JP6206113B2 - Vibrator drive circuit - Google Patents

Description

  The present invention relates to a vibrator drive circuit that vibrates a vibrator in a predetermined drive axis direction in a vibration type angular velocity sensor or the like.

  Conventionally, by vibrating the vibrator in a predetermined drive axis direction, a Coriolis force corresponding to the angular velocity acting from the outside is generated in the vibrator, and the vibrator makes the vibrator in a direction orthogonal to the vibration direction. A vibration type angular velocity sensor that detects the amount of displacement and measures the magnitude of the angular velocity is known (for example, Patent Documents 1 and 2). This type of angular velocity sensor has a drive circuit that forms a closed loop through a vibrator, and the vibrator is fixed by detecting the vibration amplitude in the drive axis direction of the vibrator and adjusting the gain of the drive signal. It is comprised so that it may vibrate with the vibration amplitude.

JP 2008-209182 A JP2012-230052A

  However, in the conventional drive circuit, when the temperature environment of the angular velocity sensor changes, the gain given to the drive signal changes accordingly, so that the vibration amplitude in the drive axis direction of the vibrator can be stabilized in a constant state. There is a problem that you can not. In particular, in the angular velocity sensor, the vibration amplitude in the driving axis direction of the vibrator affects the measurement sensitivity. Therefore, if the gain applied to the drive signal changes due to a temperature change, the angular velocity cannot be measured accurately. is there.

  Therefore, the present invention has been made to solve the above-described problems, and provides a vibrator driving circuit that can stabilize the vibration amplitude in the driving axis direction of the vibrator without being affected by temperature changes. For the purpose.

  In order to achieve the above object, the present invention provides a vibrator drive circuit that outputs a drive signal for vibrating a vibrator in a predetermined drive axis direction, and detects the vibration amplitude of the vibrator and compares it with a predetermined target value. And an amplitude detection circuit that outputs a control signal based on a predetermined reference voltage according to the difference between the vibration amplitude and the target value, and a first transistor that changes the on-resistance based on the control signal, A gain adjustment circuit that adjusts a gain applied to the drive signal in accordance with the on-resistance of the first transistor, and a second transistor having the same characteristics as the first transistor, and the on-resistance of the second transistor is a predetermined value And a reference voltage generation circuit that drives the second transistor and outputs the drive voltage of the second transistor as a reference voltage to the amplitude detection circuit. According to such a configuration, when a temperature change occurs, the drive voltage for driving the second transistor fluctuates. Therefore, the reference voltage can be fluctuated according to the temperature change, and the on-resistance of the first transistor due to the temperature change. It becomes possible to cancel the fluctuation amount.

  The present invention further includes the following configurations in the above configuration. That is, the gain adjustment circuit adjusts the gain to be applied to the drive signal within a predetermined gain adjustment range, and the reference voltage generation circuit has the on-resistance of the first transistor when the gain is an intermediate value within the gain adjustment range. The second transistor is driven so that the on-resistance of the second transistor is equivalent to the on-resistance of the second transistor, and the driving voltage of the second transistor is used as a reference voltage.

  The present invention further includes the following configurations in the above configuration. That is, the amplitude detection circuit calculates the difference between the vibration amplitude and the target value by transferring the charge accumulated in the sampling unit and the sampling unit that accumulates the charge according to the vibration amplitude in the drive axis direction of the vibrator. Accordingly, the configuration includes a charge transfer unit that generates a differential signal based on a predetermined reference voltage, and an amplification unit that amplifies and outputs the differential signal generated in the charge transfer unit.

  In addition to the above-described configuration, the present invention detects a vibration displacement in the driving axis direction of the vibrator and outputs a vibration waveform, and shifts the phase of the vibration waveform output from the vibration displacement detection circuit by 90 degrees. And a gain adjustment circuit that generates a drive signal by applying a gain corresponding to the on-resistance of the first transistor to the vibration waveform output from the phase conversion circuit. The configuration is as follows.

  Furthermore, this invention has the following structures further in the said structure. That is, the amplitude detection circuit is configured to detect the vibration amplitude in the drive axis direction of the vibrator based on the vibration waveform output from the vibration displacement detection circuit.

  According to the present invention, it is possible to realize a vibrator drive circuit that can stabilize the vibration amplitude in the drive axis direction of the vibrator without being affected by temperature changes.

It is a block diagram which shows schematic structure of an angular velocity sensor. It is a figure which shows the signal waveform of each part in a vibrator drive circuit. It is a circuit diagram which shows one structural example of a gain adjustment circuit. It is a circuit diagram which shows one structural example of an amplitude detection circuit. It is a timing chart which shows the ON / OFF state of each switch of an amplitude detection circuit. It is a circuit diagram which shows one structural example of a reference voltage generation circuit. It is a figure which shows the characteristic curve of the ON resistance of a 1st transistor. It is a signal waveform diagram for explaining the operation of the vibrator driving circuit.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the embodiments described below, members that are common to each other are denoted by the same reference numerals, and redundant descriptions thereof are omitted.

  FIG. 1 is a block diagram showing a schematic configuration of an angular velocity sensor 1 including a vibrator driving circuit 3 according to an embodiment of the present invention. The angular velocity sensor 1 is a sensor mounted on an information processing terminal such as a smartphone or a tablet terminal, for example, and includes a sensor unit 2 having a vibrator 5 formed by a MEMS (Micro Electro Mechanical Systems) structure, and a sensor unit 2. A vibrator drive circuit 3 that vibrates a provided vibrator 5 in a predetermined drive axis direction (X-axis direction), and an angular velocity detection circuit 4 that detects and outputs an angular velocity based on a signal output from the sensor unit 2. Prepare.

  The vibrator 5 provided in the sensor unit 2 is supported by a spring structure or the like so as to be displaceable in the X-axis direction and the Y-axis direction orthogonal to the X-axis direction on a substrate such as a silicon substrate. 3 oscillates in the X-axis direction by drive signals Vdp and Vdn of a predetermined frequency output from 3. The frequencies of the drive signals Vdp and Vdn are set in advance so as to coincide with the resonance frequency of the vibrator 5. When an external angular velocity acts while the vibrator 5 vibrates in the X-axis direction, a Coriolis force in the Y-axis direction perpendicular to the vibration direction (X-axis direction) acts on the vibrator 5, and the vibrator 5 Is displaced in the Y-axis direction by the Coriolis force. The angular velocity sensor 1 is configured to detect the angular velocity by detecting the displacement of the vibrator 5 in the Y-axis direction due to such Coriolis force.

  The vibrator 5 includes a plurality of movable electrodes facing each of a plurality of fixed electrodes formed on the substrate of the sensor unit 2, and a plurality of capacitors C1, C2, C3 are formed by the fixed electrodes and the movable electrodes. , C4, C5, C6. The capacitors C1 and C2 are capacitors for driving the vibrator 5 to vibrate in the X-axis direction, and the capacitors C3 and C4 are capacitors for detecting the vibration amplitude of the vibrator 5 in the X-axis direction. Capacitors C5 and C6 are capacitors for detecting the amount of displacement when the vibrator 5 is displaced in the Y-axis direction by the Coriolis force.

  The vibrator driving circuit 3 drives and vibrates the vibrator 5 in the X-axis direction by applying drive signals Vdp and Vdn to the capacitors C1 and C2, respectively. The drive signals Vdp and Vdn are sine wave signals that oscillate around a predetermined reference voltage Vref as shown in FIG. 2A, and are generated as signals whose polarities are inverted. On the other hand, the potential of the vibrator 5 is kept constant at a predetermined potential Va different from the reference voltage Vref as shown in FIG. The predetermined potential Va is supplied from the outside (not shown) of the vibrator 5 and applied to the vibrator 5. Therefore, when the drive signals Vdp and Vdn are applied to the capacitors C1 and C2, a difference occurs in the electrostatic force between the capacitors C1 and C2, and the vibrator 5 vibrates in the X-axis direction due to the difference in the electrostatic force. When the vibrator 5 vibrates in the X-axis direction, the capacitances of the capacitors C3 and C4 change. Therefore, the vibrator drive circuit 3 outputs from the sensor unit 2 according to the changes in the capacitances of the capacitors C3 and C4. The vibration amplitude of the vibrator 5 is detected based on the charge signals Sip and Sin, and the gains of the drive signals Vdp and Vdn are adjusted based on the vibration amplitude.

  The angular velocity detection circuit 4 detects the angular velocity based on the capacitance change of the capacitors C5 and C6 that occurs when the vibrator 5 is displaced in the Y-axis direction by the Coriolis force. The angular velocity detection circuit 4 includes a CV conversion circuit 16 and a signal processing unit 17. The CV conversion circuit 16 is a circuit that converts the capacitance change of the capacitors C5 and C6 into a voltage, and inputs the charge signals S1 and S2 output from the sensor unit 2 according to the capacitance change of the capacitors C5 and C6. Then, voltages V1 and V2 corresponding to the displacement amount of the vibrator 5 in the Y-axis direction due to the Coriolis force are output. That is, the CV conversion circuit 16 is a Coriolis force displacement detection circuit that detects displacement of the vibrator 5 in the Y-axis direction due to Coriolis force. The signal processing unit 17 is a circuit that removes unnecessary signal components such as a quadrature error from the voltages V1 and V2 output from the CV conversion circuit 16, and performs predetermined signal processing on the input voltages V1 and V2. By performing this, an angular velocity signal Sout corresponding to the Coriolis force is generated and output.

  Next, the vibrator driving circuit 3 will be described in detail. The vibrator drive circuit 3 includes a CV conversion circuit 10, a phase conversion circuit 11, a gain adjustment circuit 12, an amplitude detection circuit 13, a reference voltage generation circuit 14, and an initial drive signal generation circuit 15. A closed loop is formed via the vibrator 5 and controlled so that the vibration amplitude in the X-axis direction of the vibrator 5 is stabilized in a constant state.

  The CV conversion circuit 10 is a circuit that converts the capacitance change of the capacitors C3 and C4 into a voltage, and inputs the charge signals Sip and Sin output from the sensor unit 2 according to the capacitance change of the capacitors C3 and C4. Then, signals Vip and Vin corresponding to the vibration displacement of the vibrator 5 in the X-axis direction are output. That is, the CV conversion circuit 10 is a vibration displacement detection circuit that detects vibration displacement in the X-axis direction of the vibrator 5. When the vibrator 5 is driven in the X-axis direction by the drive signals Vdp and Vdn, the vibration waveform has a waveform that is 90 ° out of phase with the drive signals Vdp and Vdn. Therefore, the signals Vip and Vin output from the CV conversion circuit 10 are sine wave signals whose phases are delayed by 90 ° with respect to the drive signals Vdp and Vdn as shown in FIG. Further, the amplitudes of the signals Vip and Vin change according to the vibration amplitude of the vibrator 5 in the X-axis direction.

  The phase conversion circuit 11 is a circuit that matches the phases of the drive signals Vdp and Vdn by converting the phases of the signals Vip and Vin output from the CV conversion circuit 10. Therefore, the signals Vsp and Vsn output from the phase conversion circuit 11 are sine wave signals having the same phase as the drive signals Vdp and Vdn as shown in FIG. The signals Vsp and Vsn whose phases have been adjusted by the phase conversion circuit 11 are input to the gain adjustment circuit 12.

  The amplitude detection circuit 13 is a circuit that detects the vibration amplitude in the X-axis direction of the vibrator 5 based on the signals Vip and Vin output from the CV conversion circuit 10. The amplitude detection circuit 13 detects the vibration amplitude in the X-axis direction of the vibrator 5 by sampling the potential difference between the signals Vip and Vin at the timing when the signals Vip and Vin shown in FIG. . The amplitude detection circuit 13 compares the vibration amplitude in the X-axis direction of the vibrator 5 with a predetermined target value, and generates a control signal Vcont based on a predetermined reference voltage Vrep based on the difference between the vibration amplitude and the target value. The control signal Vcont is generated and output to the gain adjustment circuit 12. In this embodiment, the case where the amplitude detection circuit 13 detects the vibration amplitude of the vibrator 5 based on the signals Vip and Vin output from the CV conversion circuit 10 is illustrated, but the present invention is not limited to this. For example, the vibration amplitude may be detected based on the signals Vsp and Vsn output from the phase conversion circuit 11.

  The gain adjustment circuit 12 is a circuit that amplifies the signals Vsp and Vsn output from the phase conversion circuit 11 and generates drive signals Vdp and Vdn to be applied to the capacitors C1 and C2. The gain adjustment circuit 12 adjusts the gain when amplifying the signals Vsp and Vsn based on the control signal Vcont output from the amplitude detection circuit 13, and sets the vibration amplitude in the X-axis direction of the vibrator 5 to a target value. Drive signals Vdp and Vdn are generated. Therefore, the CV conversion circuit 10, the phase conversion circuit 11, the gain adjustment circuit 12, and the amplitude detection circuit 13 constitute a positive feedback for causing the vibrator 5 to oscillate.

  The reference voltage generation circuit 14 is a circuit that generates a reference voltage Vrep that serves as a reference for the control signal Vcont generated in the amplitude detection circuit 13, and outputs the reference voltage Vrep to the amplitude detection circuit 13.

  The initial drive signal generation circuit 15 is a circuit that outputs initial drive signals Vd1 and Vd2 to the gain adjustment circuit 12 when the vibrator 5 is vibrated from a stopped state where the vibrator 5 is not vibrated. For example, the initial drive signal generation circuit 15 operates when the angular velocity sensor 1 is activated, and outputs the initial drive signals Vd1 and Vd2 to the gain adjustment circuit 12 until the vibrator 5 vibrates with a predetermined vibration amplitude from the stopped state. At this time, the phase conversion circuit 11, the amplitude detection circuit 13, and the reference voltage generation circuit 14 are not operated. When the vibrator 5 starts to vibrate with a predetermined vibration amplitude by the initial drive signals Vd1 and Vd2, the initial drive signal generation circuit 15 stops the output of the initial drive signals Vd1 and Vd2, and the phase conversion circuit 11 and the amplitude detection circuit. 13 and the reference voltage generation circuit 14 start to operate. As described above, the vibrator drive circuit 3 initially vibrates the vibrator 5 with the initial drive signals Vd1 and Vd2 output from the initial drive signal generation circuit 15 at the time of startup, and then forms a positive feedback loop to form the vibrator 5. The operation to control the vibration amplitude of the target value is started.

  FIG. 3 is a circuit diagram illustrating a configuration example of the gain adjustment circuit 12. As shown in FIG. 3, the gain adjustment circuit 12 includes a fully differential operational amplifier 20, eight NMOS transistors (hereinafter simply referred to as “transistors”) 21 to 28, and six resistors R1, R1, R2, R2, and so on. R3 and R3 are provided. Resistors R1 are connected to the two feedback paths of the fully differential operational amplifier 20, respectively. The signal Vsp output from the phase conversion circuit 11 is input to the inverting input terminal of the fully-differential operational amplifier 20 through the resistor R2 and the two transistors 21 and 22, and the resistor R3 and the two transistors 25 and 27. Is input to the non-inverting input terminal of the fully-differential operational amplifier 20 through the first gain adjustment unit 29a. The signal Vsn is input to the non-inverting input terminal of the fully-differential operational amplifier 20 through the resistor R2 and the two transistors 23 and 24, and the second signal Vsn is composed of the resistor R3 and the two transistors 26 and 28. The signal is input to the inverting input terminal of the fully differential operational amplifier 20 through the gain adjustment unit 29b.

  The eight transistors 21 to 28 are transistors of the same size formed by the same manufacturing process on the same substrate, and transistors having the same characteristics. Among these, a predetermined power supply voltage Vdd is connected to the gate terminals of the transistors 21 to 26. With this power supply voltage Vdd, the transistors 21 to 26 are completely turned on, and the on-resistance becomes almost zero. On the other hand, the control signal Vcont output from the amplitude detection circuit 13 is input to the gate terminals of the two transistors 27 and 28 provided in the gain adjusting units 29a and 29b. With this control signal Vcont, the on-resistances of the transistors 27 and 28 change, and the gains applied to the signals Vsp and Vsn input to the gain adjustment circuit 12 are adjusted. That is, the two transistors 27 and 28 provided in the gain adjusting units 29a and 29b are transistors (first transistors) that change the on-resistance according to the control signal Vcont in order to adjust the gain. For example, when the control signal Vcont is small and the transistors 27 and 28 are off, the two paths of the gain adjustment units 29a and 29b are invalidated, and therefore the gain G applied to the signals Vsp and Vsn in the gain adjustment circuit 12 Is determined by the ratio of the resistor R1 and the resistor R2, and G = R1 / R2. When the control signal Vcont is large and the transistors 27 and 28 are completely turned on, the two paths of the gain adjusting units 29a and 29b operate effectively, and the on-resistances of the transistors 27 and 28 are almost zero. Therefore, the gain G applied to the signals Vsp and Vsn in the gain adjustment circuit 12 is determined by the resistor R1, the resistor R2, and the resistor R3, and becomes G = (R1 / R2) − (R1 / R3). Further, when the control signal Vcont is a value that causes each of the transistors 27 and 28 to operate in an intermediate state between the completely off state and the completely on state, the on resistance of each of the transistors 27 and 28 changes according to the control signal Vcont. Also at this time, since the two paths of the gain adjustment units 29a and 29b operate effectively, the gain G given to the signals Vsp and Vsn in the gain adjustment circuit 12 is the resistance R1, the resistance R2, the resistance R3, It is determined by the on-resistance Ron of the transistors 27 and 28, and G = {(R1 / R2) − (R1 / (R3 + Ron))}.

  Here, when the resistance R1 = 900R, the resistance R2 = 9R, and the resistance R3 = 10R, the maximum value Gmax of the gain G applied in the gain adjustment circuit 12 becomes Gmax = 900R / 9R = 100, and the signals Vsp and Vsn are The drive signals Vdp and Vdn amplified 100 times can be output. Further, the minimum value Gmin of the gain G is Gmin = (900R / 9R) − (900R / 10R) = 10, and the drive signals Vdp and Vdn obtained by amplifying the signals Vsp and Vsn 10 times can be output. Since the on-resistance Ron of the transistors 27 and 28 changes according to the control signal Vcont, the gain G applied in the gain adjustment circuit 12 is adjusted within the range between the minimum value Gmin and the maximum value Gmax. Adjustment is made within the range of 100 to 100 times. When the on-resistance Ron is Ron = R3 (= 10R), the gain G is G = 55, which is an intermediate value between the minimum value Gmin (= 10) and the maximum value Gmax (= 100).

  FIG. 4 is a circuit diagram showing a configuration example of the amplitude detection circuit 13. The amplitude detection circuit 13 transfers the charge accumulated in the sampling unit 31 by storing the charge corresponding to the vibration amplitude of the vibrator 5, and the vibration amplitude of the vibrator 5, A charge transfer unit 32 that compares a target value of the vibration amplitude and generates a differential signal based on a predetermined reference voltage Vrep based on the difference, and an amplification unit 33 that amplifies and outputs the differential signal I have. The sampling unit 31 includes switches SW1 and SW2 and a capacitor C11. The potential difference between the signals Vip and Vin output from the CV conversion circuit 10 by selectively switching the switches SW1 and SW2 to the on state. Is stored in the capacitor C11. The charge transfer unit 32 includes switches SW3 and SW4 and capacitors C12 and C13. By sequentially switching the switches SW3 and W4 to the on state, the charge accumulated in the capacitor C11 is transferred to the capacitors C12 and C13. The vibration amplitude of the vibrator 5 is compared with the target value in the transfer process, and a difference signal between the vibration amplitude of the vibrator 5 and the target value is generated. The amplifying unit 33 includes an operational amplifier 34 and resistors Ra and Rb, amplifies the difference signal at an amplification factor determined by the resistors Ra and Rb, and outputs a control signal Vcont according to the vibration amplitude of the vibrator 5. .

  FIG. 5 is a timing chart showing the on / off states of the switches SW1, SW2, SW3, SW4. As shown in FIG. 5, when the signals Vip and Vin are Vip> Vin and the timing indicates the maximum amplitude, the switch SW1 is turned on and off, and the potential difference between the signals Vip and Vin is set as the input signal Vx. Charges corresponding to Vx (charges corresponding to the vibration amplitude of the vibrator 5 in the X-axis direction) are accumulated in the capacitor C11. At this time, the switches SW2, SW3 and SW4 are off. Thereafter, when the switch SW3 is turned on, the electric charge accumulated in the capacitor C11 is transferred to the capacitor C12. At this time, the two capacitors C11 and C12 are connected in series, the reference voltage Vrep generated by the reference voltage generation circuit 14 is applied to one end of the capacitor C11, and the vibrator 5 is connected to one end of the capacitor C12. A target voltage Vdac corresponding to the target value of the vibration amplitude is applied. When the charge transfer from the capacitor C11 to the capacitor C12 is completed, the switch SW3 is turned off, and then the switch SW4 is turned on to further transfer the charge accumulated in the capacitor C12 to the capacitor C13. At this time, the two capacitors C12 and C13 are connected in series, and both ends of the capacitors C12 and C13 are grounded. The common potential Vy between the two capacitors C12 and C13 is input to the non-inverting input terminal of the operational amplifier 34. The operational amplifier 34 amplifies the potential Vy and outputs a control signal Vcont. Subsequently, when the signals Vip and Vin are Vin> Vip and the maximum amplitude is reached, the switch SW2 is turned on and off, the potential difference between the signals Vin and Vip is set as the input signal Vx, and the charge corresponding to the input signal Vx Is stored in the capacitor C11. Thereafter, similarly to the above, the electric charge accumulated in the capacitor C11 is sequentially transferred to the capacitors C12 and C13, and the control signal Vcont corresponding to the vibration amplitude of the vibrator 5 is output from the operational amplifier 34.

  In the process of charge transfer, if the potential input to the operational amplifier 34 before the charge transfer is Vy ′, the potential Vy input to the operational amplifier 34 after the charge transfer is expressed by the following equation (1). The

  Here, in the initial state before the switch SW1 is first turned on, if no electric charge is accumulated in the capacitors C12 and C13 and the potential Vy ′ input to the operational amplifier 34 is 0, the capacitor is first connected. The potential Vy input to the operational amplifier 34 when the electric charge accumulated in C12 is transferred to the capacitor C13 is represented by the first term on the right side in the above equation 1, and the current vibration amplitude (input signal Vx) of the vibrator 5 And the difference signal from the target voltage Vdac, which is the target value of the vibration amplitude, is a difference signal representing the reference voltage Vrep as a reference. In the process in which charge transfer is repeatedly performed, the second term on the right side shown in the above equation 1 is applied to the difference signal between the current vibration amplitude of the vibrator 5 and the target voltage Vdac that is the target value of the vibration amplitude. Is added to the operational amplifier 34. Such a potential Vy gradually becomes equal to the reference voltage Vrep when the vibration amplitude of the vibrator 5 converges to the target value. That is, as the input signal Vx approaches the target voltage Vdac, the potential Vy input to the operational amplifier 34 approaches the reference voltage Vrep. When the input signal Vx finally matches the target voltage Vdac, the potential Vy is the reference voltage Vdac. It corresponds to the voltage Vrep. On the other hand, when the input signal Vx does not match the target voltage Vdac, the potential Vy input to the operational amplifier 34 is a differential signal that represents the difference between the input signal Vx and the target voltage Vdac with reference to the reference voltage Vrep. . Such a potential Vy is amplified by the operational amplifier 34 and a control signal Vcont is output. The control signal Vcont output from the operational amplifier 34 is expressed by the following equation (2).

  Here, when the input signal Vx is equal to the target voltage Vdac, since the potential Vy = Vrep as described above, the control signal Vcont becomes Vcont = Vrep. When the input signal Vx does not coincide with the target voltage Vdac, the potential Vy input to the operational amplifier 34 becomes a difference signal between the input signal Vx and the target voltage Vdac, so that the control signal Vcont uses the difference signal as the resistance Ra, Rb. It is output as a signal amplified by the amplification factor.

  Therefore, the amplitude detection circuit 13 outputs the reference voltage Vrep as the control signal Vcont when the vibration amplitude of the vibrator 5 matches the target value, and controls when the vibration amplitude of the vibrator 5 does not match the target value. A signal corresponding to the difference between the vibration amplitude of the vibrator 5 and the target value is output as the signal Vcont. For example, when the vibration amplitude of the vibrator 5 is smaller than the target value, the control signal Vcont is smaller than the reference voltage Vrep, and when the vibration amplitude of the vibrator 5 is larger than the target value, the control signal Vcont is larger than the reference voltage Vrep. Also grows.

  Next, FIG. 6 is a circuit diagram showing a configuration example of the reference voltage generation circuit 14. The reference voltage generation circuit 14 includes an operational amplifier 41 and a replica circuit 42 that is substantially equivalent to the gain adjustment units 29 a and 29 b of the gain adjustment circuit 12. The replica circuit 42 is provided with two transistors 43 and 44 having the same characteristics as those of the transistors 25, 27 and 26 and 28 provided in the gain adjusting units 29a and 29b, respectively. The replica circuit 42 has a configuration in which these two transistors 43 and 44 and a resistor R4 are connected in series. That is, the transistor 43 has a drain terminal connected to the predetermined voltage Vg, a source terminal connected to the drain terminal of the transistor 44, and a gate terminal connected to the output of the operational amplifier 41. The transistor 43 is a second transistor having the same characteristics as the first transistors 27 and 28 that change the on-resistance in order to adjust the gain G in the gain adjustment circuit 12. On the other hand, the transistor 44 has a source terminal connected to one end of the resistor R4, and a gate terminal connected to a predetermined power supply voltage Vdd. The other end of the resistor R4 is grounded. Here, the resistor R4 has a resistance value equal to that of the resistor R3 provided in the gain adjusting units 29a and 29b of the gain adjusting circuit 12. It is more preferable that the resistor R4 is made of the same material as the resistor R3 and has the same electrical characteristics as the resistor R3. On the other hand, in the operational amplifier 41, the node N1 between the two transistors 43 and 44 is connected to the inverting input terminal, and the voltage Vg / 2 that is ½ of the predetermined voltage Vg is input to the non-inverting input terminal.

  In the above configuration, the transistor 44 is always completely turned on, so that the on-resistance of the transistor 44 is almost zero. The operational amplifier 41 drives the transistor 43 so that the potential of the node N1 becomes Vg / 2 by a virtual short circuit, and thus outputs a voltage such that the on-resistance of the transistor 43 is always equal to the resistance value of the resistor R4. As a result, the transistor 43 operates so that the on-resistance is always equal to the resistance value of the resistor R4. Such an operation is the same even when the environmental temperature changes. That is, when the temperature change occurs and the on-resistance of the transistor 43 changes, the operational amplifier 41 changes the output voltage accordingly, so that the on-resistance of the transistor 43 is equal to the resistance value of the resistor R4 even after the temperature change. Control to be. The reference voltage generation circuit 14 outputs the drive voltage output from the operational amplifier 41 to the amplitude detection circuit 13 as the reference voltage Vrep. Therefore, the reference voltage Vrep output from the reference voltage generation circuit 14 is a voltage that fluctuates according to a temperature change, and is a voltage that can keep the on-resistance of the transistor 43 always equal to the resistance value of the resistor R4. Is output as For example, as described above, if the resistor R3 is 10R, the resistor R4 is also 10R. Therefore, the reference voltage Vrep is a voltage for always holding the on-resistance of the transistor 43 at 10R.

  The amplitude detection circuit 13 outputs a control signal Vcont according to the difference between the vibration amplitude of the vibrator 5 and the target value to the gain adjustment circuit 12 with reference to the reference voltage Vrep. Then, the gain adjustment circuit 12 drives the transistors 27 and 28 provided in the gain adjustment units 29a and 29b based on the control signal Vcont output from the amplitude detection circuit 13, thereby providing a gain to be applied to the signals Vsp and Vsn. adjust. These transistors 27 and 28 have the same characteristics as the transistor 43 provided in the replica circuit 42 of the reference voltage generation circuit 14, and therefore change in the same manner as the transistor 43 of the replica circuit 42 when the on-resistance changes due to a temperature change. To do.

  FIG. 7 is a diagram illustrating a characteristic curve TC of on-resistances of the transistors 27 and 28 provided in the gain adjusting units 29a and 29b of the gain adjusting circuit 12. When the vibration amplitude in the X-axis direction of the vibrator 5 matches the target value, the control signal Vcont becomes the reference voltage Vrep, so that the on-resistance Ron of the transistors 27 and 28 is equal to the resistance value of the resistor R3. At this time, for example, as described above, if the gain adjustment circuit 12 is configured as the resistor R1 = 900R, the resistor R2 = 9R, and the resistor R3 = 10R, the gain G applied to the signals Vsp and Vsn is G = 55. Holds the intermediate value of the gain adjustment range. When the vibration amplitude in the X-axis direction of the vibrator 5 is smaller than the target value, the control signal Vcont is smaller than the reference voltage Vrep, so that the on-resistance Ron of the transistors 27 and 28 is larger than the resistance value of the resistor R3. Become. Therefore, the gain G given to the signals Vsp and Vsn becomes larger than the intermediate value of the gain adjustment range, and the amplitude of the drive signals Vdp and Vdn is increased to increase the vibration amplitude of the vibrator 5 in the X-axis direction. Will be able to. Further, when the vibration amplitude in the X-axis direction of the vibrator 5 is larger than the target value, the control signal Vcont becomes larger than the reference voltage Vrep, so that the on-resistance Ron of the transistors 27 and 28 is smaller than the resistance value of the resistor R3. Become. Therefore, the gain G given to the signals Vsp and Vsn is smaller than the intermediate value of the gain adjustment range, and the amplitude of the drive signals Vdp and Vdn is reduced to reduce the vibration amplitude of the vibrator 5 in the X-axis direction. Will be able to.

  When the temperature environment of the angular velocity sensor 1 changes, the characteristic curve TC shown in FIG. 7 shifts in the left-right direction according to the change. At this time, the reference voltage generation circuit 14 varies the reference voltage Vrep according to the shift amount of the characteristic curve TC. Therefore, even when the temperature changes, when the vibration amplitude in the X-axis direction of the vibrator 5 matches the target value, the control signal Vcont applied to the gate terminals of the transistors 27 and 28 is at the temperature. Since it fluctuates in accordance with the change, the on-resistance Ron of the transistors 27 and 28 can always be kept equal to the resistance value of the resistor R3. The same applies to a case where a temperature change occurs in a state where the vibration amplitude in the X-axis direction of the vibrator 5 does not coincide with the target value, and the control signal Vcont fluctuates according to the temperature change. Since the on-resistance Ron can be prevented from changing, the gain G applied in the gain adjustment circuit 12 can be stabilized.

  FIG. 8 is a signal waveform diagram for explaining the operation in the vibrator driving circuit 3. When the vibration of the vibrator 5 is started at the timing T1, the gain adjustment circuit 12 applies the drive signals Vdp and Vdn to the vibrator 5 based on the initial drive signals Vd1 and Vd2 generated by the initial drive signal generation circuit 15. As a result, the vibrator 5 gradually starts to vibrate in the X-axis direction, and the CV conversion circuit 10 outputs signals Vip and Vin corresponding to the vibration displacement. When the vibration amplitude of the vibrator 5 becomes equal to or greater than a predetermined value at timing T2, the initial drive signal generation circuit 15 stops outputting the initial drive signals Vd1 and Vd2, and the phase conversion circuit 11, the amplitude detection circuit 13, and the reference voltage generation circuit. 14 is switched to the amplitude control operation. At this time, since the vibration amplitude of the vibrator 5 is remarkably smaller than the target value, the control signal Vcont output from the amplitude detection circuit 13 becomes almost the minimum value, and the transistors 27 and 28 remain off. Therefore, the gain adjustment circuit 12 generates and outputs drive signals Vdp and Vdn in which the maximum gain value Gmax is given to the signals Vsp and Vsn input from the phase conversion circuit 11. At timing T3, as the vibration amplitude of the vibrator 5 increases, the control signal Vcont output from the amplitude detection circuit 13 starts to rise and gradually approaches the reference voltage Vrep. At time T4, the control signal Vcont matches the reference voltage Vrep. At this time, since the vibration amplitude of the vibrator 5 has already become larger than the target value, the amplitude detection circuit 13 sets the control signal Vcont to be higher than the reference voltage Vrep in order to lower the gain G applied in the gain adjustment circuit 12. Raise further. As a result, the vibration amplitude of the vibrator 5 gradually decreases and approaches the target value. Then, at timing T5, the vibration amplitude of the vibrator 5 matches the target value, and the control signal Vcont is stabilized in a state where it matches the reference voltage Vrep. At this time, the gain G given by the gain adjustment circuit 12 is held at, for example, an intermediate value in the gain adjustment range.

  Thereafter, for example, even if a temperature change occurs and the reference voltage Vrep changes as indicated by a broken line L1 in the figure, the control signal Vcont output from the amplitude detection circuit 13 changes following the reference voltage Vrep. Therefore, the gain G applied in the gain adjustment circuit 12 can be held in a constant state, and the vibration amplitude of the vibrator 5 can be stabilized in a constant state. Thereby, it is possible to satisfactorily prevent the measurement sensitivity in the angular velocity sensor 1 from fluctuating due to a temperature change.

  As described above, the vibrator drive circuit 3 of the present embodiment has the gain adjustment circuit 12 for adjusting the gain G applied to the drive signals Vdp and Vdn, and the amplitude for detecting the vibration amplitude of the vibrator 5 in the X-axis direction. A detection circuit 13 and a reference voltage generation circuit 14 that generates a reference voltage Vrep are provided. The amplitude detection circuit 13 detects the vibration amplitude of the vibrator 5 in the X-axis direction and compares it with a predetermined target value (Vdac), and according to the difference between the vibration amplitude of the vibrator 5 in the X-axis direction and the target value. A control signal Vcont based on the reference voltage Vrep is output. The gain adjustment circuit 12 includes first transistors 27 and 28 that change the on-resistance based on the control signal Vcont, and a gain G that is applied to the drive signals Vdp and Vdn according to the on-resistance of the transistors 27 and 28. Adjust. The reference voltage generation circuit 14 includes a second transistor 43 having the same characteristics as the first transistors 27 and 28, and drives the second transistor 43 so that the ON resistance of the second transistor 43 becomes a predetermined value. In addition, the driving voltage of the second transistor 43 is output to the amplitude detection circuit 13 as the reference voltage Vrep. According to such a vibrator driving circuit 3, even when the on-resistances of the first transistors 27 and 28 for adjusting the gain G change according to the temperature, the reference serving as the reference for the control signal Vcont. Since the voltage Vrep fluctuates so as to suppress a change in on-resistance due to the temperature change, there is an advantage that the vibration amplitude of the vibrator 5 can be stabilized without being affected by the temperature change.

  Further, the reference voltage generation circuit 14 in the present embodiment is equivalent to the on-resistance of the first transistors 27 and 28 when the on-resistance of the second transistor 43 is an intermediate value within the gain adjustment range in the gain adjustment circuit 12. The second transistor 43 is driven such that the drive voltage is output to the amplitude detection circuit 13 as the reference voltage Vrep. Therefore, the gain adjustment circuit 12 is configured to be able to perform gain adjustment using the center of the gain adjustment range as a stable point.

  Further, as described above, the amplitude detection circuit 13 in the present embodiment accumulates charges according to the vibration amplitude of the vibrator 5 in the X-axis direction, and sequentially transfers the accumulated charges, whereby the charge transfer process. Thus, the vibration amplitude of the vibrator 5 and the target value are compared, a difference signal corresponding to the difference is generated, and the difference signal is further amplified and output. On the other hand, it is also conceivable to employ a configuration in which the charge corresponding to the vibration amplitude in the X-axis direction of the vibrator 5 is accumulated and then the vibration amplitude is compared with a target value using an integration amplifier. However, since the integration method using an integration amplifier involves an integration operation, the response speed of the output voltage when the vibration amplitude in the X-axis direction becomes higher or lower than the target value is slow. When the shown control signal Vcont overshoots exceeding the reference voltage Vrep, the increase width becomes large, and there is a problem that it takes time until the vibration amplitude of the vibrator 5 in the X-axis direction is stabilized. On the other hand, in the process of sequentially transferring charges corresponding to the vibration amplitude of the vibrator 5 in the X-axis direction as in the amplitude detection circuit 13 of the present embodiment, the vibration amplitude of the vibrator 5 in the X-axis direction and the target In the case of a configuration in which a difference signal corresponding to the difference is amplified and output, the response speed of the output voltage accompanying a change in vibration amplitude can be increased, so the control shown in FIG. It is possible to make the rising width when the signal Vcont overshoots over the reference voltage Vrep smaller than the integration method, and to stabilize the vibration amplitude of the vibrator 5 in the X-axis direction to the target value in a short time. There is an advantage that you can.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to what was mentioned above, A various modification is applicable.

  For example, in the above embodiment, the case where the gain adjustment circuit 12 is configured using the fully differential operational amplifier 20 has been described, but the present invention is not limited to this. However, since the circuit configuration is simplified if the fully differential operational amplifier 20 is used, for example, when mounted on a relatively small information processing terminal such as a smartphone or a tablet terminal, the fully differential operational amplifier 20 is used as described above. 20 is preferably used to configure the gain adjustment circuit 12.

  DESCRIPTION OF SYMBOLS 1 ... Angular velocity sensor, 3 ... Vibrator drive circuit, 5 ... Vibrator, 10 ... CV conversion circuit (vibration displacement detection circuit), 11 ... Phase conversion circuit, 12 ... Gain adjustment circuit, 13 ... Amplitude detection circuit, 14 ... Reference | standard Voltage generating circuit 27, 28 ... first transistor, 31 ... sampling unit, 32 ... charge transfer unit, 33 ... amplifying unit, 43 ... second transistor, Vdp, Vdn ... drive signal, Vrep ... reference voltage, Vcont ... Control signal

Claims (5)

A vibrator drive circuit that outputs a drive signal for vibrating the vibrator in a predetermined drive axis direction,
An amplitude detection circuit that detects a vibration amplitude of the vibrator, compares the vibration amplitude with a predetermined target value, and outputs a control signal based on a predetermined reference voltage according to a difference between the vibration amplitude and the target value;
A gain adjustment circuit that includes a first transistor that changes an on-resistance based on the control signal, and that adjusts a gain to be applied to the drive signal in accordance with the on-resistance of the first transistor;
A second transistor having the same characteristics as the first transistor, driving the second transistor so that an on-resistance of the second transistor becomes a predetermined value, and setting a driving voltage of the second transistor to A reference voltage generation circuit that outputs the reference voltage to the amplitude detection circuit;
A vibrator driving circuit comprising: The gain adjustment circuit adjusts the gain within a predetermined gain adjustment range;
The reference voltage generation circuit is configured to make the on-resistance of the first transistor equal to the on-resistance of the second transistor when the gain is an intermediate value within the gain adjustment range. The vibrator driving circuit according to claim 1, wherein a driving voltage of the second transistor is used as the reference voltage by driving a transistor. The amplitude detection circuit includes:
A sampling unit for accumulating charges according to the vibration amplitude of the vibrator;
A charge transfer unit that generates a difference signal based on a predetermined reference voltage according to a difference between the vibration amplitude and the target value by transferring the charge accumulated in the sampling unit;
An amplifying unit for amplifying and outputting the differential signal generated in the charge transfer unit;
The vibrator drive circuit according to claim 1, further comprising: A vibration displacement detection circuit for detecting a vibration displacement of the vibrator and outputting a vibration waveform;
A phase conversion circuit for shifting the phase of the vibration waveform output from the vibration displacement detection circuit by 90 degrees;
Further comprising
The gain adjustment circuit generates the drive signal by applying a gain corresponding to an on-resistance of the first transistor to the vibration waveform output from the phase conversion circuit. 4. The vibrator driving circuit according to any one of 3 above.   The vibrator drive circuit according to claim 4, wherein the amplitude detection circuit detects a vibration amplitude of the vibrator based on a vibration waveform output from the vibration displacement detection circuit.

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