JP2007218793A - Oscillation circuit, physical quantity transducer and vibration gyro sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillation circuit capable of achieving highly accurately amplitude control in an oscillation loop and shortening an oscillation start time with a simple configuration, a physical quantity transducer and a vibration gyro sensor. <P>SOLUTION: This oscillation circuit 10 includes a gain control amplifier 20 for controlling an oscillation amplitude in the oscillation loop, and a gain control circuit 30 for outputting a control voltage for adjusting a gain of the gain control amplifier corresponding to the oscillation amplitude. The gain control circuit 30 monitors the oscillation amplitude, discriminates whether oscillation in the oscillation loop is in a steady state or in a starting process, outputs a given constant voltage as a control voltage regardless of the oscillation amplitude when discriminated that the oscillation in the oscillation loop is in the starting process, and outputs a control voltage for determining the gain corresponding to the oscillation amplitude when discriminated that the oscillation in the oscillation loop is in the steady state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an oscillation circuit, a physical quantity transducer, and a vibration gyro sensor.

  Due to external factors of electronic devices such as robots, autonomous driving systems, and other electronic devices such as car navigation systems, DSCs (Digital Still Cameras), DVCs (Digital Video Cameras), and cellular phones. A gyro sensor (physical quantity transducer in a broad sense) for detecting a changing physical quantity is incorporated. Such a gyro sensor detects angular velocity and is used for so-called camera shake correction and GPS autonomous navigation.

  In recent years, the gyro sensor is required to have a lighter and smaller size and higher detection accuracy, and a piezoelectric vibration gyro sensor has attracted attention as one of the gyro sensors. Among them, a quartz piezoelectric vibration gyro sensor using quartz as a piezoelectric material is expected to be an optimum sensor for incorporation into many devices.

  The vibration gyro sensor detects a physical quantity corresponding to a Coriolis force generated by rotation. Such a vibration gyro sensor is disclosed in Patent Document 1, for example.

  FIG. 13 schematically shows the structure of the vibrator of the vibration gyro sensor disclosed in the cited document 1.

  This vibrator is a tuning fork type piezoelectric vibrator, and has vibration elements 910 and 912 provided at the tips of the tuning fork arms 900 and 902 so that the plane of the tuning fork arms 900 and 902 and the plane thereof are orthogonal to each other. When a sinusoidal voltage is applied to the electrode 920 of the tuning fork arm 900, the tuning fork arm 900 starts to vibrate due to the inverse piezoelectric effect, and the tuning fork arm 902 also starts to vibrate due to the tuning fork vibration. At this time, the electric charge generated on the element surface by the piezoelectric effect of the tuning fork arm 902 is proportional to the voltage applied to the tuning fork arm 900. By detecting the electric charge generated in the tuning fork arm 902 and controlling the voltage of the sine wave applied to the tuning fork arm 900 so that it has a constant amplitude, stable tuning fork vibration can be obtained. For this reason, the vibrator shown in FIG. 13 is provided in an oscillation loop including the vibrator and a circuit that drives the vibrator, and is configured as an oscillation circuit by the vibrator and a circuit that drives the vibrator.

  At this time, the vibration elements 910 and 912 vibrate at a speed v in the direction shown in FIG. When the vibrator rotates around the detection axis 930 in FIG. 13, a Coriolis force is generated in a direction orthogonal to the vibration direction of the speed v.

  FIG. 14 schematically shows the detection axis 930 of FIG. 13 as viewed from above.

  In FIG. 14, the same parts as those in FIG. 13 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. In FIG. 13, assuming that the angular velocity when rotating around the detection axis 930 is Ω [dps (degree per second)] and the mass of the vibration element 910 (vibration element 912) is m, the vibration element 910 (vibration element 912) The working Coriolis force Fc is expressed by the following equation.

Fc = -2 · m · Ω · v (1)
Here, since a sinusoidal voltage is applied to the electrode 920 as described above, the velocity v can be expressed by the following equation. In the following equation, the amplitude of tuning fork vibration is a and the period of tuning fork vibration is ω ₀ .

v = a · sinω ₀ t (2)
Therefore, if the equation (2) is substituted into the equation (1), the Coriolis force Fc is expressed by the following equation.

Fc = −2 · m · Ω · a · sinω ₀ t (3)
As shown in the equation (3), the Coriolis force Fc is proportional to the mass m, proportional to the angular velocity Ω, and proportional to the velocity v.

In the case of a crystal resonator in which crystal is used as the piezoelectric material of the resonator in FIG. 13, the vibration frequency corresponding to the speed v can be stabilized. Therefore, in order to accurately detect the angular velocity Ω regardless of the mass m, it is important how stably the circuit that drives the crystal resonator can vibrate the resonator.
JP-A-3-226620

  FIG. 15 shows general input / output characteristics of an amplifier for controlling the gain in the oscillation loop.

  As shown in FIG. 15, the input / output characteristics of the amplifier have nonlinearity in which the output amplitude is saturated when the input amplitude becomes a certain level mainly due to the limitation of the power supply. A general piezoelectric vibrator oscillation circuit keeps the oscillation amplitude constant on the basis of the principle that the oscillation amplitude of the oscillation loop eventually converges to a predetermined amplitude due to the above nonlinearity.

On the other hand, there is a problem that the amplitude fluctuates due to fluctuations in the power supply voltage and temperature of the oscillation circuit and manufacturing variations of elements constituting the oscillation circuit. In particular, in order to stably detect the Coriolis force, it is necessary to control the oscillation amplitude in the oscillation loop to be constant. Therefore, the oscillation circuit includes a gain control amplifier having an AGC (Auto Gain Control) function.
By the way, considering the application of an electronic device in which a gyro sensor is incorporated, it is necessary to satisfy the demand for low power consumption. Therefore, it is necessary to appropriately stop the oscillation circuit, while it is desirable that the oscillation start-up time be as short as possible.

  In general, the gain control amplifier has a linear gain sensitivity characteristic, so in the case of an oscillation circuit using a crystal resonator, a sufficient gain in the oscillation loop cannot be obtained at startup (at the time of oscillation startup). However, there has been a problem that oscillation often does not start or oscillation start time becomes long.

  In that case, it is difficult to design a gain control amplifier having an ideal gain sensitivity characteristic that performs predetermined amplitude control in a steady state of oscillation and performs amplitude control so that the amplitude becomes sufficiently large at the time of oscillation start-up.

  Even if a gain control amplifier having an ideal gain sensitivity characteristic can be designed, the circuit configuration becomes large.

  As described above, it is desired to provide an oscillation circuit suitable for an electronic device in which a vibration gyro sensor is incorporated, which is required to be small and light, low power consumption, and high accuracy.

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to realize an oscillation start-up time while realizing amplitude control in an oscillation loop with high accuracy with a simple configuration. It is an object to provide an oscillation circuit capable of shortening the frequency, a physical quantity transducer using the oscillation circuit, and a vibration gyro sensor.

In order to solve the above problems, the present invention
A gain control amplifier for controlling the oscillation amplitude in the oscillation loop;
A gain control circuit that outputs a control voltage for adjusting the gain of the gain control amplifier according to the oscillation amplitude,
The gain control circuit includes:
Monitoring the oscillation amplitude to determine whether the oscillation in the oscillation loop is in a steady state or a startup process;
When the oscillation in the oscillation loop is determined as a starting process, a given constant voltage is output as the control voltage regardless of the oscillation amplitude,
The present invention relates to an oscillation circuit that outputs a control voltage for determining a gain according to the oscillation amplitude when oscillation in the oscillation loop is determined to be in a steady state.

  In the present invention, the oscillation amplitude in the oscillation loop is monitored to determine whether it is a steady oscillation state or an oscillation start process, and when it is determined that the oscillation start process is in progress, the gain control amplifier gain is adjusted. The control voltage is switched to a given constant voltage. When it is determined that the oscillation is in the steady state, the gain of the gain control amplifier is adjusted by switching to output a control voltage corresponding to the oscillation amplitude.

  By doing so, the gain in the oscillation loop can be adjusted in the oscillation starting process regardless of the oscillation amplitude, so that the time of the oscillation starting process can be adjusted with a simple configuration. In addition, in the steady oscillation state, the oscillation amplitude can be controlled with high accuracy by outputting a control voltage corresponding to the oscillation amplitude.

In the oscillation circuit according to the present invention,
The constant voltage may be a voltage that increases a gain in the oscillation loop in the oscillation starting process.

  According to the present invention, since the gain in the oscillation loop in the oscillation start process can be increased, the oscillation start-up time can be shortened while realizing the amplitude control in the oscillation loop with high accuracy with a simple configuration. It becomes like this.

In the oscillation circuit according to the present invention,
The gain control circuit is
A rectifier circuit for converting a signal in the oscillation loop into a DC signal;
And a differential amplifier that generates the control voltage in accordance with a difference between the DC signal and a given first reference signal.

  According to the present invention, it is possible to generate a control voltage for performing amplitude control of an oscillation loop with high accuracy with a simple configuration.

In the oscillation circuit according to the present invention,
The gain control circuit is
By comparing the signal in the oscillation loop or the DC signal with a given second reference signal, it is possible to determine whether the oscillation in the oscillation loop is in a steady state or a starting process.

  According to the present invention, it is possible to determine whether the oscillation is in a steady state (steady oscillation state) or an activation process (oscillation activation process) with a simple configuration.

In the oscillation circuit according to the present invention,
A negative resistance value R _N in the oscillation _loop, the load resonance resistance R _L in the oscillation _loop, the gain of the gain control amplifier k, the gain of the gain control amplifier in the steady state was k ₀ In case,
The gain control circuit includes:
When the input voltage of the gain control amplifier is a reference power supply voltage, a constant voltage such that k / k ₀ is greater than or equal to | R _N / R _L | can be output as the control voltage.

  According to the present invention, it is possible to increase the oscillation margin, which is a value indicating how many times the loop gain can be obtained with respect to the loop gain at the time of steady oscillation. It is possible to reduce the possibility of the occurrence of defects.

In the oscillation circuit according to the present invention,
The negative resistance value in the oscillation loop is R _N, the load resonance resistance value in the oscillation loop is R _L , the maximum value of | R _N / R _L | is M, and the control voltage in the steady oscillation state is Vc _0. If
The constant voltage may be Vc ₀ × (2-M).

  According to the present invention, it is possible to reduce the possibility of occurrence of a malfunction at the time of oscillation start according to the oscillation margin, which is the value of how many times the loop gain can be obtained with respect to the loop gain during steady oscillation. become.

In the oscillation circuit according to the present invention,
The maximum value M of | R _N / R _L | may be 5 or more.

  According to the present invention, it is possible to shorten the oscillation start-up time while realizing amplitude control in the oscillation loop with high accuracy with a simple configuration, and from the rule of thumb, the possibility of occurrence of oscillation start-up is almost zero. It is possible to provide a highly reliable oscillation circuit that can be used.

In the oscillation circuit according to the present invention,
A resonator,
A current-voltage converter that converts a current from the resonator into a voltage and outputs the voltage as an input voltage of the gain control amplifier.

  According to the present invention, it is possible to provide an oscillation circuit capable of shortening the oscillation start-up time with a simple configuration while realizing amplitude control in the oscillation loop with high accuracy.

In the oscillation circuit according to the present invention,
The resonator is
A crystal resonator may be used.

  According to the present invention, it is possible to provide an oscillation circuit capable of reducing the oscillation start-up time while realizing the amplitude control in the oscillation loop with high accuracy with a stable frequency and a simple configuration.

The present invention also provides
The present invention relates to a physical quantity transducer including any of the oscillation circuits described above.

The present invention also provides
An oscillation circuit as described above;
The present invention relates to a physical quantity transducer including a physical quantity output circuit that outputs a physical quantity that is changed by an external action in a state of being coupled with the resonator.

  According to any one of the above-described inventions, it is possible to provide a physical quantity transducer to which an oscillation circuit capable of shortening the oscillation start-up time is realized with a simple configuration and highly accurate amplitude control in the oscillation loop. .

The present invention also provides
An oscillation circuit as described above;
The present invention relates to a vibration gyro sensor including a physical quantity output circuit that outputs a charge amount that changes due to rotation in a state of being coupled with the resonator.

  According to the present invention, it is possible to provide a vibration gyro sensor to which an oscillation circuit capable of shortening the oscillation start-up time is realized with a simple configuration and highly accurate amplitude control in the oscillation loop.

  Hereinafter, 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. Oscillation Circuit FIG. 1 shows the basic configuration of the oscillation circuit of this embodiment.

  The oscillation circuit 10 in the present embodiment adjusts the gain of a gain control amplifier (Gain Control Amplifier: GCA) 20 for controlling the oscillation amplitude in the oscillation loop and the gain control amplifier 20 according to the oscillation amplitude in the oscillation loop. And a gain control circuit 30 that outputs a control voltage Vc. The gain control circuit 30 can monitor the oscillation amplitude of the oscillation loop to determine whether the oscillation in the oscillation loop is in a steady state or a starting process. The gain control circuit 30 outputs a given constant voltage as the control voltage Vc regardless of the oscillation amplitude of the oscillation loop when it is determined that the oscillation in the oscillation loop is the starting process. Here, the constant voltage is a voltage that increases the gain in the oscillation loop in the oscillation starting process.

  At this time, the gain control amplifier 20 amplifies the input amplitude of the gain control amplifier 20 with a gain corresponding to the control voltage Vc. On the other hand, when it is determined that the oscillation in the oscillation loop is in a steady state, the gain control circuit 30 outputs a control voltage Vc for determining a gain according to the oscillation amplitude of the oscillation loop. Also in this case, the gain control amplifier 20 amplifies the input amplitude of the gain control amplifier 20 with a gain corresponding to the control voltage Vc.

  More specifically, the oscillation circuit 10 can include a resonator 40 and a current-voltage converter 50. The resonator 40 outputs charges generated by resonance (vibration), and the current-voltage converter 50 converts the charges into a voltage and outputs it as an output voltage V2. In this case, the gain control amplifier 20 and the gain control circuit 30 can be referred to as an oscillation drive circuit. Based on the output voltage V2 of the current-voltage converter 50, the gain control circuit 30 can monitor the oscillation amplitude of the oscillation loop to determine whether the oscillation in the oscillation loop is in a steady state or a starting process. ing.

  FIG. 2 shows a circuit diagram of a configuration example of the oscillation circuit of FIG.

  2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The oscillation loop of the oscillation circuit 10 of FIG. 2 includes a gain control amplifier 20, a resonator 40, a current-voltage converter 50, and a phase adjustment circuit 60. A crystal resonator is used as the resonator 40, but is not limited to this.

  FIG. 3 shows a circuit diagram of a configuration example of the current-voltage converter 50 of FIG.

  Current-voltage converter 50 includes an operational amplifier 52, a feedback resistor 54, and a capacitor 56. A reference power supply voltage AGND (a ground power supply voltage of an analog circuit such as an operational amplifier) is supplied to a normal rotation input terminal (+ terminal) of the operational amplifier 52, and a resonator is connected to an inverting input terminal (− terminal) of the operational amplifier 52. Current from 40 is input. The feedback resistor 54 is connected between the inverting input terminal and the output terminal of the operational amplifier 52. The capacitor 56 is also connected between the inverting input terminal and the output terminal of the operational amplifier 52 in parallel with the feedback resistor 54.

  In such a current-voltage converter 50, the current input to the operational amplifier 52 flows through the feedback resistor 54. Therefore, the output of the operational amplifier 52 becomes a voltage determined by the current flowing through the feedback resistor 54. Capacitor 56 defines a cutoff frequency.

  In the oscillation loop of FIG. 2, a phase adjustment circuit 60 is provided at the output of the current-voltage converter 50. The phase adjustment circuit 60 is configured by a circuit that shifts the phase of the output signal with respect to the phase of the input signal, such as a known LPF (Low Pass Filter) or HPF (High Pass Filter). By this phase adjustment circuit 60, the phase condition of oscillation in the oscillation loop of the oscillation circuit 10 can be established at a desired oscillation frequency.

  The output voltage V2 of the phase adjustment circuit 60 based on the reference power supply voltage AGND of the oscillation circuit 10 is supplied to the gain control amplifier 20 and the gain control circuit 30.

  FIG. 4 shows a circuit diagram of a configuration example of the gain control amplifier 20 of FIG.

  The gain control amplifier 20 includes an operational amplifier 22, a feedback resistor 24, and a variable resistor 26. A voltage V2 is supplied to the normal rotation input terminal (+ terminal) of the operational amplifier 22. The reference power supply voltage AGND is supplied to the inverting input terminal (− terminal) of the operational amplifier 52 through the variable resistor 26. The resistance value of the variable resistor 26 is changed based on the control voltage Vc from the gain control circuit 30. The feedback resistor 24 is connected between the inverting input terminal and the output terminal of the operational amplifier 52.

  In such a gain control amplifier 20, when the resistance value of the variable resistor 26 increases due to the control voltage Vc, the output voltage of the gain control amplifier 20 decreases, and when the resistance value of the variable resistor 26 decreases due to the control voltage Vc, the gain control amplifier 20 increases. The output voltage of becomes higher.

  In FIG. 2, the gain control circuit 30 can include an oscillation start process determination circuit 32. In FIG. 2, the oscillation starting process determination circuit 32 is provided in the gain control circuit 30, but may be provided outside the gain control circuit 30. The oscillation starting process determination circuit 32 monitors the oscillation amplitude (voltage V2 in FIG. 2 or a signal corresponding to the voltage V2) to determine whether the oscillation in the oscillation loop is in a steady state or a starting process.

  Then, according to the determination result of the oscillation starting process determination circuit 32, the gain control circuit 30 sets a voltage for setting the gain of the gain control amplifier 20 according to the given constant voltage Vcs or the oscillation amplitude of the oscillation loop. Output as control voltage Vc.

  Such a gain control circuit 30 can include a full-wave rectifier circuit (rectifier circuit in a broad sense) 34, a differential amplifier 36, and a switching circuit 38.

  FIG. 5 shows a circuit diagram of a configuration example of the full-wave rectifier circuit 34 of FIG.

  The full-wave rectifier circuit 34 converts the voltage V2 that is a signal in the oscillation loop into a DC signal. More specifically, the full wave rectification circuit 34 obtains a DC signal by full wave rectifying the voltage V2.

  Such a full-wave rectifier circuit 34 includes operational amplifiers 80 and 82, resistor circuits 84 and 86, switch elements 88 and 90, an inverter circuit 92, and an LPF 35. The reference power supply voltage AGND is supplied to the normal rotation input terminal of the operational amplifier 80 and the inverting input terminal of the operational amplifier 82, respectively. The voltage V2 from the oscillation loop is supplied to the inverting input terminal of the operational amplifier 80 through the resistance circuit 84. The voltage V <b> 2 is supplied to the normal input terminal of the operational amplifier 82.

  The resistance circuit 86 is connected between the inverting input terminal and the output terminal of the operational amplifier 80. The output of the full wave rectifier circuit 34 is connected to the output terminal of the operational amplifier 80 via the switch element 90. A switch element 88 is connected between the input and output of the full-wave rectifier circuit 34.

  The switch element 88 is ON / OFF controlled by the output signal CK of the operational amplifier 82. The inverter circuit 92 outputs an inverted output signal XCK obtained by inverting the output signal CK. The switch element 90 is ON / OFF controlled by the inverted output signal XCK.

  The LPF 35 extracts a low frequency component of the signal output via the switch element 88 or the switch element 90 and outputs it as an output voltage V3.

  Assuming that the direct current output from the full-wave rectifier circuit 34 is the voltage V3, the voltage V2 has the maximum amplitude of the sine wave signal and can be expressed as the following equation.

V3 = V2 × 2 / π (4)
Returning to FIG. 2, the differential amplifier 36 of the gain control circuit 30 controls the control voltage Vc1 according to the difference between the voltage V3 that is a DC signal and a predetermined first reference voltage (reference signal) Vref1. Is generated. More specifically, the higher the difference between the voltage V3 and the first reference voltage Vref1, the higher the voltage Vc1 is generated.

  The voltage Vc1 is input to one input terminal of the switching circuit 38. A predetermined constant voltage Vcs is input to the other input terminal of the switching circuit 38. The switching circuit 38 outputs the voltage Vc1 or the constant voltage Vcs as the control voltage Vc based on the output signal of the oscillation starting process determination circuit 32.

  The oscillation starting process determination circuit 32 includes an operational amplifier 96 that operates as a comparator. A second reference voltage (reference signal) Vref <b> 2 is supplied to the normal input terminal of the operational amplifier 96. The voltage V3 is supplied to the inverting potential terminal of the operational amplifier 96. When the voltage V3 is higher than the second reference voltage Vref2, the switching circuit 38 outputs the voltage Vc1 as the control voltage Vc. When the voltage V3 is the same potential as the second reference voltage Vref2 or lower than the second reference voltage Vref2, the switching circuit 38 outputs the voltage Vcs as the control voltage Vc.

  The output of the gain control amplifier 20 whose gain is adjusted by the control voltage Vc thus output is output as the output voltage V1.

  With this configuration, according to the present embodiment, the gain in the oscillation loop can be increased with a constant voltage during the oscillation start-up process, and the oscillation start-up time of the oscillation circuit that performs stable oscillation control is shortened. become able to.

Further, in the present embodiment, by determining the constant voltage Vcs as shown below, it is possible to realize a stable oscillation start without causing an oscillation start failure while maintaining a sufficient oscillation margin. Become.
Therefore, first, the constant voltage Vcs in the present embodiment will be described in comparison with the comparative example of the present embodiment.

  FIG. 6 shows a configuration example of an oscillation circuit in a comparative example of the present embodiment.

  In FIG. 6, the same parts as those in FIG.

  In the oscillation circuit 100 of FIG. 6, a gain control circuit 110 is provided in place of the gain control circuit 30 of the oscillation circuit 10 in the present embodiment. The gain control circuit 110 has a configuration in which the oscillation start process determination circuit 32 and the switching circuit 38 are omitted from the gain control circuit 30. Therefore, the gain control circuit 110 generates the control voltage Vc according to the difference between the voltage V3 obtained by converting the voltage V2 in the oscillation loop into a direct current and the predetermined first reference voltage (reference signal) Vref1. The control voltage Vc is used for adjusting the gain of the gain control amplifier 20 as it is.

  Here, consider an oscillation condition of an oscillation loop including the above-described vibrator and a circuit that drives the vibrator.

  FIG. 7 shows a general configuration of an oscillation circuit that forms an oscillation loop.

  The oscillation circuit can include a phase change unit 950 that changes the phase in the oscillation loop and a gain change unit 960 that changes the gain in the oscillation loop. The change of the phase θ in the oscillation loop by the phase change unit 950 is mainly caused by the phases ((positive) inversion / non-inversion) of the resonator, the phase adjustment circuit 60, and the gain change unit 960. The change of the gain A in the oscillation loop by the gain changing unit 960 is mainly caused by the amplifier and the resonator. The oscillation conditions for stabilizing the oscillation state in such an oscillation circuit must satisfy the following amplitude condition and phase condition.

First, the amplitude condition is as follows, assuming that the negative resistance value corresponding to the resistance value on the oscillation circuit side viewed from the resonator 40 in the oscillation loop is R _N , and the load resonance resistance value in the oscillation loop is R _L. Must hold.

| R _N / R _L | = m = 1 (5)
Further, the phase condition must hold for the phase θ changed by the phase changing unit 950 in FIG.

θ = 2π · n (n is an integer including 0) (6)
Therefore, m of the oscillation circuit 100 shown in FIG. 6 is obtained as follows.

Here, the input amplitude of the gain control amplifier 20 V2, the input amplitude of the gain control amplifier 20 in the steady oscillation state and V2 _0. Further, the control voltage Vc, the control voltage in the steady oscillation state and Vc _0. Furthermore, the gain of the gain control amplifier 20 k, the gain of the gain control amplifier 20 in the steady oscillation state to k _0.

  As shown in FIG. 6, using the functions f and g, the control voltage Vc and the gain k are expressed by the following equations.

Vc = f (V2) (7)
k = g (Vc) (8)
Here, the ratios P _V2 , P _Vc , and P _k are defined as follows.

P _V2 = V2 / V2 ₀ (9)
P _Vc = Vc / Vc ₀ (10)
P _k = k / k ₀ (11)
In order to control the oscillation amplitude to be constant, the following relational expression must be satisfied.

P _V2 · P _k = P _Vc · P _k = 1 (12)
Therefore, when the oscillation amplitude is controlled to be constant, the Vc-k characteristic indicating the change of the gain k with respect to the control voltage Vc of the gain control amplifier 20 is a so-called 1 / x characteristic. However, the Vc-k characteristic of the gain control amplifier 20 usually has linearity. Therefore, equation (8) is a linear function.

Therefore, since it is important that the oscillation is stable in the vicinity of (P _k , P _Vc ) = (1, 1), which is a steady oscillation state, the Vc-k characteristic of the gain control amplifier 20 is (12) In the formula, it is set so as to pass (P _k , P _Vc ) = (1, 1). That is, the Vc-k characteristic of the gain control amplifier 20 is set as a derivative that passes through (1, 1) of the ideal characteristic indicated by P _Vc · P _k = 1.

  Therefore, the following equation holds.

(P _k −1) = − P _Vc ′ (1) × (P _Vc −1) (13)
P _k = −P _Vc +2 (14)
FIG. 8 shows an example of the Vc-k characteristic in the comparative example.

  In FIG. 8, the ideal characteristic shown in the equation (12) is indicated by a wavy line, and the Vc-k characteristic of the gain control amplifier 20 is indicated by a solid line.

Since the voltage V2 = 0 when oscillation starts, the control voltage Vc = 0. Therefore, at the time of starting oscillation, P _k = 2 when P _Vc = 0 as shown in FIG. Therefore, the oscillation margin, which is a value indicating how many times the maximum loop gain can be obtained with respect to the loop gain during steady oscillation, is the maximum value M of m (= | R _N / R _L |). As shown in FIG. Note that m is 1 during steady oscillation.

  By the way, a crystal resonator with a stable vibration frequency has a high Q value. Therefore, when a crystal resonator is used as the oscillator of the oscillation circuit, it is necessary to sufficiently increase the gain in the oscillation loop when starting the oscillation circuit (when starting oscillation). In that case, it is difficult to design a gain control amplifier having an ideal gain sensitivity characteristic that performs predetermined amplitude control in a steady state of oscillation and performs amplitude control so that the amplitude becomes sufficiently large at the time of oscillation start-up.

  Therefore, it is necessary to set the Vc-k characteristic of the gain control amplifier of the gain control amplifier 20 as described above to perform stable amplitude control not only in the steady oscillation state but also in the oscillation starting process. However, the oscillation circuit in the comparative example satisfies m ≦ 2 as described above.

  However, as a rule of thumb, when M is 2 or less, an oscillation failure often occurs. Further, when M is about 3, it is desirable that an oscillation defect of 1% or less occurs during mass production, and M is about 5 or more.

  Therefore, in the present embodiment, the constant voltage Vc is determined as follows.

  FIG. 9 shows an example of the Vc-k characteristic in this embodiment.

As described above, in the oscillation circuit in the comparative example, there is a slight possibility that a problem of oscillation start-up occurs, and it is desirable that M is 5 or more. Therefore, in this embodiment, it is determined whether the oscillation steady state or the oscillation starting process, and when it is determined that the oscillation starting process, the control voltage Vc is switched to the constant voltage Vcs so that P _k becomes M or more. Thereby, the gain in the oscillation loop can be increased in the oscillation starting process. Here, when M is 5, P _Vc = −3.0 from the equation shown in FIG. That is, Vc = −3.0 × Vc ₀ , and the value of Vc becomes the value of the constant voltage Vcs.

That is, when P _k = M and the expression (14) is developed, the value of the constant voltage Vcs is determined according to M as shown in the following expression.

Vcs = Vc ₀ × (2-M) (15)
Therefore, in the oscillation circuit 10, in the oscillation start-up process, the gain in the oscillation loop is increased by the constant voltage Vcs obtained by the equation (15), and normal oscillation control is performed in the steady state of oscillation. With this configuration, the oscillation start-up time can be shortened while realizing amplitude control in the oscillation loop with high accuracy.

  The gain control amplifier 20 in the present embodiment may have a negative linear characteristic or a positive linear characteristic. In this case, the phase of the differential amplifier 36 included in the gain control circuit 30 can be inverted depending on whether the linear characteristic of the gain control amplifier 20 is positive or negative, thereby satisfying the oscillation phase condition. In the present embodiment, the phase adjustment circuit 60 may be inserted at an arbitrary position in the oscillation loop. Further, the phase adjustment function of the current-voltage converter 50 may be provided in an arbitrary circuit block in the oscillation loop.

2. Physical Quantity Transducer Next, a physical quantity transducer will be described as an application example of the oscillation circuit of the present embodiment.

  FIG. 10 shows a block diagram of a configuration example of the physical quantity transducer in the present embodiment.

  The physical quantity transducer 200 can output a physical quantity that has changed due to an external factor. Such a physical quantity transducer 200 includes a resonator 210, an oscillation drive circuit 220, and a physical quantity output circuit 230. The functions of the resonator 210 and the oscillation drive circuit 220 can be realized by the oscillation circuit 10 of FIG. That is, the physical quantity output circuit 230 is capacitively, inductively or mechanically coupled with the resonator 210 while being maintained in a steady oscillation state by the resonator 210 and the oscillation drive circuit 220, and is externally actuated. Output changing physical quantity.

2.1 Vibration Gyro Sensor Next, a vibration gyro sensor will be described as an example of a physical quantity transducer in the present embodiment.

  FIG. 11 shows a block diagram of a configuration example of the vibration gyro sensor in the present embodiment.

  The vibration gyro sensor 300 detects an angular velocity due to rotation around a given detection axis. More specifically, the vibration gyro sensor 300 can generate a charge amount proportional to the Coriolis force generated by the rotation and output a sensor detection signal corresponding to the charge amount.

  The vibration gyro sensor 300 includes a vibrator 310, an oscillation drive circuit 320, a phase shifter 330, a comparator 340, a differential amplifier 350, a synchronous detector 360, an LPF 370, and an output amplifier 380.

  The vibrator 310 is a crystal vibrator in which quartz is used as a piezoelectric material, and has drive terminals A1 and A2 and detection terminals B1 and B2. As such a vibrator 310, the vibrator of the vibration gyro sensor shown in FIG. 13 can be applied. Therefore, the drive signal Arv from the oscillation drive circuit 320 is input to the drive terminal A1 of the vibrator 310, the feedback signal fb is output from the drive terminal A2 of the vibrator 310, and the feedback signal fb is sent to the oscillation drive circuit 320. Entered. That is, the oscillation circuit 400 is configured by the resonator connected to the drive terminals A 1 and A 2 of the vibrator 310 and the oscillation drive circuit 320.

  The function of the oscillation drive circuit 320 is realized by the gain control amplifier 20, the gain control circuit 30, the current-voltage converter 50, and the phase adjustment circuit 60 shown in FIG. The function of the oscillation drive circuit 320 may be realized only by the gain control amplifier 20, the gain control circuit 30, and the current-voltage converter 50 shown in FIG. Therefore, the function of the oscillation circuit 400 is realized by the oscillation circuit of FIG.

  The output of the oscillation drive circuit 320 is connected to the phase shifter 330. The phase shifter 330 shifts the phase of the input signal. This is for the purpose of matching the phases of a synchronous signal sync, which will be described later, and a synchronous detection input signal syncin.

  The output of the phase shifter 330 is connected to the comparator 340. The comparator 340 binarizes the signal whose phase is shifted by the phase shifter 330 and outputs the signal to the synchronous detector 360 as the synchronous signal sync. For example, the output of the phase shifter 330 that is a sine wave is converted into a rectangular wave by the comparator 340.

  Detection signals det1 and det2 are output from the detection terminals B1 and B2 of the vibrator 310, respectively. Due to the configuration as shown in FIG. 13, the detection signals det1 and det2 are inverted in phase. The detection signals det1 and det2 are differentially amplified by the differential amplifier 350 and output as the synchronous detection input signal syncin.

  The synchronous detector 360 synchronizes the synchronous detection input signal syncin with the synchronous signal sync, and outputs a synchronous detection output signal syncout.

  The LPF 370 cuts off a high frequency component of the synchronous detection output signal syncout. The output of the LPF 370 is amplified by the output amplifier 380 and output as a sensor detection signal.

  FIG. 12 shows an example of the operation waveform of each part of the vibration gyro sensor 300 of FIG.

  When the oscillation drive circuit 320 that receives the feedback signal fb outputs the drive signal drv that is a sine wave, the phase is shifted by the phase shifter 330, and then the synchronization signal sync that is a rectangular wave is output by the comparator 340.

  On the other hand, the detection signal det1 from the detection terminal B1 of the vibrator 310 or the detection signal det2 from the detection terminal B2 is amplitude-modulated according to the magnitude of the Coriolis force Fc. Therefore, the synchronous detection input signal syncin obtained by differentially amplifying the detection signals det1 and det2 is detected as a sine wave that is amplitude-modulated by the amplitude of the Coriolis force Fc.

  The synchronous detector 360 outputs the synchronous detection output signal syncout as shown in FIG. 12 by multiplying the synchronous detection input signal syncin and the synchronous signal sync. Therefore, the sensor detection signal shown in FIG. 12 can be output by allowing the LPF 370 to pass the frequency component of the envelope of the synchronous detection output signal syncout.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the gist of the present invention.

  In the present embodiment, the quartz resonator is described as an example. However, the present invention is not limited to this, and the piezoelectric material may be other than quartz. Further, the structure of the vibrator is not limited to the tuning fork type. Furthermore, each circuit constituting the oscillation circuit is not limited to that described in the present embodiment.

  In the invention according to the dependent claims of the present invention, a part of the constituent features of the dependent claims can be omitted. Moreover, the principal part of the invention according to one independent claim of the present invention can be made dependent on another independent claim.

The figure which shows the fundamental structure of the oscillation circuit of this embodiment. FIG. 2 is a circuit diagram of a configuration example of the oscillation circuit of FIG. 1. The circuit diagram of the structural example of the current-voltage converter of FIG. FIG. 3 is a circuit diagram of a configuration example of the gain control amplifier in FIG. 2. The circuit diagram of the structural example of the full wave rectifier circuit of FIG. The figure which shows the structural example of the oscillation circuit in the comparative example of this embodiment. The figure which shows the general structure of the oscillation circuit which forms an oscillation loop. The figure which shows an example of the Vc-k characteristic in a comparative example. The figure which shows an example of the Vc-k characteristic in this embodiment. The block diagram of the structural example of the physical quantity transducer in this embodiment. The block diagram of the structural example of a vibration gyro sensor. The figure which shows an example of the operation | movement waveform of each part of the vibration gyro sensor of FIG. The figure which shows typically the structure of the vibrator | oscillator of a vibration gyro. The figure which shows the figure which looked at the detection axis of FIG. 13 from the top. The figure which shows the general input-output characteristic of the amplifier which controls the gain in an oscillation loop.

Explanation of symbols

10, 100, 400 oscillator circuit, 20 gain control amplifier,
30, 110 Gain control circuit, 32 Oscillation start process determination circuit,
34 full wave rectifier circuit, 35 LPF, 36 differential amplifier, 38 switching circuit,
40, 210 resonator, 50 current-voltage converter, 60 phase adjustment circuit,
96 operational amplifiers, 200 physical quantity transducers,
220, 320 oscillation drive circuit, 230 physical quantity output circuit,
300 vibration gyro sensor, 310 vibrator, 330 phase shifter,
340 Comparator, 350 Differential Amplifier, 360 Synchronous Detector,
370 LPF, 380 output amplifier, AGND reference power supply voltage,
Vc control voltage, Vcs constant voltage, Vref1 first reference voltage,
Vref2 second reference voltage, V2 output voltage, det1, det2 detection signal,
drv drive signal, fb feedback signal, sync synchronization signal,
syncin synchronous detection input signal, syncout synchronous detection output signal

Claims (12)

A gain control amplifier for controlling the oscillation amplitude in the oscillation loop;
A gain control circuit that outputs a control voltage for adjusting the gain of the gain control amplifier according to the oscillation amplitude,
The gain control circuit includes:
Monitoring the oscillation amplitude to determine whether the oscillation in the oscillation loop is in a steady state or a startup process;
When the oscillation in the oscillation loop is determined as a starting process, a given constant voltage is output as the control voltage regardless of the oscillation amplitude,
An oscillation circuit that outputs a control voltage for determining a gain corresponding to the oscillation amplitude when oscillation in the oscillation loop is determined to be in a steady state. In claim 1,
2. The oscillation circuit according to claim 1, wherein the constant voltage is a voltage that increases a gain in the oscillation loop in the oscillation starting process. In claim 1 or 2,
The gain control circuit is
A rectifier circuit for converting a signal in the oscillation loop into a DC signal;
An oscillation circuit comprising: a differential amplifier that generates the control voltage according to a difference between the DC signal and a given first reference signal. In any one of Claims 1 thru | or 3,
The gain control circuit is
An oscillation circuit comprising: comparing a signal in the oscillation loop or the DC signal with a given second reference signal to determine whether the oscillation in the oscillation loop is in a steady state or a starting process. In any one of Claims 1 thru | or 4,
A negative resistance value R _N in the oscillation _loop, the load resonance resistance R _L in the oscillation _loop, the gain of the gain control amplifier k, the gain of the gain control amplifier in the steady state was k ₀ In case,
The gain control circuit includes:
An oscillation circuit characterized in that when the input voltage of the gain control amplifier is a reference power supply voltage, a constant voltage such that k / k ₀ is equal to or greater than | R _N / R _L | is output as the control voltage. In any one of Claims 1 thru | or 4,
The negative resistance value in the oscillation loop is R _N, the load resonance resistance value in the oscillation loop is R _L , the maximum value of | R _N / R _L | is M, and the control voltage in the steady oscillation state is Vc _0. If
The oscillation circuit characterized in that the constant voltage is Vc ₀ × (2-M). In claim 5 or 6,
A maximum value M of | R _N / R _L | is 5 or more. In any one of Claims 1 thru | or 7,
A resonator,
An oscillation circuit comprising: a current-voltage converter that converts a current from the resonator into a voltage and outputs the voltage as an input voltage of the gain control amplifier. In claim 8,
The resonator is
An oscillation circuit characterized by being a crystal resonator.   A physical quantity transducer comprising the oscillation circuit according to claim 1. An oscillation circuit according to claim 7 or 8,
A physical quantity transducer comprising: a physical quantity output circuit that outputs a physical quantity that is changed by an external action while being coupled to the resonator. An oscillation circuit according to claim 7 or 8,
A vibration gyro sensor comprising: a physical quantity output circuit that outputs a charge amount that changes due to rotation in a state of being coupled with the resonator.

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