JP2007292660A - Angular velocity sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an angular velocity sensor that is reduced in size and cost without using a large capacity of capacitor, and has excellent responsiveness and an excellent sensitivity temperature characteristic. <P>SOLUTION: A piezoelectric oscillator 1 is driven by the piezoelectric oscillator 1 and an oscillation circuit including the piezoelectric oscillator 1, an electromotive voltage signal generated by vibration of the piezoelectric oscillator resulting from Coriolis force is detected by a differential amplitude circuit 3, a detection timing generation circuit 6 generates a timing signal in timing other than a node and a loop of the electromotive voltage signal with an amplitude in response to a change of the Coriolis force, while synchronized with an oscillation period, and a sample holding synchronization detecting circuit 7 synchronization-detects an output signal from the differential amplitude circuit 3. A direct current amplifying circuit 8 amplifies directly an output from the sample holding synchronization detecting circuit 7 without integrating or smoothing it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an angular velocity sensor used, for example, for camera shake correction.

In digital still cameras and digital video cameras, angular velocity sensors that detect camera shake are used for camera shake correction.
Such an angular velocity sensor drives a piezoelectric vibrator, detects an electromotive voltage generated by vibration of the piezoelectric vibrator caused by Coriolis force, and outputs a voltage signal corresponding to the angular velocity.
The electromotive voltage of the piezoelectric vibrator is differentially amplified, synchronously detected in synchronization with a drive signal for driving the piezoelectric vibrator, converted into a DC voltage signal, and then DC amplified.

Patent Document 1 discloses a configuration in which, after the synchronous detection, a DC voltage signal is converted by a smoothing circuit and then DC amplified. The configuration of the smoothing circuit and the DC amplifier circuit is shown in FIG.
1A is a circuit diagram thereof, and FIG. 1B is a waveform diagram of each part of FIG.

  In FIG. 1, switches S1 and S2 are sampling switch circuits that alternately switch the output DIFF of the differential amplifier circuit and its inverted output DIFFB. The resistor R1 and the capacitor C1 form a smoothing circuit, and smooth the voltage signal sampled (detected) by the switches S1 and S2. The operational amplifier OP1 and the resistors R2 and R3 constitute a DC amplification circuit, and the DC voltage amplifies the smoothed voltage by the DC amplification circuit.

  In FIG. 1B, “detection signal” is an input signal of the smoothing circuit, and “filter output” is an output signal of the smoothing circuit.

  Further, in Patent Document 2, in a differential circuit that detects a difference in passing current of a vibrating body having a pair of piezoelectric elements on the side surfaces, the differential output is sampled and held when the displacement speed of the vibrating body becomes zero. An angular velocity sensor for detecting the angular velocity is shown.

Further, Patent Document 3 uses a sample-and-hold circuit in signal processing on the detection side of the circulation drive type vibration gyro, and samples and holds the sample at a point where the mass velocity during driving within one cycle is maximum / minimum, and is included in the output. A configuration in which the generated ripple is removed by a low-pass filter is shown.
Japanese Patent Laid-Open No. 5-45167 US Pat. No. 5,551,292 JP-A-62-150116

  When a smoothing circuit is provided and a signal that is synchronously detected is smoothed as in Patent Document 1, the frequency band of the angular velocity detected by an angular velocity sensor using a vibration gyro is generally 100 Hz or less. Using the above chip capacitor, the cutoff frequency is set to about 500 Hz. However, when the angular velocity sensor is downsized, there is no space for arranging the chip capacitor, and it cannot be built in a semiconductor integrated circuit.

  In the angular velocity sensor disclosed in Patent Document 2, since the angular velocity is detected by sampling and holding the differential output when the displacement speed of the vibrating body becomes zero, sampling is performed at the maximum displacement. However, especially when driving a tuning fork type or prismatic type piezoelectric vibrator and detecting an electromotive force generated by the Coriolis force due to the angular velocity, sampling at the point of maximum displacement deteriorates responsiveness and changes in sensitivity temperature characteristics. It became clear that it would grow.

  Further, in the angular velocity sensor shown in Patent Document 3, sampling is performed at a point where the mass velocity during driving within one cycle is maximum / minimum, that is, sampling is performed at the minimum displacement and the maximum displacement. As in the case of No. 2, there is a problem that the responsiveness is poor and the sensitivity temperature characteristic is largely changed. In addition, since a low-pass filter is used, an external component such as a chip capacitor and a mounting process thereof are required as in the case of Patent Document 1, and there is a problem that productivity and economy cannot be improved.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an angular velocity sensor that is small in size and low in cost without using a large-capacitance capacitor, and has good responsiveness and sensitivity temperature characteristics.

(1) An angular velocity sensor according to the present invention detects an electromotive voltage signal generated by vibration of the piezoelectric vibrator caused by Coriolis force while driving the piezoelectric vibrator by an oscillation circuit including the piezoelectric vibrator. An angular velocity sensor that outputs an angular velocity detection signal that is a voltage signal corresponding to the applied angular velocity,
A timing signal generation circuit that generates a timing signal at a timing other than a node and an antinode of the electromotive voltage signal that is synchronized with an oscillation cycle of the oscillation circuit and that changes in amplitude according to a change in the Coriolis force; and And a sample hold circuit for sample-holding with the timing signal, and a DC amplifier circuit for DC-amplifying the voltage signal held by the sample-hold circuit.

  (2) The electromotive voltage signal is amplified by a differential amplifier circuit, and the sample and hold circuit has a switch circuit that switches an output signal of the differential amplifier circuit, and a hold that holds an input voltage when the switch circuit is cut off. The DC amplifying circuit is a DC amplifying circuit (C-MOS configuration with an input impedance of 1 MΩ or more or FET input) having an input current of 1 pA to several pA, which amplifies the voltage of the hold capacitor.

  (3) In the piezoelectric vibrator, the fundamental vibration in the left-right opening / closing direction of the leg portion by driving is opposite to each other in a direction orthogonal to the direction of the fundamental vibration by a Coriolis force caused by an angular velocity to be detected. A tuning-fork type piezoelectric vibrator having electrodes formed and polarized so as to be converted into vibrations of the legs is used.

  (1) Driving the piezoelectric vibrator and synchronizing the electromotive voltage generated by the Coriolis force with the oscillation period of the oscillation circuit and sampling and holding at timings other than the nodes and antinodes of the electromotive voltage signal whose amplitude changes according to the change in angular velocity By doing so, an angular velocity sensor excellent in responsiveness and sensitivity temperature characteristics can be obtained.

  (2) The electromotive voltage signal is differentially amplified by a differential amplifier circuit, the output signal is switched at the timing and held in a hold capacitor, and the voltage of the hold capacitor is set to a high input with an input current of 1 pA to several pA. By amplifying with a DC amplifier circuit of impedance, the voltage of a small-capacitance hold capacitor can be directly amplified and output as an output voltage signal of the angular velocity sensor without using a conventional integrating circuit or low-pass filter.

  (3) If the piezoelectric vibrator is a tuning fork type piezoelectric vibrator, the responsiveness and sensitivity temperature characteristics that are greatly deteriorated by sampling at the point of maximum displacement can be kept good.

An angular velocity sensor according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 2 is a block diagram showing the configuration of the angular velocity sensor 21. In FIG. 2, the vibrator 1 is provided with a left electrode 1L, a right electrode 1R, and a common electrode 1C, and a voltage + V is applied to the left electrode 1L and the right electrode 1R through a resistor. An L signal and an R signal including Coriolis force are taken out from the left electrode 1L and the right electrode 1R, respectively, and given to the adder circuit 2 and the differential amplifier circuit 3. The adder circuit 2 adds the L signal and the R signal and outputs an L + R signal. In this way, the addition circuit 2 adds the L signal and the R signal to cancel the Coriolis force and obtain a stable feedback signal.

  By supplying the feedback signal to the amplitude control circuit 4, a drive voltage having a constant amplitude is obtained, and this drive voltage is applied to the common electrode 1 </ b> C of the vibrator 1 through the phase shift circuit 5. The phase shift circuit 5 adjusts the phase of the output of the adder circuit 2, and adjusts the phase of the drive voltage applied to the common electrode 1C so that the vibrator 1 oscillates stably at a desired frequency. These vibrator 1, adder circuit 2, amplitude control circuit 4, and phase shift circuit 5 constitute an oscillation circuit. The adder circuit 2, the amplitude control circuit 4, and the phase shift circuit 5 constitute a drive circuit that drives the vibrator 1.

  The output signal of the adder circuit 2 is given to the detection timing generation circuit 6, and the detection timing generation circuit 6 gives a rectangular wave detection timing signal to the sample and hold synchronous detection circuit 7.

  The sample hold synchronous detection circuit 7 performs synchronous detection by sampling the signal output from the differential amplifier circuit 3 at the timing output from the detection timing generation circuit 6. The output voltage of the sample and hold synchronous detection circuit 7 is a DC voltage that is substantially proportional to the angular velocity applied to the piezoelectric vibrator 1. The direct current amplifier circuit 8 amplifies the direct current and outputs it as an angular velocity detection signal Vo. The reference voltage generation circuit 9 outputs a reference voltage Vref to the inside and outside of the angular velocity sensor 21.

  The detection timing generation circuit 6 can take several forms. One of them is a circuit that shifts the phase of an input signal by a CR phase shift circuit using a capacitor and a resistor and outputs a rectangular wave signal by a waveform shaping circuit by a comparator. Further, waveform shaping is performed by comparing the input signal which is a sine wave with a predetermined threshold value by a comparator, and the phase is shifted by changing the threshold value of the comparator.

  In the example shown in FIG. 2, the timing signal of the detection timing is generated based on the output of the adder circuit 2, but the timing signal is generated based on the drive voltage that is the output of the phase shift circuit 5. It may be.

FIG. 3 is a diagram showing the configuration and waveform of the sample-and-hold synchronous detection circuit 7 shown in FIG.
The switch circuit S is turned on / off by a timing signal output from the detection timing generation circuit 6 shown in FIG. The hold capacitor C is a capacitor having a small capacity of about 100 pF, and the hold capacitor C and the switch circuit S constitute a sample hold circuit.

  The operational amplifier OP2 and the resistors R12 and R13 constitute a DC amplifier circuit. In this DC amplifier circuit, a resistor R12 is connected between the output terminal of the operational amplifier OP2 and the inverting input terminal (−), and a resistor R13 is connected between the inverting input terminal (−) and the ground (reference voltage). Type feedback circuit.

Here, when the open loop gain of the operational amplifier OP2 is A, the input impedance of the operational amplifier OP2 itself is Zi, the resistance value of the feedback resistor R12 is Zf, and the impedance of the input side resistor R13 is Z1, the input impedance Zif is
Zif = AZi / (1 + Zf / Z1)
It is represented by Since the operational amplifier OP2 is a C-MOS circuit, the input impedance Zi of the operational amplifier itself is a large value. Since A is also a large value, the input impedance Zif of this non-inverting amplifier circuit is a very large value.

  Accordingly, when the capacitance of the hold capacitor C is 100 pF and the charging voltage is within the input dynamic range of the DC amplifier circuit, the input current to the non-inverting amplifier circuit can be suppressed to an extremely low value of about 1 pA to several pA. Therefore, even if the capacitance of the hold capacitor C is as small as about 100 pF and the oscillation frequency of the oscillation circuit including the piezoelectric vibrator is relatively low, 30 kHz, the charging voltage of the hold capacitor C is decreased in the sampling period. Is kept low.

  By sampling and holding the input signal DIFF of the sample-hold synchronous detection circuit 7 with the timing signal from the detection timing generation circuit 6, the detection output signal that is the output signal of the operational amplifier OP2 is as shown in FIG. It can be output as a voltage signal with almost no direct current with little ripple.

  The output signal DIFF of the differential amplifier circuit 3 is a sine waveform whose amplitude changes depending on the magnitude of the Coriolis force. The purpose of detection is to detect the amplitude of this signal DIFF. However, as apparent from FIG. 3, the DC voltage of the detection output varies depending on the sampling timing of the output signal DIFF from the differential amplifier circuit 3 input to the sample hold synchronous detection circuit 7. Therefore, it is necessary to make the sampling timing (phase angle) of the signal DIFF constant. Next, how to determine the sampling timing will be described.

  FIG. 4 is a diagram showing the phase relationship between the electromotive voltage generated by the Coriolis force due to the angular velocity and the oscillation waveform. In FIG. 4, a waveform A is an oscillation waveform and is a waveform of a signal (L + R signal that is not affected by Coriolis force) given from the adder circuit 2 to the detection timing generation circuit 6. Further, the gray colored portion shows the fluctuation range of the output signal of the differential amplifier circuit 3 (hereinafter referred to as “detected waveform” since it is a signal for detecting Coriolis force) measured over 10 seconds. . Sa is a waveform when a constant angular velocity of clockwise (+300 deg / s) is given, Sb is a waveform when giving a constant angular velocity of counterclockwise (−300 deg / s), and Sc is a waveform at rest.

  Thus, when the amplitude of the detection signal changes in accordance with the change in the Coriolis force, nodes Pn and antinodes Ps are generated in the detection signal. This node and antinode are determined by the phase of the oscillation loop of the oscillation circuit and the detuning frequency of the piezoelectric vibrator (the difference between the frequency of the detection signal and the oscillation frequency of the oscillation circuit).

  Depending on the phase angle at which the detection signal is sampled during this oscillation period, the characteristics of the angular velocity sensor (the SN ratio, the responsiveness, the sensitivity temperature characteristic change amount and the inclination) vary. For example, if sampling is performed with Coriolis antinodes on piezoelectric vibrators having the same detuning frequency, the sensitivity of the angular velocity sensor increases, but the responsiveness deteriorates. On the other hand, if you sample at the Coriolis section, the sensitivity decreases. Therefore, if the sampling is performed at the timing excluding the Coriolis antinodes and nodes in one oscillation period, all the characteristics of the angular velocity sensor can be satisfied.

  5 and 6 show sensitivity temperature characteristics and responsiveness when the sampling timing is changed. Here, the sampling timing is a phase angle from the time of zero crossing of the rise of the L + R signal. Even with a piezoelectric vibrator having the same detuning frequency, various characteristics can be obtained depending on the sampling timing. As shown in FIG. 5, when the sampling timing is 45 °, the rate of change in sensitivity varies by +5 to −17% in the range of −10 ° to + 75 °. The sensitivity change rate falls within +2 to -15%, and if the sampling timing is set to 94 °, the sensitivity change rate falls within the range from +1 to -5% within the above temperature range. In this example, by sampling at the timing of the phase angle of 94 °, the change amount and the inclination of the sensitivity temperature characteristic become the best.

  In FIG. 4, the phase angle of the antinode Ps of the detection signal is around 45 °, and the phase angle of the node Pn is around 135 ° which is 90 ° away from the phase angle. When the phase shift from the antinode Pn is represented by θ, the SN ratio of the angular velocity detection decreases at a rate obtained by multiplying the sensitivity when sampling is performed by the antinode Ps by cos θ. Therefore, the S / N ratio decreases as the sampling timing approaches the node Pn of the detection signal, but a practically satisfactory SN ratio can be ensured unless sampling is performed at the timing of the node Pn of the detection signal.

  As shown in FIG. 6, when sampling is performed at a timing of 45 ° which is the phase angle of the antinode Ps point of the detection signal, the phase angle changes by −3 to −32 ° in the range of the displacement frequency of 10 to 50 Hz. When the sampling timing is shifted to 60 °, the phase delay is reduced to −1 to −20 ° within the range of the displacement frequency. Accordingly, the responsiveness increases accordingly. Thus, it can be seen that the sampling timing is improved as the phase angle of the antinode Ps point of the detection signal deviates from 45 °.

  In the above embodiment, the tuning fork type piezoelectric vibration is used. However, the piezoelectric vibrator is not limited to the tuning fork type, and a prismatic sound piece type piezoelectric vibrator or a so-called unimorph type piezoelectric vibration is used. It may be a child.

It is a figure which shows the partial structure of the angular velocity sensor shown by patent document 1. FIG. It is a block diagram which shows the structure of the angular velocity sensor which concerns on embodiment of this invention. It is a waveform diagram of a configuration of a sample and hold synchronous detection circuit in the same angular velocity sensor and each part thereof. It is a figure which shows the detection signal of a Coriolis force, and the waveform of an oscillation signal. It is a figure which shows the sensitivity temperature characteristic by sampling timing. It is a figure which shows the responsiveness by a sampling timing.

Explanation of symbols

1-piezoelectric vibrator 21-angular velocity sensor

Claims (3)

Applied with a piezoelectric vibrator and a circuit for driving the piezoelectric vibrator with an oscillation circuit including the piezoelectric vibrator and detecting an electromotive voltage signal generated by vibration of the piezoelectric vibrator caused by Coriolis force In an angular velocity sensor that outputs an angular velocity detection signal that is a voltage signal corresponding to the angular velocity,
A timing signal generation circuit that generates a timing signal at a timing other than a node and an antinode of the electromotive voltage signal that is synchronized with an oscillation period of the oscillation circuit and that changes in amplitude according to a change in the Coriolis force;
A sample hold circuit that samples and holds the electromotive voltage signal with the timing signal;
A direct current amplifier circuit for direct current amplification of the voltage signal held by the sample and hold circuit;
Angular velocity sensor with   A differential amplifying circuit for differentially amplifying the electromotive voltage signal, wherein the sample-and-hold circuit is a switch circuit that switches an output signal of the differential amplifying circuit, and a hold capacitor that holds an input voltage when the switch circuit is conductive 2. The angular velocity sensor according to claim 1, wherein the DC amplifier circuit is a DC amplifier circuit having a high input impedance in which an input current is 1 pA to several pA for the voltage of the hold capacitor.   The piezoelectric vibrator is configured such that the fundamental vibrations of the left and right opening / closing directions of the leg portions due to driving are opposite to each other in a direction perpendicular to the direction of the fundamental vibrations due to Coriolis force caused by an angular velocity to be detected. The angular velocity sensor according to claim 1, wherein the angular velocity sensor is a tuning-fork type piezoelectric vibrator having electrodes formed and polarized so as to be converted into vibration.

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