JP6237532B2 - Self-excited oscillation circuit - Google Patents

Description

  The present invention relates to a self-excited oscillation circuit that oscillates a vibrator by a positive feedback circuit.

  A capacitance vibration type pressure / differential pressure sensor or the like includes a self-excited oscillation circuit for causing a vibrator to oscillate at a resonance frequency. FIG. 8 is a diagram illustrating a configuration example of a conventional capacitance oscillation type self-excited oscillation circuit. As shown in the figure, the self-excited oscillation circuit 500 includes a positive feedback circuit for causing the vibrator 511 to oscillate and a negative feedback circuit for controlling the oscillation amplitude of the vibrator 511.

  The positive feedback circuit is formed by a loop that passes from the first fixed electrode 512 to the vibrator 511, the second fixed electrode 513, the I / V converter 520, the inverting amplifier 530, and the variable gain amplifier 560. In general, the vibrator 511 is vacuum-sealed in order to increase the Q value.

  The negative feedback circuit is formed of a circuit that passes through an absolute value circuit 540 that detects an absolute value of a signal output from the inverting amplifier 530, an error amplifier 550, and a variable gain amplifier 560.

  In the positive feedback circuit, the vibrator 511 is fixed to the GND potential, and the bias voltage VBIAS is applied to the first fixed electrode 512 and the second fixed electrode 513 through a DC voltage source. At this time, a charge corresponding to the capacitance is charged between the vibrator 511 and the first fixed electrode 512 and between the vibrator 511 and the second fixed electrode 513.

  In addition to the bias voltage VBIAS, the output voltage VGAO of the variable gain amplifier 560 is applied to the first fixed electrode 512, and the vibrator 511 vibrates in accordance with the potential change of the first fixed electrode 512.

  Due to the vibration of the vibrator 511, charge and discharge occur, and a current output signal from the second fixed electrode 513 is input to the I / V converter 520 and output as a voltage signal IVO. The voltage signal IVO is inverted and amplified by the inverting amplifier 530 and output as the voltage signal INVO. The voltage signal INVO is amplified by the variable gain amplifier 560 and applied to the first fixed electrode 512 as the voltage signal VGAO. By such a positive feedback circuit, the vibrator 511 vibrates at its own resonance frequency.

  In the negative feedback circuit, the absolute value circuit 540 detects the amplitude of the voltage signal INVO output from the inverting amplifier 530. The absolute value circuit 540 can be configured using a full-wave rectifier circuit or the like. The voltage signal ABSO output from the absolute value circuit 540 corresponds to the oscillation amplitude of the vibrator 511.

  The difference between the voltage signal ABSO and the reference voltage VCONT is detected by the error amplifier 550 as the error signal ERRO, and the gain of the variable gain amplifier 560 changes by the error signal ERRO. In the case of this figure, when the amplitude of the vibrator 511 is small and the error signal ERRO is large, the gain of the variable gain amplifier 560 is large, and when the amplitude of the vibrator 511 is large and the error signal ERRO is small, the variable gain amplifier 560 Gain decreases. By adjusting the gain of the variable gain amplifier 560, the amplitude of the vibrator 511 is constantly controlled to be constant.

International Publication No. 2011/102062

  When such a self-excited oscillation circuit 500 is applied to a device that requires low power consumption, such as a two-wire instrument, for example, it is difficult to satisfy the specifications of low power consumption when configured with discrete components. It is necessary to configure with an ASIC that can easily reduce power consumption.

  However, in the conventional self-excited oscillation circuit 500, since the gain of the variable gain amplifier 560 used for positive feedback is changed by the output of the negative feedback circuit, the positive feedback circuit and the negative feedback circuit are mutually dependent, The interface is complicated. Therefore, strict adjustment is required between the positive feedback circuit and the negative feedback circuit. For example, when a design change occurs in the I / V converter 520 or the inverting amplifier 530, the design of the variable gain amplifier 560 is not changed. In other words, it was an increase in design man-hours and a barrier to ASIC implementation.

  Accordingly, an object of the present invention is to realize a self-excited oscillation circuit without using a variable gain amplifier that complicates the interface between a positive feedback circuit and a negative feedback circuit.

In order to solve the above-mentioned problem, the present invention is a self-excited oscillation circuit including a vibration part having a vibrator and a positive feedback path for positively feeding back a signal based on vibration of the vibrator to the vibration part, Based on a comparison result between a value according to the amplitude of the vibrator and a reference value, a negative feedback circuit that generates a pulse width modulation signal having a frequency lower than the vibration frequency of the vibrator, and the pulse width modulation signal And a switch circuit that switches connection and disconnection of the positive feedback path.
Here, you may make it further provide the synchronizer which synchronizes the signal based on the vibration of the said vibrator | oscillator, and the switching timing of the said switch circuit.
A buffer that can be switched between enabled and disabled by the pulse width modulation signal may be provided in the positive feedback path.
Further, the negative feedback circuit can generate the pulse width modulation signal so that the pulse width becomes longer as the difference between the value corresponding to the amplitude of the vibrator and the reference value is larger.

  According to the present invention, a self-excited oscillation circuit can be realized without using a variable gain amplifier.

It is a figure which shows the structure of the self-excited oscillation circuit based on 1st Example of this invention. It is a wave form diagram explaining operation | movement of a PWM part. It is a figure which shows the structure of the self-excited oscillation circuit based on 2nd Example of this invention. It is a figure which shows the structure of the self-excited oscillation circuit based on 3rd Example of this invention. It is a wave form diagram explaining operation | movement of a synchronizer. It is a figure which shows the modification of each Example. It is a figure which shows the modification of each Example. It is a figure which shows the structural example of the conventional electrostatic capacitance oscillation type self-excited oscillation circuit.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a self-excited oscillation circuit 100 according to a first embodiment of the present invention. Note that the self-excited oscillation circuit of the present invention is not limited to the electrostatic oscillation type self-excited oscillation circuit, and can be applied to various self-excited oscillation circuits having a positive feedback circuit.

  As shown in this figure, the self-excited oscillation circuit 100 of the first embodiment has a positive feedback circuit for oscillating the vibrator 111 and a negative feedback circuit for controlling the oscillation amplitude of the vibrator 111.

  The positive feedback circuit is formed by a loop that passes from the first fixed electrode 112 to the vibrator 111, the second fixed electrode 113, the I / V converter 120, the inverting amplifier 130, and the SW circuit 170. In general, the vibrator 111 is vacuum-sealed in order to increase the Q value. The first fixed electrode 112, the vibrator 111, and the second fixed electrode 113 constitute a vibration unit, and a positive feedback path is formed by a path that is input from the output of the inverting amplifier 130 to the first fixed electrode 112 via the SW circuit 170. It is composed.

  The negative feedback circuit is formed of a circuit that passes through an absolute value circuit 140 that detects the absolute value of the voltage signal INVO output from the inverting amplifier 130, an error amplifier 150, a PWM unit 160, and an SW circuit 170.

  The SW circuit 170 is switched and controlled by the output signal PWMO of the PWM unit 160. Specifically, when the output signal PWMO is H, the voltage signal INVO output from the inverting amplifier 130 is fed back to the first fixed electrode 112 to form a positive feedback loop of the positive feedback circuit, and the output signal PWMO is L When the positive feedback loop of the positive feedback circuit is released.

  In the positive feedback circuit, the vibrator 111 is fixed to the GND potential, and the bias voltage VBIAS is applied to the first fixed electrode 112 and the second fixed electrode 113 via the DC voltage source regardless of the state of the SW circuit 170. At this time, a charge corresponding to the capacitance is charged between the vibrator 111 and the first fixed electrode 112 and between the vibrator 111 and the second fixed electrode 113.

  Since the positive feedback loop is formed by the SW circuit 170 when the output signal PWMO is H, the voltage signal INVO output from the inverting amplifier 130 is applied to the first fixed electrode 112 in addition to the bias voltage VBIAS, and the vibrator 111 vibrates according to the potential change of the first fixed electrode 112.

  Due to the vibration of the vibrator 111, charging and discharging of the charge occur, and the current output signal from the second fixed electrode 113 is input to the I / V converter 120 and output as the voltage signal IVO. The voltage signal IVO is inverted and amplified by the inverting amplifier 130 and output as the voltage signal INVO. By such a positive feedback circuit, the vibrator 111 vibrates at its own resonance frequency.

  In the negative feedback circuit, the absolute value circuit 140 detects the amplitude of the voltage signal INVO output from the inverting amplifier 130. The absolute value circuit 140 can be configured using a full-wave rectifier circuit or the like. The voltage signal ABSO output from the absolute value circuit 140 corresponds to the oscillation amplitude of the vibrator 111.

  The difference between the voltage signal ABSO and the reference voltage VCONT is detected by the error amplifier 150 as the error signal ERRO. The error signal ERRO is pulse width modulated by the PWM unit 160 and output as a PWMO signal.

  As shown in FIG. 2, the PWMO signal can be generated by comparing the error signal ERRO with a triangular wave (sawtooth wave) TRI by a comparator 161. At this time, a frequency lower than the resonance frequency of the vibrator 111 is used for the pulse width modulation frequency, that is, the triangular wave frequency. This is to ensure a sufficient positive feedback loop formation period with respect to the vibration period and to oscillate the vibrator 111 stably.

  The smaller the amplitude of the transducer 111 and the larger the error signal ERRO, the longer the H pulse width of the PWMO signal in each cycle. The larger the amplitude of the transducer 111 and the smaller the error signal ERRO, the greater the PWMO signal in each cycle. The pulse width of H is shortened.

  When the PWMO signal is H, that is, when the error signal ERRO is larger than the triangular wave TRI, a positive feedback loop is formed, so that the amplitude of the vibrator 111 grows. On the other hand, when the PWMO signal is L, that is, when the error signal ERRO is smaller than the triangular wave TRI, the positive feedback loop is released, and the amplitude of the vibrator 111 is attenuated. By repeating the growth and attenuation of the amplitude, the amplitude of the vibrator 111 is constantly controlled to be constant.

  As described above, since the Q of the vibrator 111 is generally designed to be relatively high, the amplitude growth and attenuation become extremely gradual with respect to the oscillation period of the vibrator 111. For this reason, even if the vibrator 111 is operated intermittently by the SW circuit 170, the hunting width of the amplitude of the vibrator 111 can be reduced, and the amplitude can be constantly controlled to be substantially constant.

  According to the self-excited oscillation circuit 100 of the first embodiment, the variable gain amplifier that complicates the interface between the positive feedback circuit and the negative feedback circuit becomes unnecessary, and the positive feedback circuit and the negative feedback circuit are separated from each other. The interface adjustment is simplified. That is, the characteristic on the positive feedback circuit side is uniquely determined by the design of the I / V converter 120 and the inverting amplifier 130, and the characteristic on the negative feedback circuit side is uniquely determined by the design of the error amplifier 150 and the PWM unit 160. As a result, the positive feedback circuit and the negative feedback circuit can be adjusted independently, the design man-hour can be reduced, and ASIC implementation is facilitated. Furthermore, instead of the variable gain amplifier lacking in versatility, the PWM unit 160 that can be configured by a general-purpose comparator and a triangular wave oscillator is used, so that the mounting can be facilitated and low voltage and low power consumption can be realized. it can.

  FIG. 3 is a diagram showing the configuration of the self-excited oscillation circuit 200 according to the second embodiment of the present invention. As shown in this figure, the self-excited oscillation circuit 200 of the second embodiment also has a positive feedback circuit for oscillating the vibrator 111 and a negative feedback circuit for controlling the oscillation amplitude of the vibrator 111. However, in the self-excited oscillation circuit 200 according to the second embodiment, the negative feedback circuit is digitized.

  Since the positive feedback circuit is the same as that of the first embodiment, the same reference numerals are given. That is, a loop is formed from the first fixed electrode 112 to the vibrator 111, the second fixed electrode 113, the I / V converter 120, the inverting amplifier 130, and the SW circuit 170.

  The negative feedback circuit includes an AD converter 210 that digitally converts the voltage signal INVO output from the inverting amplifier 130, a digital value that is compared with a reference value, a digital error detection unit 220 that detects an error, and a pulse of the detected error. It is formed by a circuit that passes through a digital PWM unit 230 that performs width modulation and an SW circuit 170. The digital error detection unit 220 can be composed of, for example, a subtractor that calculates a difference from a digital reference voltage and a digital filter that controls the digital PWM unit 230 according to the error.

  The SW circuit 170 is switched and controlled by the output signal PWMO of the digital PWM unit 230. Specifically, when the output signal PWMO is H, a positive feedback loop of the positive feedback circuit is formed, and when the output signal PWMO is L, the positive feedback loop of the positive feedback circuit is released.

  In the self-excited oscillation circuit 200 of the second embodiment, the negative feedback circuit is digitized, but the basic operation principle is the same as that of the self-excited oscillation circuit 100 of the first embodiment. In the self-excited oscillation circuit 200 of the second embodiment, in addition to the features of the self-excited oscillation circuit 100 of the first embodiment, the elements of the analog circuit are reduced, so that the design man-hour can be further reduced. Further, it is possible to reduce the manufacturing cost by reducing the degree of integration of the analog circuits in the ASIC.

  FIG. 4 is a diagram showing a configuration of a self-excited oscillation circuit 300 according to the third embodiment of the present invention. As shown in this figure, the self-excited oscillation circuit 300 of the third embodiment has a configuration in which a synchronization unit 180 is added to the self-excited oscillation circuit 100 of the first embodiment. Note that a configuration in which a synchronization unit 180 is added to the self-excited oscillation circuit 200 of the second embodiment may be employed.

  The synchronization unit 180 includes a comparator and a D-FF so that the SW circuit 170 is switched at a timing when the voltage signal INVO (AC component) output from the inverting amplifier 130 changes from negative to positive. Specifically, when the voltage signal INVO (AC component) changes from negative to positive, that is, when the voltage signal SWO becomes equal to the bias voltage VBIAS, the comparator outputs a CMPO2 signal (voltage rising), and D-FF To work. Then, the SW circuit 170 is switched by the D-FFQ signal output from the D-FF. However, the timing may be changed from positive to negative, or may be switched at every half cycle.

  When the synchronization unit 180 is not provided, the switching of the SW circuit 170 and the vibration of the vibrator 111 are not synchronized. Therefore, when the SW circuit 170 is switched, a sudden change occurs in the voltage signal SWO applied to the first fixed electrode 112. The voltage signal SWO may be disturbed.

  In contrast, by providing the synchronization unit 180, the switching of the SW circuit 170 and the vibration of the vibrator 111 are synchronized as shown in FIG. That is, the SW circuit 170 is switched when the voltage signal SWO becomes equal to the bias voltage VBIAS. As a result, the voltage signal SWO does not suddenly change when the SW circuit 170 is switched, and the disturbance of the voltage signal SWO can be reduced.

  In each of the above embodiments, the bias voltage VBIAS is applied to the first fixed electrode 112 via the SW circuit 170 as shown in FIG. In this case, both the H terminal and L terminal of the SW circuit 170 are connected to a DC voltage source.

  On the other hand, as shown in FIG. 6B, the bias voltage VBIAS may be applied to the first fixed electrode 112 without using the SW circuit 170. In this case, the L terminal of the SW circuit 170 may be connected to the DC voltage source, or may float and not be connected to the DC voltage source as shown in FIG.

  Incidentally, a certain amount of parasitic capacitance (for example, about 30 pF) exists between the first fixed electrode 112 and GND. For this reason, it is necessary to supply a current for driving the parasitic capacitance to the inverting amplifier 130, which causes an increase in current consumption.

  In each of the above-described embodiments, it is only necessary to drive the parasitic capacitance during the period in which the positive feedback loop is formed. Therefore, the drive capability is increased when the signal PWMO is H, and the drive capability is reduced when the signal PWMO is L. Operation becomes possible.

  For this reason, for example, as shown in FIG. 7, a buffer 190 having an enable function is arranged between the inverting amplifier 130 and the SW circuit 170, the drive capability is ensured only when the signal PWMO is H, and the signal PWMO is The power consumption can be reduced by disabling the buffer 190 so that no current is consumed in the buffer 190. The buffer 190 having the enable function can be applied to any of the above-described embodiments.

DESCRIPTION OF SYMBOLS 100 ... Self-excited oscillation circuit, 111 ... Vibrator, 112 ... 1st fixed electrode, 113 ... 2nd fixed electrode, 120 ... I / V converter, 130 ... Inverting amplifier, 140 ... Absolute value circuit, 150 ... Error amplifier, 160 ... PWM unit, 161 ... comparator, 170 ... SW circuit, 180 ... synchronizing unit, 190 ... buffer, 200 ... self-excited oscillation circuit, 210 ... AD converter, 220 ... digital error detection unit, 230 ... digital PWM unit, 300 ... Self-excited oscillation circuit

Claims (4)

A self-excited oscillation circuit including a vibration part having a vibrator and a positive feedback path for positively feeding back a signal based on vibration of the vibrator to the vibration part;
Based on a comparison result between a value corresponding to the amplitude of the vibrator and a reference value, the frequency is lower than the vibration frequency of the vibrator and is based on a periodic signal generated separately from the vibration of the vibrator A negative feedback circuit for generating a pulse width modulation signal of
A switch circuit that switches connection and disconnection of the positive feedback path with the pulse width modulation signal;
A self-excited oscillation circuit comprising:   The self-excited oscillation circuit according to claim 1, further comprising a synchronization unit that synchronizes a signal based on vibration of the vibrator and a switching timing of the switch circuit.   3. The self-excited oscillation circuit according to claim 1, further comprising a buffer in the positive feedback path that can be switched between enabled and disabled by the pulse width modulation signal.   The negative feedback circuit generates the pulse width modulation signal so that a pulse width becomes longer as a difference between a value corresponding to an amplitude of the vibrator and the reference value is larger. The self-excited oscillation circuit according to any one of the above.