Resonance frequency tracking circuit and resonance frequency tracking method for vibrator

Abstract

To provide a resonance frequency tracking circuit and a resonance frequency tracking method of a vibrator capable of stably tracking a resonance frequency by automatically correcting a damping capacity.SOLUTION: A resonance frequency tracking circuit of a vibrator includes a capacitance correction circuit of a damping capacitor (C0), and the capacitance correction circuit is configured to connect a voltage signal (Vf) of the vibrator to an input of a differentiation circuit, connect an output of the differentiation circuit to an input of a variable gain circuit, and subtract an output of the variable gain circuit from a current signal (If), and controls a correction amount of the damping capacitor (C0) by controlling a gain of the variable gain circuit to bring a selected anti-resonance frequency or the like (fa ") close to a target frequency (fCAL) and reduce an influence of the damping capacitor (C0).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a drive circuit for tracking the resonance frequency of a vibrator and a method for tracking the resonance frequency of a vibrator, and more particularly, to a feature of stably tracking the resonance frequency by automatically correcting damping capacitance. [Background technology]

[0002] FIG. 1 of Patent Document 1 and its accompanying description show an example in which a correction capacitor Cc is connected in parallel to the ultrasonic vibrator 11, the current flowing through the correction capacitor Cc is subtracted from the current flowing through the capacitor Cd, and the correction capacitor Cc is adjusted so as to cancel out the capacitance of the damping capacitor Cd.

[0003] FIG. 1 of Patent Document 2 and its explanation show an example in which a correction coil 11 (Ld) is connected in parallel to an ultrasonic vibrator 1 to resonate in parallel with a damping capacitor (Cd), and the inductance of the correction coil 11 is adjusted so that the frequency coincides with the resonance frequency fr.

[0004] In principle, the present invention uses the terms defined in Non-Patent Document 1 for terms related to vibrators, but may define and use other terms as necessary. (For example, the portion (Cd) corresponding to the "damping capacitor portion" in Patent Documents 1 and 2 is defined as the "parallel capacitance of the equivalent circuit" in Non-Patent Document 1, but since the term "parallel capacitance C0 (also called damping capacitance)" is also included, the present invention will refer to it as "damping capacitance C0.") [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-117687 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-84485 [Non-patent literature]

[0006] [Non-Patent Document 1] Japan Electronics and Information Technology Industries Association Standard JEITA EM-4501A Electrical Test Method for Piezoelectric Ceramic Resonators Revised October 2015 Summary of the Invention [Problem to be solved by the invention]

[0007] In FIG. 1 of Patent Document 1 and its explanation, a correction capacitor Cc and a circuit for measuring the current flowing through the correction capacitor Cc are required, and furthermore, it is only possible to try to equivalently set the damping capacitor Cd to zero based on the current flowing through the correction capacitor Cc. Therefore, it is not possible to know what the anti-resonance frequency and the like will be, which poses a problem that the PLL may not be able to lock depending on the start frequency of the PLL.

[0008] In Figure 1 of Patent Document 2 and its explanation, a circuit for measuring the current flowing through the correction coil 11 (Ld) and the correction coil 11 (Ld) are required, and there is also the problem that when the correction coil 11 (Ld) and the capacitor (Cd) are resonated in parallel, an unnecessary anti-resonance frequency occurs near the resonant frequency of the vibrator (see Figure 4(B) and its explanation below). [Means for solving the problem]

[0009] In order to solve the above problems, the present invention is provided with a capacitance correction circuit for a damping capacitance (C0), and the capacitance correction circuit is configured to connect a voltage signal (Vf) of a vibrator to the input of a differentiation circuit, connect the output of the differentiation circuit to the input of a gain variable circuit, and subtract the output of the gain variable circuit from a current signal (If), and by controlling the gain of the gain variable circuit, the correction amount of the damping capacitance (C0) is controlled, and a selected anti-resonance frequency (fa") is set to a target frequency (f CAL ) and reduce the influence of the damping capacitance (C0).

[0010] In the resonant frequency tracking circuit for the vibrator according to the present invention, the characteristics of the vibrator to be targeted and the values ​​of the equivalent circuit elements are measured in advance, and one of the anti-resonant frequencies (fa') close to the resonant frequency (fr) is selected based on the measurement results, and the selected anti-resonant frequency (fa') is set as the selected anti-resonant frequency (fa"), and the correction amount of the damping capacitance (C0) is controlled so that the frequency difference between the selected anti-resonant frequency (fa") and the resonant frequency (fr) exceeds or is equal to or greater than the required frequency difference, and the frequency of the selected anti-resonant frequency (fa") at that time is set to the target frequency (f CAL ) can be expressed as follows.

[0011] In the resonant frequency tracking circuit of the vibrator according to the present invention, the selected anti-resonant frequency (fa") is set to the target frequency (f CAL ), and in this circuit, the correction amount of the damping capacitance (C0) is initialized, the operation of the PLL is started, and after the time required for the operation of the PLL has elapsed, the selected anti-resonance frequency (fa") and the target frequency (f CAL ) frequency high-low relationship, and compare the selected anti-resonance frequency (fa") and the target frequency (f CAL ) match, the correction amount is used as the result, and the selected anti-resonance frequency (fa") is set to the target frequency (f CAL ), the correction amount of the damping capacity (C0) is increased, and the selected anti-resonance frequency (fa") is adjusted to the target frequency (f CAL ), the amount of correction of the braking capacity (C0) can be reduced.

[0012] In the resonant frequency tracking circuit of the vibrator according to the present invention, the selected anti-resonant frequency (fa") and the target frequency (f CALAs a circuit for checking the high / low relationship of the frequency of the target frequency (f), the high / low relationship can be checked by using a circuit that knows the direction of change of the output frequency after the PLL starts operating, or by using a circuit that has been modified so that the PLL locks at the anti-resonance frequency (fa') and directly knowing the frequency of the selected anti-resonance frequency (fa"). Or, the high / low relationship can be checked by forcibly locking the PLL to the target frequency (f CAL ) and check the high / low relationship based on the duty ratio of the phase comparator output.

[0013] In the resonant frequency tracking circuit of the vibrator according to the present invention, the selected anti-resonant frequency (fa") and the target frequency (f CAL After checking the high and low relationship of the frequencies of the selected anti-resonance frequency (fa") and the target frequency (f CAL The compensation circuit may include a circuit that increases or decreases a certain amount of compensation each time until the high-low relationship of the frequency of the equivalent capacitance (Cx) is reversed, a circuit that reduces the increase or decrease in the compensation amount by half each time, or a circuit that uses the relationship between the change in the capacitance value of the equivalent capacitance (Cx) after compensation and the selected anti-resonance frequency (fa").

[0014] In the resonant frequency tracking circuit for a vibrator according to the present invention, the differentiating circuit may be an imperfect differentiating circuit.

[0015] In the resonant frequency tracking circuit for a vibrator according to the present invention, the correction amount of the damping capacitance (C0) can be changed from a predetermined value when the PLL starts operating, and then returned to the predetermined value.

[0016] In the resonant frequency tracking circuit for a vibrator according to the present invention, the operation of returning the correction amount of the damping capacitance (C0) to the predetermined value can be performed by returning it when the PLL is locked, by continuously returning it after the PLL starts operating, or by gradually returning it after the PLL starts operating.

[0017] The resonant frequency tracking circuit for a vibrator according to the present invention further comprises an inductance correction circuit for an inductor (Lp) connected in parallel with the vibrator, the inductance correction circuit being configured to connect the voltage signal (Vf) of the vibrator to an input of an integrating circuit, connect the output of the integrating circuit to an input of a second variable gain circuit, and subtract the output of the second variable gain circuit from the current signal (If), and by controlling the gain of the second variable gain circuit, the correction amount of the inductance correction circuit is controlled to reduce the influence of the inductor (Lp) connected in parallel with the vibrator, and then by controlling the gain of the variable gain circuit, the correction amount of the damping capacitance (C0) is controlled to adjust the selected anti-resonant frequency etc. (fa") to the target frequency (f CAL ) to reduce the influence of the damping capacity (C0).

[0018] In the resonant frequency tracking circuit for a vibrator according to the present invention, the integrating circuit may be an imperfect integrating circuit.

[0019] In the resonant frequency tracking circuit for a vibrator according to the present invention, the inductor (Lp) connected in parallel with the vibrator may be a power factor correction inductor, a step-up transformer, a step-down transformer, or an isolation transformer.

[0020] In the resonant frequency tracking circuit for a vibrator according to the present invention, the current detection means can be provided at a position where it detects the sum of the current flowing through the vibrator and the current flowing through an inductor (Lp) connected in parallel with the vibrator.

[0021] The present invention also provides a capacitance correction circuit for a damping capacitance (C0), wherein the capacitance correction circuit is configured to connect a voltage signal (Vf) of a vibrator to an input of a differentiation circuit, connect an output of the differentiation circuit to an input of a gain variable circuit, and subtract the output of the gain variable circuit from a current signal (If), and controls the gain of the gain variable circuit to control the correction amount of the damping capacitance (C0) and adjust a selected anti-resonance frequency (fa") to a target frequency (f CAL) to reduce the influence of the damping capacitance (C0).

[0022] In the resonant frequency tracking method of the present invention, the characteristics of the resonator to be targeted and the values ​​of equivalent circuit elements are measured in advance, and one of the anti-resonant frequencies (fa') close to the resonant frequency (fr) is selected based on the measurement results, and the selected anti-resonant frequency (fa') is set as the selected anti-resonant frequency (fa"), and the damping capacity (C0) is controlled to be corrected so that the frequency difference between the selected anti-resonant frequency (fa") and the resonant frequency (fr) exceeds or is equal to or greater than the required frequency difference, and the frequency of the selected anti-resonant frequency (fa") at that time is set to the target frequency (f CAL ) can be expressed as follows.

[0023] In the resonant frequency tracking method of the present invention, the selected anti-resonant frequency (fa") is set to the target frequency (f CAL ), the correction amount of the damping capacitance (C0) is initialized, the operation of the PLL is started, and after the time required for the operation of the PLL has elapsed, the selected anti-resonance frequency (fa") and the target frequency (f CAL ) frequency high-low relationship, and compare the selected anti-resonance frequency (fa") and the target frequency (f CAL ) match, the correction amount is used as the result, and the selected anti-resonance frequency (fa") is set to the target frequency (f CAL ), the correction amount of the damping capacity (C0) is increased, and the selected anti-resonance frequency (fa") is adjusted to the target frequency (f CAL ), the amount of correction of the braking capacity (C0) can be reduced.

[0024] In the resonant frequency tracking method of the vibrator according to the present invention, the selected anti-resonant frequency (fa") and the target frequency (f CALAs a method for checking the high / low relationship of the frequency of the anti-resonance frequency (fa"), the high / low relationship can be checked by using a circuit that knows the direction of change of the output frequency after the PLL starts operating, or by using a circuit that has been modified so that the PLL locks at the anti-resonance frequency (fa'), the high / low relationship can be checked by directly knowing the frequency of the selected anti-resonance frequency (fa"), or by forcibly locking the PLL to the target frequency (f CAL ) and check the high / low relationship based on the duty ratio of the phase comparator output.

[0025] In the resonant frequency tracking method of the vibrator according to the present invention, the selected anti-resonant frequency (fa") and the target frequency (f CAL After checking the high / low relationship of the frequencies, the amount of correction can be increased or decreased by comparing the selected anti-resonance frequency (fa") and the target frequency (f CAL The compensation circuit may include a circuit that increases or decreases a certain amount of compensation each time until the high-low relationship of the frequency of the equivalent capacitance (Cx) is reversed, a circuit that reduces the increase or decrease in the compensation amount by half each time, or a circuit that uses the relationship between the change in the capacitance value of the equivalent capacitance (Cx) after compensation and the selected anti-resonance frequency (fa").

[0026] In the resonant frequency tracking method of the vibrator according to the present invention, the correction amount of the damping capacitance (C0) can be changed from a predetermined value when the PLL starts operating, and then returned to the predetermined value.

[0027] In the resonant frequency tracking method of the vibrator according to the present invention, the operation of returning the correction amount of the damping capacitance (C0) to the predetermined value can be performed by returning it when the PLL is locked, by continuously returning it after the PLL starts operating, or by gradually returning it after the PLL starts operating.

[0028] The resonant frequency tracking method for a vibrator according to the present invention further includes an inductance correction circuit for an inductor (Lp) connected in parallel with the vibrator, the inductance correction circuit being configured to connect the voltage signal (Vf) of the vibrator to an input of an integrating circuit, connect the output of the integrating circuit to an input of a second variable gain circuit, and subtract the output of the second variable gain circuit from the current signal (If), and by controlling the gain of the second variable gain circuit, the correction amount of the inductance correction circuit is controlled to reduce the influence of the inductor (Lp) connected in parallel with the vibrator, and then by controlling the gain of the variable gain circuit, the correction amount of the damping capacitance (C0) is controlled to match the selected anti-resonant frequency (fa") to the target frequency (f CAL ) to reduce the influence of the damping capacity (C0). [Effects of the Invention]

[0029] According to the present invention, a correction capacitor or a correction coil is not required, and a circuit for measuring the current flowing through them is also not required, which has the effect of reducing costs. Furthermore, in the present invention, not only is the damping capacitance C0 equivalent to zero, but the selected anti-resonance frequency fa" (described later) is set to the target frequency f CAL Since the control is performed so that the frequency approaches the reference frequency (described later), the vibrator driving PLL can be locked more reliably.

[0030] Furthermore, the present invention not only cancels out the influence of the damping capacitance C0, which can be automatically corrected, but also has the effect of automatically performing correction selected in accordance with the characteristics of the vibrator.

[0031] Furthermore, the present invention has the advantage that even if a parallel inductor Lp is connected in parallel to the vibrator, an unnecessary anti-resonance frequency does not occur near the resonant frequency of the vibrator, and the vibrator driving PLL can operate more stably. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 is a diagram illustrating a basic configuration of a general PLL. [Figure 2] FIG. 1 is a diagram illustrating a basic configuration of a PLL for driving a vibrator. [Figure 3] (A) A diagram showing the basic equivalent circuit of a vibrator, (B) the frequency characteristics of its impedance and phase, and (C) the influence of mechanical load on the vibrator. [Figure 4] 1A is a diagram showing the effects of Patent Document 1 and FIG. 1B is a diagram showing the effects of Patent Document 2. [Figure 5] FIG. 10 is a diagram illustrating an example of a capacitance correction circuit for a damping capacitance C0. [Figure 6] 1A and 1C are diagrams illustrating examples of differential circuits, and FIG. 1B and FIG. 1D are diagrams illustrating their frequency characteristics. [Figure 7] 10A and 10B are graphs showing the frequency characteristics of impedance and phase when the damping capacitance C0 is corrected. (A) Cx≧0, (B) Cx≦0, (C) Cx=0 [Figure 8] (A) shows the equivalent circuit of a vibrator having another vibration mode higher than the resonant frequency fr, and (B) shows the frequency characteristics of impedance and phase when the damping capacitance C0 is corrected. (C) shows the frequency characteristics of impedance and phase when Cx≧0 and Cx≦0. [Figure 9] (A) shows the equivalent circuit of a vibrator having another vibration mode lower than the resonant frequency fr, and (B) shows the frequency characteristics of impedance and phase when the damping capacitance C0 is corrected. (C) shows the frequency characteristics of impedance and phase when Cx≧0 and Cx≦0. [Figure 10] (A) shows the equivalent circuit of a vibrator having both a vibration mode higher than the resonance frequency fr and a vibration mode lower than the resonance frequency fr, and (B) shows the frequency characteristics of impedance and phase when the damping capacitance C0 is corrected. (C) shows the frequency characteristics of impedance and phase when Cx≧0 and Cx≦0. [Figure 11] FIG. 10 is a diagram illustrating an example of selection of a target frequency fCAL. [Figure 12] FIG. 10 is a flowchart showing an outline of a method for correcting a braking capacity C0. [Figure 13]FIG. 10 is a diagram showing the relationship between the magnitude of the selected anti-resonance frequency fa″ and the target frequency fCAL and the increase / decrease in the correction amount. [Figure 14] 10A and 10B are diagrams illustrating examples of methods for increasing or decreasing the correction amount. (A) A fixed amount of increase or decrease, (B) Binary search [Figure 15] FIG. 10 is a diagram showing frequency characteristics of impedance and phase when there is another vibration mode lower than the resonance frequency fr and the resonance frequency varies. [Figure 16] 10A and 10B are diagrams showing the frequency characteristics of impedance and phase when there is another vibration mode lower than the resonance frequency fr, Cx=470 pF, (A) fr=30 kHz, (B) fr=31 kHz, and (C) fr=29 kHz. [Figure 17] FIG. 10 is a diagram showing frequency characteristics of impedance and phase when fa′=31.5 kHz, and when there is another vibration mode lower than the resonance frequency fr and the resonance frequency varies. [Figure 18] FIG. 10 is a diagram showing the relationship between the value of equation (7) and I'res when there is another vibration mode lower than the resonance frequency fr and the resonance frequency varies. [Figure 19] FIG. 10 is a diagram showing frequency characteristics of impedance and phase when there is another vibration mode higher than the resonance frequency fr and the resonance frequency varies. [Figure 20] 10A and 10B are diagrams showing the frequency characteristics of impedance and phase when there is another vibration mode higher than the resonance frequency fr, Cx=-470 pF, (A) fr=30 kHz, (B) fr=31 kHz, and (C) fr=29 kHz. [Figure 21] FIG. 10 is a diagram showing frequency characteristics of impedance and phase when fa′=28.5 kHz, and when there is another vibration mode higher than the resonance frequency fr and the resonance frequency varies. [Figure 22] FIG. 10 is a diagram showing the relationship between the value of equation (7) and I'res when there is another vibration mode higher than the resonance frequency fr and the resonance frequency varies. [Figure 23] FIG. 10 is a diagram illustrating an example of an inductance correction circuit for a parallel inductor Lp. [Figure 24] 1A and 1C are diagrams illustrating examples of an integrating circuit, and FIG. 1D are diagrams illustrating examples of its frequency characteristics. [Figure 25] FIG. 10 is a diagram illustrating an example in which a capacitance correction circuit for a damping capacitance C0 and an inductance correction circuit for a parallel inductor Lp are used in combination. DETAILED DESCRIPTION OF THE INVENTION

[0033] All documents mentioned herein are incorporated by reference in their entirety.

[0034] <Common matters>

[0035] In the following explanation, we may omit the frequency type, signal name, etc. and only use the symbols. For example, the resonant frequency fr may be written simply as fr, and the voltage signal Vf may be written simply as Vf. Also, one notation may indicate either the signal name or its value. For example, the voltage signal Vf may be used as the signal name, and the voltage may be written as Vf.

[0036] First, the prior art that is the premise of the present invention will be described in order.

[0037] <Premise 1 of the present invention>

[0038] As a premise of the present invention, a general PLL and a PLL for driving a vibrator will first be briefly explained.

[0039] Figure 1 shows the basic configuration of a commonly used PLL. In such a general PLL, if the division ratio of the divider is 1 / N, the frequency of the output signal fout and the reference signal fref can be expressed as fout = fref × N.

[0040] Figure 2 shows the basic configuration of a vibrator drive PLL. This vibrator drive PLL can lock the voltage signal Vf and the current signal If in phase and drive the vibrator Vib by tracking the resonant frequency fr, where the phase of the impedance becomes zero. This will be described in more detail later.

[0041] First, the points common to the PLLs of FIG. 1 and FIG. 2 will be explained, but an explanation specific to the PLL for driving the vibrator of FIG. 2 will also be included as necessary.

[0042] Each component of a PLL may be an analog circuit or a digital circuit, and the signals between the components may be analog or digital signals, and if necessary, analog and digital circuits or analog and digital signals can be used together by using AD conversion or DA conversion. When all or most of the components are composed of analog circuits, it is called an analog PLL, and when all or a certain proportion of the components are composed of digital circuits, it is called a digital PLL.

[0043] The vibrator driving PLL of FIG. 2 needs to be locked to the resonant frequency fr with the voltage signal Vf and the current signal If in phase.

[0044] When implementing a phase comparator using an analog circuit, an analog multiplier can be used, but in this case the phase difference between Vf and If will be locked at 90°. Therefore, by using a phase shift circuit (not shown) that shifts the phase by +90° or -90° between either Vf or If and the phase comparator, it can be operated to lock to the resonant frequency fr with the phases of Vf and If in agreement, and can be used as a PLL for driving an oscillator.

[0045] Typical examples of phase comparators implemented as digital circuits include 1. exclusive OR (hereinafter referred to as "XOR"), 2. edge-triggered RS flip-flop (hereinafter referred to as "RS-FF"), and 3. phase frequency comparator (hereinafter referred to as "PFD"), which are built into Texas Instruments CD74HC4046, a PLL IC commonly used by those skilled in the art, and equivalent products from other companies, but are not limited to these three types.

[0046] Like an analog multiplier, an XOR locks when the phase difference between Vf and If is 90°. Therefore, like an analog multiplier, by using a phase shift circuit (not shown) that shifts the phase by +90° or -90° between either Vf or If and the phase comparator, it can be operated so that it locks to the resonant frequency fr with the phases of Vf and If coinciding, and can be used as a PLL for driving an oscillator.

[0047] The RS-FF locks when the phase difference between Vf and If is out of phase (180°). Therefore, by using an inverting circuit (not shown) that shifts the phase by 180° between either Vf or If and the phase comparator, the RS-FF can be used as a PLL to drive an oscillator, locking to the resonant frequency fr with the phases of Vf and If in agreement. Inverting circuits are easier to implement and less expensive than 90° phase-shift circuits, so the RS-FF can be suitably used as a PLL to drive an oscillator.

[0048] In the general PLL shown in Figure 1, a combination of a PFD and a charge pump circuit is often used, but in a resonance point tracking PLL where the phase difference detection range is 0°±360° and the frequencies of the two comparison signals are always the same, there is a risk of positive feedback, so a PFD is usually not suitable for the oscillator driving PLL shown in Figure 2.

[0049] Whether the phase comparator is implemented as an analog circuit or a digital circuit, it may be necessary to convert the signal level, signal waveform, etc. so that the voltage signal Vf and the current signal If satisfy conditions such as the input voltage range of the phase comparator; however, this is not shown in the figure.

[0050] The loop filter may be configured as an integrator using analog elements such as transistors and operational amplifiers. In the case of a PFD, it may also be a low-pass filter configured only with CR elements or a low-pass filter using analog elements such as transistors and operational amplifiers. The loop filter may also be configured with a digital circuit that performs the same function as these.

[0051] The term voltage-controlled oscillator (VCO) shown in Figures 1 and 2 typically refers to an analog circuit, but it can also be used as a digital circuit called a numerically controlled oscillator (NCO), a specific example of which is a digital direct synthesis synthesizer (DDS).

[0052] Next, the vibrator driving PLL of FIG. 2 will be further explained.

[0053] A signal based on the drive signal voltage Vvib applied to the vibrator is a voltage signal Vf, and a signal based on the drive signal current Ivib flowing through the vibrator is a current signal If. (The triangle symbol, whose input is connected across the drive signal voltage Vvib and whose output is the voltage signal Vf, represents voltage detection means. The part with a square symbol in the current path of the drive signal current Ivib and whose output is the current signal If is current detection means. Figure 2 is an example and does not limit the connection points of the voltage detection means and current detection means.)

[0054] The vibrator drive PLL locks to the resonant frequency fr when the voltage signal Vf and the current signal If are in phase, making it possible to drive at the resonant frequency fr where the impedance phase is zero. More specifically, by increasing the frequency when the phase is negative and decreasing the frequency when the phase is positive, it locks to the resonant frequency fr (the frequency where the phase becomes zero when the phase increases as the frequency increases). Conversely, by operating so as to increase the frequency when the phase is positive and decrease the frequency when the phase is negative, it locks to the anti-resonant frequency fa (the frequency where the phase becomes zero when the phase decreases as the frequency increases).

[0055] Ideally, a vibrator should be driven at the series resonant frequency fs, but in reality, fr is close to fs, so the difference between fr and fs is often not a problem. (As an example, in the basic equivalent circuit of a vibrator shown in Figure 3 below, the series resonant frequency fs is 30 kHz (30.0000 kHz), but the resonant frequency fr is 30.0016 kHz, a difference of only about 0.005%.)

[0056] The signal waveform of the PLL output Vo may be any signal suitable for driving the vibrator Vib, and may be an analog signal (e.g., a sine wave), a digital binary signal, or, if necessary, a ternary or higher value signal or a digital code signal for DA conversion.

[0057] If the output Vo of the vibrator drive PLL has sufficient power to drive the vibrator Vib, the amplifier in Figure 2 is not necessary and can be omitted. If the driving power is insufficient, an amplifier can be used as needed, as shown in Figure 2. Such an amplifier may be an amplifier that amplifies an analog signal, or a digital switching circuit. If it is preferable to drive the vibrator Vib with a sine wave, a low-pass filter or band-pass filter may be provided at the output of the switching circuit to convert the square wave into a waveform close to a sine wave.

[0058] Hereinafter, when simply referred to as "PLL," it refers to a PLL for driving a vibrator.

[0059] <Premise of the present invention-2>

[0060] Next, the basic equivalent circuit of the vibrator that is the premise of the present invention and its frequency characteristics of impedance and phase will be shown, and the influence when the mechanical load on the vibrator becomes heavy will be explained.

[0061] Figure 3(A) shows an example of the basic equivalent circuit of a vibrator and the constants of the elements that make up that equivalent circuit. Figures 3(B) and 3(C) show the simulation results for the equivalent circuit of Figure 3(A). Figure 3(B) shows the frequency characteristics of impedance and phase when the equivalent circuit of Figure 3(A) is constant. Figure 3(C) shows the characteristics when the value of resistor R1 in the equivalent circuit is changed, and indicates the effect of the mechanical load on the vibrator.

[0062] Similarly, the graphs including the frequency characteristics of impedance and phase below also show the simulation results of a predetermined equivalent circuit, and as a general rule, the phase is represented by a solid line and the impedance by a dashed line.

[0063] In Figure 3(A), the values ​​of the series inductor L1 and series capacitance C1 are expressed to four significant digits in order to make the series resonant frequency fs sufficiently close to 30 kHz for ease of explanation. With these constants, the series resonant frequency fs is 30 kHz (30.0000 kHz), and the resonant frequency fr is 30.0016 kHz.

[0064] In Figure 3(C), the plot with the largest peak in impedance and phase indicates when R1 = 300 Ω, as in Figures 3(A) and 3(B). The plot with the smallest peak in impedance and phase indicates when R1 = 3 kΩ, and the plot with intermediate peaks in impedance and phase indicates when R1 = 800 Ω.

[0065] When the mechanical load on the vibrator increases, the resistance of the series resonant circuit in the equivalent circuit increases, and the Q value decreases. This is because the viscous resistance acting on the vibrator appears as resistance in the equivalent circuit due to the piezoelectric effect. (The Q value can generally be expressed as Q=1 / (R·√(L / C)).)

[0066] The plot for R1 = 800 Ω crosses the phase 0 degrees, so it can be driven at the resonant frequency fr. However, in this case, the resonant frequency fr is 30.0157 kHz, which is a large difference of +0.52% from the series resonant frequency fs of 30 kHz.

[0067] Furthermore, if the mechanical load on the vibrator becomes heavier, the phase will no longer cross 0°, as shown in the plot for R1 = 3 kΩ, causing the PLL to be unable to lock onto the resonance frequency fr.

[0068] <Premise of the present invention-3>

[0069] Finally, the effects and differences between Patent Document 1 and Patent Document 2 will be explained.

[0070] Figure 4(A) shows an example where the capacitance of the damping capacitance C0 (Cd in Figure 1 of Patent Document 1) is cancelled out according to Figure 1 of Patent Document 1 and the method described therein. Figure 4(B) shows an example where a correction coil is connected in parallel to the vibrator to resonate in parallel with the damping capacitance C0 (Cd in Figure 1 of Patent Document 2) and the frequency is made to coincide with the series resonance frequency fs according to Figure 1 of Patent Document 2 and the method described therein.

[0071] In Figure 4(A), the plot with a phase peak and impedance dip near the series resonance frequency fs (30 kHz) represents the constant values ​​in Figure 3(A), just like in Figure 3(B). The remaining two plots represent the results when the capacitance of the damping capacitance C0 is cancelled out and equivalently set to 0 pF; the plot with the steepest change at the resonance frequency fr (30 kHz) is for R1 = 300 Ω, and the plot with the gradual change is for R1 = 3 kΩ.

[0072] By making the damping capacitance C0 equivalent to 0 pF, it is possible to lock onto the resonant frequency fr and drive it by making the phase cross 0°, regardless of the load on the vibrator. When the damping capacitance C0 is equivalent to 0 pF, the resonant frequency fr coincides with the series resonant frequency fs.

[0073] In Figure 4(B), the plot with a phase peak and impedance dip near the series resonance frequency fs (30 kHz) represents the constants in Figure 3(A), just like in Figure 3(B). The remaining two plots show an example where a 0.3816 mH correction coil is connected in parallel to the vibrator, causing parallel resonance with a 3000 pF damping capacitance C0, and the frequency is set to match the resonance frequency fr of 30 kHz. The plot with the steepest changes in impedance and phase is for R1 = 300 Ω, while the plot with the gradual changes is for R1 = 3 kΩ.

[0074] In Figure 4(B), the correction coil and damping capacitance C0 are resonated in parallel to eliminate the influence of the damping capacitance C0 at the series resonance frequency fr. In this case as well, it can be seen that regardless of the load on the vibrator, the phase crosses 0°, making it possible to lock onto the resonance frequency fr and drive it. Note that in this case as well, the resonance frequency fr coincides with the series resonance frequency fs.

[0075] In FIG. 4(B), when a correction coil is provided, a frequency occurs in the vicinity of 30 kHz ±3% where the phase becomes zero when the phase decreases as the frequency increases, similar to the anti-resonance frequency fa. However, it is difficult to say that the frequency in the vicinity of 30 kHz - 3% is the anti-resonance frequency fa of the vibrator.

[0076] In the present invention, the frequency at which the phase becomes zero when the phase decreases as the frequency increases is collectively referred to as the "anti-resonance frequency fa'." (That is, the anti-resonance frequency fa is a typical example of the anti-resonance frequency fa'.)

[0077] Furthermore, when the vibrator has another vibration mode, there may be a frequency that is different from the resonant frequency fr of the main resonance, but at which the phase becomes zero when the phase increases as the frequency increases, and these will be collectively referred to as the "resonant frequency, etc. fr'." (That is, the resonant frequency fr is a typical example of the resonant frequency, etc. fr'.)

[0078] Furthermore, the series resonance frequency fs corresponding to each of the resonance frequencies fr' will be referred to as the "series resonance frequency fs'." (That is, the series resonance frequency fs is a representative example of the series resonance frequency fs'.)

[0079] In addition, when a correction coil is included as shown in FIG. 4B, if the output frequency of the vibrator driving PLL temporarily becomes farther from the resonance frequency fr than one of the anti-resonance frequencies fa', the vibrator driving PLL will be unable to lock onto the resonance frequency fr. As a specific example, if the output frequency of the vibrator driving PLL temporarily becomes lower than the anti-resonance frequency fa' (approximately 29.1 kHz) that is lower than the resonance frequency fr, the phase becomes positive. As mentioned above, the vibrator driving PLL operates to lower the frequency when the phase is positive. If a resonance frequency fr' due to another vibration mode with a lower frequency exists, the vibrator driving PLL will lock onto that frequency. However, if no such frequency exists, the frequency of the vibrator driving PLL will continue to decrease as much as possible. In contrast, such problems are less likely to occur in FIG. 4A, and in this respect, the method of Patent Document 1 is superior to the method of Patent Document 2.

[0080] <Contents of the present invention>

[0081] The contents of the present invention will be explained below.

[0082] <1. Capacitance compensation circuit>

[0083] First, the capacitance correction of the damping capacitance C0 in the present invention will be described.

[0084] Fig. 5 shows an example in which a capacitance correction circuit with a damping capacitance C0 of the present invention is added to a PLL for driving a vibrator. Fig. 6(A) shows an imperfect differential circuit using CR, and Fig. 6(B) shows an example of the frequency characteristics of its gain. Fig. 6(C) shows an imperfect differential circuit using an operational amplifier, and Fig. 6(D) shows an example of the frequency characteristics of its gain. (It is assumed that both the vertical and horizontal axes of Fig. 6(B) and Fig. 6(D) are displayed logarithmically.)

[0085] First, the differentiation circuit included in the capacitance correction circuit of Fig. 5 will be explained using Fig. 6(A) to Fig. 6(D). In Fig. 6(A) and Fig. 6(C), the capacitance constituting the differentiation circuit is defined as capacitance C, the resistance constituting the differentiation circuit is defined as resistance R, and the input resistance of the differentiation circuit using an operational amplifier is defined as resistance Rin.

[0086] The imperfect differential circuit using CR in Figure 6(A) operates as a differential circuit at frequencies lower than the angular frequency ω = 1 / RC, as shown in the gain frequency characteristics in Figure 6(B), where ω is the angular frequency (= 2πf). The relationship between the input Vin and output Vout of the differential circuit in the frequency range in which it operates as a differential circuit is given by equation (1).

[0087]

number

[0088] The imperfect differential circuit using an operational amplifier in Figure 6(C) operates as a differential circuit at frequencies lower than ω=1 / Rin·C, as shown in the gain frequency characteristics in Figure 6(D). The relationship between the input Vin and output Vout of a differential circuit operating as a differential circuit is given by equation (2).

[0089]

number

[0090] In either case, the constants of the circuit elements are selected so that the frequency that drives the oscillator Vib (the output frequency Vo of the PLL) falls within the frequency range at which the circuit operates as a differentiating circuit.

[0091] We will now explain the capacitance correction circuit for the damping capacitance C0 in Figure 5. However, when applying the imperfect differential circuit using the operational amplifier in Figure 6(C), the negative sign in equation (2) is omitted, and the positive / negative relationship is absorbed by either a variable gain circuit or an adding / subtracting circuit, which will be described later.

[0092] For ease of explanation, let us assume that the voltage signal Vf = Vvib. Also, let us assume that the current signal If = Ivib, but since If is a voltage signal, we will assume that the current value [A] is converted into a voltage value [V] of the same value.

[0093] In the equivalent circuit of the vibrator, if the current flowing through C0 is Ic and the current flowing through L1, C1, and R1 is Ires, the current If flowing through the vibrator can be expressed as in equation (3).

[0094]

number

[0095] 5, the part with an x ​​inside a circle represents a variable gain circuit, and its gain G can be changed by a gain control signal. The output of the variable gain circuit is designated as I'c.

[0096] The part with a + inside a circle represents an adder / subtractor circuit, where inputs with a + are added and inputs with a - are subtracted. In other words, the value obtained by subtracting I'c from If is the output of the adder / subtractor circuit, which is I'res.

[0097] Here, Ic can be expressed as equation (4) by differentiating the voltage signal Vf. (As mentioned above, the negative sign in equation (2) can be omitted.)

[0098]

number

[0099] Therefore, the relationship between I'c and Ic can be expressed as in equation (5).

[0100]

number

[0101] By subtracting I'c from the current signal If, I'res can be expressed as in equation (6).

[0102]

number

[0103] In other words, the current Ic flowing through C0 appears to be multiplied by the amount given by equation (7).

[0104]

number

[0105] For example, when G is zero, the current Ic flowing through C0 is multiplied by 1, so the equivalent capacitance of C0 does not change. When G CR is equal to the capacitance of C0, the current Ic flowing through C0 is multiplied by 0, so it behaves in the same way as when the capacitance of C0 is equivalent to zero. Furthermore, when G CR is greater than C0, C0 behaves as equivalent "negative capacitance."

[0106] In this way, the apparent capacitance when capacitance correction of C0 is performed is referred to as "equivalent capacitance Cx." (It may also be referred to as equivalent capacitance Cx when capacitance correction of C0 is not performed.)

[0107] Hereinafter, the capacitance correction amount for the damping capacitance C0 will be simply referred to as the "correction amount." Also, decreasing the capacitance value of Cx will be referred to as "increasing the correction amount," and increasing the capacitance value of Cx will be referred to as "decreasing the correction amount." (When Cx is a negative capacitance, increasing the absolute value of the capacitance value of Cx will be referred to as "increasing the correction amount," and decreasing the absolute value of the capacitance value of Cx will be referred to as "decreasing the correction amount.")

[0108] When the signal input and gain control input of a variable gain circuit are both analog signals, an analog multiplier can be used as an example of a variable gain circuit. When both the signal input and gain control input are digital signals, a digital multiplier can be used as an example. When the signal input of a variable gain circuit is an analog signal and the gain control input is a digital signal, a multiplying DA converter can be used as an example.

[0109] When the input and output of an adding / subtracting circuit are analog signals, an analog adder (for example, an inverting adder circuit using an operational amplifier) ​​can be used, and when the input and output are digital signals, a digital adder can be used. When the input and output are a mixture of analog and digital signals, AD conversion or DA conversion can be performed as appropriate.

[0110] The correction capacitor Cc in FIG. 1 of Patent Document 1 corresponds to the capacitor C and resistor R in the differential circuit in FIG. 6(A), and the variable gain amplifier circuit 46 corresponds to the variable gain circuit in FIG. 6(A). However, in reality, there is no component equivalent to the resistor R in the differential circuit in FIG. 6(A), and R is infinite, resulting in a configuration equivalent to a complete differential circuit. For this reason, as can be seen from FIG. 6(B), the gain G increases with increasing frequency up to frequencies much higher than the frequencies actually used (theoretically, up to an infinite frequency). As a result, external noise such as radio waves and harmonic components of the vibrator drive signal, which are higher in frequency than the frequencies actually used, are amplified to a greater extent, resulting in errors.

[0111] In the present invention, to avoid such problems, an imperfect differentiating circuit is intentionally used to prevent unintentional large amplification of frequency components higher than the frequency actually used. The frequency (ω=1 / RC in FIG. 6(B) and ω=1 / Rin·C in FIG. 6(D)) that is the reference boundary for operation as a differentiating circuit is preferably, for example, several times to several tens of times the frequency actually used, but is not limited to this.

[0112] When implementing a differentiation circuit using a digital circuit, it is sufficient to use the difference between the sampled data at a certain point in time and the sampled data immediately before for the voltage signal Vf and the current signal If. However, since this will operate as a perfect differentiation, it is preferable to appropriately filter out components above the frequency that is the boundary for operation as a differentiation circuit, thereby converting them into an imperfect differentiation.

[0113] <2. Effect of the capacitance of the equivalent capacitance Cx on the anti-resonance frequency fa' etc.>

[0114] In the present invention, the damping capacitance C0 is corrected so that one selected from the anti-resonance frequencies fa' becomes the desired frequency, so the influence of the capacitance of the equivalent capacitance Cx on the anti-resonance frequency fa' will be explained.

[0115] As mentioned above, the anti-resonance frequency fa' is a general term for the frequency at which the phase becomes zero when the phase decreases as the frequency increases, so in the following explanation of the frequency characteristics of phase and impedance, we will focus on the phase and, as a general rule, omit explanations of the frequency characteristics of impedance.

[0116] <2-1. When there is no other vibration mode>

[0117] First, the influence of the capacitance of the equivalent capacitance Cx when the vibrator does not have another vibration mode will be described.

[0118] Figures 7(A) to 7(C) show the frequency characteristics of impedance and phase when capacitance compensation for C0 is performed on the equivalent circuit of Figure 3(A). Figure 7(A) shows the results when the equivalent capacitance Cx is 3000 pF (no capacitance compensation for C0), 200 pF, and 0 pF. Figure 7(B) shows the results when the equivalent capacitance Cx is 0 pF, -200 pF, and -3000 pF. Figure 7(C) shows the results when the equivalent capacitance Cx is 0 pF, but over a wider frequency range.

[0119] In Figure 7(A), Cx=3000pF has a phase peak just above 30.0kHz, and Cx=200pF has fa' just above 30.8kHz. Cx=0pF approaches approximately -90° below 30kHz and approaches approximately +90° above 30kHz.

[0120] In Figure 7(B), Cx=-3000pF has a phase dip just under 30.0kHz, and Cx=-200pF has fa' just under 29.2kHz. Cx=0pF approaches approximately -90° below 30kHz and approaches approximately +90° above 30kHz.

[0121] Figure 7(C) shows the frequency characteristics when Cx = 0 pF, with a wide frequency range (horizontal axis) and a logarithmic display. Even over a wider frequency range, it can be seen that the angle remains approximately -90° below 30 kHz and approximately +90° above 30 kHz. When Cx = 0 pF, the series resonant frequency fs = resonant frequency fr = 30 kHz, and the impedance at this point is 300 Ω (the value of R1).

[0122] When the vibrator does not have another vibration mode, the results shown in Table 1 can be seen from FIGS. 7(A) to 7(C).

[0123] When Cx>0, "small correction amount" indicates that the correction amount is small and Cx is close to C0, while "increasing correction amount" indicates that the correction amount increases and Cx approaches 0pF. Also, when Cx<0, "small correction amount" indicates that the correction amount is slightly larger than the amount that would result in Cx being 0pF, and Cx is a negative value close to 0pF, while "increasing correction amount" indicates that the correction amount increases and the negative value (absolute value) of Cx increases. (The same applies to the following tables.)

[0124] [Table 1]

[0125] <2-2.If there is another vibration mode with a higher frequency than fr>

[0126] Next, the influence of the capacitance of the equivalent capacitance Cx when the vibrator has another vibration mode with a frequency higher than the resonance frequency fr will be described.

[0127] Figure 8(A) is an example of an equivalent circuit when there is another vibration mode (due to L2, C2, and R2) with a frequency higher than the resonance frequency fr. Since inductor L2 has half the inductance of inductor L1, there is a series resonance frequency of another vibration mode (approximately 42.4 kHz) that is √2 times the series resonance frequency fs of the main resonance.

[0128] Figures 8(B) and 8(C) show the frequency characteristics of impedance and phase when capacitance compensation for C0 is performed on the equivalent circuit of Figure 8(A). Figure 8(B) shows the results when the equivalent capacitance Cx is 3000 pF (no capacitance compensation for C0), 200 pF, and 0 pF. Figure 8(C) shows the results when the equivalent capacitance Cx is 0 pF, -200 pF, and -3000 pF. (In particular, when Cx is ±3000 pF, there are times when the phase does not cross 0°. In such cases, for the sake of convenience, the anti-resonance frequency, e.g., fa', will refer to the center of the frequency range where the phase decreases as the frequency increases, and this will also apply hereinafter.)

[0129] In Figure 8(B), Cx=3000pF has phase peaks at just over 30.0kHz and just under 42.5kHz, Cx=200pF has fa' at just over 30.7kHz and just over 43.6kHz, and Cx=0pF has fa' at just over 34.6kHz.

[0130] In Figure 8(C), Cx=-3000pF has phase dips at slightly less than 30.0kHz and slightly more than 42.4kHz, Cx=-200pF has fa' at slightly less than 29.1kHz and slightly more than 41.3kHz, and Cx=0pF has fa' at slightly more than 34.6kHz.

[0131] When the vibrator has another vibration mode with a frequency higher than the resonant frequency fr, the results shown in Table 2 can be seen from FIGS. 8(B) and 8(C).

[0132] [Table 2]

[0133] <2-3. When there is another vibration mode with a frequency lower than the resonance frequency fr>

[0134] The influence of the capacitance of the equivalent capacitance Cx when the vibrator has another vibration mode with a frequency lower than the resonance frequency fr will be described.

[0135] Figure 9(A) is an example of an equivalent circuit when there is another vibration mode (due to L9, C9, and R9) with a frequency lower than the resonance frequency fr. Since C9 has twice the capacitance of C1, there is a series resonance frequency of another vibration mode (approximately 21.2 kHz) that is √2 of the series resonance frequency fs of the main resonance.

[0136] Figures 9(B) and 9(C) show the frequency characteristics of impedance and phase when capacitance compensation for C0 is performed for the equivalent circuit of Figure 9(A). Figure 9(B) shows the results when the equivalent capacitance Cx is 3000 pF (no capacitance compensation for C0), 200 pF, and 0 pF. Figure 9(C) shows the results when the equivalent capacitance Cx is 0 pF, -200 pF, and -3000 pF.

[0137] In Figure 9(B), Cx=3000pF has phase peaks at just under 21.2kHz and just over 30.0kHz, Cx=200pF has fa' at just over 22.2kHz and just under 30.9kHz, and Cx=0pF has fa' at just under 26.0kHz.

[0138] In Figure 9(C), phase dips at just under 21.2 kHz and just under 30.0 kHz are present when Cx=-3000 pF, fa' at just under 19.9 kHz and just under 29.3 kHz is present when Cx=-200 pF, and fa' at just under 26.0 kHz is present when Cx=0 pF.

[0139] When the vibrator has another vibration mode with a frequency lower than the resonant frequency fr, the results shown in Table 3 can be seen from FIGS. 9(B) and 9(C).

[0140] [Table 3]

[0141] <2-4. When there are other vibration modes at frequencies both higher and lower than the resonance frequency fr>

[0142] A brief description will be given of the effect of the capacitance of the equivalent capacitance Cx when the vibrator has both other vibration modes at frequencies higher and lower than the resonance frequency fr.

[0143] 10(A) shows an example of an equivalent circuit having both another vibration mode (due to L2, C2, and R2) with a higher frequency than the resonance frequency fr and another vibration mode (due to L9, C9, and R9) with a lower frequency than the resonance frequency fr. The series resonance frequency of the other vibration mode is √2 times the series resonance frequency fs of the main resonance (approximately 42.4 kHz), and the series resonance frequency of the other vibration mode is √1 / √2 of fs (approximately 21.2 kHz).

[0144] Figures 10(B) and 10(C) show the frequency characteristics of impedance and phase when capacitance compensation for C0 is performed on the equivalent circuit of Figure 10(A). However, because the horizontal axis (frequency) range is wider than Figure 8(B) and others, they are displayed logarithmically over one decade. Figure 10(B) shows the results when the equivalent capacitance Cx is 3000 pF (no compensation for C0), 200 pF, and 0 pF. Figure 10(C) shows the results when the equivalent capacitance Cx is 0 pF, -200 pF, and -3000 pF.

[0145] FIG. 10(B) can be considered as a combination of FIG. 8(B) and FIG. 9(B), and FIG. 10(C) can be considered as a combination of FIG. 8(C) and FIG. 9(C), so further explanation will be omitted.

[0146] <2-5. Selection of anti-resonance frequency fa'>

[0147] Here, the concept of selecting a desired anti-resonance frequency fa' will be explained.

[0148] First, what can be seen from the examples of impedance and phase frequency characteristics in 2-1. to 2-3. above can be summarized with reference to Tables 1 to 3 as follows: When the value of Cx is zero: The highest anti-resonance frequency fa' does not occur, and the resonance frequency fr and the series resonance frequency fs coincide. (The resonance frequency fr' of another vibration mode also coincides with its series resonance frequency fs'.) The anti-resonance frequency fa' between the resonance frequencies fr' is an intermediate frequency. When the value of Cx is not zero: Increasing the amount of correction increases the anti-resonance frequency fa', and decreasing the amount of correction decreases the anti-resonance frequency fa'.

[0149] If, even temporarily, the output frequency of the vibrator drive PLL becomes farther from the resonance frequency fr than the anti-resonance frequency fa' due to external noise or the like, the vibrator drive PLL will be unable to lock onto the resonance frequency fr. (As a specific example of this, if the output frequency of the vibrator drive PLL temporarily becomes even higher than the anti-resonance frequency fa of the main resonance, the phase will become negative. When the phase is negative, the vibrator drive PLL operates to increase the frequency, so the frequency of the vibrator drive PLL will increase as much as possible.)

[0150] In other words, the farther the anti-resonance frequency fa' is from the resonance frequency fr, the better. Therefore, the correction amount of the damping capacitance C0 is adjusted so that both the anti-resonance frequency fa' with a lower frequency than the resonance frequency fr and the anti-resonance frequency fa' with a higher frequency are sufficiently far away from the resonance frequency fr. (When only an anti-resonance frequency fa' with a high or low frequency exists, the anti-resonance frequency fa' is made sufficiently far away from the resonance frequency fr.) If the capacitance value of Cx after correction is close to zero, the resonance frequency fr and the series resonance frequency fs can be made closer, so the correction amount should be adjusted taking this into consideration, if necessary.

[0151] Specifically, first measure the impedance and phase characteristics of the vibrator to be used using an impedance analyzer or similar. Based on the results of this measurement, and taking into account what can be seen from the example of impedance and phase frequency characteristics above, adjust the correction amount for the damping capacitance C0 so that the anti-resonance frequency fa' is as far away as necessary from the resonance frequency fr. This allows the vibrator driving PLL to stably lock onto the resonance frequency fr.

[0152] When the capacitance value of Cx after correction is negative, or when there is another vibration mode with a frequency lower than the resonance frequency fr, an anti-resonance frequency fa' lower than the resonance frequency fr occurs. In such cases, the fa' must also be set as far away as necessary from the resonance frequency fr.

[0153] As one example, if the relationship between the VCO's control voltage and frequency is linear, it is preferable to make the frequency difference between the higher fa' and fr and the frequency difference between fr and the lower fa' approximately the same. As another example, if the relationship between the VCO's control voltage and frequency is logarithmic, it is preferable to make the frequency ratio between the higher fa' and fr and the frequency ratio between fr and the lower fa' approximately the same. As yet another example, if the relationship between the VCO's control voltage and frequency is a different functional relationship, that functional relationship should be taken into consideration so that both fa' are as far away as necessary from the resonant frequency fr. These are all examples, and the present invention is not limited to these.

[0154] The anti-resonance frequency fa' selected as the target to be moved away from the resonance frequency fr as much as necessary will be referred to as the "selected anti-resonance frequency fa". (When there are both higher and lower fa's relative to the resonance frequency fr, one of them will be selected.) The frequency obtained by adjusting the correction amount of the damping capacity C0 to move the selected anti-resonance frequency fa" away from the resonance frequency fr as much as necessary will be referred to as the "target frequency f CAL "

[0155] FIG. 11 shows an example in which Cx=-38.4 pF in the circuit of FIG. 8(A). In this case, the anti-resonance frequency fa is approximately 38.1 kHz, and the anti-resonance frequency fa' lower than the resonance frequency fr is approximately 21.9 kHz, i.e., 30 kHz ± approximately 8.1 kHz of the resonance frequency fr. This is a suitable example when the relationship between the VCO control voltage and frequency is linear. In this example, there are two anti-resonance frequencies fa', namely the anti-resonance frequency fa and the low anti-resonance frequency fa', and one is selected from the existing anti-resonance frequencies fa' and set as the selected anti-resonance frequency fa". In this example, the frequency change with respect to the change in Cx is larger for the low anti-resonance frequency fa' than for the anti-resonance frequency fa, so this can be taken into consideration when making the selection. When the anti-resonance frequency fa higher than the resonance frequency fr is set as the selected anti-resonance frequency fa", the target frequency f CAL is 38.1kHz, the low anti-resonance frequency fa' is the selected anti-resonance frequency fa'', and the target frequency f CAL is 21.9kHz.

[0156] Generally, resonators are manufactured so that the resonant frequency fr and the series resonant frequency fs are close to the rated frequency, so there is little error in the values ​​of the series LC (L1 and C1 in Figure 3(A)). In contrast, the value of the damping capacitance (C0 in Figure 3(A)) generally varies widely.

[0157] Therefore, to cancel the value of the damping capacitance, it is necessary to measure the capacitance value of the damping capacitance, which differs for each vibrator, and to adjust the amount of capacitance correction each time the vibrator is replaced.

[0158] In contrast, in the present invention, as will be described later, the selected anti-resonance frequency fa" is the target frequency f CAL Therefore, regardless of the magnitude of the capacitance value of C0 before correction, Cx after correction can be made approximately constant. Therefore, the present invention has the advantageous effect of being almost completely unaffected by variations in the damping capacitance C0.

[0159] As a more specific example, the target frequency f CALWhen the selected anti-resonance frequency fa” is a frequency equivalent to Cx=0pF, no matter what pF the damping capacitance C0 before correction is (for example, whether C0 is 3000pF, 3100pF, or 2900pF), the selected anti-resonance frequency fa” is the target frequency f CAL Therefore, even if there is a large variation in the damping capacity C0 before correction, there is an advantageous effect that the effect is hardly felt.

[0160] <3. How to correct braking capacity C0>

[0161] A method of correcting the damping capacitance C0 so that the selected anti-resonance frequency fa'' becomes a desired frequency will be described.

[0162] <3-1. Overview of the braking capacity C0 correction method>

[0163] First, an outline of a method for correcting the damping capacitance C0 so that the selected anti-resonance frequency fa'' becomes a desired frequency will be described.

[0164] FIG. 12 is a flowchart showing an outline of a method for correcting the damping capacitance C0 so that the selected anti-resonance frequency fa'' becomes a desired frequency.

[0165] First, the correction amount of the damping capacity C0 is initialized. The initial value of the correction amount is set to the target frequency f CAL However, the initial value may be shifted by an appropriate amount as needed. (Examples of the contents that require initialization other than the correction amount will be described later.)

[0166] Next, start the PLL operation. In principle, the target frequency f CAL It is preferable to start the PLL at the target frequency f CAL (For ease of understanding, in Figure 12, "f CALIn some cases, as will be explained later, the PLL output frequency may be higher than the target frequency f CAL In some cases, the system may remain forced to

[0167] After the time required for PLL operation has elapsed, the selected anti-resonance frequency fa” and the target frequency f CAL Check the frequency relationship of (f CAL There is also a method for checking the relationship between high and low frequencies.) Any method can be used to check the relationship between high and low frequencies, and some examples will be described later.

[0168] The selected anti-resonance frequency fa” and the target frequency f CAL If they match, the amount of correction for the braking capacity C0 at that time was appropriate, so that correction amount is the result. Here, fa" and f CAL The "match" does not have to be a perfect match, for example, fa" and f CAL A difference equal to or less than the measurement resolution may be regarded as a match, or a difference within a predetermined range may be regarded as a match.

[0169] The anti-resonance frequency fa is the target frequency f CAL If it is lower than , increase the correction amount of the damping capacity C0. As mentioned above, increasing the correction amount increases the anti-resonance frequency fa', so increase the selected anti-resonance frequency fa" to reach the target frequency f CAL Conversely, if the anti-resonance frequency fa” is close to the target frequency f CAL If it is higher than the reference value, the correction amount of the braking capacity C0 is reduced. The method for increasing or decreasing the correction amount is arbitrary, and some detailed examples will be described later.

[0170] If the predetermined requirements are not met, the above procedure is repeated.

[0171] Once the amount of C0 correction has been determined, if necessary, such as if some settings or circuits have been changed to correct C0, then perform termination processing so that the PLL can operate as a vibrator drive PLL. (Examples of the content requiring termination processing will be described later.)

[0172] Figure 13 shows the relationship between fa” and f CAL 11 and its explanation, the anti-resonance frequency fa' lower than the resonance frequency fr is set as the selected anti-resonance frequency fa".

[0173] The solid line plot in Figure 13 is for Cx = -38.4 pF, and the target frequency f CAL is 21.934 kHz, which is a higher resolution than that described in FIG. 11, and the phase at this time is 0°.

[0174] The dashed line plot in Figure 13 is when Cx = -37.4 pF, and the selected anti-resonance frequency fa" at this time is 21.582 kHz and the target frequency f CAL lower than f CAL In this case, the phase must be increased to approach the solid line plot.

[0175] The dashed line plot in Figure 13 is when Cx = -39.4 pF, and the selected anti-resonance frequency fa" at this time is 22.260 kHz and the target frequency f CAL higher than f CAL In this case, the correction amount must be reduced to bring the plot closer to the solid line.

[0176] fa” and f CAL After checking the relationship between the high and low frequencies of fa and f, it is checked whether the specified requirements are met. If the specified requirements are met, the amount of correction for C0 is determined. If the specified requirements are not met yet, the amount of correction is increased or decreased and the process returns to the start of PLL operation. Here, the "specified conditions" are arbitrary, but for example, fa" and f CAL The condition may be that the difference between the two is within a predetermined range, or that a predetermined number of repetitions is set as a condition. Also, when the predetermined requirements are met, if there is no need to increase or decrease the amount of correction immediately before (for example, if fa" and f CALIf the difference is within a predetermined range, the previous correction may be undone and the process may be terminated.

[0177] Once the amount of correction for C0 has been determined, if necessary, such as if some settings or circuits have been changed to correct C0, then perform termination processing so that the PLL can operate as a vibrator drive PLL. (Examples of the contents requiring termination processing will be described later.)

[0178] This kind of "fa" to f CAL For example, the following timings are possible for performing an operation to bring the camera closer to the target. When replacing the vibrator (to absorb the difference in damping capacity C0 between vibrators). When the vibrator starts to drive. (To absorb the change over time in the damping capacitance C0. For example, the damping capacitance C0 of the vibrator may change due to changes in the ambient temperature or the temperature rise of the vibrator when it is driven. Therefore, when the vibrator is driven intermittently, fa" is set to f CAL )

[0179] <3-2.fa” and f CAL Check the frequency relationship

[0180] Next, compare the selected anti-resonance frequency fa with the target frequency f CAL Specific examples of methods for checking the relationship between the high and low frequencies will be described below, but the present invention is not limited to these methods.

[0181] <3-2-1. Direction of change in output frequency>

[0182] The selected anti-resonance frequency fa” and the target frequency f CAL As an example of a method for checking the high / low relationship of the frequencies, the direction of change in the output frequency after the PLL operation starts can be used.

[0183] More specifically, the PLL synchronizes to the target frequency f CALIf the PLL output frequency increases after starting operation from fa, it means that the starting phase is a negative value and the amount of correction needs to be increased. <f CAL Conversely, when the PLL output frequency drops, the starting phase is a positive value, which means that the amount of correction needs to be reduced, so fa”>f CAL It can be determined that:

[0184] More specific detailed examples for finding the direction of frequency change of the PLL output frequency are given below, but the present invention is not limited to these.

[0185] <3-2-1-1.f CAL How to know when ±Δf is reached>

[0186] The output frequency of the PLL is f CAL If it reaches or becomes higher than +Δf, fa” <f CAL It is judged that f CAL -When Δf is reached or falls below fa”>f CAL Here, +Δf and -Δf are arbitrary frequency differences, and their absolute values ​​may differ. It is preferable that +Δf and -Δf are both small frequencies, but if they are too small, there is a risk of malfunction.

[0187] Specifically, using a frequency comparison means, f CAL +Δf or f CAL It is enough to detect when -Δf is reached or exceeded. CAL +Δf and f CAL −Δf is set in “Initialization of correction amount, etc.” in FIG.

[0188] More specifically, a means for measuring the frequency of the PLL output (Vo), such as a frequency counter, and a CAL +Δf or f CAL A frequency comparison means can be used to detect when -Δf is reached or exceeded. When a VCO is used, a voltage comparison means (comparator) is used as the frequency comparison means to detect when the VCO control voltage is f CAL+Δf equivalent voltage or f CAL The voltage comparison means can also detect whether a voltage equivalent to -Δf has been reached or exceeded. If a digital NCO is used, the frequency setting data for the NCO can be used to set f CAL +Δf or f CAL It is possible to detect when -Δf is reached or exceeded.

[0189] If necessary, the operation of the frequency measuring means and frequency comparing means is terminated as a termination process.

[0190] <3-2-1-2. How to repeatedly measure frequency>

[0191] By repeatedly measuring the frequency of the PLL output (Vo), it is possible to directly determine the direction of change in the PLL output frequency within a specified time after the PLL operation starts. (As an example, the relationship between the elapsed time and the PLL output frequency can be linearly interpolated, and the direction of change can be determined by the positive or negative slope of the line.) If the output frequency increases, fa <f CAL If it goes down, fa”>f CAL It can be determined that:

[0192] The specific frequency measurement means is arbitrary. A frequency counter for measuring the output frequency of the PLL may be used, or a voltage measurement means for measuring the control voltage of the VCO may be used to determine the direction of change in the output frequency based on the measured voltage, or if a digital NCO is used, the frequency setting value of the NCO may be used to determine the direction of change in the output frequency (similarly hereinafter).

[0193] If necessary, the operation of the frequency measuring means is terminated as a termination process.

[0194] <3-2-2. PLL that locks at anti-resonance frequency fa' etc.>

[0195] The selected anti-resonance frequency fa” and the target frequency f CALAs another example of a method for checking the high-low relationship of the frequencies, the PLL can be temporarily changed so that it locks at the anti-resonance frequency fa', and the frequency of the selected anti-resonance frequency fa'' can be directly determined.

[0196] The vibrator driving PLL increases the frequency when the phase is negative and decreases the frequency when the phase is positive, thereby matching the phases of the voltage signal Vf and the current signal If and locking to the resonant frequency fr', etc. If such a PLL is modified to increase the frequency when the phase is positive and decrease the frequency when the phase is negative, it will lock to the anti-resonant frequency fa', etc.

[0197] A more specific example of such a PLL modification is to invert the phase of either the voltage signal Vf or the current signal If, or to swap the connections of the voltage signal Vf and the current signal If. (When an RS-FF is used as the PLL phase comparator, as mentioned above, an inverting circuit that shifts the phase by 180° is often used in conjunction with either Vf or If and the phase comparator, but this inverting circuit can be bypassed or changed to a non-inverting circuit.)

[0198] If the frequency of the anti-resonance frequency fa selected by changing the PLL can be directly known using a frequency measurement means, the target frequency f CAL You can easily find out the difference between high and low.

[0199] In this method, the function is changed so that the PLL is locked at the anti-resonance frequency fa' as an initialization, and the function is returned to the state where the PLL is locked at the resonant frequency fr as a termination process.

[0200] <3-2-3. Duty ratio of phase comparator output>

[0201] The selected anti-resonance frequency fa” and the target frequency f CAL As another example of how to check the high / low relationship of the frequencies, we can forcibly set the PLL to the target frequency f CALAnother method is to operate the circuit at 100 Hz and check the duty ratio of the phase comparator output.

[0202] If a digital circuit such as an XOR or RS-FF is used as the phase comparator, knowing whether the duty ratio of its output is higher or lower than 50% will tell you whether the PLL output frequency is being increased or decreased.

[0203] Assuming that increasing the VCO control voltage increases the VCO output frequency, when the duty ratio of the phase comparator output is lower than 50%, the target frequency f CAL The phase at is negative, which means we are trying to increase the PLL output frequency, so fa <f CAL Conversely, when the duty ratio of the phase comparator output is higher than 50%, the target frequency f CAL The phase at is positive, which means that we are trying to decrease the PLL output frequency, so fa”>f CAL Therefore, the amount of correction can be reduced.

[0204] When the duty ratio of the phase comparator output is 50%, the amount of correction at that time is appropriate, and fa” = f CAL Here, the duty ratio being 50% does not necessarily have to be exactly 50%, and it may be 50% when the difference is less than or equal to the measurement resolution of the duty ratio, or it may be 50% if it is within a predetermined range of difference.

[0205] As a specific means for determining the duty ratio, for example, the duty ratio may be calculated by measuring the high level and low level times of the phase comparator output, or by calculating the high level or low level times and the target frequency f CAL Alternatively, the duty ratio can be calculated from the average voltage by passing the output of the phase comparator through a low-pass filter, but the present invention is not limited to these.

[0206] This method forces the PLL to synchronize to the desired frequency f CAL As a finalization step, the PLL is forced to operate at the target frequency f CAL The function is returned to locking at the resonance frequency fr, and if necessary, the means for determining the duty ratio is stopped.

[0207] <3-3. Increasing or decreasing the amount of correction>

[0208] The selected anti-resonance frequency fa” and the target frequency f CAL After checking the high-low relationship of the frequencies, specific examples of methods for increasing or decreasing the amount of correction will be described, but the present invention is not limited to these methods.

[0209] <3-3-1. Increasing or decreasing the fixed correction amount>

[0210] First, select the anti-resonance frequency fa and the target frequency f CAL A method of increasing or decreasing a certain amount of correction each time until the high-low relationship of the frequencies is reversed will be described. Fig. 14(A) shows an example of this method.

[0211] After initializing the correction amount of the braking capacity C0, first fa” and f CAL When checking the frequency relationship, fa”>f CAL If so, the correction amount needs to be reduced. The correction amount (initial value) at this time is O, which corresponds to the number of repetitions = 1 in Figure 14(A), and the correction amount is reduced by a certain amount each time thereafter. When the number of repetitions reaches 8, <f CAL Since the condition is reversed to , it is determined that the specified requirements are met, and the correction value at that time is fa” = f CAL (In the flowchart of FIG. 12, the correction amount is further reduced at the final iteration, so the reduction in the correction amount must be restored before the end.)

[0212] Conversely, if we start from the initial state, <f CALIf so, the correction amount needs to be increased. The correction amount (initial value) at this time is △, which corresponds to the number of repetitions = 1 in Figure 14(A), and a certain amount of correction is increased each time thereafter. When the number of repetitions reaches 8, fa” > f CAL Since the condition is reversed to , it is determined that the specified requirements are met, and the correction value at that time is fa” = f CAL (Similarly, in the flowchart of FIG. 12, the final increase in the correction amount must be restored before the end.)

[0213] In this method, fa”=f CAL The resulting correction value will have an error of less than the fixed correction amount each time. To make the maximum error smaller, the fixed correction amount each time can be reduced. Another method is to use fa” and f CAL After the relationship is reversed, the correction amount can be increased or decreased again in the opposite direction, with smaller correction amounts each time. However, in either case, the number of iterations will be greater and it will take longer to achieve the final result.

[0214] <3-3-2. Binary Exploration>

[0215] Next, a method of reducing the amount of increase or decrease in the correction amount by half each time (binary search) will be described. Figure 14(B) shows an example of this method.

[0216] After initializing the correction amount of the braking capacity C0, first fa” and f CAL When checking the frequency relationship, fa”>f CAL If so, the amount of correction must be reduced. The amount of correction (initial value) at this time is the circle corresponding to the number of repetitions = 1 in Figure 14(A), and the amount of correction to be reduced when the number of repetitions changes from 1 to 2 is 1 (4 divisions on the vertical axis in Figure 14(B)).

[0217] When the number of repetitions is 2, fa” <f CALTherefore, the amount of correction must be increased. When the number of repetitions changes from 2 to 3, the amount of correction to be increased is half of the previous amount, 0.5 (two vertical scales in Figure 14(B)). In the subsequent repetitions, the amount of correction increases similarly to fa" and f CAL The amount of correction is increased or decreased depending on the frequency of the signal, and each time the amount of correction is increased or decreased is half of the previous amount. (In the flowchart of Figure 12, the amount of correction is further increased or decreased in the final repetition of 8, so the amount of correction must be returned to its original value before the process ends.)

[0218] According to this method, the more iterations you do, the more the final correction value becomes fa” = f CAL However, if the number of repetitions is increased too much, it will take a long time to obtain the final result, so an appropriate number of repetitions should be set as a predetermined requirement.

[0219] fa” and f CAL In checking the frequency relationship between fa and f CAL If the frequency difference between the two frequencies can be known, it is also possible to set the predetermined requirement that the frequency difference be equal to or less than a predetermined value. Furthermore, it is also possible to set the predetermined requirement as the OR of the frequency difference being equal to or less than a predetermined value and the number of repetitions.

[0220] <3-3-3. Method using the relationship between the amount of correction and the amount of frequency change>

[0221] In the above 2-4., the selected anti-resonance frequency fa” and the target frequency f CAL When determining the target frequency f, it is also possible to use the relationship between the change in the capacitance value of Cx after correction and the selected anti-resonance frequency f a ”. (In the example of FIG. 13, f a ” is 21.582 kHz when Cx=−37.4 pF, and fa ” is 21.582 kHz when Cx=−38.4 pF.) CAL The relationship is -352Hz / pF. Also, when Cx=-39.4pF, the fa" of 22.260kHz is calculated, and the relationship is -326Hz / pF. As an example, let's assume a linear relationship and calculate the target frequency f CALThe relationship was found for one frequency point above and one above, but it is possible to find a more accurate relationship by finding the relationship for more frequencies and performing curve interpolation.)

[0222] On the other hand, in the above 3-2-2., the selected anti-resonance frequency fa” can be directly known, so the target frequency f CAL By applying the relationship between the amount of change in the capacitance value of Cx after correction and the selected anti-resonance frequency fa”, the currently selected anti-resonance frequency fa” can be adjusted to the target frequency f CAL (In the example of FIG. 13, when the selected anti-resonance frequency fa is 21.758 kHz, the correction amount for the target frequency f CAL To achieve 21.934 kHz, the frequency difference is 176 Hz, so the correction amount should be reduced by 0.5 pF, taking into account -352 Hz / pF.)

[0223] In the next iteration, fa” and f CAL When the relationship between the frequency difference and the frequency of the signal is found, if the frequency difference is within a predetermined range, the predetermined requirement is satisfied and the process ends. If the frequency difference exceeds the predetermined range, the process can be repeated to reduce the frequency difference.

[0224] <4. When another vibration mode exists near fr>

[0225] The case where another vibration mode exists at a frequency close to fr will be explained.

[0226] <4-1. When another vibration mode exists at a frequency lower than fr> <4-1-1. Frequency characteristics when there is variation in fr>

[0227] As an example, consider a vibrator in which fr varies within 30 kHz±1 kHz and another vibration mode exists at a frequency 0.7 kHz lower than fr.

[0228] Figure 15 shows the frequency characteristics of impedance and phase when fr is set to 29 kHz, 30 kHz, and 31 kHz. fr' for each vibration mode is 28.3 kHz, 29.3 kHz, and 30.3 kHz. The damping capacitance C0 is 3000 pF in both cases.

[0229] The equivalent circuit for each fr in Figure 15 is the same as in Figure 9, where the constants of L1 and C1 when fr is 30 kHz are the same as in Figure 9, and the constants of L9 and C9 were selected so that fr' is 29.3 kHz. The constants of L1 and C1 associated with other frs and the constants of L9 and C9 associated with other vibration modes were each determined by the frequency ratio with respect to the constants at 30 kHz. (For example, when fr is 29 kHz, L1 and C1 were each set to 30 / 29 times the values ​​at 30 kHz.) Also, as in Figure 9, the resistor R1 associated with fr was set to 300 Ω, and the resistor R9 associated with another vibration mode was set to 1 kΩ. This method of determining the constants is the same throughout Section 4, so a detailed explanation will be omitted below.

[0230] <4-1-2. Target frequency f CAL and the frequency at which the PLL starts operating>

[0231] If fr is 30 kHz and there is no variation, for example, if the equivalent capacitance Cx after correction of the damping capacitance C0 is set to 470 pF, the frequency characteristics of impedance and phase will be as shown in Figure 16(A). In this case, the anti-resonance frequency fa' will be about 30 kHz ± 0.5 kHz, so for example, 30.5 kHz can be set as the target frequency f CAL Then, the operation of the PLL for driving the vibrator can be started at around 30 kHz.

[0232] However, when the variation in fr is taken into consideration, the frequency characteristics of impedance and phase when the corrected equivalent capacitance Cx is 470 pF will be as shown in Figure 16(B) when fr is 31 kHz, and as shown in Figure 16(C) when fr is 29 kHz.

[0233] In Figure 16(B), when the PLL starts operating at around 30 kHz, the phase at 30 kHz is a negative value, so the PLL frequency increases, and it locks at a resonant frequency fr' of 30.3 kHz or the like due to another vibration mode.

[0234] On the other hand, if the PLL starts operating at around 30 kHz in Figure 16(C), the phase at 30 kHz is a negative value, so the PLL frequency will increase. If there is no higher resonant frequency, such as fr', the PLL frequency will continue to increase as much as possible.

[0235] That is, when another vibration mode exists at a frequency slightly lower than fr, the PLL for driving the vibrator may not be able to lock onto fr due to variations in fr.

[0236] As an example of a method to prevent such a problem from occurring, a frequency higher than the highest fr within the range of variation is set to the target frequency f CAL At the same time, there is a method of starting the operation of the PLL for driving the oscillator from near the highest fr within the range of variation.

[0237] As a specific example, assuming that the operation of the PLL for driving the oscillator starts from 31 kHz, which is equal to the highest frequency f, the target frequency f CAL The corrected frequency response (three fr values ​​superimposed) when fr is set to 31.5 kHz is shown in Figure 17. (In this case, Cx was approximately 111 pF when fr was 29 kHz, approximately 179 pF when fr was 30 kHz, and approximately 459 pF when fr was 31 kHz.)

[0238] When fr is 31 kHz, the PLL starts operating at 31 kHz and locks quickly. On the other hand, when fr is 30 kHz or 29 kHz, the phase at 31 kHz is positive, so the PLL frequency drops and locks when it reaches fr.

[0239] <4-1-3. Further problems and their solutions>

[0240] In the oscillator driving PLL shown in Figure 5 above or Figure 23 below, when the I'res signal level is small, the signal may be buried in noise. In such a case, the phase information is not transmitted accurately to the phase comparator, causing the PLL to malfunction and making it impossible to lock onto the resonant frequency fr.

[0241] As an example, Figure 18 shows the relationship between the amount of damping capacitance C0 correction and I'res at 31 kHz, when the PLL in Figure 17 starts operating. The horizontal axis represents the value of equation (7) above, with 1 at the far right indicating no damping capacitance C0 correction (Cx = 3000 pF in this example). When the correction amount is increased to 0 in the middle, the equivalent capacitance Cx after correction is zero. When the correction amount is further increased to -1 at the far left, Cx represents a capacitance with the positive and negative polarity of damping capacitance C0 reversed (Cx = -3000 pF in this example). The vertical axis represents the value of I'res, which is converted into a voltage signal or logic signal and then provided to the phase comparator. The vibrator drive voltage Vvib was set to 10 V.

[0242] The top plot in Figure 18 is when fr is 31 kHz, and the left vertical axis is applied. Because L1 and C1 resonate in series at 31 kHz, when the PLL starts operating, the resonator appears to be roughly R1 (300 Ω). The minimum value of I'res is approximately 33.35 mA, which is slightly larger than Vvib: 10 V ÷ R1: 300 Ω ≒ 33.33 mA, and I'res also changes slightly depending on the amount of compensation.

[0243] The bottom two plots in Figure 18 show when fr is 30 kHz (solid line) and 29 kHz (dashed line), and the right vertical axis is applied. I'res becomes zero when the value of equation (7) is just under 0.1 (approximately 0.085 when fr is 30 kHz, and approximately 0.046 when fr is 29 kHz). I'res increases whether the value of equation (7) is above or below that value. Also, the phase of I'res is reversed when the value of equation (7) is above and below that value. (In Figure 18, the value of equation (7) at which I'res becomes zero is relatively close to zero, and the difference between when fr is 30 kHz and when fr is 29 kHz is relatively small. However, these values ​​and differences will vary depending on the target frequency, the presence or absence of fr variation, the presence or absence of other vibration modes, and the frequency difference between fr and other vibration modes.)

[0244] In Figure 17, when fr is 30 kHz, Cx is ≈ 179 pF, and the value of equation (7) is ≈ 0.06, and when fr is 29 kHz, Cx is ≈ 111 pF, and the value of equation (7) is ≈ 0.04. With these values ​​of equation (7), I'res approaches zero in Figure 18, and there is a risk that the PLL may malfunction due to the influence of noise.

[0245] By increasing the correction amount, the target frequency f CAL If I'res is increased above 31.5 kHz, I'res can be made larger. However, the anti-resonance frequency fa' between the resonant frequency fr' of another resonant mode slightly lower than fr and fr approaches fr if the amount of correction is large. (See Figure 9 and its explanation above.) If fa' is too close to fr, the PLL may lose lock due to the transient response when locking to fr or the effects of noise after locking to fr.

[0246] In order to solve this problem, the present invention can take the following measures. When starting the PLL operation, the correction amount is temporarily increased to increase I'res (the anti-resonance frequency fa becomes higher than 31.5kHz). ◎When the PLL is locked, return to the original correction amount (the correction amount from the last time automatic correction was performed). (If the PLL is locked to fr, I'res will increase.) ◎Alternatively, the amount of correction can be gradually or stepwise returned to the original amount of correction between the start of PLL operation and when the PLL is locked. (Even if fa' is too close to fr when the amount of correction is temporarily increased, the amount of correction will be gradually or stepwise reduced, so that fa' will move away from fr by the time the PLL locks.) However, if I'res approaches 0 while gradually or stepwise changing the amount of correction to the original amount of correction, it is desirable to minimize the time during which I'res approaches 0, and it is even better if that time can be reduced to zero. (Methods of gradually or stepwise changing the amount of correction to the original amount of correction include minimizing or zeroing the time during which I'res approaches 0.)

[0247] By adopting this method, it is possible to stably start the operation of the PLL, and after the PLL has locked, it is possible to maintain the locking state stably.

[0248] <4-2.When another vibration mode exists at a frequency higher than fr> <4-2-1. Frequency characteristics when fr varies>

[0249] As an example, consider a vibrator in which fr varies within 30 kHz±1 kHz and another vibration mode exists at a frequency 0.7 kHz higher than fr.

[0250] Figure 19 shows the frequency characteristics of impedance and phase when fr is set to 29 kHz, 30 kHz, and 31 kHz. fr' for each of the different vibration modes is 29.7 kHz, 30.7 kHz, and 31.7 kHz. The damping capacitance C0 is set to 3000 pF for both cases.

[0251] The equivalent circuit at each fr in Figure 19 is the same as that in the above-mentioned Figure 8. The only difference between Figure 19 and Figure 15 is whether another vibration mode exists at a frequency higher or lower than fr, so further explanation will be omitted.

[0252] <4-2-2. Target frequency f CAL and the frequency at which the PLL starts operating>

[0253] As an example, the frequency characteristics of impedance and phase at fr of 30 kHz, 31 kHz, and 29 kHz when the equivalent capacitance Cx after correction for the damping capacitance C0 is set to -470 pF are shown in Figures 20(A), 20(B), and 20(C), respectively. Even if another vibration mode exists at a frequency slightly higher than fr, variations in fr may prevent the vibrator driving PLL from locking to fr.

[0254] As an example of a method for starting the PLL operation stably when fr has such a variation, a frequency lower than the highest fr within the range of the variation can be set as the target frequency f CAL At the same time, there is a method of starting the operation of the PLL for driving the vibrator from near the lowest fr within the range of variation.

[0255] As a specific example, assuming that the operation of the PLL for driving the oscillator starts from 29 kHz, which is equal to the lowest frequency f CAL FIG. 21 shows the frequency response after correction (three fr values ​​superimposed) when is set to 28.5 kHz.

[0256] When fr is 29 kHz, starting the PLL operation from 29 kHz will lock quickly. On the other hand, when fr is 30 kHz or 31 kHz, the phase at 29 kHz is negative, so the PLL frequency rises and locks when it reaches fr.

[0257] <4-2-3. Further problems and their solutions>

[0258] In the oscillator driving PLL shown in Figure 5 above or Figure 23 below, when the I'res signal level is small, the signal may be buried in noise. In such a case, the phase information is not transmitted accurately to the phase comparator, causing the PLL to malfunction and making it impossible to lock onto the resonant frequency fr.

[0259] As an example, Figure 22 shows the relationship between the amount of damping capacitance C0 correction and I'res at 29 kHz, when the PLL in Figure 21 starts operating. The horizontal axis represents the value of equation (7) above, with 1 at the far right indicating no damping capacitance C0 correction (Cx = 3000 pF in this example). When the correction amount is increased to 0 in the middle, the equivalent capacitance Cx after correction is zero. When the correction amount is further increased to -1 at the far left, Cx represents a capacitance with the positive and negative polarity of damping capacitance C0 reversed (Cx = -3000 pF in this example). The vertical axis represents the value of I'res, which is converted into a voltage signal or logic signal and provided to the phase comparator. The vibrator drive voltage Vvib was set to 10 V.

[0260] The top plot in Figure 22 is when fr is 29 kHz, and the left vertical axis is applied. Because L1 and C1 resonate in series at 29 kHz, when the PLL starts operating, the resonator appears to be roughly R1 (300 Ω). The minimum value of I'res is approximately 33.35 mA, which is slightly larger than Vvib: 10 V ÷ R1: 300 Ω ≒ 33.33 mA, and I'res also changes slightly depending on the amount of compensation.

[0261] The bottom two plots in Figure 22 show when fr is 30 kHz (solid line) and 31 kHz (dashed line), and the right vertical axis is applied. I'res becomes zero when the value of equation (7) is just over -0.1 (approximately -0.089 when fr is 30 kHz, approximately -0.050 when fr is 31 kHz), and I'res increases whether the value of equation (7) is above or below that value. Furthermore, the phase of I'res is reversed when the value of equation (7) is above and below that value.

[0262] In Figure 21, when fr is 30 kHz, Cx is approximately -189 pF, and the value of equation (7) is approximately -0.06, and when fr is 31 kHz, Cx is approximately -122 pF, and the value of equation (7) is approximately -0.04. With these values ​​of equation (7), I'res approaches zero in Figure 22, and there is a risk that the PLL may malfunction due to the influence of noise.

[0263] The correction amount is reduced to the target frequency f CAL If I'res is set lower than 28.5 kHz, I'res can be made larger. However, the half-resonant frequency fa between fr' and fr, such as the resonant frequency of another vibration mode slightly higher than fr, approaches fr if the amount of correction is small. (See Figure 8 and its explanation above.) If fa is too close to fr, the PLL may lose lock due to the transient response when locking to fr or the effects of noise after locking to fr.

[0264] In order to solve this problem, the present invention can take the following measures. When starting PLL operation, temporarily reduce the amount of correction to increase I'res (the anti-resonance frequency fa' becomes lower than 28.5kHz). ◎When the PLL is locked, return to the original correction amount (the correction amount from the last time automatic correction was performed). (When the PLL is locked, I'res will increase.) ◎Alternatively, the correction amount can be gradually or stepwise returned to the original correction amount between the start of PLL operation and when the PLL is locked. (Even if fa is too close to fr when the correction amount is temporarily reduced, the correction amount will be gradually or stepwise reduced, so by the time the PLL locks, fa will be farther away from fr.) However, when I'res passes near 0 while the correction amount is gradually or stepwise changed back to the original correction amount, it is desirable to minimize the time that I'res is near 0, and it is even better if that time can be reduced to zero. By adopting this method, it is possible to stably start the operation of the PLL, and after the PLL has locked, it is possible to maintain the locking state stably.

[0265] <5. Inductance correction of parallel inductor Lp>

[0266] The inductance correction of the parallel inductor Lp connected in parallel with the vibrator will be described.

[0267] <5-1. Inductance compensation circuit>

[0268] First, the circuit for inductance correction will be described.

[0269] FIG. 23 shows an example in which a parallel inductor Lp is connected in parallel with the vibrator of FIG. 5, and the capacitance compensation circuit with damping capacitance C0 is replaced with an inductance compensation circuit with parallel inductor Lp. FIG. 24(A) shows an imperfect integrator circuit using CR, and FIG. 24(B) shows an example of the frequency characteristics of its gain. FIG. 24(C) shows an imperfect integrator circuit using an operational amplifier, and FIG. 24(D) shows an example of the frequency characteristics of its gain. (Both the vertical and horizontal axes of FIGS. 24(B) and 24(D) are assumed to be logarithmic.)

[0270] First, the integrating circuit included in Fig. 23 will be described with reference to Fig. 24(A) to Fig. 24(D). In Fig. 24(A) and Fig. 24(C), the capacitance constituting the integrating circuit is defined as capacitance C, the resistance constituting the integrating circuit is defined as resistance R, and the feedback resistance of the integrating circuit using an operational amplifier is defined as resistance Rf.

[0271] As shown in the gain frequency characteristics of Figure 24(B), the imperfect integrator circuit using CR in Figure 24(A) operates as an integrator circuit at frequencies higher than the angular frequency ω = 1 / RC, where ω is the angular frequency (= 2πf). The relationship between the input Vin and output Vout of the integrator circuit in the frequency range in which it operates as an integrator circuit is given by equation (8).

[0272]

number

[0273] As shown in the gain frequency characteristics of Figure 24(D), the imperfect integrator circuit using the operational amplifier in Figure 24(C) operates as an integrator circuit at frequencies higher than ω = 1 / Rin C. The relationship between the input Vin and output Vout of the integrator circuit in the frequency range in which it operates as an integrator circuit is given by equation (9).

[0274]

number

[0275] In either case, the constants of the circuit elements are selected so that the frequency that drives the oscillator Vib (the output frequency Vo of the PLL) falls within the frequency range at which the circuit operates as an integrator circuit.

[0276] The current flowing through Lp is I L In the equivalent circuit of the vibrator, if the current flowing through C0 is Ic and the current flowing through L1, C1, and R1 is Ires, the current If flowing through the vibrator and Lp can be expressed as in equation (10).

[0277]

number

[0278] The concept of the inductance compensation circuit for the parallel inductor Lp connected in parallel with the vibrator is simply the difference between differentiation and integration. If the differentiation circuit is replaced with an integration circuit, I can be calculated in the same way as the capacitance compensation circuit for the damping capacitance C0 mentioned above. L can be cancelled out, so further explanation will be omitted.

[0279] When the gain of the variable gain circuit is G and CR / G is equal to the inductance of Lp, the current I L becomes 0 times, it behaves as if the inductance of Lp is equivalent to infinity, and it behaves as if Lp is not connected. Furthermore, when CR / G is larger than Lp, Lp behaves as equivalent to "negative inductance."

[0280] In this way, the apparent inductance when the inductance of Lp is corrected will be referred to as the "equivalent inductance Lx." (It may also be referred to as the "equivalent inductance Lx" when the inductance of Lp is not corrected.)

[0281] In addition, increasing the inductance of Lp is referred to as "increasing the correction amount," and decreasing the inductance of Lp is referred to as "decreasing the correction amount." (When Lp is a negative inductance, decreasing the absolute value of the inductance of Lp is referred to as "increasing the correction amount," and increasing the absolute value of the inductance of Lp is referred to as "decreasing the correction amount.")

[0282] The variable gain circuit and the adder / subtractor circuit are similar to the capacitance correction circuit of C0.

[0283] In Patent Document 2, Figure 1 and other figures use a correction coil Ld, resulting in a configuration equivalent to a perfect integrator circuit. Therefore, as can be seen from Figure 24(B), the gain G increases as the frequency decreases, up to frequencies much lower than the frequencies actually used (theoretically down to DC). As a result, DC components such as the bias current of an operational amplifier and low-frequency components such as hum from a commercial power supply, which are lower than the frequencies actually used, are amplified to a greater extent, resulting in errors.

[0284] In the present invention, to avoid such problems, an imperfect integrator circuit is intentionally used to prevent unintentional large amplification of frequency components lower than the frequency actually used. The frequency (ω=1 / RC in FIG. 24(B), ω=1 / Rf·C in FIG. 24(D)) that is the boundary for operation as an integrator circuit is preferably, for example, a frequency that is several times to several tens of times lower than the frequency actually used, but is not limited to this.

[0285] When the integrator circuit is implemented as a digital circuit, it is sufficient to add up each sampled data for the voltage signal Vf and the current signal If. However, in this case, it will operate as a perfect integrator, so it is preferable to appropriately filter out components below the frequency that is the boundary for operation as an integrator circuit.

[0286] The parallel inductor Lp, which is connected in parallel with the vibrator, is provided between the PLL output Vo (or the amplifier output when an amplifier is used) and the vibrator. The current detection means is provided between the PLL output Vo (or the amplifier output when an amplifier is used), Lp, and the vibrator so as to detect the sum of the current flowing in the vibrator and the current flowing in Lp. Specific examples of the parallel inductor include, but are not limited to, a power factor correction inductor, a step-up transformer, a step-down transformer, or an isolation transformer. When a step-up transformer, a step-down transformer, or an isolation transformer (collectively referred to as "various transformers") is used and a current detection means is provided on the primary side, the self-inductance of the primary side becomes the parallel inductor Lp.

[0287] <5-2.Parallel resonance of Lp and C0>

[0288] 23, the equivalent inductance of the parallel inductor Lp can be freely controlled by the resistance R and capacitance C of the integrator circuit and the gain G of the variable gain circuit. By utilizing this, as in Patent Document 2, the influence of the damping capacitance C0 can be canceled by making the parallel resonance frequency of the equivalent inductor of the damping capacitance C0 and the parallel inductor Lp approach or match the resonance frequency fr or the series resonance frequency fs.

[0289] However, in this case, two anti-resonance frequencies, fa', occur near the resonant frequency fr and the series resonant frequency fs. If the PLL goes beyond the anti-resonant frequency fa' even temporarily, the PLL will no longer be able to lock onto the resonant frequency fr. (See Figure 4(B) and its explanation.)

[0290] <5-3. Combination of inductance compensation circuit and capacitance compensation circuit>

[0291] In order to prevent such a problem from occurring, the present invention uses both an inductance correction circuit for the parallel inductor Lp and a capacitance correction circuit for the damping capacitance C0.

[0292] FIG. 25 shows an example of a circuit that includes both an inductance correction circuit and a capacitance correction circuit before the phase comparator of a PLL, and the circuitry after the phase comparator is not shown.

[0293] In the present invention, first, the equivalent inductance of the parallel inductor Lp is made to approach infinity (the same state as when Lp is not connected) using the inductance compensation circuit. To achieve this, the constants of the inductance compensation circuit are determined by calculation based on the value of Lp measured in advance. More precisely, with the vibrator Vib not connected and only Lp connected, the gain of the variable gain circuit is adjusted so that the corrected current (I'res in Figures 25 and 23) becomes 0. Alternatively, the frequency characteristics of the impedance and phase when neither Lp nor the inductance compensation circuit are connected are measured in advance, and the constants of the inductance compensation circuit are determined so that the same frequency characteristics are obtained when Lp and the inductance compensation circuit are connected.

[0294] Here, if the parallel inductor Lp is a power factor correction inductor or a transformer, as previously mentioned, its inductance hardly changes, so once the gain G of the variable gain circuit connected to the output of the integrator circuit is set, there is almost no need to change it thereafter. Therefore, the gain G may be semi-fixed or fixed.

[0295] In the present invention, the equivalent inductance of the parallel inductor Lp is set to infinity (same as when Lp is not connected), and then the selected anti-resonance frequency fa is adjusted to the target frequency f by the damping capacitance C0 capacitance correction circuit and method described above. CAL Get closer to.

[0296] In this way, by using both the inductance compensation circuit and the capacitance compensation circuit, it is possible to operate the PLL stably, just as when the parallel inductor Lp is not connected.

[0297] <5-4. Current detection methods when using various transformers>

[0298] When the parallel inductor Lp is one of the various transformers exemplified above, providing a current detection means on the secondary side of the various transformers may pose safety problems such as electric shock or leakage current. When the current detection means is provided on the primary side of the various transformers, the drive signal current Ivib flowing through the vibrator can be calculated and detected based on the winding ratio between the primary and secondary sides of the various transformers, and the inductance correction of the present invention can be applied. [Explanation of symbols]

[0299] C0 Braking capacity Vf voltage signal If current signal fa” selected anti-resonance frequency etc. f CAL target frequency fa' anti-resonance frequency etc. Cx equivalent capacitance Lp parallel inductor

Claims

1. A capacitance correction circuit for a damping capacitance (C0) is provided, The capacitance correction circuit includes: The voltage signal (Vf) of the vibrator is connected to the input of the differentiation circuit, an output of the differentiating circuit is connected to an input of a variable gain circuit; The output of the variable gain circuit is subtracted from the current signal (If), The gain of the gain variable circuit is controlled to control the amount of correction of the damping capacitance (C0), and the selected anti-resonance frequency (fa") is adjusted to the target frequency (f ＣＡＬ ) to reduce the influence of the damping capacitance (C0).

2. The characteristics of the target resonator and the values ​​of the equivalent circuit elements are measured in advance, Based on the measurement results, one of the anti-resonance frequencies (fa') close to the resonance frequency (fr) is selected, The selected anti-resonance frequency (fa') is set as the selected anti-resonance frequency (fa''), Controlling the correction amount of the damping capacity (C0) so that the frequency difference between the selected anti-resonance frequency (fa") and the resonance frequency (fr) exceeds or is equal to or greater than a required frequency difference; The frequency of the selected anti-resonance frequency (fa") at that time is set to the target frequency (f ＣＡＬ 2. The resonant frequency tracking circuit for a vibrator according to claim 1 , wherein

3. The selected anti-resonance frequency (fa") is set to the target frequency (f ＣＡＬ ) and a circuit that allows it to approach the In the circuit, The correction amount of the braking capacity (C0) is initialized, Start the PLL operation. After the time required for the PLL operation has elapsed, the selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) frequency relationship, The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) match, the correction amount is the result, The selected anti-resonance frequency (fa") is the target frequency (f ＣＡＬ ), the correction amount of the braking capacity (C0) is increased, The selected anti-resonance frequency (fa") is the target frequency (f ＣＡＬ 2. The resonant frequency tracking circuit for a vibrator according to claim 1, wherein when the resonant frequency is higher than the reference frequency, the amount of correction of the damping capacitance (C0) is reduced.

4. The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) as a circuit to check the high and low relationship of the frequency, Use a circuit to check the direction of change in the output frequency after the PLL starts operating, or By directly knowing the frequency of the selected anti-resonant frequency (fa") using a circuit modified so that the PLL locks at the anti-resonant frequency (fa'), the high / low relationship can be confirmed, or The PLL is forced to the target frequency (f ＣＡＬ 2. The resonant frequency tracking circuit for a vibrator according to claim 1, wherein a high / low relationship is confirmed by a duty ratio of the output of the phase comparator using a circuit that operates at a frequency of 100 kHz.

5. The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) After checking the high and low relationship of the frequency, the circuit increases or decreases the amount of correction. The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ a circuit for increasing or decreasing a certain amount of correction each time until the high-low relationship of the frequencies of the a circuit that reduces the amount of correction by half after each iteration, or 2. The resonant frequency tracking circuit for a vibrator according to claim 1, comprising a circuit that uses the relationship between the amount of change in capacitance value of the corrected equivalent capacitance (Cx) and the selected anti-resonant frequency (fa'').

6. 2. The resonant frequency tracking circuit for a vibrator according to claim 1, wherein the differentiating circuit is an imperfect differentiating circuit.

7. 2. The resonant frequency tracking circuit for a vibrator according to claim 1, wherein the correction amount of said damping capacitance (C0) is changed from a predetermined value when the operation of the PLL starts, and then returned to said predetermined value.

8. An operation of returning the correction amount of the braking capacity (C0) to the predetermined value, Once the PLL has locked, Returning continuously after the PLL starts operating, or After the PLL starts operating, the PLL is gradually restored. The resonant frequency tracking circuit for a vibrator according to claim 7.

9. Further provided is an inductance correction circuit for an inductor (Lp) connected in parallel with the vibrator, The inductance correction circuit The voltage signal (Vf) of the vibrator is connected to an input of an integrating circuit; an output of the integrator circuit is connected to an input of a second variable gain circuit; configured to subtract the output of the second variable gain circuit from the current signal (If); By controlling the gain of the second variable gain circuit, the amount of correction of the inductance correction circuit is controlled to reduce the influence of the inductor (Lp) connected in parallel with the vibrator, and then By controlling the gain of the gain variable circuit, the correction amount of the damping capacitance (C0) is controlled, and the selected anti-resonance frequency (fa") is adjusted to the target frequency (f ＣＡＬ 9. The resonant frequency tracking circuit for a vibrator according to claim 1, wherein the resonant frequency of the vibrator is brought closer to the damping capacitance (C0) to reduce the influence of the damping capacitance (C0).

10. 10. The resonant frequency tracking circuit for a vibrator according to claim 9, wherein the integrator circuit is an imperfect integrator circuit.

11. 10. The resonant frequency tracking circuit for a vibrator according to claim 9, wherein an inductor (Lp) connected in parallel with the vibrator is a power factor correction inductor, a step-up transformer, a step-down transformer, or an isolation transformer.

12. 10. The resonant frequency tracking circuit for a vibrator according to claim 9, wherein a current detection means is provided at a position where it detects the sum of the current flowing through the vibrator and the current flowing through an inductor (Lp) connected in parallel with the vibrator.

13. A capacitance correction circuit for a damping capacitance (C0) is provided, The capacitance correction circuit includes: The voltage signal (Vf) of the vibrator is connected to the input of the differentiation circuit, an output of the differentiating circuit is connected to an input of a variable gain circuit; The output of the variable gain circuit is subtracted from the current signal (If), The gain of the gain variable circuit is controlled to control the amount of correction of the damping capacitance (C0), and the selected anti-resonance frequency (fa") is adjusted to the target frequency (f ＣＡＬ ) to reduce the influence of the damping capacitance (C0).

14. The characteristics of the target resonator and the values ​​of the equivalent circuit elements are measured in advance, Based on the measurement results, one of the anti-resonance frequencies (fa') close to the resonance frequency (fr) is selected, The selected anti-resonance frequency (fa') is set as the selected anti-resonance frequency (fa''), Controlling the correction amount of the damping capacity (C0) so that the frequency difference between the selected anti-resonance frequency (fa") and the resonance frequency (fr) exceeds or is equal to or greater than a required frequency difference; The frequency of the selected anti-resonance frequency (fa") at that time is set to the target frequency (f ＣＡＬ 14. The method for tracking the resonance frequency of a vibrator according to claim 13, wherein

15. The selected anti-resonance frequency (fa") is set to the target frequency (f ＣＡＬ ) as a way to get closer to The correction amount of the braking capacity (C0) is initialized, Start the PLL operation. After the time required for the PLL operation has elapsed, the selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) frequency relationship, The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) match, the correction amount is the result, The selected anti-resonance frequency (fa") is the target frequency (f ＣＡＬ ), the correction amount of the braking capacity (C0) is increased, The selected anti-resonance frequency (fa") is the target frequency (f ＣＡＬ 14. The method for tracking the resonance frequency of a vibrator according to claim 13, wherein the amount of correction for the damping capacitance (C0) is reduced when the resonance frequency is higher than the reference frequency (C1).

16. The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ ) as a way to check the high and low frequency relationship. Use a circuit to check the direction of change in the output frequency after the PLL starts operating, or By directly knowing the frequency of the selected anti-resonant frequency (fa") using a circuit modified so that the PLL locks at the anti-resonant frequency (fa'), the high / low relationship can be confirmed, or The PLL is forced to the target frequency (f ＣＡＬ 14. The method for tracking the resonance frequency of a vibrator according to claim 13, wherein the high / low relationship is confirmed by the duty ratio of the phase comparator output using a circuit that operates at a frequency of 1 / 2.

17. The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ After checking the frequency relationship, you can increase or decrease the amount of correction as follows: The selected anti-resonance frequency (fa") and the target frequency (f ＣＡＬ a circuit for increasing or decreasing a certain amount of correction each time until the high-low relationship of the frequencies of the a circuit that reduces the amount of correction by half after each iteration, or The resonant frequency tracking method for a vibrator according to claim 13, further comprising a circuit that uses the relationship between the amount of change in capacitance value of the corrected equivalent capacitance (Cx) and the selected anti-resonant frequency (fa'').

18. 14. The method for tracking the resonance frequency of a vibrator according to claim 13, wherein the correction amount of the damping capacitance (C0) is changed from a predetermined value when the PLL operation starts, and then returned to the predetermined value.

19. An operation of returning the correction amount of the braking capacity (C0) to the predetermined value, Once the PLL has locked, Returning continuously after the PLL starts operating, or After the PLL starts operating, the PLL is gradually restored. The method for tracking the resonance frequency of a vibrator according to claim 18.

20. Further provided is an inductance correction circuit for an inductor (Lp) connected in parallel with the vibrator, The inductance correction circuit The voltage signal (Vf) of the vibrator is connected to an input of an integrating circuit; an output of the integrator circuit is connected to an input of a second variable gain circuit; configured to subtract the output of the second variable gain circuit from the current signal (If); By controlling the gain of the second variable gain circuit, the amount of correction of the inductance correction circuit is controlled to reduce the influence of the inductor (Lp) connected in parallel with the vibrator, and then By controlling the gain of the gain variable circuit, the correction amount of the damping capacitance (C0) is controlled, and the selected anti-resonance frequency (fa") is adjusted to the target frequency (f ＣＡＬ 20. The method for tracking the resonance frequency of a vibrator according to claim 13, wherein the resonance frequency of the vibrator is brought closer to the damping capacitance (C0) to reduce the influence of the damping capacitance (C0).

Images