JP2010135623A - Sounding suppressing method in circuit device, and circuit device provided with sounding suppressing function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit device including a ceramic capacitor for periodically charging and discharging, which can effectively suppress sounding caused by a piezoelectric phenomenon caused by charge and discharge of the ceramic capacitor without changing a mounting structure of the ceramic capacitor. <P>SOLUTION: The circuit device 11 includes the ceramic capacitor 16 for charging and discharging periodically wherein one period 24 corresponding to an audible frequency range includes a charging period 24c and a discharging period 24d. The sounding suppressing method of the circuit device for suppressing sounding generated by the piezoelectric phenomenon caused by the charge and discharge of the ceramic capacitor charges the ceramic capacitor to maintain a predetermined voltage value until a next charging period when a voltage between terminals of the ceramic capacitor at a charging period end time point Te decreases to the predetermined voltage value v2 in the discharge period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for suppressing ringing caused by a piezoelectric phenomenon associated with charging and discharging of a capacitor in a circuit device including a ceramic capacitor that is periodically charged and discharged. The present invention also relates to a circuit device having a function of suppressing the ringing.

  As is well known, a ceramic capacitor vibrates due to a piezoelectric phenomenon accompanying charge / discharge. FIG. 7 shows the principle of vibration. The ceramic capacitor 1 shown here is a surface mount type, has a box-shaped outer shape, and has terminals 2 at both left and right ends of the box. A pad 4 connected to the terminal 2 is formed on the substrate 3 on which the ceramic capacitor 1 is mounted. The ceramic capacitor 1 is connected to the substrate 3 by connecting the terminal 2 and the pad 4 by soldering or the like. Implemented above.

  When the ceramic capacitor 1 is periodically charged and discharged, the ceramic capacitor 1 vibrates in the vertical direction due to the piezoelectric phenomenon (arrow 5). Since the ceramic capacitor 1 is fixed on the substrate 3, the upper and lower vibrations 5 become a force 6 for expanding and contracting the substrate 3 left and right, and as a result, the substrate 3 bends periodically. At this time, if the charge / discharge cycle is in the audible frequency range, the vibration of the ceramic capacitor 1 causes the substrate 3 to ring. If it resonates with the substrate 3, the sound volume due to the ringing is further increased. Of course, the ceramic capacitor 1 itself may ring. The audible frequency range is generally about 20 Hz to 20 KHz, although there are individual differences.

FIG. 8 and FIG. 9 show conventional examples of methods for suppressing the ringing caused by the vibration of the ceramic capacitor 1 described above. In the ringing suppression method shown in FIG. 8, the terminal 2 of the ceramic capacitor 1 is mounted so as to be lifted from the substrate 3 so that vibrations in the ceramic capacitor 1 are not directly transmitted to the substrate 3. In addition, vibration is absorbed by a member (a lead pin, a solder bump, etc.) 7 for floating from the substrate 3. In the method shown in FIG. 9, vibrations are canceled by mounting the same ceramic capacitors (1 a, 1 b) on the upper and lower objects with the substrate 3 interposed therebetween. The conventional ringing suppression method is described in the following patent documents.
JP 2000-235931 A JP 2000-23320 A

  In the conventional example shown in FIG. 8, since the ceramic capacitor is mounted while being floated from the substrate, the mounting strength is lower than when mounted directly on the surface. Therefore, quality control and reliability tests for ensuring the strength are required, and equipment costs for the quality control and reliability tests are required. In addition, the manufacturing cost increases due to the time and labor costs required for the management and testing. In the conventional example shown in FIG. 9, a single-sided mounting substrate is not applicable, and cannot be applied to a wide variety of mounting substrates and circuit devices including the substrates. As a matter of course, it is extremely difficult to suppress the ringing of the ceramic capacitor itself by the method of suppressing the ringing by the ceramic capacitor mounting structure.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and the object thereof is to mount a ceramic capacitor in a circuit device including a ceramic capacitor that is periodically charged / discharged due to a piezoelectric phenomenon caused by charging / discharging of the ceramic capacitor. It is to suppress effectively, without changing a structure. Another object of the present invention is to provide a circuit device having a function of suppressing ringing caused by the vibration of the ceramic capacitor.

  In order to achieve the above object, the present invention provides a circuit device including a ceramic capacitor that is provided with a charging period and a discharging period in one cycle corresponding to an audible frequency range and is periodically charged and discharged. A method for suppressing ringing caused by a piezoelectric phenomenon associated with charging / discharging, wherein a voltage between the terminals of the ceramic capacitor at the end of the charging period drops to a predetermined voltage value during the discharging period, and the next charging period This is a method for suppressing ringing in a circuit device that charges the ceramic capacitor so as to maintain the predetermined voltage value.

  Further, the circuit device includes a display element connected to an output terminal of a voltage between terminals of the ceramic capacitor, and the display element variably controls a ratio of the charging period and the discharging period during the one cycle. In a circuit device in which a gradation is displayed in a display state for a predetermined time in one cycle and the voltage value maintained during the discharge period is less than a threshold voltage at which the display element is in a display state. It is good also as a method.

The present invention extends to a circuit device, and the present invention according to the circuit device mainly divides one cycle corresponding to an audible frequency range into a charging period and a discharging period, and outputs a charging control signal during the charging period. A circuit device connected to the charge control circuit,
A charging circuit; a ceramic capacitor charged by a charging signal output from the charging circuit; and a ringing suppression circuit for suppressing ringing caused by a piezoelectric phenomenon associated with charging and discharging of the ceramic capacitor,
The ringing suppression circuit includes a sample hold circuit, a comparison signal output circuit, a voltage comparison circuit, a sub charge control circuit, and a signal mixing circuit,
The sample hold circuit is connected to an output terminal side of the voltage between terminals in the ceramic capacitor, and connected to an output terminal of a charging period instruction signal generated by the main charging control circuit and output during the charging cycle, Holding the output side voltage value v1 of the voltage between the terminals of the ceramic capacitor at the end of the charging cycle until the start of the next charging cycle, and outputting the signal of the held value v1;
The comparison signal circuit inputs a signal of the voltage value v1, outputs a comparison signal of a voltage value v2 of a predetermined ratio of the voltage value v1,
The voltage comparison circuit compares the comparison signal of the voltage value v2 with the output side voltage value v3 of the voltage between the terminals of the ceramic capacitor during the discharge period, and outputs a charge instruction signal when v2> v3,
The sub charge control circuit is connected to the output terminal of the voltage comparison circuit, and outputs a sub charge control signal during an input period of the charge instruction signal.
The signal mixing circuit inputs signals from the output terminals of the main charge control circuit and the sub charge control circuit, and outputs the main charge control signal and the sub charge control signal input during the one cycle. To do.

  The charging circuit is connected to an output terminal of the signal mixing circuit, and has a ringing suppression function that generates and outputs a charging signal for charging the ceramic capacitor from the main charging control signal or the sub charging control signal. Circuit device.

The circuit device may be constituted by a digital circuit, and the invention relating to the circuit device constituted by the digital circuit divides one cycle corresponding to an audible frequency range into a charging period and a discharging period, and A circuit device connected to the main charge control means for outputting a charge control signal during the period,
Charging means, a ceramic capacitor that is charged by a charging signal output from the charging means, a charging means that is connected to and charges the ceramic capacitor, and a ringing caused by a piezoelectric phenomenon associated with charging and discharging of the ceramic capacitor Including ringing suppression means for suppressing,
The ringing suppression means includes sample hold means, comparison signal output means, voltage comparison means, sub-charge control means, and signal mixing means,
The sample and hold means is connected to the output terminal side of the inter-terminal voltage in the ceramic capacitor and to the output terminal of the charging period instruction signal generated by the charging circuit and output during the charging cycle, and the charging cycle The voltage value v1 obtained by converting the output voltage of the voltage between the terminals of the ceramic capacitor at the end of the A / D conversion into digital data is stored until the start of the next charging cycle,
The comparison signal output means calculates a voltage value v2 that is a predetermined ratio of the voltage value v1 and stores data of the calculated voltage value v2.
The voltage comparison means compares the voltage value v3 obtained by converting the output side voltage of the voltage between the terminals of the ceramic capacitor during the discharge period into digital data, and the voltage value v2, and v2> v3 Output charging instruction data when
The sub charge control means is connected to the output terminal of the voltage comparison means and outputs a sub charge control signal during the input period of the charge instruction data,
The signal mixing means inputs signals from the output terminals of the main charge control means and the sub charge control means, and outputs the main charge control signal and the sub charge control signal input during the one cycle. To do.

  The charging means is connected to an output terminal of the signal mixing circuit, and has a ringing suppression function for generating and outputting a charge signal for charging the ceramic capacitor from the main charge control signal or the sub charge control signal. Circuit device.

  In any one of the above circuit devices, it is more preferable that v1 and v3 are voltage values obtained by level-shifting the voltage between the terminals of the ceramic capacitor and dropping the voltage by a predetermined voltage.

  Further, in any one of the above circuit devices, the display device includes a display element connected to an output terminal of a voltage between terminals of the ceramic capacitor, and the display element has a variable ratio of the charging period and the discharging period during the one cycle. By being controlled, the display state is displayed for a predetermined time in one cycle and gradation display is performed, and when the charging circuit charges the ceramic capacitor based on the sub-charge control signal, between the terminals of the ceramic capacitor The voltage may be a circuit device having a ringing suppression function smaller than a threshold voltage at which the display element is in a display state.

  According to the present invention, in a circuit device including a ceramic capacitor that is periodically charged and discharged, ringing caused by vibration of the ceramic capacitor can be effectively suppressed without changing the mounting structure of the capacitor. Therefore, an increase in cost due to a change in the mounting structure is prevented.

=== Configuration Example of Charging Circuit ===
FIG. 1 is an example of a circuit for periodically charging and discharging a ceramic capacitor. This circuit 10 is an LED lighting circuit 10 capable of dimming control, and its basic component is a charging circuit 11 for a ceramic capacitor 16. The charging circuit 11 in this example has a typical booster circuit configuration using the coil 12. In this charging circuit 11, the field effect transistor (FET) 13 is turned on / off at high speed in accordance with a drive signal from the main charging control circuit 20 applied to the input terminal s1 on the gate 13g side, and the drain 13d side of the FET 13 One end of a coil 12 is connected to. The other end of the coil 12 is connected to a power supply 14 having a predetermined voltage. Further, the anode 15 a of the diode 15 is connected to the drain 13 d of the FET 13. One end s2 of the ceramic capacitor 16 to be charged is connected to the cathode 15c side of the diode 15, and the other end side is grounded. That is, the connection point s <b> 2 between the diode 15 and the ceramic capacitor 16 becomes an output terminal of the voltage between the terminals of the ceramic capacitor 16. The LED 17 is connected to the output terminal s2 and lights up when the voltage between the terminals of the ceramic capacitor 16 output here becomes equal to or higher than a predetermined voltage (lighting threshold).

  In the lighting circuit 10, the LED 17 is dimmed and controlled by a time gray scale method. That is, a period in which a voltage equal to or higher than the lighting threshold is applied and a period in which a voltage lower than the lighting threshold is applied during a period (hereinafter referred to as a flashing period) corresponding to a frequency (for example, 30 Hz or higher) at which a person cannot visually recognize blinking The brightness of the LED 17 is adjusted by variably controlling the time ratio of each period. The main charge control circuit 20 generates a signal (main drive signal) for performing the dimming control, and drives the FET 13 by this main drive signal. The charging circuit 11 boosts the ceramic capacitor 16 by a predetermined period during the blinking cycle according to a signal output from the FET 13 according to the main drive signal, and discharges the ceramic capacitor 16 without boosting the remaining period of the blinking cycle. Let Thereby, during one blinking period, the voltage between the terminals of the ceramic capacitor 16 is divided into a lighting period in which the LED 17 is equal to or more than the lighting threshold value and a light-out period in which the voltage is less than the subsequent threshold value.

=== Main charge control circuit ===
FIG. 2 shows the drive signals of the FET 13 output from the main charge control circuit 20 and the waveforms (A) to (C) of signals for generating the drive signals. Further, (D) shows the relationship between the drive signal of the FET 13 and the voltage between the terminals of the ceramic capacitor 16. In these (A) to (D), signal waveforms are shown with time on the horizontal axis and voltage on the vertical axis. (A) shows the drive signal 21 of the FET 13 and has a waveform such that the high-frequency signal 22 is periodically output only during the period 24c corresponding to the gradation. During one cycle 24, a charging period 24c for charging the ceramic capacitor 16 and a discharging period 24d for discharging are provided. The charging circuit 11 generates a signal (charging signal) obtained by boosting the voltage of the power supply 14 from the high-frequency signal (main charging control signal) 22 during the charging period 24c, and charges the ceramic capacitor 16 with this charging signal.

  (B) and (C) show signal waveforms for generating the above-mentioned FET drive signal (hereinafter referred to as main drive signal) 21. The main drive signal 21 is an AND signal of the main charge control signal 22 shown in (B) and the pulse-like signal 23 shown in (C). This pulse signal (charging period instruction signal) 23 is a signal in which H and L are in a predetermined time ratio during one cycle, and the main charging control circuit 20 is, for example, a charging period instruction signal 23 that is a charging period. By providing a circuit that variably controls the pulse width 24c, the time ratio between the charging period 24c and the discharging period 24d can be variably set.

  (D) shows the relationship between the main drive signal 21 and the signal waveform 25 of the voltage between the terminals of the ceramic capacitor 16, and the ceramic capacitor 16 is charged by the charging circuit 11 during the charging period 24c to obtain the voltage between the terminals. The voltage is increased to reach the maximum value v1 at the end of the charging period 24c, and then discharged during the discharging period 24d to gradually decrease the inter-terminal voltage. This charge / discharge cycle is repeated. Note that the lighting period and the extinguishing period of the LED 17 correspond to a period 27a that is equal to or higher than the lighting threshold v4 and a period that is equal to or lower than the threshold 27b in the voltage waveform 26 between terminals for one cycle.

=== Ringing caused by condenser ===
As described above, the ceramic capacitor 16 that is periodically charged and discharged vibrates due to the piezoelectric phenomenon. 2 (D), the ringing due to vibration is such that one period 24 of the drive signal 21 corresponds to the audible frequency range, that is, the reciprocal of the time of one period 24 is within the audible frequency range. This is a case where the fluctuation range vc of the inter-terminal voltage is large enough to cause vibration. Note that the ringing caused by the ceramic capacitor 16 becomes a problem in the lighting circuit 10 of the LED 17 of this embodiment, for example, when the LED 17 is used for a backlight or illumination of a liquid crystal display. In such a case, if the time of the charging period 24c is varied in order to dim the LED 17, an unnecessary sound is generated from the display or the lighting fixture at a certain brightness.

=== Ringing suppression circuit ===
The present invention is characterized in that the ringing caused by the ceramic capacitor 16 that is periodically charged and discharged is controlled not by the mounting structure of the capacitor 16 but by an electrical signal. FIG. 3 shows a configuration example of the ringing suppression circuit 100, which is the main part of the circuit device having the ringing suppression function of the present invention. The ringing suppression circuit 100 includes circuit configurations of a sample hold circuit 30, a comparison signal output circuit 40, a voltage comparison circuit 50, a sub charge control circuit 60, and a signal mixing circuit 70 for each function. In FIG. 3, the schematic configuration of the main charging control circuit 20 and the connection points (s1, s2) with the charging circuit 11 shown in FIG. 1 are also shown.

<Sample hold circuit>
The sample and hold circuit 30 shown in FIG. 3 has a typical circuit configuration, and holds an analog switch 31, a voltage follower 32, and a voltage that are turned on / off at each timing of holding the voltage between the terminals of the ceramic capacitor 16. For this purpose, a capacitor (hold capacitor) 33 is included. The analog switch 31 has a hold capacitor 33 connected to the output terminal s3 and an output terminal s2 of the voltage between the terminals of the ceramic capacitor 16 connected to the input terminal s4. The main charge control circuit 20 operates using the output s5 of the charge period instruction signal 23 generated in the process of generating the main drive signal 21 as a trigger, and the switch 31 is disconnected at the falling edge of the charge period instruction signal 23. That is, the hold capacitor 33 is charged by the voltage between the terminals of the ceramic capacitor 16 during the charging period 24c. The voltage across the terminals of the hold capacitor 33 is input to the plus side input s7 of the voltage follower 32 obtained by negatively feeding back the output s6 of the operational amplifier 34, and the voltage across the terminals of the hold capacitor 33 at the end of the charging period 24c The voltage follower 32 continues to output until the start of the period 24c. That is, the maximum voltage v1 shown in FIG. 2 is maintained in the voltage between the terminals of the ceramic capacitor 16 during the charging period 24c.

<Comparison signal output circuit>
The comparison signal output circuit 40 is a circuit that divides the charging voltage v1 held by the sample hold circuit 30 by two resistors 41 and 42, and v1 is dropped to a voltage (hereinafter referred to as v2) by the resistor 41. v2 is output as a comparison voltage.

<Voltage comparison circuit>
The voltage comparison circuit 50 includes a comparator 51, compares the comparison voltage v2 with the voltage between the terminals of the ceramic capacitor 16 (hereinafter referred to as v3), and outputs an H signal (sub-charge instruction) during a period of v2> v3. Signal).

<Sub charge control circuit>
The sub-charge control circuit 60 is mainly composed of a two-terminal AND circuit 61. The sub-charge control circuit 60 inputs a sub-charge instruction signal from the output terminal s8 of the voltage comparison circuit 50, and a high-frequency signal (sub-charge) for driving the FET 13. Control signal) is input from the oscillator 62. As a result, the sub charge control signal from the oscillator 62 is output only during the period when the sub charge instruction signal is input. Note that the oscillator for generating the main charge control signal 22 which is a high-frequency signal in the main charge control circuit 20 may be the oscillator 62 of the sub charge control circuit 60. That is, the main charge control signal 22 and the sub charge control signal may be the same.

<Signal mixing circuit>
The signal mixing circuit 70 is composed of an OR circuit 71, and a main drive signal 21 from the main charge control device 20, an intermittent sub charge control signal (sub drive signal) which is an AND output in the sub charge control circuit 60, and Are entered individually. The output terminal s9 of the signal mixing circuit 70 is connected to the driving signal input terminal s1 of the FET 13 in the charging circuit 11, and the charging circuit 11 inputs a signal obtained by mixing the signals input to the OR circuit 71 as a driving signal for the FET 13. To do. FIG. 4 shows input signals and output signals of the signal mixing circuit 70. (A), (B), and (C) show a main drive signal, a sub drive signal, and a synthesized signal of these signals, respectively. During one cycle 24, the main drive signal 21 and the sub drive signal 72 are input. The output signal 73 has a waveform in which the main charging control signal 22 is output in the charging cycle 24c and the sub charging instruction signal 74 is intermittently output in the discharging period 24d.

=== Ringing suppression operation ===
FIG. 5 shows the relationship between the output signal 74 from the signal mixing circuit 70 and the voltage across the terminals of the ceramic capacitor 16. In addition, the voltage 25 between the terminals of the ceramic capacitor 16 in the charging circuit 11 having no ringing suppression function is also shown. When the value of the inter-terminal voltage v3, which has reached the peak value v1 at the end time Te of the charging period 24c, gradually decreases during the discharging period 24d and the voltage value v3 becomes smaller than the threshold value v2, the sub-charging control signal 73 is sent to the charging circuit 11. Is input. Accordingly, the ceramic capacitor 16 is temporarily charged, v3 exceeds the threshold value v2, and the output of the sub charge control signal 73 is stopped. Then, the ceramic capacitor 16 is discharged again, and the inter-terminal voltage v3 decreases again and is temporarily charged. Such a charge / discharge operation is repeated until the start time Ts of the next charging period 24c. Thereby, the voltage v3 between the terminals of the ceramic capacitor 16 is maintained substantially at the threshold value v2.

  In order to suppress the ringing caused by the vibration of the ceramic capacitor 16, the two resistors (41, 42) of the comparison signal output circuit 40 are appropriately selected so that the vibration of the ceramic capacitor 16 does not cause the ringing. What is necessary is just to adjust the difference (DELTA) v of v1 and v2 so that it may become amplitude. When the ringing suppression circuit of FIG. 3 is added to the lighting circuit 10 of the LED 17 shown in FIG. 1, it is necessary to make the voltage between the terminals of the ceramic capacitor 16 when the ringing is suppressed smaller than the lighting threshold voltage v4 of the LED 17. It becomes. That is, as shown in FIG. 5, the maximum value v5 of the inter-terminal voltage when the charging circuit 11 temporarily charges the ceramic capacitor 16 based on the sub-drive signal needs to be smaller than the lighting threshold v4. Thereby, the dimming control due to the vibration of the ceramic capacitor 16 can be suppressed while the light control of the LED 17 is controlled to a desired brightness.

  Thus, in the circuit device having the above-described ringing suppression function, ringing due to the vibration of the ceramic capacitor 16 can be effectively suppressed without depending on the mounting structure. For this reason, it is not necessary to change manufacturing equipment and a new reliability test due to a change in the mounting structure, thereby preventing an increase in cost. Further, the ringing can be suppressed only by adding the ringing suppression circuit 100 of the present embodiment to the existing circuit device in which the ringing due to the vibration of the ceramic capacitor 16 has occurred. Therefore, it can be expected that existing circuit devices are effectively used.

=== Configuration by Digital Circuit ===
The ringing suppression circuit 100 shown in FIG. 3 is configured by an analog circuit, but can also be configured by a digital circuit. FIG. 6 illustrates a functional block configuration of a ringing suppression unit in which the ringing suppression circuit 100 is configured by a digital circuit. Corresponding to each circuit (30, 40, 50, 60, 70) constituting the ringing suppression circuit 100 shown in FIG. 3, the ringing suppression unit 100b includes a sample hold unit 130, a comparison signal output unit 140, and a voltage comparison unit. 150, a sub-charge control unit 160, and a signal mixing unit 170. In the sample and hold unit 130, the voltage v1 is held by the v1 holding unit 131 formed of an analog circuit similar to the sample and hold circuit 30, and the v1 is generated by A / D conversion and digitized by the v1 data generation unit 132. Then, the v1 storage unit 133 configured by a register or the like stores the value of v1. The v1 data generation unit 132 performs A / D conversion on the output from the v1 holding unit 131 as needed, and updates the value of v1 as needed. The v1 storage unit rewrites the value of v1 each time v1 is updated.

  The comparison signal output unit 140 stores a predetermined coefficient, generates a value v2 of a predetermined ratio with respect to v1, for example, by multiplying the value of v1 stored in the v1 storage unit 133 by the coefficient, Store v2. Also, v2 is updated every time v1 is updated. The voltage comparison unit 150 converts the voltage v3 between the terminals of the ceramic capacitor 16 in real time by A / D conversion in the v3 data generation unit 151 and digitizes it. The comparison unit compares v2 and v3, and if v2> v3, For example, an H signal having a predetermined voltage value corresponding to binary data “1” is output as a sub-charge instruction signal.

  The sub charge control unit 160 and the signal mixing unit 170 are the same as the sub charge control circuit 60 and the signal mixing circuit 70 shown in FIG. 3, and the sub charge control unit 160 receives the sub charge instruction signal. The sub charging control signal is output from the oscillator 161, and the signal mixing unit 170 outputs the mixed signal of the sub charging control signal and the main charging control signal as a drive signal for the FET 13 in the charging circuit 11.

=== About the level shift of the voltage between terminals ===
In the present embodiment, the charging circuit 11 of the ceramic capacitor 16 is a booster circuit, and the voltage between the terminals of the ceramic capacitor 16 may exceed the rated voltage of the element used in the circuit configuration shown in FIGS. There is also. Therefore, it is desirable to drop the voltage between terminals by a known level shifter, for example, by a predetermined voltage so that the maximum value of the voltage between terminals is about the maximum rated voltage of the circuit element. Then, the level-shifted voltage is input to the ringing suppression circuit 100 and the ringing suppression unit 100b.

It is a circuit diagram of the LED lighting circuit containing the structure of a typical charging circuit. It is a figure which shows the relationship between the drive signal of the transistor which comprises the said charging circuit, and the charging voltage waveform of the ceramic capacitor charged with the said charging circuit. It is a circuit diagram of a ringing suppression circuit constituting a circuit device in an embodiment of the present invention. It is a figure which shows the waveform of the signal produced | generated by the said ringing suppression circuit. It is a figure which shows the relationship between the signal produced | generated in the said sound suppression circuit, and the charge voltage waveform of a ceramic capacitor. It is a functional block diagram at the time of comprising the said ringing suppression circuit with a digital circuit. It is a figure which shows the principle of the ringing resulting from the vibration of the ceramic capacitor to charge / discharge. It is a figure which shows the conventional method for suppressing the ringing resulting from the vibration of a ceramic capacitor. It is a figure which shows the other example of the said conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,16 Ceramic capacitor 3 Board | substrate 11 Charging circuit 13 Field effect transistor 20 Main charge control circuit 21 Main drive signal 22 Main charge control signal 23 Charging period instruction signal 30 Sample hold circuit 40 Comparison voltage output circuit 50 Voltage comparison circuit 60 Sub charge Control circuit 70 Signal mixing circuit 72 Sub drive signal 73 Signal obtained by mixing main charge control signal and sub charge instruction signal 74 Sub charge control signal 100 Ringing suppression circuit 100b Ringing suppression unit 130 Sample hold unit 140 Comparison signal output unit 150 Voltage comparison 160 Sub-charge control unit 170 Signal mixing unit

Claims (6)

In a circuit device including a ceramic capacitor that is charged and discharged periodically in one cycle corresponding to an audible frequency range, the ringing caused by the piezoelectric phenomenon accompanying the charging and discharging of the ceramic capacitor is performed. A method for suppressing,
When the voltage between the terminals of the ceramic capacitor at the end of the charging period drops to a predetermined voltage value during the discharging period, the ceramic capacitor is charged so as to maintain the predetermined voltage value until the next charging period. Method for suppressing ringing in a circuit device.   2. The circuit device according to claim 1, wherein the circuit device includes a display element connected to an output terminal of a voltage between terminals of the ceramic capacitor, and the display element can change a ratio of the charging period and the discharging period during the one period. By controlling, the display state is displayed for a predetermined time in one cycle to perform gradation display, and the voltage value maintained during the discharge period is less than the threshold voltage at which the display element is in the display state. A method for suppressing ringing in a circuit device. A circuit device connected to a main charge control circuit that divides one cycle corresponding to an audible frequency range into a charge period and a discharge period and outputs a main charge control signal during the charge period,
A charging circuit; a ceramic capacitor charged by a charging signal output from the charging circuit; and a ringing suppression circuit for suppressing ringing caused by a piezoelectric phenomenon associated with charging and discharging of the ceramic capacitor,
The ringing suppression circuit includes a sample hold circuit, a comparison signal output circuit, a voltage comparison circuit, a sub charge control circuit, and a signal mixing circuit,
The sample hold circuit is connected to an output terminal side of the voltage between terminals in the ceramic capacitor, and connected to an output terminal of a charging period instruction signal generated by the main charging control circuit and output during the charging cycle, Holding the output side voltage value v1 of the voltage between the terminals of the ceramic capacitor at the end of the charging cycle until the start of the next charging cycle, and outputting the signal of the held value v1;
The comparison signal circuit inputs a signal of the voltage value v1, outputs a comparison signal of a voltage value v2 of a predetermined ratio of the voltage value v1,
The voltage comparison circuit compares the comparison signal of the voltage value v2 with the output side voltage value v3 of the voltage between the terminals of the ceramic capacitor during the discharge period, and outputs a charge instruction signal when v2> v3,
The sub charge control circuit is connected to the output terminal of the voltage comparison circuit, and outputs a sub charge control signal during an input period of the charge instruction signal.
The signal mixing circuit inputs signals from the output terminals of the main charge control circuit and the sub charge control circuit, and outputs the main charge control signal and the sub charge control signal input during the one cycle. To do.
The charging circuit is connected to an output terminal of the signal mixing circuit, and generates and outputs a charging signal for charging the ceramic capacitor from the main charging control signal or the sub charging control signal. A circuit device with a ringing suppression function. A circuit device connected to main charge control means for dividing one cycle corresponding to an audible frequency range into a charge period and a discharge period and outputting a charge control signal during the charge period,
Charging means, a ceramic capacitor that is charged by a charging signal output from the charging means, a charging means that is connected to and charges the ceramic capacitor, and a ringing caused by a piezoelectric phenomenon associated with charging and discharging of the ceramic capacitor Including ringing suppression means for suppressing,
The ringing suppression means includes sample hold means, comparison signal output means, voltage comparison means, sub-charge control means, and signal mixing means,
The sample and hold means is connected to the output terminal side of the inter-terminal voltage in the ceramic capacitor and to the output terminal of the charging period instruction signal generated by the charging circuit and output during the charging cycle, and the charging cycle The voltage value v1 obtained by converting the output voltage of the voltage between the terminals of the ceramic capacitor at the end of the A / D conversion into digital data is stored until the start of the next charging cycle,
The comparison signal output means calculates a voltage value v2 that is a predetermined ratio of the voltage value v1 and stores data of the calculated voltage value v2.
The voltage comparison means compares the voltage value v3 obtained by converting the output side voltage of the voltage between the terminals of the ceramic capacitor during the discharge period into digital data, and the voltage value v2, and v2> v3 Output charging instruction data when
The sub charge control means is connected to the output terminal of the voltage comparison means and outputs a sub charge control signal during the input period of the charge instruction data,
The signal mixing means inputs signals from the output terminals of the main charge control means and the sub charge control means, and outputs the main charge control signal and the sub charge control signal input during the one cycle. To do.
The charging unit is connected to an output terminal of the signal mixing circuit, and generates and outputs a charging signal for charging the ceramic capacitor from the main charging control signal or the sub charging control signal. A circuit device with a ringing suppression function.   5. The circuit device having a ringing suppression function according to claim 3, wherein the v1 and the v3 are voltage values obtained by level-shifting a voltage between the terminals of the ceramic capacitor and dropping the voltage by a predetermined voltage. .   6. The display element according to claim 3, further comprising a display element connected to an output terminal of a voltage between terminals of the ceramic capacitor, wherein the display element has a variable ratio between the charging period and the discharging period during the one cycle. By being controlled, the display state is displayed for a predetermined time in one cycle and gradation display is performed, and when the charging circuit charges the ceramic capacitor based on the sub-charge control signal, between the terminals of the ceramic capacitor A circuit device having a ringing suppression function, wherein the voltage is smaller than a threshold voltage at which the display element is in a display state.

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