JP2012233730A - Physical quantity detector and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical quantity detector which allows the structure of a capacitive element to produce displacement with high linearity for the input of a physical quantity.SOLUTION: A physical quantity detector comprises a physical quantity detecting element which has a structure producing displacement in response to a physical quantity and allows the capacitance to vary in response to the displacement of the structure, an electric charge supply circuit which supplies a certain amount of electric charges to the physical quantity detecting element, and an output circuit which outputs a signal corresponding to the capacitance of the physical quantity detecting element after the supply of the electric charges from the electric charge supply circuit.

Description

  The present invention relates to a capacitance type physical quantity detection device.

A capacitance type physical quantity detection device that detects physical quantities such as acceleration and pressure as a change in capacitance of a structure (for example, a capacitive element including a movable electrode and a fixed electrode) that deforms according to these physical quantities. Are known. Patent Document 1 discloses a capacitance detection circuit that operates in a discrete time with a single end type. Patent Document 2 discloses a fully differential capacitance detection circuit. Patent Document 3 is an acceleration sensor that detects an inertial force acting on a weight due to acceleration by a change in capacitance, and has a feedback loop that always makes the displacement of the weight zero.
A closed loop type capacitance detection circuit is disclosed.

JP 2001-91535 A JP 2007-171171 A US Pat. No. 6,386,032

In Patent Documents 1 and 2, charges accumulated by applying a constant voltage to the capacitive element were measured. However, these techniques have a problem that the displacement of the structure does not become linear with respect to the input of the physical quantity. In Patent Document 3, control is performed so that the displacement of the structure is always zero, but there is a problem that a complicated circuit is required to perform this control. Further, in Patent Document 3, there is a problem that the stability of the feedback loop may be lost if an acceleration input exceeding the maximum value of feedback is given.
In contrast, the present invention provides a physical quantity detection device in which a structure of a capacitive element is displaced with high linearity with respect to an input of a physical quantity.

The present invention includes a physical quantity detection element having a structure that is displaced in accordance with a physical quantity, a capacitance that changes in accordance with the displacement of the structure, and a charge supply circuit that supplies a predetermined amount of charge to the physical quantity detection element And an output circuit that outputs a signal corresponding to the capacitance of the physical quantity detection element after the certain amount of charge is supplied by the charge supply circuit.
According to this physical quantity detection device, the structure can be displaced with respect to the input of the physical quantity with higher linearity as compared with the configuration in which the capacitance is detected by applying a constant voltage to the physical quantity detection element. .

In a preferred aspect, the charge supply circuit includes an operational amplifier having two input terminals and an output terminal, a power supply line used for supplying a constant voltage, a first terminal connected to the power supply line, and the operational amplifier. A second capacitor connected to one of the two input terminals, and a first capacitive element for accumulating charges supplied to the physical quantity detection element, wherein the physical quantity detection element You may connect to the position which forms a feedback circuit with respect to an amplifier.
According to this physical quantity detection device, in a circuit using an operational amplifier, compared with a configuration in which a constant voltage is applied to the physical quantity detection element to detect the capacitance, the input of the physical quantity has higher linearity. The structure can be displaced.

In another preferable aspect, the charge supply circuit includes a first switch connected between the power line and the first terminal of the first capacitor element, and the first terminal of the first capacitor element and the ground. A second switch connected to the potential line; and a third switch connected in parallel to the physical quantity detection element, and the other input terminal of the operational amplifier is connected to the ground potential line. The first switch and the second switch may be closed exclusively, and the second switch and the third switch may be closed exclusively.
According to this physical quantity detection device, in a circuit using a capacitive element switched by a switch and an operational amplifier, compared to a configuration in which a constant voltage is applied to the physical quantity detection element to detect capacitance,
The structure can be displaced with respect to the input of the physical quantity with higher linearity.

In still another preferred aspect, the output circuit may include an inverse arithmetic circuit that calculates an inverse of a value indicated by a voltage output from an output terminal of the operational amplifier.
According to this physical quantity detection device, a linear output can be obtained with respect to the capacity change.

In still another preferred embodiment, the charge supply circuit is connected to the operational amplifier having two input terminals and an output terminal, an AC voltage source that outputs an AC voltage having a constant effective voltage, and the AC voltage source. A first capacitance element having a first terminal and a second terminal connected to one of the two input terminals of the operational amplifier and storing charges supplied to the physical quantity detection element; and the physical quantity A resistance element connected in parallel to the detection element;
The physical quantity detection element may be connected to a position where a feedback circuit is formed with respect to the operational amplifier, and the other input terminal of the operational amplifier may be connected to a ground potential line.
According to the physical quantity detection device, in a circuit using an AC voltage source, compared to a configuration in which a constant voltage is applied to the physical quantity detection element to detect the capacitance, the input of the physical quantity has higher linearity. The structure can be displaced.

In still another preferred aspect, the physical quantity detection element includes a first capacitance whose capacitance changes in a certain direction with respect to a change in physical quantity, and an electrostatic capacitance in a direction opposite to the first capacitance with respect to the change in physical quantity. The charge supply circuit includes two input terminals and 2
A fully differential operational amplifier having two output terminals, a power supply line used for supplying a constant voltage, a ground potential line used for supplying a ground potential, and one of the power supply line and the ground potential line exclusively. A switch circuit to be connected; a first terminal connected to the switch circuit; and a second terminal connected to one input terminal of the two input terminals of the fully differential operational amplifier;
A first capacitive element for accumulating charges supplied to the physical quantity detection element; a first terminal connected to the switch circuit; and the other input terminal of the two input terminals of the fully differential operational amplifier. A second capacitor for storing the charge supplied to the physical quantity detection element, a first switch connected in parallel to the first capacitor, and a second capacitor. A second switch connected in parallel; and an input common feedback circuit for setting a common mode voltage of the two input terminals of the fully differential operational amplifier to a ground potential, wherein the first capacitor and the second capacitor are The first switch and the second switch may be controlled in association with the switch circuit. The first switch and the second switch may be connected to positions that form different feedback circuits with respect to the fully differential operational amplifier.
According to this physical quantity detection device, in a circuit using a fully differential operational amplifier, compared with a configuration that detects a capacitance by applying a constant voltage to a physical quantity detection element, with higher linearity,
The structure can be displaced with respect to the input of the physical quantity.

In still another preferred aspect, the charge supply circuit includes a constant current supply circuit, a first switch connected in parallel to the physical quantity detection element, and one end connected to the physical quantity detection element,
A timing generation circuit for outputting a second switch having the other end connected to the constant current supply circuit, a first timing signal for controlling opening and closing of the first switch, and a second timing signal for controlling opening and closing of the second switch And the first timing signal is a first time and the first timing signal.
The second timing signal may be a signal for closing the second switch for a second time after the first switch is opened.
According to this physical quantity detection device, in a circuit using a constant current supply circuit, compared to a configuration in which a constant voltage is applied to a physical quantity detection element to detect a capacitance, a physical quantity is input with higher linearity. In contrast, the structure can be displaced.

In still another preferred embodiment, the charge supply circuit includes a current mirror circuit having a first current terminal and a second current terminal, a first switch connected in parallel to the physical quantity detection element, and one end of the physical quantity detection element Is connected to the second current terminal, and the other end is connected to the first current terminal.
A switch, a capacitive element having one end connected to the second current terminal, a third switch connected in parallel to the capacitive element, a first input terminal to which a constant voltage is input, and a voltage at one end of the capacitive element When a voltage input from the second input terminal is lower than a voltage input from the first input terminal, a first level signal is output from the second input terminal. A comparator having an output terminal for outputting a second level signal when the input voltage reaches the voltage input from the first input terminal, and the first switch and the third switch are: Opening and closing is controlled by a first timing signal, the second switch is controlled to open and close by a second timing signal, a signal output from the comparator is used as the second timing signal, and the first signal It may be a signal to close a predetermined time the first switch.
According to this physical quantity detection device, in a circuit using a current mirror circuit, compared with a configuration in which a constant voltage is applied to a physical quantity detection element to detect a capacitance, the input of a physical quantity has higher linearity. The structure can be displaced.

In still another preferred embodiment, the physical quantity may be acceleration.
According to this physical quantity detection device, it is possible to displace the structural body with respect to the input of acceleration with higher linearity compared to a configuration in which a constant voltage is applied to the physical quantity detection element to detect capacitance. .

In still another preferred embodiment, the physical quantity may be a pressure.
According to this physical quantity detection device, the structure can be displaced with respect to the input of pressure with higher linearity as compared with a configuration in which a capacitance is detected by applying a constant voltage to the physical quantity detection element. .

In still another preferred embodiment, the physical quantity may be a force.
According to this physical quantity detection device, the structure can be displaced with respect to the input of force with higher linearity compared to a configuration in which a constant voltage is applied to the physical quantity detection element to detect capacitance. .

In still another preferred embodiment, the physical quantity may be an angular velocity.
According to this physical quantity detection device, the structure can be displaced with respect to the input of the angular velocity with higher linearity as compared with the configuration in which the capacitance is detected by applying a constant voltage to the physical quantity detection element. .

The present invention also provides an electronic apparatus having any one of the physical quantity detection devices described above.
According to this electronic apparatus, the structure can be displaced with respect to the input of the physical quantity with higher linearity as compared with the configuration in which a constant voltage is applied to the physical quantity detecting element to detect the capacitance.

The figure which illustrates the structure of the acceleration detection element 11. The figure which shows the equivalent circuit of the acceleration detection element 11. The figure which illustrates an electrostatic capacitance detection circuit. FIG. 4 is a schematic diagram showing a mechanical configuration of a capacitor 113. The figure which shows the structure of the physical quantity detection apparatus 10 which concerns on this invention. The figure which shows the structure of the electrostatic capacitance detection circuit 1 which concerns on 1st Embodiment. The figure which illustrates clock signal (PHI) 1 and (PHI) 2. The figure which illustrates the structure of an inverse arithmetic circuit. The figure which shows the structure of the electrostatic capacitance detection circuit 2 which concerns on 2nd Embodiment. The figure which shows the structure of the electrostatic capacitance detection circuit 3 which concerns on 3rd Embodiment. The figure which shows the structure of the electrostatic capacitance detection circuit 4 which concerns on 4th Embodiment. The figure which illustrates timing signal (PHI) 3 and (PHI) 4. The figure which shows the structure of the electrostatic capacitance detection circuit 5 which concerns on the modification 1. FIG. The figure which shows the structure of the electrostatic capacitance detection circuit 6 which concerns on the modification 2. FIG. 6 is a timing chart illustrating timing signals Φ3 and Φ4. The figure which shows the structure of the reciprocal arithmetic circuit which concerns on the modification 3. The figure which shows the structure of the force detection element 71 which concerns on the modification 4. FIG. The figure which shows the structure of the pressure detection element 72 which concerns on the modification 5. FIG. FIG. 10 illustrates a configuration of an electronic device 1000.

0. Outline of Capacitance Type Physical Quantity Detection Device FIG. 1 is a diagram illustrating the structure of an acceleration detection element 11. The acceleration detection element 11 is an example of a capacitance type physical quantity detection element. The acceleration detection element 11 detects acceleration as a physical quantity. In other words, the acceleration detecting element 11 has a structure that is displaced by receiving an external force (in particular, an inertial force due to acceleration in this example), and an electrostatic capacity is changed according to the displacement of the structure. is there. 1A shows a state in which the acceleration is zero, and FIG. 1B shows a state in which an acceleration a (> 0) is applied in the right direction (y-axis direction) in the drawing. The acceleration detection element 11 includes a fixed part 111 and a movable part 112. The fixing portion 111 is a member that is fixed to a substrate (not shown) regardless of the acceleration applied to the acceleration detecting element 11. The movable part 112 is
It is an example of a structure that is displaced according to acceleration, and includes a weight portion 1121 and a spring portion 1122. One end of the spring portion 1122 is fixed to the substrate, and the other end is connected to the weight portion 1121. The weight portion 1121 is supported by the spring portion 1122. The weight portion 1121 has a mass m. When acceleration a is applied to the acceleration detecting element 11, a force of F = ma is applied to the weight portion 1121. By this force, the spring portion 1122 is deformed and the weight portion 1121 is displaced relative to the fixed portion 111. The weight portion 1121 has a movable electrode 1123 and a movable electrode 1124. More specifically, the fixed portion 111 includes a fixed electrode 1111, a fixed electrode 1112, and a fixed electrode 1.
113 and a fixed electrode 1114. The fixed electrode 1111 and the fixed electrode 1112 are opposed to each other, and a movable electrode 1123 is provided at a position facing both. Similarly, the fixed electrode 1113 and the fixed electrode 1114 are opposed to each other, and the movable electrode 1 is located at a position facing both.
124 is provided. The acceleration detecting element 11 is formed by using a semiconductor material such as Si (silicon) and a semiconductor processing technique, for example.

FIG. 2 is a diagram illustrating an equivalent circuit of the acceleration detection element 11. The acceleration detection element 11 has two capacitors, a capacitor 113 and a capacitor 114, connected in series. An input terminal 115 is connected to one end of the capacitor 113. An input terminal 116 is connected to one end of the capacitor 114. The other ends of the capacitor 113 and the capacitor 114 are connected to each other, and an input terminal 117 is connected thereto. The capacitor 113 includes the movable electrode 1123, the fixed electrode 1111 and the movable electrode 1
124 and the fixed electrode 1113. The capacitor 114 is a capacitor including the movable electrode 1123 and the fixed electrode 1112, and the movable electrode 1124 and the fixed electrode 1114. As illustrated in FIG. 1B, when a rightward acceleration a is applied in the figure, the movable electrode 112 is applied.
3 and the fixed electrode 1112 and the distance between the movable electrode 1124 and the fixed electrode 1114 are shortened,
The distances between the movable electrode 1123 and the fixed electrode 1111 and between the movable electrode 1124 and the fixed electrode 1113 are increased. That is, the capacitor 113 and the capacitor 114 have a so-called differential configuration in which the capacitance changes in opposite directions according to the input acceleration. By detecting the change in capacitance, the acceleration applied to the weight 1121 can be detected. Although FIG. 2 shows an example of a differential detection element, a single-end detection element may be used.

FIG. 3 is a diagram illustrating a capacitance detection circuit according to the related art. In order to detect a change in capacitance in the capacitors 113 and 114, it is necessary to apply a voltage to these capacitors. This capacitance detection circuit includes an operational amplifier (operational amplifier) 12, a capacitive element 93, and a resistive element 94. The operational amplifier 12 has a non-inverting input terminal (plus input terminal) 121, an inverting input terminal (minus input terminal) 122, and an output terminal 123. The inverting input terminal 122 is connected to the input terminal 117. The non-inverting input terminal 121 has a voltage VDD /
2 is applied. Due to the virtual short-circuit of the operational amplifier 12, the inverting input terminal 122 becomes the same potential as the non-inverting input terminal 121, so that the voltage VDD / 2 is applied to the input terminal 117. A voltage signal that periodically changes from the voltage VDD to the ground potential GND is input to the input terminal 115. A voltage signal that periodically changes from the voltage VDD to the ground potential GND and has a phase opposite to that of the signal input to the input terminal 115 is input to the input terminal 116. That is, capacity 1
13 and the capacitor 114 are applied with a voltage whose polarity is periodically reversed and whose absolute value is VDD / 2.

The voltage Vo output from the output terminal 123 is expressed by the following equation.
Vo = (Cs1-Cs2) Vcs / Cf (1)
Here, Cs1 and Cs2 indicate the capacities of the capacitor 113 and the capacitor 114, respectively. Vcs is
The voltage between the input terminal 115 and the input terminal 116 is shown. Cf represents the capacitance of the capacitive element 93. That is, the capacitance detection circuit of FIG. 3 has the sensing capacitance C of the acceleration detection element 11.
s (capacitor 113 and capacitor 114) with a constant voltage Vref (Vref = VD in the above example)
D / 2) is added to measure the charge Q = Cs · Vref accumulated in the sensing capacitor.

ここで、Ａは固定電極１１１１および可動電極１１２３の面積を、ε０は真空の誘電率を
、εｒは電極間にある媒質の比誘電率を、Ｖは電極間の電圧を、ｘは、電極間の初期間隔
ｘ０を基準とした電極の変位を、それぞれ表す。式（２）によれば、静電力Ｆｅｓは、電
極の変位ｘに単純に比例する形では変化しないことがわかる。 FIG. 4 is a schematic diagram showing a mechanical configuration of the capacitor 113. Here, in order to simplify the explanation, only the capacitance formed by the fixed electrode 1111 and the movable electrode 1123 will be considered. When a voltage is applied between both electrodes, an electrostatic force Fes works between the electrodes. The electrostatic force Fes is expressed by the following equation.

Here, A is the area of the fixed electrode 1111 and the movable electrode 1123, ε0 is the dielectric constant of vacuum, εr is the relative dielectric constant of the medium between the electrodes, V is the voltage between the electrodes, and x is the voltage between the electrodes. Represents the displacement of the electrode with reference to the initial interval x0. According to Equation (2), it can be seen that the electrostatic force Fes does not change in a form that is simply proportional to the electrode displacement x.

Consider the influence of equation (2) on the acceleration detecting element 11. When the acceleration a is applied, the weight part 1121 is displaced. Considering only the effect of acceleration a, this displacement is linear with respect to acceleration a. When the weight 1121 is displaced, the electrostatic force acting between the electrodes changes nonlinearly according to the equation (2). Since this electrostatic force causes displacement of the movable electrode 1123, that is, the weight portion 1121, the displacement of the weight portion 1121 is not linear with respect to the acceleration a as a whole.
The linearity of the displacement of the weight 1121 with respect to the acceleration a (that is, the linearity of the capacitance change) is one of important performance indicators of the detection element (sensor), and it is required to further improve the linearity.

式（３）から明らかなように、電荷Ｑを一定とした場合、電極間に働く静電力は変位ｘに
よらずに一定である。 The measurement principle in the capacitance detection circuit of FIG. 3 is to detect a capacitance by applying a constant voltage to the sensing capacitance Cs. However, according to this measurement principle, there is a problem that the displacement of the weight 1121 does not become linear with respect to the acceleration a, as can be seen from Equation (2). Therefore, in the present embodiment, the electrostatic capacity is detected by storing a constant charge Q in the sensing capacitor Cs. When the charge Q stored in the sensing capacitor Cs is constant, the electrostatic force Fes acting between the electrodes is expressed by the following equation.

As is clear from equation (3), when the charge Q is constant, the electrostatic force acting between the electrodes is constant regardless of the displacement x.

Consider the influence of equation (3) on the acceleration detection element 11. According to Expression (3), an effect of a constant electrostatic force, that is, a constant offset is given to the displacement of the weight portion 1121, but the linearity of the displacement with respect to the acceleration a is not affected. Therefore, by applying a constant charge to the sensing capacitor Cs and detecting the capacitance of the sensing capacitor Cs, the linearity can be further improved as compared with the case where a constant voltage is applied to the sensing capacitor Cs.

FIG. 5 is a diagram showing a configuration of the physical quantity detection device 10 according to the present invention. Physical quantity detection device 10
Includes a charge supply circuit 100 and an output circuit 200. The charge supply circuit is a circuit for supplying a certain amount of charge to the sensing capacitor Cs. Here, the “constant amount of charge” means a charge controlled to have a certain amount, and does not necessarily mean the same amount of charge. In addition, the “constant amount of charge” in this paper is a concept that includes a certain amount of charge that does not vary with time in the case of direct current, and a charge that has a constant effective value in the case of alternating current. The output circuit 200 extracts a signal (for example, the terminal voltage of the sensing capacitor Cs) corresponding to the capacitance of the sensing capacitor Cs after a certain amount of charge is supplied to the sensing capacitor Cs by the charge supply circuit 100. Circuit. In this paper, “after a certain amount of charge has been supplied” means that a certain amount of charge in the case of direct current is accumulated in the sensing capacitor Cs, and in addition, a charge having a constant effective value in the case of alternating current. This is a concept including a state where the sensing capacitor Cs is supplied. Hereinafter, some specific examples of these circuits will be described. Hereinafter, in the description of the circuit, “sensing capacitor Cs” is used instead of the acceleration detecting element 11. For the sake of simplicity, the sensing capacitor Cs has a single-ended structure unless otherwise specified.

1. First Embodiment FIG. 6 is a diagram illustrating a configuration of a capacitance detection circuit 1 according to a first embodiment. The capacitance detection circuit 1 is an example of a physical quantity detection device 10 having a single-ended configuration using a switched capacitor. The charge supply circuit 100 includes a switch 15, a switch 16, a switch 17, an operational amplifier 12, and a capacitor 13. The output circuit 200 is a switch 1
8 and the capacitor element 14. The sensing capacitor Cs is connected to a position where a feedback circuit is formed with respect to the operational amplifier 12. The non-inverting input terminal 121 of the operational amplifier 12 is connected to a ground potential line (hereinafter simply referred to as “grounded”). Note that the ground potential may be arbitrarily set according to the circuit configuration. In this embodiment, the description proceeds with the ground potential GND set to 0V. The capacitive element 13 is connected to the inverting input terminal 122. The capacitive element 13 is an element that accumulates a certain amount of charge to be supplied to the sensing capacitor Cs. The capacitive element 13 has an input terminal 131 and an output terminal 132. The output terminal 132 is the inverting input terminal 12
2 is connected. The input terminal 131 is connected to one end of the switch 15 and one end of the switch 16. The other end of the switch 15 is connected to a power supply line. This power line has
A constant voltage Vref is applied. The other end of the switch 16 is grounded. The switch 17 is connected in parallel to the sensing capacitor Cs. The switch 17 is a switch for discharging the electric charge accumulated in the sensing capacitor Cs. The output terminal 123 of the operational amplifier 12
Is connected to one end of the switch 18. The switch 18 is a switch for sampling a voltage in the capacitive element 14. The other end of the switch 18 is connected to the capacitive element 14. The capacitive element 14 is a load capacitance. The switch 18 and the capacitive element 14 are connected to the operational amplifier 12.
However, if the sampling function is not necessary as the output circuit 200, these elements are not essential. In this case, the operational amplifier 12 also serves as an output circuit. As will be described below, switch 15 and switch 16, and switch 16 and switch 17 are each closed exclusively.

FIG. 7 is a diagram illustrating clock signals Φ1 and Φ2. The clock signal Φ1 is a signal that controls the opening and closing of the switch 15 and the switch 17, and the clock signal Φ2 is the switch 1
6 and a signal for controlling opening and closing of the switch 18. The switches 15 to 18 are, for example, n-channel MOS (Metal-Oxide-Semiconductor) transistors, and H (High) is connected to the gate.
) When a level signal (voltage) is input, the source and drain become conductive (the switch closes)
When an L (Low) level signal is input to the gate, the source and the drain are insulated (the switch is opened). In this example, the clock signals Φ1 and Φ2 are non-overlapping clocks that do not become H level at the same time. That is, switch 15 and switch 1
6 can be said to constitute a switch circuit that exclusively switches the potential of the input terminal 131 of the capacitive element 13 to Vref or GND.

First, consider a case where the clock signal Φ1 is at the H level and the clock signal Φ2 is at the L level. The potential of the output terminal 132 of the capacitive element 13 is the ground potential GND due to the virtual short circuit of the operational amplifier 12. A constant voltage Vre is applied to the input terminal 131 of the capacitive element 13.
f is applied. Accordingly, the charge Q expressed by the following formula is accumulated in the capacitive element 13 with the output terminal 132 as the positive side.
Q = −Cc · Vref (4)
Here, Cc is the capacitance of the capacitive element 13. At this time, since the switch 17 is closed, the electric charge accumulated in the sensing capacitor Cs is discharged and becomes zero.

Next, consider a case where the clock signal Φ1 is at L level and the clock signal Φ2 is at H level. The potential of the input terminal 131 of the capacitive element 13 becomes the ground potential GND. Operational amplifier 1
2 due to the virtual short, the potential of the output terminal 132 of the capacitive element 13 is also the ground potential GND.
It is. Accordingly, all the charge Q accumulated in the capacitive element 13 during the period when the clock signal Φ1 is at the H level flows into the sensing capacitor Cs. That is, a constant charge Q = −Cc · Vref is given to the sensing capacitor Cs during the period when the clock signal Φ2 is at the H level. At this time, the output voltage Vo of the operational amplifier 12 is expressed by the following equation.
Vo = Q / Cs = − (Cc / Cs) · Vref (5)
The output voltage Vo is held (sampled) in the capacitive element 14 via the switch 18.

The initial value of the sensing capacitance Cs (capacity when acceleration is zero) is Cs0, and acceleration a (> 0)
) Is input, the sensing capacitance Cs is expressed by the following equation.
Cs = Cs0 + ΔCs (6)
When Expression (6) is substituted into Expression (5), the output voltage Vo of the operational amplifier 12 is expressed by the following expression.
Vo = − (Cc · Vref) / (Cs0 + ΔCs) (7)
If the reciprocal of the output voltage Vo is taken, the capacitance change ΔCs can be obtained. That is, acceleration a
An output ΔCs that is linear with respect to the input can be obtained.

FIG. 8 is a diagram illustrating the configuration of the reciprocal arithmetic circuit. In the capacitance detection circuit 1, the output circuit 200 has this reciprocal arithmetic circuit. With this circuit, the capacitance change ΔCs can be obtained from the output voltage Vo held in the capacitive element 14. This circuit is an ADC (Analog to
Digital Converter (Analog / Digital Converter) 21 and reciprocal arithmetic circuit 82. The ADC 81 has an analog input terminal 811, a reference voltage input terminal 812, and a digital output terminal 813. The ADC 81 quantizes the analog voltage input from the analog input terminal 811 using the voltage input from the reference voltage input terminal 812 as a reference, and outputs it as an n-bit digital signal (digital code). The reciprocal arithmetic circuit 82 has an input terminal 821.
And an output terminal 822. The reciprocal arithmetic circuit 82 is a circuit that calculates the reciprocal of the value indicated by the digital signal input from the input terminal 821 and outputs it from the output terminal 822.
In this example, the polarity of the voltage Vo held in the capacitive element 14 is inverted and input to the analog input terminal 811. This is for matching the polarity of the signal, but it may not be inverted depending on how the circuit ground potential GND is selected. Further, in the example of FIG. 8, 2Vref is used as the reference voltage, but the reference voltage is not limited to this.

As described above, according to the capacitance detection circuit 1, the displacement of the weight portion 1121 (that is, the detected capacitance change) is linear with respect to the acceleration a as compared with the case where a constant voltage is applied to the sensing capacitance Cs. Can be improved.

2. Second Embodiment FIG. 9 is a diagram illustrating a configuration of a capacitance detection circuit 2 according to a second embodiment. The capacitance detection circuit 1 is an example using a discrete time circuit using a switch. The capacitance detection circuit 2 is an example of the physical quantity detection device 10 using a time continuous circuit. In the capacitance detection circuit 2, the charge supply circuit 100 includes an operational amplifier 12, a capacitive element 13, an AC voltage source 21, and a resistive element 2.
2. The sensing capacitor Cs is connected to a position where a feedback circuit is formed with respect to the operational amplifier 12. The non-inverting input terminal 121 of the operational amplifier 12 is grounded. The capacitive element 13 is connected to the inverting input terminal 122. The output terminal 132 is the inverting input terminal 12
2 is connected. The input terminal 131 is connected to the AC voltage source 21. The AC voltage source 21 outputs an AC voltage Vi having a constant effective value. That is, the AC voltage Vi is applied to the input terminal 131. The resistance element 22 is connected in parallel to the sensing capacitor Cs.
The resistance element 22 is a feedback resistor.

ここで、「||」は並列インピーダンスを表している。１／Ｒｆ≪ωＣｓの場合（すなわち
、ω≪１／（ＲｆＣｓ）の場合）、伝達関数Ｈ（ｊω）は、次式のように近似される。

式（７）の伝達関数によれば、入力電圧Ｖｉに対する出力電圧Ｖｏは、次式で表される。

式（１０）からわかるように、出力電圧Ｖｏから、センシング容量Ｃｓの容量変化ΔＣｓ
を得ることができる。なお、出力回路２００についての図示および説明は省略したが、静
電容量検出回路１と同様である（以下、他の実施形態についても同様）。 The transfer function H (jω) of the capacitance detection circuit 2 is expressed by the following equation.

Here, “||” represents the parallel impedance. When 1 / Rf << ωCs (that is, when ω << 1 / (RfCs)), the transfer function H (jω) is approximated by the following equation.

According to the transfer function of Expression (7), the output voltage Vo with respect to the input voltage Vi is expressed by the following expression.

As can be seen from the equation (10), the capacitance change ΔCs of the sensing capacitor Cs from the output voltage Vo.
Can be obtained. Although illustration and description of the output circuit 200 are omitted, the output circuit 200 is the same as the capacitance detection circuit 1 (hereinafter, the same applies to other embodiments).

In the capacitance detection circuit 2, the inverting input terminal 122 of the operational amplifier 12 is in a virtual ground state due to a virtual short circuit regardless of the input voltage Vi. A voltage corresponding to the difference between the ground potential GND and the input voltage Vi is applied to the capacitive element 13. That is, the capacitive element 13
Is stored with a charge Q (t) represented by the following equation.
Q (t) = Cc · Vi (t) (11)
Here, to emphasize that the charge Q is an alternating charge and the input voltage Vi is an alternating voltage,
Q (t) and Vi (t). The capacitive element 13 has a maximum of Qmax = Cc · V
The electric charge of imax is accumulated (Vimax is the maximum value of the input voltage Vi (t)). For example, when the input voltage Vi (t) is equal to the ground potential GND, the charge accumulated in the capacitive element 13 becomes zero. All the charges previously stored in the capacitive element 13 are transferred to the sensing capacitor Cs. In other words, Q (t) expressed by Equation (11) is accumulated in the sensing capacitor Cs (actually, the charge accumulated in the capacitive element and the charge accumulated in the sensing capacitor are inverted in phase. ) Since the input voltage Vi (t) is an alternating current with a constant amplitude, the charge accumulated in the sensing capacitor Cs is also an alternating charge with a constant amplitude, that is, an alternating charge with a constant effective value. At this time, an electrostatic force Fes expressed by Equation (3) works between the electrodes. Since the effective value of the charge Q (t) is constant, the effective value of the electrostatic force Fes is constant. That is, an output ΔCs linear with respect to the input of the acceleration a can be obtained.

3. Third Embodiment FIG. 10 is a diagram illustrating a configuration of a capacitance detection circuit 3 according to a third embodiment. Although the capacitance detection circuit 1 is an example of a single-ended circuit, the capacitance detection circuit 3 is a differential circuit.
1 is an example of a physical quantity detection device 10. That is, in the capacitance detection circuit 3, the sensing capacitor Cs has a differential configuration. The sensing capacitor Cs is a sensing capacitor Cs1 (11
3) and a sensing capacitor Cs2 (114). The capacitances of the sensing capacitor Cs1 and the sensing capacitor Cs2 change in opposite directions with respect to the input acceleration change. For example, when the capacitance of the sensing capacitor Cs1 increases, the capacitance of the sensing capacitor Cs2 decreases. In the capacitance detection circuit 3, the charge supply circuit 100 includes a fully differential operational amplifier 32, a capacitive element 331, a capacitive element 332, a capacitive element 341, and a capacitive element 34.
2 and ICMFB (Input Common Mode FeedBack) 35
A switch 35, a switch 36, a switch 371, and a switch 372.
The fully differential operational amplifier 32 has a non-inverting input terminal 321, an inverting input terminal 322, an inverting output terminal 323, and a non-inverting output terminal 324. In the capacitance detection circuit 3, the sensing capacitance Cs is shown by distinguishing the sensing capacitance Cs1 and the sensing capacitance Cs2.

The sensing capacitor Cs1 and the sensing capacitor Cs2 are respectively a fully differential operational amplifier 3
2 are connected to positions where different feedback circuits are formed. A voltage V _i ⁺ and a voltage V _i ⁻ are input to the non-inverting input terminal 321 and the inverting input terminal 322. Inverted output terminal 323
The non-inverted output terminal 324 outputs a voltage V _o ⁻ and a voltage V _o ⁺ . The input common mode voltage V _icm = (V _i ⁺ + V _i ⁻ ) / 2 of the fully differential operational amplifier 32 is controlled by the _{ICMFB 38} so that V _icm = GND. The output common mode voltage V _ocm = (V _o ⁺ + V _o ⁻ ) / 2 of the fully differential operational amplifier 32 is controlled by an output common feedback circuit (not shown) so that V _ocm = GND. Furthermore, a fully differential operational amplifier 32
Since V _i ⁺ = V _i ⁻ due to the virtual short circuit, the non-inverting input terminal 321 and the inverting input terminal 322 are in the virtual ground state.

The switch 35, the switch 36, the switch 371, and the switch 372 are, for example, n-channel MOS transistors. The switch 35, the switch 371, and the switch 372 are driven by the clock signal Φ1 (FIG. 7). The switch 36 is driven by the clock signal Φ2. That is, the switch 35 and the switch 36 are connected to the power supply line Vref.
Alternatively, a switch circuit exclusively connected to the ground potential line GND is configured. The capacitance detection circuit 3 basically operates in the same manner as the capacitance detection circuit 1. A constant charge Q is accumulated in the capacitor 331 and the capacitor 332 during the period when the clock signal Φ1 is at the H level. During the period in which the clock signal Φ2 is at the H level, the charge Q is transferred to the sensing capacitor Cs1 and the sensing capacitor Cs2. Sensing capacitance Cs1 and sensing capacitance Cs2
Since the charge Q accumulated in the electrode is constant, the electrostatic force acting between the electrodes is constant. Therefore,
A linear output ΔCs can be obtained with respect to the input of the acceleration a. Note that the clock signals Φ1 and Φ2 applied to the switch 35 and the switch 36 may be interchanged. In this case, in the period in which the charges of the sensing capacitors Cs1 and Cs2 are reset, similarly, the capacitive elements 331 and 332
The charge of is also zero. When the switches 371 and 372 are opened and the switch 35 is turned on, a certain amount of charge flows into the capacitive elements 331 and 332, and all of the current flows through the sensing capacitor C.
It flows into s1 and Cs2. In this way, a constant charge is supplied to the sensing capacitors Cs1 and Cs2.

4). Fourth Embodiment FIG. 11 is a diagram illustrating a configuration of a capacitance detection circuit 4 according to a fourth embodiment. 1st to 3rd
In the embodiment, the example of the circuit that transfers a constant charge to the sensing capacitor Cs using the voltage source and the capacitive element has been described. The capacitance detection circuit 4 is an example of the physical quantity detection device 10 using a constant current supply circuit. In the capacitance detection circuit 4, the charge supply circuit 100 includes a constant current supply circuit including a constant current source 41 and a current mirror circuit 42, a timing generation circuit 43, a switch 44, and a switch 45. The current mirror circuit 42 has a first current terminal 421 and a second current terminal 422. The current mirror circuit 42 is a circuit that outputs the same current I ₂ as the current I ₁ output from the first current terminal 421 from the second current terminal 422 (I ₁ = I ₂ ). A constant current source 41 is connected to the first current terminal 421. A sensing capacitor Cs is connected to the second current terminal 422 via a switch 45. The switch 44 is connected in parallel to the sensing capacitor Cs. The timing generation circuit 43 is a circuit that outputs a signal for controlling the opening / closing timing of the switch 44 and the switch 45. The timing generation circuit 43 has a signal output terminal 431 and a signal output terminal 432.
The signal output terminal 431 is a terminal that outputs a timing signal Φ 3 for controlling the switch 44. The signal output terminal 432 is a terminal that outputs a timing signal Φ 4 for controlling the switch 45. The switches 44 and 45 are, for example, n-channel MOS transistors. The drain and source of the switch 45 are connected to the second current terminal 422 and one end of the sensing capacitor Cs. The drain and source of the switch 44 are connected to one end and the other end of the sensing capacitor Cs. The gates of the switch 44 and the switch 45 are connected to the signal output terminal 431 and the signal output terminal 432. A voltage output terminal Vo is provided at one end of the sensing capacitor Cs.

FIG. 12 is a diagram illustrating timing signals Φ3 and Φ4. In a period T1 in which the timing signal Φ3 is at the H level (at this time, the timing signal Φ4 is at the L level),
Both electrodes of the sensing capacitor Cs are short-circuited, and the charge accumulated up to that time is discharged. That is, the sensing capacitor Cs is reset. The sensing capacitor Cs is charged by the constant current I during the period T2 in which the timing signal Φ4 is at the H level (at this time, the timing signal Φ3 is at the L level). The timing signal Φ4 becomes L level after a certain period Tinteg has elapsed. The charge Q accumulated in the sensing capacitor Cs during the period Tinteg is expressed by the following equation.
Q = I · Tinteg (12)
FIG. 12 also shows the change with time of the charge Q. After the period T2 ends, the capacitance of the sensing capacitor Cs is calculated by the following equation.
Cs = Cs0 + ΔCs = Q / Vo (13)

5. Other Embodiments The present invention is not limited to the above-described embodiments, and various modifications can be made. Hereinafter, some modifications will be described. Two or more of the following modifications may be used in combination.

5-1. Modification 1
FIG. 13 is a diagram illustrating a configuration of the capacitance detection circuit 5 according to the first modification. The capacitance detection circuit 5 is a modification of the capacitance detection circuit 1 (FIG. 6). The capacitance detection circuit 5 includes a switch 51 and a switch 52 in addition to the configuration of the capacitance detection circuit 1. Switch 51
One end is connected to the output terminal 132 and the other end is grounded. The switch 52 has one end connected to the output terminal 132 and the other end connected to the inverting input terminal 122. Switch 51
Is driven by the clock signal Φ1, and the switch 52 is driven by the clock signal Φ2. According to the capacitance detection circuit 5, when charging the capacitive element 13, the ground potential via the switch 51 can be applied as the potential of the output terminal 132, not the virtual ground potential due to the virtual short circuit of the operational amplifier 12.

Note that the configuration of the switch is not limited to that illustrated in FIGS. 6 and 13. Any configuration of switches may be used as long as a constant charge can be supplied to the sensing capacitor Cs. The configuration of the switch may be designed according to the polarity of the desired output signal or the timing of the output signal.

5-2. Modification 2
FIG. 14 is a diagram illustrating a configuration of the capacitance detection circuit 6 according to the second modification. The capacitance detection circuit 6 is a modification of the capacitance detection circuit 4 (FIG. 11). In the capacitance detection circuit 4, the sensing capacitance Cs is set to a constant time Tint using the constant current I output from the constant current source 41.
A constant charge was accumulated in the sensing capacitor Cs by charging for eg. In the capacitance detection circuit 6, the charge accumulated in the sensing capacitor Cs is measured. When the charge accumulated in the sensing capacitor Cs reaches a certain value, supply of current to the sensing capacitor Cs is stopped.

The capacitance detection circuit 6 includes a current mirror circuit 42, a switch 44, a switch 45, a capacitive element 61, a switch 62, a comparator 63, and a resistance element 64.
A sensing capacitor Cs is connected to the first current terminal 421 of the current mirror circuit 42 via the resistance element 64 and the switch 45. The switch 44 is connected in parallel to the sensing capacitor Cs. The resistance element 64 is a load resistance. The second of the current mirror circuit 42
A capacitive element 61 is connected to the current terminal 422. The capacitive element 61 is a capacitance for measuring the charge accumulated in the sensing capacitance Cs. The other end of the capacitive element 61 is grounded. The switch 62 is connected to the capacitive element 61 in parallel. The switch 62 is a switch for discharging the electric charge accumulated in the capacitive element 61. The comparator 63 is the first
It has an input terminal 631, a second input terminal 632, and an output terminal 633. The comparator 63 outputs an H level voltage when the voltage input from the second input terminal 632 is lower than the voltage input from the first input terminal 631, and is input from the second input terminal 632. When the voltage reaches the voltage input from the first input terminal 631, an L level voltage is output. A predetermined voltage Vref is input to the first input terminal 631. The second input terminal 632 is connected to one end of the capacitive element 61, and the voltage Vint corresponding to the charge accumulated in the capacitive element 61 is input to the second input terminal 632. That is, the comparator 63 has a voltage V
When int reaches a predetermined voltage Vref, an L level voltage is output. Comparator 63
Is used as a timing signal Φ3 for controlling opening and closing of the switch 45.

FIG. 15 is a timing chart illustrating timing signals Φ3 and Φ4 according to the second modification. When the timing signal Φ3 becomes H level, the switch 44 and the switch 62 are closed, and the charge accumulated in the sensing capacitor Cs and the capacitor element 61 is discharged (the sensing capacitor Cs and the capacitor element 61 are reset). When the charge accumulated in the capacitive element 61 is discharged, Vint <Vref is satisfied, so that the timing signal Φ4 becomes the H level. When the timing signal Φ4 becomes H level, the switch 45 is closed and the sensing capacitance C
A current I is supplied to s. At this time, the current I is also supplied to the capacitive element 61 by the current mirror circuit 42. However, during this time, both electrodes of the sensing capacitor Cs and the capacitive element 61 are short-circuited by the switch 44 and the switch 62, so that no charge is accumulated in these capacitors. FIG. 15 shows the terminal voltage Vint and output voltage Vo of the capacitive element 61.
Also shown in the figure. The broken line of the output voltage Vo shows the voltage change according to the change of the sensing capacitance.

When a certain time T1 has elapsed, the timing signal Φ3 becomes L level. Timing signal Φ
When 3 becomes L level, the switch 44 and the switch 62 are opened, and electric charges start to be accumulated in the sensing capacitor Cs and the capacitive element 61. Since the same amount of current I is supplied by the current mirror circuit 42, an amount of charge corresponding to the amount of charge accumulated in the sensing capacitor Cs is accumulated in the capacitive element 61. That is, observing the electric charge accumulated in the capacitive element 61 is equivalent to observing the electric charge accumulated in the sensing capacitor Cs. A change in the charge accumulated in the capacitive element 61 appears in the voltage Vint. That the voltage Vint has reached the predetermined voltage Vref is equivalent to the fact that the charge accumulated in the sensing capacitor Cs has reached a predetermined amount. When the voltage Vint reaches a predetermined voltage Vref,
The timing signal Φ4 becomes L level. A constant charge is held in the sensing capacitor Cs. In this state, the capacitance of the sensing capacitor Cs is obtained by the following equation.
Cs = Cs0 + ΔCs = Q / Vo (14)
here,
Q = Cint · Vref (15)
It is. Cint is the capacitance of the capacitive element 61.

5-3. Modification 3
FIG. 16 is a diagram illustrating a configuration of an inverse operation circuit according to the third modification. The configuration of the circuit that calculates the capacitance change from the output voltage Vo is not limited to that illustrated in FIG. The circuit of Modification 3 is
It has ADC81. A reference voltage Vref / 2 is input to the analog input terminal 811. The reference voltage input terminal 812 receives the output voltage −Vo whose polarity is inverted. The digital code output from the output terminal 822 corresponds to (Vref / 2) / (− Vo). The output voltage Vo is
Vo = − (Cc · Vref) / (Cs0 + ΔCs) (16)
Therefore, the output digital code is
(Vref / 2) / (− Vo) = (Cs0 + ΔCs) / (2Cc) (17)
It corresponds to. In the digital code output from the ADC 81, the capacitance change Δ
Cs is included in the denominator. That is, the digital code output from the ADC 81 changes linearly with respect to the capacitance change ΔCs.

5-4. Modification 4
FIG. 17 is a diagram illustrating a configuration of a force detection element 71 according to the fourth modification. The physical quantity detection element is
It is not limited to the acceleration detection element 11. The physical quantity detected by the physical quantity detection element is
It is not limited to acceleration. The force detection element 71 is an example of a physical quantity detection element, and detects force as a physical quantity. The force detection element 71 includes a fixed part 711 and a movable part 712. Fixed part 71
Reference numeral 1 denotes a member that is substantially fixed to a substrate (not shown) regardless of the force applied to the force detection element 71. The movable part 712 includes a weight part 7121, a spring part 7122, and a force detection part 712.
And 5. One end of the spring portion 7122 is fixed to the substrate, and the other end is connected to the weight portion 7121. The weight portion 7121 is supported by the spring portion 7122. Force detector 712
When a force F is applied to 5, the spring portion 7122 is deformed and the weight portion 7121 is displaced relative to the fixed portion 711. The weight portion 7121 includes a movable electrode 7123 and a movable electrode 7124. More specifically, the fixed portion 711 includes a fixed electrode 7111 and a fixed electrode 7112. The fixed electrode 7111 and the fixed electrode 7112 are opposed to the movable electrode 7123 and the movable electrode 7124, respectively, and form a sensing capacitor Cs. Although the force detection element 71 in FIG. 17 has a single-ended configuration, it may have a differential configuration as in the acceleration detection element 11 in FIG.

5-5. Modification 5
FIG. 18 is a diagram illustrating a configuration of a pressure detection element 72 according to Modification 5. 18A is a top view of the pressure detection element 72, and FIG. 18B is a cross-sectional view taken along line AA of the pressure detection element 72. FIG. The pressure detection element 72 is an example of a physical quantity detection element, and detects pressure as a physical quantity. The pressure detection element 72 has a diaphragm 721 and a base 722. Diaphragm 721
A sealed space 723 is formed by the base 722. Diaphragm 721
Deforms in response to external pressure. In the space 723, the movable electrode 724 is disposed on the diaphragm 721, and the fixed electrode 7 is disposed on the surface (bottom surface) of the base 722 facing the diaphragm 721.
25 are provided. The movable electrode 724 and the fixed electrode 725 form a sensing capacitor Cs. When the diaphragm 721 is deformed by an external pressure change, the movable electrode 724 is displaced relative to the fixed electrode 725, and the electrostatic capacitance is changed.

5-6. Modification 6
The physical quantity detected by the physical quantity detection element may be an angular velocity. That is, the physical quantity detection element may be a gyro sensor. The structure of the gyro sensor is the same as the structure of the acceleration sensor exemplified in FIG. In the case of a gyro sensor, the fixed part 111 and the movable part 112 are vibrated in the x-axis direction. When the gyro sensor rotates around the z-axis in a vibrating state, a Coriolis force acts in the y-axis direction. The weight 1121 is displaced by the Coriolis force, and the capacitance of the sensing capacitor Cs changes.

5-7. Other Modifications FIG. 19 is a diagram illustrating a configuration of an electronic apparatus 1000 using the physical quantity detection device 10 described above. The electronic device 1000 is, for example, a mobile phone, a game machine, a digital camera, a car navigation device, an automobile, or a robot. The electronic apparatus 1000 includes a physical quantity detection device 10
And a control device 1010. The control device 1010 includes a CPU (Central Processing U).
nit) and memory. The control device 1010 controls other components using a signal output from the physical quantity detection device 10.

DESCRIPTION OF SYMBOLS 1 ... Electrostatic capacity detection circuit, 2 ... Electrostatic capacity detection circuit, 3 ... Electrostatic capacity detection circuit, 4 ... Electrostatic capacity detection circuit, 5 ... Electrostatic capacity detection circuit, 6 ... Electrostatic capacity detection circuit, 10 ... Physical quantity detection device 11
Acceleration detection element, 12 ... operational amplifier, 13 ... capacitive element, 14 ... capacitive element, 15 ... switch, 16 ... switch, 17 ... switch, 18 ... switch, 21 ... AC voltage source, 22 ... resistance element, 32 ... fully differential Operational amplifier, 35 ... switch, 36 ... switch, 38 ... ICMFB, 4
DESCRIPTION OF SYMBOLS 1 ... Constant current source, 42 ... Current mirror circuit, 43 ... Timing generation circuit, 44 ... Switch, 45 ... Switch, 51 ... Switch, 52 ... Switch, 61 ... Capacitance element, 62 ... Switch, 63 ... Comparator, 64 ... Resistance element 71 ... Force detection element 72 ... Pressure detection element 8
DESCRIPTION OF SYMBOLS 1 ... ADC, 82 ... Reciprocal arithmetic circuit, 93 ... Capacitance element, 94 ... Resistance element, 100 ... Charge supply circuit, 111 ... Fixed part, 112 ... Movable part, 113 ... Capacity, 114 ... Capacity, 115 ... Input terminal, 116 ... input terminal, 117 ... input terminal, 121 ... non-inverting input terminal, 122 ... inverting input terminal, 123 ... output terminal, 131 ... input terminal, 132 ... output terminal, 200 ... output circuit, 3
21 ... Non-inverting input terminal, 322 ... Inverting input terminal, 323 ... Inverting output terminal, 324 ... Non-inverting output terminal, 331 ... Capacitance element, 332 ... Capacitance element, 341 ... Capacitance element, 342 ... Capacitance element, 371 ... Switch, 372 ... Switch, 421 ... First current terminal, 422 ... Second current terminal, 431 ... Signal output terminal, 432 ... Signal output terminal, 631 ... First input terminal, 632 ... Second
Input terminal 633 ... Output terminal, 711 ... Fixed part, 712 ... Movable part, 721 ... Diaphragm, 722 ... Base, 723 ... Space, 724 ... Movable electrode, 725 ... Fixed electrode, 811 ... Analog input terminal, 812 ... Reference voltage Input terminal, 813 ... Digital output terminal, 821 ... Input terminal, 822 ... Output terminal, 1000 ... Electronic equipment, 1111 ... Fixed electrode, 1112 ... Fixed electrode,
1113 ... Fixed electrode, 1114 ... Fixed electrode, 1121 ... Weight part, 1122 ... Spring part, 112
DESCRIPTION OF SYMBOLS 3 ... Movable electrode, 1124 ... Movable electrode, 7121 ... Weight part, 7122 ... Spring part, 7123 ... Movable electrode, 7124 ... Movable electrode, 7125 ... Force detection part

Claims (9)

A physical quantity detecting element having a structure that is displaced according to a physical quantity, and a capacitance that is changed according to the displacement of the structure;
A charge supply circuit for supplying a certain amount of charge to the physical quantity detection element;
A physical quantity detection device comprising: an output circuit that outputs a signal corresponding to a capacitance of the physical quantity detection element after the constant amount of charge is supplied by the charge supply circuit. The charge supply circuit includes:
An operational amplifier having two input terminals and an output terminal;
A power line used to supply a constant voltage;
A first terminal connected to the power supply line and a second terminal connected to one input terminal of the two input terminals of the operational amplifier, and stores a charge supplied to the physical quantity detection element; 1 capacitive element,
The physical quantity detection device according to claim 1, wherein the physical quantity detection element is connected to a position where a feedback circuit is formed with respect to the operational amplifier. The charge supply circuit includes:
A first switch connected between the power line and the first terminal of the first capacitor;
A second switch connected between the first terminal of the first capacitive element and a ground potential line;
A third switch connected in parallel to the physical quantity detection element,
The other input terminal of the operational amplifier is connected to the ground potential line;
The first switch and the second switch are closed exclusively;
The physical quantity detection device according to claim 2, wherein the second switch and the third switch are exclusively closed. The physical quantity detection device according to claim 3, wherein the output circuit includes an inverse arithmetic circuit that calculates an inverse of a value indicated by a voltage output from an output terminal of the operational amplifier. The charge supply circuit includes:
An operational amplifier having two input terminals and an output terminal;
An AC voltage source that outputs an AC voltage having a constant effective voltage;
A first terminal connected to the AC voltage source and a second terminal connected to one input terminal of the two input terminals of the operational amplifier, and accumulates electric charges supplied to the physical quantity detection element A first capacitive element;
A resistance element connected in parallel to the physical quantity detection element,
The physical quantity detection element is connected to a position where a feedback circuit is formed with respect to the operational amplifier,
The physical quantity detection device according to claim 1, wherein the other input terminal of the operational amplifier is connected to a ground potential line. The physical quantity detection element includes a first capacitance whose capacitance changes in a certain direction with respect to a change in physical quantity, and a second capacitance whose capacitance changes in a direction opposite to the first capacitance with respect to the change in physical quantity. And
The charge supply circuit includes:
A fully differential operational amplifier having two input terminals and two output terminals;
A power line used to supply a constant voltage;
A ground potential line used to supply the ground potential;
A switch circuit exclusively connected to one of the power supply line and the ground potential line;
A first terminal connected to the switch circuit and a second terminal connected to one of the two input terminals of the fully differential operational amplifier, and charge supplied to the physical quantity detection element A first capacitor element for storage;
A first terminal connected to the switch circuit and a second terminal connected to the other input terminal of the two input terminals of the fully differential operational amplifier, and charge supplied to the physical quantity detection element A second capacitive element to be accumulated;
A first switch connected in parallel to the first capacitor;
A second switch connected in parallel to the second capacitor;
An input common feedback circuit for setting a common mode voltage of the two input terminals of the fully differential operational amplifier to a ground potential;
The first capacitor and the second capacitor are connected to positions that form different feedback circuits for the fully differential operational amplifier,
The physical quantity detection device according to claim 1, wherein the first switch and the second switch are controlled in association with the switch circuit. The charge supply circuit includes:
A constant current supply circuit;
A first switch connected in parallel to the physical quantity detection element;
A second switch having one end connected to the physical quantity detection element and the other end connected to a constant current supply circuit;
A timing generation circuit that outputs a first timing signal that controls opening and closing of the first switch and a second timing signal that controls opening and closing of the second switch;
The first timing signal is a signal for closing the first switch for a first time,
The physical quantity detection device according to claim 1, wherein the second timing signal is a signal for closing the second switch for a second time after the first switch is opened. The charge supply circuit includes:
A current mirror circuit having a first current terminal and a second current terminal;
A first switch connected in parallel to the physical quantity detection element;
A second switch having one end connected to the physical quantity detection element and the other end connected to the first current terminal;
A capacitive element having one end connected to the second current terminal;
A third switch connected in parallel to the capacitive element;
A first input terminal to which a constant voltage is input, a second input terminal to which a voltage at one end of the capacitive element is input, and a voltage input from the second input terminal is a voltage input from the first input terminal. A first level signal is output when the voltage is low, and a second level signal is output when the voltage input from the second input terminal reaches the voltage input from the first input terminal. A comparator and
The first switch and the third switch are controlled to open and close by a first timing signal,
The second switch is controlled to open and close by a second timing signal,
A signal output from the comparator is used as the second timing signal;
The physical quantity detection device according to claim 1, wherein the first signal is a signal for closing the first switch for a certain period of time.   An electronic apparatus comprising the physical quantity detection device according to claim 1.

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