonance behavior of the three mass coupled oscillation configuration. The frequency of the actuating force is swept and the displacement of the actuated mass is measured with respect to the DC displacement. Hence, the y-axis of FIG. 3 is representative for the quality factor of the oscillation peaks. In-between response peaks f1 and f3 a substantially flat response region is obtained. These two resonance peaks f1 and f3 are determined by the mass m1 and mass m3, when the resonance frequency of mass m2 is selected to be higher than either of both resonance peaks.
In order to achieve a flat and large mass m3 response and a mechanical amplification between mass m1 and mass m3, the following design method is applied. First, mass m2 is considered to be a non-moving rigid body whereby k2 is assumed to be infinitive. Hence, the motion of mass m1 and mass m3 can be determined separately. Then, the resonant frequencies f1 and f3 of respectively mass m1 and mass m3 are equated to each other, assuming that mass m2 had no impact, as shown in equation (3):




  
    
      
        k
        1
      
      +
      
        k
        12
      
    
    
      m
      1
    
  
  =
  
    
      
        k
        23
      
      +
      
        k
        3
      
    
    
      m
      3
    
  




If the damping levels b1 and b2, and when coupled to the substrate b3, are low enough, the finite k2 value will cause the resonant frequencies f1 of mass m1 and f3 of mass m3 to separate from each other and form a robust response plateau in-between and a mechanical amplification between mass m1 and mass m3. The separation of mass m1 and mass m3 resonant frequencies and the response level of mass m3 at the plateau depend on the value of k2. The higher k2 is, the smaller the separation and the larger the response will be.
This mechanical amplification can be further improved by increasing the vacuum level of the environment in which the gyroscope operates or the quality factor of the individual peaks.
The position of the anti-resonance frequency of mass m1, where the mechanical amplification is the highest from mass m1 towards mass m3, can be tuned by changing k1. The value of k1 can be easily tuned if parallel plate actuators are used to actuate mass m1. However, from the application point of view, one might prefer to not operate at the anti-resonance frequency of mass m1, because that will be unstable for mass m1. In that case, the gyroscope is operated slightly off the anti-resonance frequency of mass m1 and the mechanical amplification ratio from mass m1 to mass m3 will be around 20-30 regardless of the vacuum level.
The damping levels b1, b2 (and b3 when present) or the quality factors of each resonant peak f1 and f3 have an important role on the operation of the gyroscope. If the quality factors are not large enough, the coupling cannot occur and the plateau cannot be formed.
The selection of the quality factors of the resonance frequencies f1 and f3 is a design criterion. The larger k2 is, the larger the quality factors of both resonance frequencies should be. As a rule of thumb, these quality factor values should be one order of magnitude larger than the ratio of mass m2 resonant frequency to the average frequency of the plateau between the resonance frequency f1 and f3 of mass m1 and m3 when coupled via mass m2 due to the finite value of spring k2.
The position of the anti-resonance of mass m1 does not have to be at the mid-point of this plateau. This position depends on the ratio of mass m1 to mass m3, but can be tuned by altering k1. So, although during the initial design phase the resonant frequencies of m1 and m3 are equated to each other f1 ̃f3, thereby assuming mass m2 to be a non-moving body, at the end, equation (3) does not have to hold due to changed k1.
The mechanical amplification between m1 and m3 depends on the operating frequency. If the operating frequency is at the anti-resonance of mass m1, the amplification ratio will be the maximum. However, this situation can bring instability to the mass m1 motion. It is proposed to operate slightly off anti-resonance. In this case the mechanical amplification ratio can realistically be 20-30.
FIGS. 4, 5, and 6 show alternative embodiments. The proposed three-mass coupled oscillation technique can be used wherever a 1-DOF oscillator is used within vibrating gyroscopes. Decoupled or non-decoupled sense and drive schemes and a tuning fork topology can be used. Moreover, this three-mass oscillation topology can be used in the sensing part of the gyroscope to achieve a large bandwidth and an amplified sensitivity.
FIG. 4 illustrates a micromachined gyroscope comprising three driving masses m1, m2, and m3 with mass m1 is coupled (k1, b1) to the substrate and to (k12) mass mz, m2 is coupled to the substrate (k2,b2) and to (k23), while the mass m3 and mass m3drive drives the sensing mass msense via the decoupling mass mdecoupling.
FIG. 5 illustrates a micromachined gyroscope comprising three driving masses m1, m2, and m3 with mass m1 being coupled (k1, b1) to the substrate and to (k12) mass m2, m2 is coupled to the substrate (k2, b2) and to (k23) the mass m3 and mass m3 drives the sensing mass msense via the decoupling mass mdecoupling. In this embodiment also the sensing mass msense is configured as a connection for the masses msense—1, msense—2, msense—3, whereby mass msense—2 is coupled to the substrate and to mass msense—2, msense—2 is coupled to the substrate and the mass msense—3. In this configuration a stable oscillation frequency range for the driving masses is obtained whereby the movement of mass m1 is mechanically amplified to mass m3, but also a stable sensing frequency range is obtained whereby the movement of mass msense—1 is mechanically amplified to mass msense—3.
FIG. 6 illustrates a micromachined gyroscope comprising three driving masses m1, m2, and m3 in a tuning fork configuration with mass m1 being coupled (k1, b1) to the substrate and to (k12) mass m2, mass m2 being coupled to the substrate (k2,b2) and to (k23) the mass m3, and mass m3drive driving the sensing mass msense. It further comprises a second series of three driving masses m1′, m2′, and m3′ with mass m1′ being coupled to mass m1 and to (k12′) mass m2′, m2′ being coupled to the substrate and to (k23′) the mass m3′, and mass m3′ driving the sensing mass msense′. Both series of three mechanically coupled driving mass m1, m2, and m3 and m1′, m2′, and m3′ are actuated by the same actuators.
A number of example embodiments are contemplated. In one example embodiment, a micromachined gyroscope may include a substrate and three masses configured to oscillate along a first direction. The first mass m1 may be mechanically coupled to the substrate, the second mass m2 may be mechanically coupled to the first mass m1 and to substrate, and the third mass m3 may be mechanically coupled to the second mass m2. The gyroscope may be defined as follows: [(k2+k12+k23)/m2]>>([(k1+k12)/m1] ̃[(k23)/m3]), where m1, m2, m3 are the weights of, respectively, the masses m1, m2 and m3, k1, k2 being the spring constant of the mechanical connection between of the respective mass and the substrate, and k12, k23 being the spring constant of the mechanical connection between m2 and m1 and m2 and m3, respectively.
In some embodiments, the third mass m3 may be mechanically coupled to the substrate and the following relationship may exist:

[(k2+k12+k23)/m2]>>[(k1+k12)/m1] ̃[k3+k23)/m3]

where k3 is the spring constant of the mechanical connection between of the mass m3 and the substrate.

In some embodiments, the three masses may be driving masses. The gyroscope may further include driving means to drive the first mass m1. The driving means may be, for example, one or more parallel plate electrostatic actuators.
In some embodiments, the three masses may be sensing masses configured to move when the gyroscope rotates.
In some embodiments, the gyroscope may further include a duplicate of the three-mass configuration. The duplicate may be configured to oscillate along the first direction in opposite phase with the three-mass configuration.
In some embodiments, the masses may be configured to oscillate linearly.
In another example embodiment, a method for designing a micromachined gyroscope may include selecting m1, m3, k1 and k3 such that [(k1+k12)/m1] ̃[k3+k23)/m3]. The method may further include selecting m2, k2 such that during operation:

[(k2+k12+k23)/m2]>>[(k1+k12)/m1]>[k3+k23)/m3].

In some embodiments, the method may further comprises selecting a mechanical amplification between the movement of mass m1 and mass m3, and dimensioning k2 in view of this desired mechanical amplification.

## Claims

1. A micromachined gyroscope comprising a three-mass configuration that includes a substrate and three masses configured to oscillate in a first direction, wherein:
a first mass having a first weight m1 is mechanically coupled to the substrate;
a second mass having a second weight m2 is mechanically coupled to the first mass and to the substrate; and
a third mass having a third weight m3 is mechanically coupled to the second mass, wherein the following relationship exist:


[(k2+k12+k23)/m2]>>([(k1+k12)/m1] ̃[(k23)/m3])

wherein k1 is a spring constant of a mechanical connection between the first mass and the substrate, k2 is a spring constant of a mechanical connection between the second mass and the third substrate, k12 is a spring constant of a mechanical connection between the first mass and the second mass, and k23 is a spring constant of a mechanical connection between the second mass and the third mass.

2. The micromachined gyroscope of claim 1, wherein the third mass is mechanically coupled to the substrate, and wherein the following relationship exists:


[(k2+k12+k23)/m2]>>[(k1+k12)/m1] ̃[k3+k23)/m3]

wherein k3 is a spring constant of a mechanical connection between the third mass and the substrate.

3. The micromachined gyroscope of claim 1, wherein the three masses are driving masses, and further comprising driving means to drive the first mass.

4. The micromachined gyroscope of claim 3, wherein the driving means are parallel plate electrostatic actuators.

5. The micromachined gyroscope claim 1, wherein the three masses are sensing masses configured to move when the micromachined gyroscope is rotated.

6. The micromachined gyroscope of claim 1, further comprising a duplicate of the three-mass configuration, wherein the duplicate is configured to oscillate in the first direction but in an opposite phase of the three-mass configuration.

7. The micromachined gyroscope of claim 1 wherein, the three masses are configured to oscillate linearly.

8. A method for designing a micromachined gyroscope comprising:
selecting a first mass having a first weight m1;
selecting a second mass having a second weight m2;
selecting a third mass having a third weight m3;
selecting a first spring constant k1 for a mechanical connection between the first mass and a substrate;
selecting a second spring constant k2 for a mechanical connection between the second mass and the substrate;
selecting a third spring constant k3 for a mechanical connection between the third mass and the substrate;
selecting a fourth spring constant k12 for a mechanical connection between the first mass and the second mass; and
selecting a fifth spring constant k23 for a mechanical connection between the second mass and the third mass, wherein:


[(k1+k12)/m1] ̃[k3+k23)/m3];


and wherein, during operation of the micromachined gyroscope:


[(k2+k12+k23)/m2]>>[(k1+k12)/m1]>[k3+k23)/m3].

9. A method according to claim 8, further comprising:
selecting a mechanical amplification between a movement of the first mass and a movement of the third mass; and
dimensioning the second spring constant k2 in view of the mechanical amplification.