JP2012220310A - Drive circuit, integrated circuit device and sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit which is capable of reducing start-up time fluctuation caused by fluctuation of a power supply voltage or variation of a resistance value, an integrated circuit device and a sensor device.SOLUTION: A determination circuit 260 determines a magnitude relationship between a voltage of a determination target signal LPFO, which is obtained on the basis of a signal resulting from converting a drive current outputted from a sensor element 4 into a voltage by an I/V conversion circuit 200, and a determination voltage. A drive signal generation circuit 230, on the basis of the determination result of the determination circuit 260, generates a drive signal on the basis of an oscillation signal of an oscillator 280 which supports self-oscillation of the sensor element, until the voltage of the determination target signal LPFO exceeds a determination voltage VR2, and generates the drive signal on the basis of the signal converted into the voltage by the I/V conversion circuit 200 after the voltage of the determination target signal LPFO exceeds the determination voltage VR2. The determination voltage VR2 is a voltage obtained by adding or subtracting a voltage which is obtained by allowing a constant current to flow to one or more resistors, and a reference voltage.

Description

  The present invention relates to a drive circuit, an integrated circuit device, and a sensor device.

  Today, gyro sensors are installed in various electronic devices such as digital cameras, navigation devices, and mobile phones. In recent years, downsizing of gyro sensors and high detection accuracy have been demanded, and as a gyro sensor that satisfies these requirements, for example, a vibration gyro sensor using a resonance phenomenon of a crystal resonator is widely used.

JP 2007-292680 A

  By the way, in a system using a vibration gyro sensor, in order to reduce power consumption, the vibration gyro sensor is often operated only when angular velocity data is necessary, and otherwise the vibration gyro sensor is powered down. Even if the power-down is released and the vibration gyro sensor is activated, proper detection cannot be performed until the crystal oscillator starts oscillating and oscillates stably. The idea is to make the time as short as possible. Whether or not the crystal oscillator has reached stable oscillation is determined by converting the current (crystal current) output from the crystal oscillator into a voltage by an I / V converter and determining whether or not the amplitude exceeds a threshold value. Is done. This determination processing is performed using a Schmitt circuit (hysteresis comparator) as shown in FIG. In this Schmitt circuit, a determination voltage VR1 at which the output voltage is changed from a high level (VDD) to a low level (VSS) and a determination voltage VR2 at which the output voltage is changed from a low level (VSS) to a high level (VDD) are respectively Calculated in 1) and (2).

  Since the formula (1) includes the power supply voltage VDD, the determination voltage VR1 varies due to the fluctuation of the power supply voltage. Therefore, the time (start-up time) for determining that the crystal resonator has reached stable oscillation in the Schmitt circuit varies according to the variation of the power supply voltage. As a result, the time (start-up time) for determining that the crystal resonator has reached stable oscillation in the Schmitt circuit varies.

  Further, from the equations (1) and (2), even if the resistance values R1 and R2 deviate from the design values due to manufacturing variations, if the two resistors are made of the same material, the resistance values R1 and R2 are in the same direction. Therefore, the determination voltages VR1 and VR2 do not change. On the other hand, since the resistance value of the resistor included in the I / V converter also deviates from the design value due to manufacturing variations, the voltage of the input signal IN of the Schmitt circuit deviates from the design value. That is, the determination voltages VR1 and VR2 do not vary according to the manufacturing variation of the resistance, but the input signal IN varies. Therefore, it is determined that the crystal resonator has reached stable oscillation in the Schmitt circuit (startup time). Will vary.

  As described above, in the conventional configuration, the start-up time fluctuates due to fluctuations in the power supply voltage and resistance values, so the Max value of the start-up time increases, and the time for starting processing using angular velocity data is slow. The problem of becoming.

  The present invention has been made in view of the above problems, and according to some aspects of the present invention, it is possible to reduce fluctuations in start-up time due to fluctuations in power supply voltage and fluctuations in resistance value. It is possible to provide a drive circuit, an integrated circuit device, and a sensor device that can be used.

  (1) The present invention is a drive circuit that generates a drive signal for driving a sensor element that detects a given physical quantity, the current-voltage converter that converts the drive current output from the sensor element into a voltage, A determination unit for determining a magnitude relationship between a voltage of a determination target signal obtained based on a signal converted into a voltage by a current-voltage conversion unit and a determination voltage; and an oscillation signal for assisting self-excited oscillation of the sensor element Based on the determination result of the oscillator and the determination unit, the drive signal is generated based on the oscillation signal until the voltage of the determination target signal exceeds the determination voltage, and the voltage of the determination target signal is the determination voltage. A drive signal generation unit that generates the drive signal based on a signal converted into a voltage by the current-voltage conversion unit, and the determination voltage is a constant current in one or a plurality of resistors. A voltage with a reference voltage and the addition or subtraction to the voltage obtained obtained by flowing.

  According to the present invention, based on the determination result of the determination unit, the sensor element starts to oscillate by generating the drive signal based on the oscillation signal of the oscillator until the drive current of the sensor element exceeds a desired current value. Then, the time (start-up time) until stable oscillation can be shortened. Further, after the oscillation of the sensor element is stabilized, the stable oscillation of the sensor element can be continued by generating a drive signal based on a signal obtained by converting the drive current of the sensor element into a voltage. Then, the voltage obtained by adding or subtracting the voltage obtained by passing a constant current through one or a plurality of resistors and the reference voltage is used as the determination voltage of the determination unit, thereby changing the resistance value of the current-voltage conversion unit. Can be canceled out, so that fluctuations in the start-up time due to variations in resistance value can be reduced.

  Further, according to the present invention, since the determination voltage of the determination unit does not depend on the power supply voltage, it is possible to reduce the variation in the start-up time due to the variation in the power supply voltage.

  (2) In this drive circuit, the drive current determination unit uses the first voltage as the determination voltage until the voltage of the determination target signal exceeds the first voltage, and the voltage of the determination target signal is the first voltage. After the voltage of 1 is exceeded, the second voltage may be used as the determination voltage.

  As described above, when the determination unit determines with hysteresis, it is possible to prevent an erroneous determination due to the influence of noise superimposed on the determination target signal.

  (3) In this drive circuit, the drive current determination unit may include a switch unit that selects one of the first voltage and the second voltage as the determination voltage according to the determination result. Good.

  (4) The present invention is an integrated circuit device including any one of the drive circuits described above.

  (5) The present invention is a sensor device including the integrated circuit device described above and a sensor element that detects a given physical quantity.

The functional block diagram of the angular velocity detection apparatus which is an example of the sensor apparatus of this embodiment. The figure which shows the structural example of the drive circuit of this embodiment. The figure which shows the structural example of an I / V conversion circuit. FIG. 3 is a diagram illustrating a configuration example of a part of a reference circuit and a determination circuit according to the present embodiment. The figure which shows an example of the waveform of the input signal of the determination circuit of this embodiment, and an output signal. The figure which shows the structure of the drive circuit of simulation object. The figure which shows an example of the waveform of a simulation result. The figure which shows an example of the drive current value calculated from the simulation result in each simulation condition. The figure which shows the structure of the drive circuit of a comparative example. The figure which shows an example of the drive current value calculated from the simulation result of a comparative example. FIG. 9 is a diagram illustrating a configuration example of a part of a reference circuit and a determination circuit according to Modification 1; The figure which shows an example of the waveform of the input signal of the determination circuit of the modification 1, and an output signal. FIG. 10 is a diagram illustrating a configuration example of a part of a reference circuit and a determination circuit according to Modification 2; The figure which shows an example of the waveform of the input signal of the determination circuit of the modification 2, and an output signal. The figure which shows the structural example of the conventional determination circuit.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. Also, not all of the configurations described below are essential constituent requirements of the present invention.

1. Configuration of Sensor Device FIG. 1 is a functional block diagram of an angular velocity detection device that is an example of the sensor device of the present embodiment. An angular velocity detection device 1 according to the present embodiment includes a sensor element 4 and an angular velocity detection IC (integrated circuit device) 2.

In the sensor element 4 of the present embodiment, two drive electrodes and two detection electrodes are formed on a so-called double T-type crystal vibrating piece having two T-type drive vibration arms and one detection vibration arm therebetween. These are sealed in a package (not shown). However, the vibration piece of the sensor element 4 may not be a double T type, and may be, for example, a tuning fork type or a comb tooth type, or a sound piece type having a shape such as a triangular prism, a quadrangular prism, or a cylindrical shape. Also good. Moreover, as a material of the resonator element of the sensor element 4, for example, a piezoelectric single crystal such as lithium tantalate (LiTaO ₃ ) or lithium niobate (LiNbO ₃ ) or lead zirconate titanate instead of quartz (SiO ₂ ). A piezoelectric material such as a piezoelectric ceramic such as (PZT) may be used, or a silicon semiconductor may be used. Further, for example, a structure in which a piezoelectric thin film such as zinc oxide (ZnO) or aluminum nitride (AlN) sandwiched between drive electrodes is arranged on a part of the surface of a silicon semiconductor may be used.

  When an AC voltage signal is given as a drive signal, the two drive vibration arms of the sensor element 4 are subjected to bending vibration (excitation vibration) in which the tips of each other repeat approach and separation due to the inverse piezoelectric effect. If the amplitudes of the bending vibrations of the two driving vibrating arms are equal, the two driving vibrating arms always bend and vibrate in a line-symmetric relationship with respect to the detection vibrating arm, so that the detecting vibrating arm does not vibrate.

  In this state, when an angular velocity having an axis perpendicular to the excitation vibration surface of the sensor element 4 as a rotation axis is applied, the two drive vibration arms are subjected to Coriolis force in a direction perpendicular to both the bending vibration direction and the rotation axis. Get. As a result, the symmetry of the bending vibration of the two drive vibrating arms is lost, and the detection vibrating arm performs bending vibration so as to maintain a balance. The phase of the bending vibration of the detection vibrating arm and the bending vibration (excitation vibration) of the driving vibrating arm due to the Coriolis force is shifted by 90 °.

  However, actually, even if no Coriolis force is applied, the amplitudes of the bending vibrations of the two drive vibrating arms are slightly different, so that the detection vibrating arms slightly bend and vibrate so as to maintain a balance. This bending vibration is called leakage vibration and is in phase with the drive signal. Then, AC charges having opposite phases (phases differ by 180 °) based on these bending vibrations are generated in the two detection electrodes by the piezoelectric effect. The AC charge generated based on the Coriolis force changes according to the magnitude of the Coriolis force (in other words, the angular velocity applied to the sensor element 4), whereas the AC charge generated based on the leakage vibration is It is constant irrespective of the magnitude of the angular velocity applied to the sensor element 4.

  The two drive electrodes of the sensor element 4 are connected to the DS terminal and DG terminal of the angular velocity detection IC 2, respectively. The two detection electrodes of the sensor element 4 are connected to the S1 terminal and the S2 terminal of the angular velocity detection IC 2, respectively.

  The angular velocity detection IC 2 of this embodiment includes a power supply circuit 10, a drive circuit 20, a detection circuit 30, a reference circuit 40, a nonvolatile memory 50, and a serial interface circuit 60. Note that the angular velocity detection IC 2 of the present embodiment may have a configuration in which some of these configurations (elements) are omitted or a new configuration (element) is added.

  The power supply circuit 10 is supplied with a power supply voltage (for example, 3 V) and a ground voltage (0 V) from the VDD terminal and the VSS terminal, respectively, and generates a power supply voltage inside the angular velocity detecting IC 2.

  The reference circuit 40 generates a reference voltage VREF (analog ground voltage or other constant voltage) or a constant current from the power supply voltage VDD generated by the power supply circuit 10 and supplies it to the drive circuit 20 or the detection circuit 30.

  The drive circuit 20 generates a drive signal for exciting and vibrating the sensor element 4 and supplies the drive signal to one drive electrode (first drive electrode) of the sensor element 4 via the DS terminal. The drive circuit 20 receives a drive current (crystal current) generated in the other drive electrode (second drive electrode) by the excitation vibration of the sensor element 4 via the DG terminal, and the amplitude of this drive current is constant. The amplitude level of the drive signal is feedback-controlled so that Further, the drive circuit 20 generates a reference signal for the synchronous detection circuit included in the detection circuit 30 and a clock signal for the switched capacitor filter (SCF).

  The detection circuit 30 receives AC charges (detection currents) generated in the two detection electrodes of the sensor element 4 via the S1 terminal and the S2 terminal, respectively, and these AC charges (detection currents) are detected by synchronous detection. Only the angular velocity component included in the signal is detected, a signal having a voltage level (angular velocity signal) corresponding to the magnitude of the angular velocity is generated, and output to the outside via the VO terminal. This angular velocity signal is A / D converted by a microcomputer (not shown) connected to the VO terminal, for example, and used for various processing as angular velocity data. Note that the angular velocity detection IC 2 of this embodiment may include an A / D converter and output digital data representing the angular velocity to the outside via the serial interface circuit 60, for example.

  The nonvolatile memory 50 holds various adjustment data for the drive circuit 20 and the detection circuit 30, and can be configured as, for example, an EEPROM (Electrically Erasable Programmable Read-Only Memory).

  The serial interface circuit 60 performs processing of writing and reading adjustment data to and from the nonvolatile memory 50 by two-line logic using a clock signal and a serial data signal, respectively, via the CLK terminal and the DATA terminal. When writing data to the nonvolatile memory 50, a high power supply voltage (for example, 15 V or more) is supplied via the VPP terminal in order to supply energy sufficient to invert the data held in the memory element. .

2. Configuration of Drive Circuit FIG. 2 is a diagram illustrating a configuration example of the drive circuit 20 of the present embodiment. As shown in FIG. 2, the drive circuit 20 in this embodiment includes an I / V conversion circuit 200, a high-pass filter 210, a comparator 220, a drive signal generation circuit 230, a full-wave rectification circuit 240, a low-pass filter 250, and a determination circuit 260. , A counter circuit 270, an oscillator 280, a comparator 290, and switches 292, 294, and 296. Note that the drive circuit 20 of this embodiment may have a configuration in which some of these configurations (elements) are omitted or a new configuration (element) is added.

The I / V conversion circuit 200 (an example of a current / voltage conversion unit) converts the drive current Idr of the sensor element 4 input via the DG terminal into an AC voltage signal. As shown in FIG. 3, in the I / V conversion circuit 200 of this embodiment, a resistor 204 and a capacitor 206 are connected between an inverting input terminal (−input terminal) and an output terminal of an operational amplifier 202, and the non-inverting of the operational amplifier 202 is performed. A reference voltage VREF (analog ground voltage) is supplied to the input terminal (+ input terminal). The voltage V _iv of the output signal IVO of the I / V conversion circuit 200 is expressed by the following equation (3), where R _iv is the resistance value of the resistor 204.

  The output signal of the I / V conversion circuit 200 is full-wave rectified by a full-wave rectifier circuit 240. The output signal of the I / V conversion circuit 200 is input to the comparator 220 after the offset is canceled by the high-pass filter 210 and the phase is adjusted.

  The comparator 220 amplifies the output signal of the high pass filter 210 and outputs a binarized signal (square wave voltage signal). However, in this embodiment, the comparator 220 is an open drain output comparator that can output only a low level.

  The drive signal generation circuit 230 (an example of a drive signal generation unit) generates a drive signal for driving the sensor element 4 to oscillate based on the output signal of the comparator 220 and the output signal of the full-wave rectification circuit 240. Specifically, for example, the drive signal generation circuit 230 includes an integrator (not shown) that integrates a difference between a desired voltage value VR3 and the output voltage of the full-wave rectifier circuit 240, and outputs the output voltage of the integrator. While outputting as a high level via a pull-up resistor (not shown), the output signal of the comparator 220 is output as a low level. Thereby, the amplitude of the drive signal generated by the drive signal generation circuit 230 varies according to the output voltage of the full-wave rectification circuit 240. That is, when the output voltage of full-wave rectifier circuit 240 is higher than desired voltage value VR3, the amplitude of the drive signal decreases, and when the output voltage is lower than VR3, the amplitude of the drive signal increases.

  This drive signal is supplied to the first drive electrode of the sensor element 4 via the switch 294 and the DS terminal, and a drive current Idr corresponding to the amplitude of the drive signal is generated at the second drive electrode of the sensor element 4. . By this loop, feedback control is applied so that the output voltage of the full-wave rectifier circuit 240 matches the desired voltage value VR3, and therefore the amplitude of the drive signal is constant (the current value of the drive current Idr is constant). By making the amplitude of the drive signal constant, the sensor element 4 can oscillate extremely stably, and the detection accuracy of the angular velocity can be improved.

  The comparator 290 amplifies the output signal of the high pass filter 210 and outputs a binarized signal (square wave voltage signal). This binarized signal is used as a reference signal SDET for synchronous detection in the detection circuit 30. Since the output signal of the comparator 220 fluctuates at a high level, if the high level does not exceed the logic threshold value in the synchronous detection of the detection circuit 30, a malfunction occurs, so that it is not used as a reference signal. A lator 290 is provided separately.

  The output signal of the full-wave rectifier circuit 240 is low-pass processed by the low-pass filter 250, and the voltage of the output signal LPFO of the low-pass filter 250 is compared with a predetermined voltage value in the determination circuit 260. The determination circuit 260 (an example of a determination unit) determines whether the voltage of the output signal LPFO of the low-pass filter 250 is higher or lower than a predetermined determination voltage. For example, if the voltage is lower than the determination voltage, the determination circuit 260 is high. A selection signal SW is generated.

  The oscillator 280 is an oscillator that generates an oscillation signal OSC that assists self-excited oscillation of the sensor element 4, and the oscillation frequency thereof matches the resonance frequency of the sensor element 4. The oscillator 280 can be realized by, for example, a ring oscillator or an RC oscillation circuit.

  The switch 292 is turned on (closed) when the selection signal SW is at a high level, inputs the output signal (oscillation signal OSC) of the oscillator 280 to the comparator 220, and is turned off (opened) when the selection signal SW is at a low level. .

  The switch 294 is turned on (closed) when the selection signal SW is at a low level, connects the output of the drive signal generation circuit 230 and the DS terminal, and turned off (opens) when the selection signal SW is at a high level. On the other hand, the switch 296 is turned on (closed) when the selection signal SW is at a high level, connects the output of the comparator 290 and the DS terminal, and turned off (opens) when the selection signal SW is at a low level.

  As a result, the output signal of the comparator 290 (the binary signal of the oscillation signal OSC) is selected until the drive current Idr reaches a desired current value after the sensor element 4 starts excitation, and the drive current Idr is desired. The output signal of the drive signal generation circuit 230 (binarized signal of the output signal OSC of the oscillator 280) is selected and supplied to the second drive electrode of the sensor element 4 via the DS terminal. The In this way, while the drive current Idr is small, the sensor element 4 is driven using the oscillation signal OSC having a large amplitude (large energy) as the drive signal. Time (start-up time) can be shortened. In addition, after the drive current Idr reaches a desired current value, stable oscillation of the sensor element 4 can be continued by supplying a drive signal having a constant amplitude generated by the drive signal generation circuit.

  The counter circuit 270 starts counting when the selection signal SW changes from the high level to the low level as a trigger, and counts a sufficient time for the sensor element 4 to start stable oscillation. An SWB signal that changes to is generated, and the oscillation of the oscillator 280 is stopped by this SWB signal. Thereby, the current consumed by the oscillator 280 can be reduced.

Incidentally, the resistance value R _iv of the resistor 204 included in the I / V conversion circuit 200 has a variation of about ± 20% with respect to the design value for each IC due to manufacturing variations. The conversion rate varies from IC to IC. As a result, even when the drive current Idr is constant, the output voltage of the I / V conversion circuit 200, and hence the voltage of the output signal LPFO of the low-pass filter 250, varies from IC to IC. For this reason, unless this variation is canceled, the determination timing in the determination circuit 260 (timing when SW changes from high level to low level) also varies, and the activation time varies from IC to IC.

  Therefore, in the present embodiment, the reference circuit 40 generates a determination voltage that varies in accordance with the variation in the resistance value of the resistor 204, and the determination circuit 260 compares the voltage of the output signal LPFO of the low-pass filter 250 with this determination voltage. This suppresses fluctuations in the startup time.

  FIG. 4 is a diagram illustrating a configuration of a part of the reference circuit 40 and the determination circuit 260 according to the present embodiment. FIG. 5 is a waveform diagram of an input signal and an output signal of the determination circuit 260.

  As shown in FIG. 4, the determination circuit 260 of this embodiment includes an operational amplifier 262 and two switches 264 and 266 (an example of a switch unit).

  The output signal LPFO of the low-pass filter 250 is input to the inverting input terminal (−input terminal) of the operational amplifier 262.

  The switch 264 is turned on (closed) when the output signal (selection signal SW) of the operational amplifier 262 is at a high level, and inputs the determination voltage VR2 to the non-inverting input terminal (+ input terminal) of the operational amplifier 262. It turns off (opens) when the signal (selection signal SW) is at a low level.

  On the other hand, the switch 266 is turned on (closed) when the output signal (selection signal SW) SW of the operational amplifier 262 is at a low level, and inputs the determination voltage VR1 to the non-inverting input terminal (+ input terminal) of the operational amplifier 262. It is turned off (opened) when the output signal (selection signal SW) 262 is at a high level.

  That is, the determination circuit 260 of this embodiment uses VR2 as the determination voltage until the voltage of the output signal LPFO (an example of a determination target signal) of the low-pass filter 250 exceeds VR2 (an example of the first voltage), and the low-pass filter 250 After the voltage of the output signal LPFO exceeds VR2, the Schmitt circuit generates the selection signal SW using VR1 (an example of the second voltage) as a determination voltage. As described above, the determination circuit 260 makes a determination with hysteresis, thereby preventing an erroneous determination due to the influence of noise superimposed on the output signal LPFO of the low-pass filter 250.

  In this embodiment, in particular, in the reference circuit 40, a constant current source 400, a resistor 410, and a resistor 420 are connected in series in this order between the power supply voltage VDD and the reference voltage VREF, and a constant current is applied to the resistors 410 and 420. By flowing, two determination voltages VR1 and VR2 are generated. However, the determination circuit 260 may include the constant current source 400, the resistor 410, and the resistor 420, and the determination voltages VR1 and VR2 may be generated inside the determination circuit 260.

Incidentally, the voltage V _lpf of the output signal LPFO of the low-pass filter 250 is expressed by the following equation (4).

Further, when the current value of the constant current from the constant current source 400 is I _ref , the resistance value of the resistor 410 is R1, and the resistance value of the resistor 420 is R2, VR1 and VR2 are expressed by the following equations (5) and (6), respectively. Is done.

When V _lpf = VR2, the selection signal SW changes from the high level to the low level, and the drive current Idr at that time is calculated by the following equation (7) from the equations (4) and (6).

On the other hand, when V _lpf = VR1, the selection signal SW changes from the low level to the high level, and the drive current Idr at that time is calculated by the following equation (8) from the equations (4) and (5).

  According to the equations (7) and (8), when the resistor 410 and the resistor 420 are made of the same material as the resistor 204 of the I / V conversion circuit 200, the resistance when the resistance value of the resistor 204 is increased is increased. Each resistance value of 410 and resistor 420 also increases, and when the resistance value of resistor 204 swings in the direction of decreasing, each resistance value of resistor 410 and resistor 420 also decreases, so that variations in resistance values can be offset. . Thereby, it is possible to suppress variations in the drive current Idr when the selection signal SW changes from high level to low level or from low level to high level.

  Further, since the power supply voltage VDD is not included in the expressions (7) and (8), the drive current Idr does not change even if the power supply voltage is changed.

3. Next, a simulation result of the drive circuit 20 performed by changing simulation conditions such as a resistance value, a power supply voltage value, and a temperature will be described. FIG. 6 is a diagram illustrating a configuration of a drive circuit to be simulated, and FIG. 7 is a waveform diagram illustrating a simulation result performed under one predetermined simulation condition. The upper part of FIG. 7 shows the waveform of the selection signal SW when the amplitude of the drive current Idr as an input signal is varied, and the lower part shows the waveforms of the output signal LPFO of the low-pass filter 250 and the two determination voltages VR1 and VR2. Show. As shown in FIG. 7, when the voltage of the output signal LPFO of the low-pass filter 250 exceeds VR2, the selection signal SW changes from high level to low level, and then when the voltage of the output signal LPFO of the low-pass filter 250 falls below VR1. The selection signal SW changes from the low level to the high level.

  FIG. 8A is a diagram obtained by calculating and displaying the drive current Idr when the selection signal SW changes from the high level to the low level from the simulation result under each simulation condition, and FIG. FIG. 10 is a diagram obtained by calculating and displaying a drive current Idr when a selection signal SW changes from a low level to a high level.

  8A and 8B, G1 indicates the value of the drive current Idr under the typical condition (power supply voltage 3.0 V, temperature 25 ° C.). G2 and G3 indicate the values of the drive current Idr when the power supply voltage is changed to 2.7 V and 3.6 V, respectively, for the typical conditions. G4 and G5 respectively show the values of the drive current Idr when the temperature is changed to −40 ° C. and 85 ° C. with respect to the typical conditions. G6 and G7 indicate the values of the drive current Idr when the resistance values are changed to 75% and 125%, respectively, for the typical conditions. G8 and G9 indicate the values of the drive current Idr when the constant current value Iref is changed to 95% and 105%, respectively, for the typical condition. G10 and G11 indicate the values of the drive current Idr when the reference voltage VREF is changed to 99% and 101% with respect to the typical condition, respectively.

  For comparison, when the selection signal SW changes from a high level to a low level from each simulation result obtained by performing a similar simulation on the drive circuit shown in FIG. 9 in which the determination circuit 260 is configured by a conventional Schmitt circuit. FIG. 10A shows the drive current Idr obtained by calculation, and FIG. 10B shows the drive current Idr obtained by calculation when the selection signal SW changes from the low level to the high level.

  In FIG. 10A, the drive current values vary considerably between G1 and G7, whereas in FIG. 8A, the drive current values are almost constant between G1 and G7. That is, in the drive circuit configured by the conventional Schmitt circuit, the drive current Idr when the selection signal SW changes from the high level to the low level changes according to the fluctuation of the power supply voltage, temperature, or the resistance value. On the other hand, in the drive circuit according to the present embodiment, the drive current Idr when the selection signal SW changes from the high level to the low level is substantially constant even if the power supply voltage, temperature, or resistance value varies. In other words, the start-up time fluctuates in the drive circuit configured with the conventional Schmitt circuit with respect to fluctuations in the power supply voltage, temperature, or resistance value, but the start-up time is kept almost constant in the drive circuit of this embodiment. Can do.

  Further, when comparing G1 to G7 in FIG. 8A and G1 to G7 in FIG. 10B, the fluctuation in the drive current value is smaller in FIG. 8A. That is, it can be said that the drive circuit of this embodiment has a smaller fluctuation of the drive current Idr when the selection signal SW changes from the low level to the high level with respect to fluctuations in the power supply voltage, temperature, or resistance value. .

  As described above, according to the present embodiment, the determination circuit 260 determines whether the sensor element 4 is stably oscillating based on the drive current of the sensor element 4, and the sensor element 4 is stably oscillated. Up to this point, the drive time based on the oscillation signal OSC of the oscillator 280 can be supplied to the sensor element 4 to shorten the startup time. After the oscillation of the sensor element 4 is stabilized, the stable oscillation of the sensor element 4 can be continued by supplying the sensor element 4 with a drive signal whose amplitude is adjusted according to the drive current of the sensor element 4. .

  Then, by using the determination voltages VR1 and VR2 obtained by flowing the constant current Iref through the resistors 410 and 420, the variation in the resistance value of the resistor 204 of the I / V conversion circuit 200 is canceled in the determination processing of the determination circuit 260. Therefore, it is possible to reduce the variation in the start-up time due to the variation in resistance value.

  In addition, according to the present embodiment, the determination voltages VR1 and VR2 do not depend on the power supply voltage, so that it is possible to reduce the start-up time fluctuation due to the power supply voltage fluctuation.

  In this embodiment, the angular velocity detection device has been described as an example. However, the present invention can also be applied to a sensor device that detects angular velocity, angular acceleration, acceleration, force, and the like.

4). The present invention is not limited to this embodiment, and various modifications can be made within the scope of the present invention. For example, the following modifications can be considered.

[Modification 1]
FIG. 11 is a diagram illustrating a configuration of a part of the reference circuit 40 and the determination circuit 260 according to the first modification. FIG. 12 is a waveform diagram of an input signal and an output signal of the determination circuit 260 according to the first modification.

  The determination circuit 260 of the first modification uses VR2 as a determination voltage until the voltage of the output signal LPFO of the low-pass filter 250 falls below VR2, and changes VR1 after the voltage of the output signal LPFO of the low-pass filter 250 exceeds VR2. It is configured as a Schmitt circuit that generates a selection signal SW as a determination voltage.

  In this modification, in the reference circuit 40, a resistor 420, a resistor 410, and a constant current source 400 are connected in series in this order between the reference voltage VREF and the ground voltage VSS, and a constant current is caused to flow through the resistor 410 and the resistor 420. Two determination voltages VR1 and VR2 are generated. However, the determination circuit 260 may include the constant current source 400, the resistor 410, and the resistor 420, and the determination voltages VR1 and VR2 may be generated inside the determination circuit 260.

In the first modification, the configuration of the full-wave rectifier circuit 240 is further changed so that the polarity of the output signal of the full-wave rectifier circuit 240 is inverted. Thereby, the voltage V _lpf of the output signal LPFO of the low-pass filter 250 is expressed by the following equation (9).

Also, assuming that the current value of the constant current from the constant current source 400 is I _ref , the resistance value of the resistor 410 is R1, and the resistance value of the resistor 420 is R2, VR1 and VR2 are expressed by the following equations (10) and (11), respectively. Is done.

When V _lpf = VR2, the selection signal SW changes from the high level to the low level, and the drive current Idr at that time is calculated by the following equation (12) from the equations (9) and (11).

On the other hand, when V _lpf = VR1, the selection signal SW changes from the low level to the high level, and the drive current Idr at that time is calculated by the following equation (13) from the equations (9) and (10).

  According to the equations (12) and (13), when the resistor 410 and the resistor 420 are made of the same material as the resistor 204 of the I / V conversion circuit 200, the resistance when the resistance value of the resistor 204 swings increases. Each resistance value of 410 and resistor 420 also increases, and when the resistance value of resistor 204 swings in the direction of decreasing, each resistance value of resistor 410 and resistor 420 also decreases, so that variations in resistance values can be offset. . Thereby, it is possible to suppress variations in the drive current Idr when the selection signal SW changes from high level to low level or from low level to high level.

  In addition, since the power supply voltage VDD is not included in the expressions (12) and (13), the drive current Idr does not change even if the power supply voltage is changed.

  Therefore, also in this modification, it is possible to reduce the variation in the startup time due to the variation in the power supply voltage and the variation in the resistance value.

[Modification 2]
FIG. 13 is a diagram illustrating a configuration of a part of the reference circuit 40 and the determination circuit 260 according to the second modification. FIG. 14 is a waveform diagram of an input signal and an output signal of the determination circuit 260 according to the second modification.

  The determination circuit 260 of the second modification is configured as a simple comparator that determines whether the voltage of the output signal LPFO of the low-pass filter 250 is higher or lower than the determination voltage VR.

In the second modification, if the current value of the constant current from the constant current source 400 is I _ref and the resistance value of the resistor 410 is R, VR is expressed by the following equation (14).

The voltage V _lpf of the output signal LPFO of the low-pass filter 250 is expressed by equation (4). When V _lpf = VR, the selection signal SW changes from high level to low level or from low level to high level. The drive current Idr is calculated by the following equation (15) from the equations (4) and (14).

  From equation (15), by making the resistor 410 the same material as the resistor 204 of the I / V conversion circuit 200, the resistance value of the resistor 410 increases when the resistance value of the resistor 204 swings in the direction of increasing, When the resistance value of the resistor 204 swings in the direction of decreasing, the resistance value of the resistor 410 also decreases, so that variations in resistance value can be offset. Thereby, it is possible to suppress variations in the drive current Idr when the selection signal SW changes from high level to low level or from low level to high level.

  Further, since the power supply voltage VDD is not included in Expression (15), the drive current Idr does not change even if the power supply voltage is changed.

  Therefore, also in this modification, it is possible to reduce the variation in the startup time due to the variation in the power supply voltage and the variation in the resistance value.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

1 angular velocity detection device, 2 angular velocity detection IC, 4 sensor element, 10 power supply circuit, 20 drive circuit, 30 detection circuit, 40 reference circuit, 50 non-volatile memory, 60 serial interface circuit, 200 I / V conversion circuit, 202 operational amplifier, 204 resistors, 206 capacitors, 210 high-pass filters, 220 comparators, 230 drive signal generation circuits, 240 full-wave rectifier circuits, 250 low-pass filters, 260 decision circuits, 262 operational amplifiers, 264, 266 switches, 270 counter circuits, 280 oscillators, 290 Comparator, 292, 294, 296 switch, 400 constant current source, 410, 420 resistance

Claims (5)

A drive circuit that generates a drive signal for driving a sensor element that detects a given physical quantity,
A current-voltage converter that converts the drive current output by the sensor element into a voltage;
A determination unit that determines a magnitude relationship between the voltage of the determination target signal obtained based on the signal converted into a voltage by the current-voltage conversion unit and the determination voltage;
An oscillator that generates an oscillation signal that assists self-excited oscillation of the sensor element;
Based on the determination result of the determination unit, the drive signal is generated based on the oscillation signal until the voltage of the determination target signal exceeds the determination voltage, and the voltage of the determination target signal exceeds the determination voltage And a drive signal generation unit that generates the drive signal based on a signal converted into a voltage by the current-voltage conversion unit,
The determination voltage is
A drive circuit which is a voltage obtained by adding or subtracting a voltage obtained by passing a constant current through one or a plurality of resistors and a reference voltage. In claim 1,
The drive current determination unit
The first voltage is used as the determination voltage until the voltage of the determination target signal exceeds the first voltage, and the second voltage is determined as the determination voltage after the voltage of the determination target signal exceeds the first voltage. A drive circuit with voltage. In claim 2,
The drive current determination unit
A drive circuit including a switch unit that selects one of the first voltage and the second voltage as the determination voltage according to the determination result.   An integrated circuit device comprising the drive circuit according to claim 1. An integrated circuit device according to claim 4,
A sensor device for detecting a given physical quantity.