Patent Publication Number: US-RE45439-E

Title: Microelectromechanical gyroscope with self-test function and control method

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a microelectromechanical gyroscope with self-test function and to a method for controlling a microelectromechanical gyroscope. 
     2. Description of the Related Art 
     As is known, the use of microelectromechanical systems or MEMS has witnessed an ever-increasing diffusion in various sectors of technology and has yielded encouraging results especially in the production of inertial sensors, microintegrated gyroscopes, and electromechanical oscillators for a wide range of applications. 
     MEMS of the above type are usually based upon microelectromechanical structures having at least one mass, which is connected to a fixed body (stator) by springs and is movable with respect to the stator according to pre-set degrees of freedom. The movable mass and the stator are capacitively coupled by a plurality of respective comb-fingered and mutually facing electrodes, forming capacitors. The movement of the movable mass with respect to the stator, for example on account of application of an external force, modifies the capacitance of the capacitors; whence it is possible to trace back to the relative displacement of the movable mass with respect to the fixed body and hence to the applied force. Instead, by supplying appropriate biasing voltages, it is possible to apply an electrostatic force on the movable mass to set it in motion. In addition, in order to obtain electromechanical oscillators, the frequency response of inertial MEMS structures is exploited, which typically is of a second-order low-pass type, with a resonance frequency. By way of example,  FIGS. 1 and 2  show the plot of the magnitude and phase of the transfer function between the force applied on the movable mass and its displacement with respect to the stator, in an inertial MEMS structure. 
     In particular, MEMS gyroscopes have a more complex electromechanical structure, which includes two masses that are movable with respect to the stator and are coupled to one another so as to have a relative degree of freedom. The two movable masses are both capacitively coupled to the stator. One of the masses is dedicated to driving and is kept in oscillation at the resonance frequency. The other mass is drawn along in oscillating motion and, in the case of rotation of the microstructure with respect to a pre-determined gyroscopic axis with an angular velocity, is subjected to a Coriolis force proportional to the angular velocity itself. In practice, the driven mass operates as an accelerometer that enables detection of the Coriolis force and acceleration and hence makes it possible to trace back to the angular velocity. 
     As practically any other device, MEMS gyroscopes are subject to defects of fabrication (which can regard both the microstructure and the electronics) and wear, which can diminish the reliability or jeopardize operation thereof completely. 
     For this reason, gyroscopes, before being installed, are subjected to tests in the factory for proper operation thereof, which enable identification and rejection of defective items. 
     In many cases, however, it would be important or even vital to be able to carry out sample inspections at any stage of the life of the gyroscope, after installation. In addition to the fact that, in general, it is advantageous to be able to locate components affected by failures in order to proceed to their replacement, MEMS gyroscopes are used also in critical applications, in which a malfunctioning can have disastrous consequences. Just to provide an example, in the automotive field the activation of many air-bag systems is based upon the response supplied by gyroscopes. It is thus evident how important is the function of MEMS gyroscopes with devices capable of carrying out frequent tests on proper operation. 
     It should moreover be noted that the circuits necessary for the tests must not affect significantly the encumbrance and the level of consumption, which are of ever increasing importance in a large number of applications. 
     BRIEF SUMMARY 
     The present disclosure is to provide a microelectromechanical gyroscope and a method for controlling a microelectromechanical gyroscope that will enable the problems described to be overcome. 
     In accordance with one embodiment of the present disclosure, a microelectromechanical gyroscope is provided that includes a microstructure, including a first mass and a second mass, wherein the first mass is oscillatable according to a first axis and the second mass is constrained to the first mass so as to be drawn along by the first mass according to the first axis and oscillate according to a second axis in response to a rotation of the microstructure; a driving device coupled to the microstructure to maintain the first mass in oscillation at the driving frequency; a reading device for detecting displacements of the second mass according to the second axis; and a self-test actuation system coupled to the second mass for applying an electrostatic force at the driving frequency so as to move the second mass according to the second axis. 
     In accordance with another embodiment of the present disclosure, a method for controlling a microelectromechanical gyroscope is provided, the method including the steps of providing a microstructure including a first mass, oscillatable according to a first axis, and a second mass; constraining the second mass to the first mass so that the second mass is drawn along by the first mass according to the first axis and oscillates according a second axis in response to a rotation of the microstructure; feedback controlling a velocity of the first mass to maintain the first mass in oscillation at a driving frequency; and applying an electrostatic force to the second mass at the driving frequency so as to move the second mass according to the second axis. 
     In accordance with another embodiment of the present disclosure, a circuit is provided, the circuit including a driving circuit coupled to the first mass to drive the first mass in oscillation at a driving frequency; a reading device coupled to the second mass and adapted to detect displacements of the second mass; and a self-test actuation system coupled to the second mass and adapted to drive the second mass by applying an electrostatic force at a driving frequency in order to move the second mass. 
     In accordance with another aspect of the foregoing embodiment, a circuit adapted for use with a microelectromechanical gyroscope having a first mass and a second mass oscillatable in response to oscillations of the first mass, is provided, the circuit including a driving circuit coupled to the first mass to drive the first mass in oscillation at a driving frequency; a reading device coupled to the second mass and adapted to detect displacements of the second mass; and a self-test actuation system coupled to the second mass and adapted to drive the second mass by applying an electrostatic force at a driving frequency in order to move the second mass. 
     In accordance with another embodiment of the present disclosure, a system is provided, the system including a control circuit; a microelectromechanical gyroscope that includes a microstructure having a first mass and a second mass coupled to the first mass to oscillate in response to oscillations of the first mass; a driving circuit having a driving circuit coupled to the first mass to drive the first mass in oscillation at a driving frequency; a reading device coupled to the second mass and adapted to detect displacements of the second mass; and a self-test actuation system coupled to the second mass and adapted to drive the second mass by applying an electrostatic force at a driving frequency in order to move the second mass. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       For a better understanding of the disclosure, an embodiment thereof is now described, purely by way of non-limiting example and with reference to the attached drawings, wherein: 
         FIGS. 1 and 2  show graphs of the frequency response of a known microelectromechanical gyroscope; 
         FIG. 3  is a simplified block diagram of a microelectromechanical gyroscope, according to the present disclosure; 
         FIG. 4  is a schematic top plan view of a part of the microelectromechanical gyroscope illustrated of Figure; 
         FIG. 5  is a graph that illustrates a first set of quantities regarding the microelectromechanical gyroscope of  FIG. 3 ; 
         FIG. 6  is a more detailed block diagram of the microelectromechanical gyroscope of  FIG. 3 ; 
         FIG. 7  is a graph that illustrates a second set of quantities regarding the microelectromechanical gyroscope of  FIG. 3 ; 
         FIGS. 8a and 8b  show details of the gyroscope of  FIG. 3  in different operating configurations; and 
         FIG. 9  is a simplified block diagram of an electronic system incorporating a microelectromechanical gyroscope according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the sequel of the description, reference will be made to the use of the disclosed embodiments in a microelectromechanical gyroscope of the “yaw” type. This is not, however, to be considered in any way limiting, in so far as the disclosed embodiments can advantageously be exploited for the fabrication of MEMS gyroscopes of any type, in particular of the roll type, pitch type, and with multiple axes (biaxial or triaxial gyroscopes). 
     For reasons of convenience, moreover, the term “frequency” will be used to indicate angular frequencies (pulsations, rad/s). It is understood in any case that a frequency f and the corresponding angular frequency or pulsation ω are linked by the well-known relation ω=2πf. 
     A microelectromechanical gyroscope  100 , illustrated in a simplified way in the block diagram of  FIG. 3 , includes a microstructure  102 , obtained using MEMS technology, a driving device  103 , a reading device  104 , and a self-test device  106 , housed on a support  101 . The microstructure  102  is provided with a driving actuation system  5  and an inertial sensor  6 , including respective movable masses made of semiconductor material. More precisely, the driving actuation system  5  includes a driving mass  107 , oscillating about a resting position according to a degree of freedom of its own, in particular along a first axis X. The driving actuation system  5  is moreover provided with read outputs  5 a (defined by two stator terminals), for detecting displacements of the driving mass  107  along the first axis X, and with driving actuation inputs  5 b (defined by two further stator terminals), for receiving actuation signals such as to maintain the driving mass  107  in oscillation at the resonance frequency ω R , in a known way. The read outputs  5 a and the driving actuation inputs  5 b are capacitively coupled to the driving mass  107  in a known way, through comb-fingered electrodes (not illustrated herein). The inertial sensor  6  has an axis of detection having the same direction as a second axis Y perpendicular to the first axis X and comprises a detection mass  108 , mechanically connected to the driving mass  107  by springs (not illustrated herein), so as to be drawn in movement along the first axis X when the driving mass  107  is excited. 
     In addition, the detection mass  108  is relatively movable with respect to the driving mass  107  in the direction of the second axis Y and hence has a further degree of freedom. A read input  6 a (directly connected to the detection mass  108 ) and two detection outputs  6 b,  6 c (stator terminals) of the inertial sensor  6  enable, respectively, issuing of a read signal V S  to the detection mass  108  and detection of the displacements thereof. The read input  6 a is directly connected to the detection mass  108 , whereas the detection outputs  6 b,  6 c are capacitively coupled thereto in a known way, by parallel-plate detection electrodes  6 g (see  FIG. 4 , where the driving mass  107  is not illustrated for reasons of simplicity). In addition, the inertial sensor  6  is provided with a first self-test input  6 d and a second self-test input  6 e, capacitively coupled to the detection mass  108  by self-test actuation electrodes  6 h ( FIG. 4 ), but insulated from the detection outputs  6 b,  6 c. 
     In particular, the self-test actuation electrodes  6 h are shaped so that the detection mass  108  is subjected to an electrostatic force F E  parallel to the axis Y in the presence of an on average non-zero voltage between the detection mass  108  itself and the first and second self-test inputs  6 d,  6 e. In the non-limiting embodiment described herein, the self-test actuation electrodes  6 h are plane plates extending longitudinally along the axis X and perpendicular to the plane defined by the axes X, Y The first and second self-test inputs  6 d,  6 e and the self-test actuation electrodes  6 h thus form a self-test actuation system capable of moving the detection mass  108  according to the second axis Y, in response to a rotation of the microstructure  102 . 
     The driving device  103  is connected to the microstructure  102  so as to form a feedback control loop  105 , including the driving mass  107 . As will be clarified hereinafter, the driving device  103  exploits the feedback control loop  105  to maintain the driving mass  107  in self-oscillation along the first axis X at its mechanical resonance frequency ω R  (for example, 25 krad/s). In addition, the driving device  103  generates a first clock signal CK, synchronous with the oscillations of the driving mass  107  at the resonance frequency ω R , and a second clock signal CK 90  , 90° out of phase, and supplies them to the reading device  104  in order to synchronize the operations of reading of the microstructure  102 . The first clock signal CK is supplied also to the self-test device  106 . 
     The reading device  104  is of the open-loop type and, in the embodiment described herein, is configured for executing a so-called “double-ended” reading of the displacements of the detection mass  108  along the second axis Y. In particular, the reading device  104  has: a first input  104 a, connected to the driving device  103  for acquiring a demodulation signal V DEM  (in this case a voltage); second inputs, connected to respective detection outputs  6 b,  6 c of the inertial sensor  6 ; a first output, connected to the read input  6 a of the inertial sensor  6  and issuing the read signal V S ; and a second output  104 b, which supplies an output signal S OUT , correlated to the angular velocity Ω of the microstructure  102 . 
     The self-test device  106  is coupled to the driving device  103  for receiving the first clock signal CK, and has a first output and a second output. The first output is connected to the first self-test input  6 d and supplies a first self-test signal V ST1 , and the second output is connected to the second self-test input  6 e and supplies a second self-test signal V ST2 . In addition, the self-test device  106  has an enabling input  106 a, receiving an operating-mode signal N, which is controlled manually from outside the gyroscope  100 . The operating-mode signal N has a normal operating value, which disables the self-test device  106 , and a self-test value, which enables the self-test device  106 . 
     The gyroscope  100  operates in the way hereinafter described. During normal operation, the driving mass  107  is set in oscillation along the first axis X by the driving device  103 . For this purpose, the driving device  103  is coupled to the read outputs  5 a of the driving actuation system  5  for receiving detection currents I RD1 , I RD2 , which are correlated to the linear velocity of oscillation of the driving mass  107  along the first axis X. On the basis of the detection currents I RD1 , I RD2 , the driving device  103  generates feedback driving voltages V FBD1 , V FBD2  having an amplitude and phase such as to ensure the conditions of oscillation of the feedback control loop  105  (unit loop gain and phase equal to 2πN, where N is any integer, zero included). 
     The detection mass  108  is drawn in movement along the first axis X by the driving mass  107 . Consequently, when the microstructure  102  rotates about a gyroscopic axis perpendicular to the plane of the axes X, Y with a certain instantaneous angular velocity Ω, the detection mass  108  is subjected to a Coriolis force, which is parallel to the second axis Y and is proportional to the instantaneous angular velocity Ω of the microstructure  102  and to the linear velocity of the two masses  107 ,  108  along the first axis X. More precisely, the Coriolis force (F C ) is given by the equation:
 
F C =2M S ΩX′
 
where M S  is the value of the detection mass  108 , Ω is the angular velocity of the microstructure  102 , and X′ is the linear velocity of the two masses  107 ,  108  along the first axis X. As a result of the driving at the resonance frequency ω R , the detection signals, determined by the rotation of the gyroscope and correlated to the angular velocity, are amplitude modulated: the carrier is in this case the velocity of oscillation X′ of the driving mass  107  and has a frequency equal to the mechanical resonance frequency ω R .
 
     The Coriolis force and acceleration to which the detection mass  108  is subjected are read through the inertial sensor  6 . In response to the excitation of the detection mass  108  by the read signal V S , the inertial sensor  6  issues differential detection charge packets Q RS1 , Q RS2 , which are proportional to the capacitive unbalancing caused by the displacement of the detection mass  108  along the second axis Y. The detection charge packets Q RS1 , Q RS2  are hence correlated to the Coriolis force (and acceleration) and to the instantaneous angular velocity of the microstructure  102 . More precisely, the charge transferred with the detection charge packets Q RS1 , Q RS2  in successive reading cycles is amplitude modulated proportionally to the instantaneous angular velocity of the microstructure  102 . The frequency band associated to the modulating quantity, i.e., the instantaneous angular velocity, is, however, much lower than the resonance frequency ω R  (for example, approximately 250 rad/s). The detection charge packets Q RS1 , Q RS2  are converted and processed by the reading device  104 , which generates the output signal S OUT , as explained hereinafter. 
     When the self-test operating mode is selected, the self-test device  106  is activated and generates the first and second self-test signals V ST1 , V ST2 . As illustrated in  FIG. 5 , the first and second self-test signals V ST1 , V ST2  are square-wave signals that vary between a supply voltage VDD of the gyroscope  100  and a ground voltage GND (0 V), as likewise the read signal V S . The first and second self-test signals V ST1 , V ST2  have, however, a duty cycle different from the read Signal V S . The duty cycle of the first and second self-test signals V ST1 , V ST2  is a first fraction α, for example ½, whilst the duty cycle of the read signal V S  is a second fraction β, for example ⅖. In this way, during the self-test step, the mean voltage between the self-test actuation electrodes  6 h and the detection mass  108  is equal to αV DD −βV DD , and hence the detection mass  108  is subjected to an electrostatic force F E  which is on average non-zero and parallel to the axis Y. As a result of the electrostatic force F E , the detection mass  108  is displaced in the direction of the axis Y and causes an unbalancing in the capacitive coupling with the detection electrodes  6 g and the detection outputs  6 b,  6 c. The displacement of the detection mass  108  is equivalent, in practice, to a fictitious rotation of the gyroscope  100  with known angular velocity Ω and, as such, is detected by the reading device  104 . The output signal S OUT  is thus an indication of proper operation of the gyroscope  100 . If, in fact, in the self-test operating mode the output signal S OUT  does not vary in accordance with the forces exerted through the self-test signals V ST1 , V ST2 , necessarily either the microstructure  102  or the reading device  104  is damaged and does not function properly. If, instead, the output signal S OUT  assumes pre-determined values, both the microstructure  102  and the reading device  104  are operating properly. 
     Proper operation of the gyroscope  100  can thus be readily verified at any moment of its life, using the self-test device  106 . Advantageously, the self-test device  106  exploits self-test signals V ST1 , V ST2  that produce the same effects caused by a rotation of the gyroscope  100 . In fact, the first and second self-test signals V ST1 , V ST2  oscillate at the resonance frequency ω R  of the driving mass  107 . Also the electrostatic force F E  varies at the same frequency. More precisely, the electrostatic force F E  has a non-zero d.c. component, as explained above, and multiple harmonic components of the resonance frequency ω R  (Mω R , with M=1, 2, . . . ). The principal component (M=1), in particular, has the same frequency as the carrier signal (i.e., the velocity X′ of the driving mass  107 ), which, in the normal operating mode, is modulated by the angular velocity Ω. Consequently, the principal component of the electrostatic force F E  applied to the detection mass  108  is perfectly compatible with the processing of the reading device  104 , as will be seen also hereinafter. Precisely for this reason, moreover, the self-test device  106  is suitable for testing also proper operation of the reading device  104  and, in particular, the synchronous demodulation that must be performed. In addition, this presupposes that also the driving device  103  is functioning, therefore if  104  passes the test, also proper operation of the driving device  103  can be considered as tested. A further advantage resides in that the self-test device  106  is completely integrated in the gyroscope  100  and does not require signals from outside to be supplied. Once the self-test mode has been selected, the self-test device  106  operates in a fully automatic way and is thus particularly simple to use in any application. 
       FIG. 6  shows a more detailed diagram of the inertial sensor  6 , of the reading device  104 , and of the self-test device  106 . 
     As regards the inertial sensor  6 ,  FIG. 6  shows: differential detection capacitances  110  that are present between the detection mass  108  and respective detection outputs  6 b,  6 c; differential self-test capacitances  111 , present between the detection mass  108  and respective self-test inputs  6 d,  6 e; parasitic coupling capacitances  112 , between the self-test inputs  6 d,  6 e and the detection outputs  6 b,  6 c; and parasitic substrate capacitances  113 . 
     The reading device  4  includes a reading generator  115 , coupled to the read input  6 a of the inertial sensor  6  so as to issue the read signal V S , a fully differential charge amplifier  116 , a demodulator stage  117 , a lowpass filter  118 , and a sampler  120 . 
     The charge amplifier  116  is connected to the detection outputs  6 b,  6 c of the inertial sensor  6  and is provided with feedback capacitors  122 . By reset switches  123 , the inputs of the charge amplifier  116  are moreover selectively connectable to a common-mode line  125 , supplying a common-mode voltage V CM . 
     The demodulator stage  117 , the lowpass filter  118 , and the sampler  120  are cascaded to the charge amplifier  116 , with which they form a chain for reading the detection charge packets Q RS1 , Q RS2  produced by the inertial sensor  6 . The demodulator stage  117  acquires from the feedback loop  105 , in a known way, a demodulation signal V DEM , synchronous and in phase with the velocity X′ of the driving mass  107 . The lowpass filter  118  has a cutoff frequency lower than the resonance frequency ω R  and such as to suppress also the higher-order harmonic components of the signals produced by the electrostatic force F E  (M≧2). The output of the sampler  120  forms the second output  104 b of the reading device  104  and supplies the output signal S OUT . 
     The self-test device  106  includes a phase generator  128 , a first self-test generator  130 a and a second self-test generator  130 b, which supply, respectively, the first self-test signal V ST1  and the second self-test signal V ST2 , and enabling switches  132 . 
     The phase generator  128  receives the clock signal CK and the operating-mode signal N and generates a first phase signal F 1  and a second phase signal F 2 , for controlling the first and second self-test generators  130 a,  130 b, and a reset signal RES, for controlling the reset switches  123  of the charge amplifier  116 . As illustrated in  FIG. 7 , the first phase signal F 1  is synchronous and in phase with the clock signal CK, while the second phase signal F 2  has the same frequency and is 180° out of phase. 
     The first self-test generator  130 a and the second self-test generator  130 b are respectively connected to the first and second self-test inputs  6 d,  6 e of the inertial sensor  6  and operate as switching circuits ( 130 a,  130 b), for connecting the self-test terminals  6 d,  6 e alternatively to the supply line  137  and to the ground line  138 . In greater detail, the first and second self-test generators  130 a,  130 b each comprise a supply switch  134  and a ground switch  135 . The supply switches  134  are each connected to a respective self-test input  6 d,  6 e of the inertial sensor  6  and to a supply line  137 , issuing the supply voltage V DD . The ground switches  135  are connected to a respective self-test input  6 d,  6 e of the inertial sensor  6  and to a ground line  138 , set at the ground voltage GND. 
     In the first self-test generator  130 a, the supply switch  134  is controlled by the first phase signal F 1 , and the ground switch  135  is controlled by the second phase signal F 2 . Instead, in the second self-test generator  130 a, the supply switch  134  is controlled by the second phase signal F 2 , and the ground switch  135  is controlled by the first phase signal F 1 . Since the phase signals F 1 , F 2  are 180° out of phase with respect to one another, the first and second self-test inputs  6 d,  6 e of the inertial sensor  6  are always one at the supply voltage V DD  and the other at the ground voltage GND. In addition, leading edges of the first self-test voltage V ST1  correspond to trailing edges of the second self-test voltage V ST2  and vice versa, as illustrated in  FIGS. 8a and 8b . 
     The enabling switches  132  are located between respective self-test inputs  6 d,  6 e of the inertial sensor  6  and a reference line  140  set at a constant reference voltage V REF  and are controlled by the operating-mode signal N. In particular, in the normal operating mode the enabling switches  132  are closed and maintain the self-test inputs  6 d,  6 e at the reference voltage V REF , whereas they are open in the self-test mode. The reference voltage V REF  is chosen so as to prevent the so-called phenomenon of “electrostatic softening” and is preferably equal to half the supply voltage V DD /2 or else to the common-mode voltage V CM  of the charge amplifier  116 . 
     The reset signal RES determines closing of the reset switches  123  and is generated so as to mask the edges of the self-test signals V ST1 , V ST2 . In the reset step, in fact, the charge amplifier is in practice decoupled from the detection outputs  6 b,  6 c of the inertial sensor  6  and is not affected by any possible undesirable transfer of charge caused by the parasitic coupling capacitances  112  when self-test signals V ST1 , V ST2  switch. 
     The self-test device  106  described above is particularly efficient, because it is obtained only using appropriately timed switches. The encumbrance is hence extremely small, and the impact on the consumption levels is altogether negligible. 
     As previously mentioned, moreover, the self-test device  106  exploits signals that have the same carrier frequency as the normal read signals. Self-test hence enables verification also of whether the demodulation of the signals is performed properly. 
     A portion of a system  200  according to one embodiment of the present disclosure is illustrated in  FIG. 9 . The system  200  may be used in devices such as, for example, a palmtop computer (personal digital assistant, PDA), a laptop or portable computer, possibly with wireless capacity, a cell phone, a messaging device, a digital music reader, a digital camera, or other devices designed to process, store, transmit or receive information. For example, the gyroscope  100  may be used in a digital camera for detecting movements and carrying out an image stabilization. In other embodiments, the gyroscope  100  is included in a portable computer, a PDA, or a cell phone for detecting a free-fall condition and activating a safety configuration. In a further embodiment, the gyroscope  100  is included in a user interface activated by movement for computers or videogame consoles. 
     The system  200  may include a controller  210 , an input/output (I/O) device  220  (for example, a keyboard or a screen), the gyroscope  100 , a wireless interface  240 , and a memory  260 , of a volatile or nonvolatile type, connected to one another through a bus  250 . In an embodiment, a battery  280  may be used for supplying the system  200 . It is to be noted that the scope of the present disclosure is not limited to embodiments having necessarily one or all of the devices referred to above. 
     The controller  210  may include, for example, one or more microprocessors, microcontrollers, and the like. 
     The I/O device  220  may be used for generating a message. The system  200  may use the wireless interface  240  for transmitting and receiving messages to and from a wireless-communication network with a radiofrequency (RF) signal. Examples of wireless interface may comprise an antenna, a wireless transceiver, such as a dipole antenna, even though the scope of the present disclosure is not limited from this standpoint. In addition, the I/O device  220  may supply a voltage that represents what is stored either in the form of digital output (if digital information has been stored) or in the form of analog information (if analog information has been stored). 
     Finally, it is evident that modifications and variations can be made to the microelectromechanical gyroscope and to the method described, without thereby departing from the scope of the present disclosure, as defined in the annexed claims. In the first place, the microstructure  102  may have a shape different from the one described, both in the case of gyroscopes of a “roll” type and, especially, in the cases of gyroscopes of the “pitch” type and with multiple axes. The self-test signals can have a different waveform, provided that they contain the frequency of oscillation of the driving mass  107  along the axis X, i.e., the resonance frequency ω R . Reading of the inertial sensor  6  can be of a “single-ended” type. In this case, two read signals 180° out of phase are supplied to the detection outputs  6 b,  6 c (now used as read inputs), and detection charge packets are acquired from the read input  6 a, which in this case functions as detection output. The self-test signal is always of the square-wave type with a frequency equal to the resonance frequency ω R  and a duty cycle different from that of the read signals. 
     The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.