JP2007078648A - Sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor device capable of reducing variation in detection sensitivity of physical quantity between a plurality of sensor devices. <P>SOLUTION: The sensor device comprises: a capacitor 21 for detecting physical quantity that has a semiconductor micro machine structure and has capacity varying according to the physical quantity provided from the outside; a capacitor 22 for reference whose variation in capacity according to the physical quantity is smaller than that of the capacitor 21 for detecting physical quantity; and a detecting section 3 for detecting the physical quantity based on the difference between the capacity Cs of the capacitor 21 and the capacity Cref of the capacitor 22. The capacitor 22 for reference has a semiconductor micro machine structure and is formed on the same substrate as the capacitor 21 for detecting physical quantity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensor device having a semiconductor micromechanical structure.

  Conventionally, as a sensor device for detecting physical quantities such as pressure and acceleration, a capacitor is formed by a semiconductor micromechanical structure formed using a micromachine technology based on a semiconductor process, so-called MEMS (Micro Electro Mechanical System) technology, 2. Description of the Related Art A sensor device is known in which a physical quantity is detected from the electrostatic capacity by utilizing the fact that the electrostatic capacity of a capacitor changes according to an applied physical quantity.

  FIG. 9 is a block diagram showing the configuration of the sensor device according to the background art as described above (see, for example, Patent Document 1). A sensor device 101 shown in FIG. 9 has a capacitor 102 for detecting a physical quantity configured on a MEMS substrate, and a capacitance Cr that is the same as the capacitance of the capacitor 102 when no physical quantity is applied. Capacitor 103, which is an individual component, and an operational amplifier 104, a feedback capacitor 105 of the operational amplifier 104, and an AC voltage source that outputs an AC voltage V1 having a constant amplitude to the inverting input terminal of the operational amplifier 104 via the capacitor 103. 106, and an adder 107 that adds the AC voltage V 1 output from the AC voltage source 106 to the output voltage V 2 of the operational amplifier 104 and outputs the added voltage to the inverting input terminal of the operational amplifier 104 via the capacitor 102. It has.

  Since the capacitors 102 and 103 are connected to the inverting input terminal of the operational amplifier 104, the capacitance Cs of the capacitor 102 changes depending on the physical quantity given to the capacitor 102, and the capacitance 102 If a difference occurs between them, the potential of the inverting input terminal of the operational amplifier 104 changes, and as a result, the operational amplifier 104 is set so that the potential of the inverting input terminal becomes equal to the reference potential (the potential of the non-inverting input terminal of the operational amplifier 104). The output voltage V2 changes. Then, the relationship shown by the following formula (1) is established.

Cr · V1 = Cs · V2 (1)
Accordingly, from equation (1), when a physical quantity is applied to the capacitor 102 and the capacitance Cs changes, the output voltage V2 of the operational amplifier 104 changes, and therefore the physical quantity applied to the capacitor 102 is detected from the output voltage V2. Be able to.
JP 2000-65664 A

  By the way, in the sensor device configured as described above, the capacitance Cs of the capacitor 102 and the capacitance Cr of the capacitor 103 vary due to manufacturing variations and the like. As a result, the output voltage V2, which is a detection value obtained with respect to the change amount of the same capacitance Cs for each sensor device 101 in Formula (1), is different, and as a result, per unit physical quantity among the plurality of sensor devices 101. In other words, the detection values obtained, that is, the detection sensitivities of physical quantities vary.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a sensor device that can reduce variations in detection sensitivity of a physical quantity among a plurality of sensor devices.

  In order to achieve the above-described object, a sensor device according to the present invention includes a semiconductor micromechanical structure and a physical quantity detection capacitor whose electrostatic capacity changes according to a physical quantity applied from the outside, and an electrostatic capacity with respect to the physical quantity. A reference capacitor having a capacitance change smaller than that of the physical quantity detection capacitor; and a detection unit that detects the physical quantity based on a difference between a capacitance of the physical quantity detection capacitor and a capacitance of the reference capacitor. The reference capacitor is formed to have the semiconductor micromechanical structure on the same substrate as the physical quantity detection capacitor.

  Further, in the above-described sensor device, the detection unit includes an operational amplifier and a voltage source that outputs a voltage to one signal input terminal of the operational amplifier via the physical quantity detection capacitor. The output signal of the operational amplifier is fed back as a feedback signal to the one signal input terminal via the reference capacitor.

  In the above-described sensor device, the detection unit includes a fully differential operational amplifier, and a voltage source that outputs a voltage to one signal input terminal of the fully differential operational amplifier via the physical quantity detection capacitor. The fully differential operational amplifier feeds back the output signal of the fully differential operational amplifier as a feedback signal to the other signal input terminal of the fully differential operational amplifier via the reference capacitor. It is characterized by.

  Further, in the above-described sensor device, the detection unit outputs a voltage to the first signal input terminal of the first operational amplifier via the first and second operational amplifiers and the physical quantity detection capacitor. And the difference between the output signal of the first operational amplifier and the output signal of the second operational amplifier as a feedback signal is fed back to one signal input terminal of the second operational amplifier via the reference capacitor. And a differential output unit.

  In the above sensor device, the voltage source is an AC voltage source.

  Further, in the above-described sensor device, a comparison unit that compares the feedback signal with a preset threshold value, a periodic signal generation unit that generates a periodic signal having a preset frequency, and a comparison result by the comparison unit And a counting unit that counts the number of periods of the periodic signal generated by the periodic signal generation unit and outputs the count value as a detection value of the physical quantity.

  The sensor device having such a configuration has a semiconductor micromechanical structure and a physical quantity detection capacitor whose capacitance changes according to a physical quantity applied from the outside, and a change in the capacitance with respect to the physical quantity applied from the outside. Since the reference capacitor smaller than the physical quantity detection capacitor is formed on the same substrate with a semiconductor micromechanical structure, variation in the capacitance difference between the physical quantity detection capacitor and the reference capacitor Variation in the detection sensitivity of the physical quantity based on the difference between the capacitance of the physical quantity detection capacitor and the capacitance of the reference capacitor is reduced among the plurality of sensor devices.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a block diagram showing an example of the configuration of the sensor device according to the first embodiment of the present invention. A sensor device 1 shown in FIG. 1 includes a MEMS substrate 2, a detection unit 3, a DC voltage source 4, and a voltage adjustment circuit 5. Further, a physical quantity detection capacitor 21 and a reference capacitor 22 are formed on the MEMS substrate 2 by the MEMS technology. The detection unit 3 is a circuit unit that detects a physical quantity applied to the physical quantity detection capacitor 21 based on a difference between the electrostatic capacity Cs of the physical quantity detection capacitor 21 and the electrostatic capacity Cref of the reference capacitor 22. 31 and a feedback impedance 32.

  The feedback impedance 32 is, for example, a resistor. The feedback impedance 32 is connected between the output terminal and the inverting input terminal of the operational amplifier 31, and the non-inverting input terminal of the operational amplifier 31 is connected to the ground. Thereby, the operational amplifier 31 operates as an inverting amplifier.

  FIG. 2 is a front view showing an example of the structure of the MEMS substrate 2. The MEMS substrate 2 illustrated in FIG. 2 includes, for example, a physical quantity detection capacitor 21 whose capacitance changes according to applied acceleration (physical quantity), and a reference in which the change in capacitance with respect to acceleration is smaller than that of the physical quantity detection capacitor 21. 2 is an example of a structure with the capacitor 22 for use, and a main substrate 201 made of a flat silicon substrate is roughly carved into a shape as shown in FIG. The physical quantity detection capacitor 21 and the reference capacitor 22 are formed on the main substrate 201 by being laminated on a support substrate made of a glass substrate. The main substrate 201 is bonded to the support substrate by, for example, anodic bonding.

  The physical quantity detection capacitor 21 is attached to the support substrate by beams 203 and 204 whose both end surfaces in the AA ′ direction can be bent and deformed so that the movable member 202 can be displaced in the AA ′ direction in FIG. It is supported. From the support substrate, a pair of support pillars 205 and 206 are erected on one end side of the movable member 202, and the support pillars 205 and 206 support the other end side of the movable member 202. Beams 207 and 208 are extended. Electrodes 209 and 210 are connected to the support beams 207 and 208 in a comb-like shape. Correspondingly, comb-like electrodes 211 and 212 are provided on both end faces of the movable member 202 in the BB 'direction in FIG.

  Accordingly, when acceleration is applied to the MEMS substrate 2 and the movable member 202 is displaced in the AA ′ direction, the electrostatic capacitance Cs between the electrodes 209 and 210 and the electrodes 211 and 212 changes. Further, the displacement of the movable member 202 in the BB ′ direction in FIG. 2 is suppressed by the shapes of the beams 203 and 204. On the other hand, although it is freely displaceable in the AA ′ direction in FIG. 2 as the detection direction, stoppers 213 and 214 are erected from the support substrate in order to limit excessive displacement.

  The reference capacitor 22 is configured in the same manner as the physical quantity detection capacitor 21 except that the beams 221 and 222 are provided instead of the beams 203 and 204 in the physical quantity detection capacitor 21. The beams 221 and 222 are thicker and thicker than the beams 203 and 204 to increase the rigidity, and the reference capacitor 22 has a capacitance between the electrodes 209 and 210 and the electrodes 211 and 212. The change of Cref with respect to the acceleration is smaller than that of the physical quantity detection capacitor 21 and is substantially zero.

  Since the reference capacitor 22 is formed by the same structure as the physical quantity detection capacitor 21 except for the structures of the beams 221, 222, the static capacity of the physical quantity detection capacitor 21 can be reduced when acceleration is not applied. The capacitance Cs and the capacitance Cref of the reference capacitor 22 are made substantially the same.

  Further, since the physical quantity detection capacitor 21 and the reference capacitor 22 are formed on the same MEMS substrate 2 by the same semiconductor process, the physical quantity detection capacitor 21 and the reference capacitor 22 have characteristic variations due to manufacturing variations. As a result, the influence of manufacturing variations on the difference between the capacitance Cs of the physical quantity detection capacitor 21 and the capacitance Cref of the reference capacitor 22 is reduced.

  The physical quantity detection capacitor 21 has been shown as an example in which the capacitance changes due to acceleration. For example, a capacitor whose capacitance changes with respect to other physical quantities such as temperature and humidity may be used. The reference capacitor 22 is formed on the same MEMS substrate 2 as these physical quantity detection capacitors 21. Ideally, the capacitance change with respect to these physical quantities is preferably zero (insensitive). It is sufficient that the capacitance change with respect to these physical quantities is smaller than that of the capacitor 21.

  Returning to FIG. 1, the DC voltage source 4 outputs the DC voltage Vdc to the inverting input terminal of the operational amplifier 31 through the physical quantity detection capacitor 21. The operational amplifier 31 feeds back the output signal Vd to the inverting input terminal via the voltage adjustment circuit 5 and the reference capacitor 22. The voltage adjustment circuit 5 is configured using, for example, an amplifier circuit that amplifies the output signal Vd of the operational amplifier 31. The voltage adjustment circuit 5 amplifies the output signal Vd output from the operational amplifier 31, and performs electrostatic capacitance in the physical quantity detection capacitor 21. The detection signal Vout indicating the change in the capacitance Cs, that is, the detected physical quantity, is output to the outside and output to the reference capacitor 22 as a feedback signal.

  Next, the operation of the sensor device 1 configured as described above will be described. First, when acceleration is applied to the MEMS substrate 2, the movable member 202 in the physical quantity detection capacitor 21 is displaced, and the capacitance Cs of the physical quantity detection capacitor 21 changes. On the other hand, the capacitance Cref does not change with respect to the acceleration, and the output voltage from the voltage adjustment circuit 5 is also maintained in the initial state. Then, the potential of the inverting input terminal of the operational amplifier 31 changes based on the difference in capacitance generated between the capacitance Cs and the capacitance Cref in accordance with the change in the capacitance Cs in the physical quantity detection capacitor 21. The voltage generated between the inverting input terminal and the non-inverting input terminal is amplified and output to the voltage adjusting circuit 5 as the output signal Vd.

  In this case, the capacitance Cref is equal to the initial capacitance value when no acceleration is applied to the physical quantity detection capacitor 21, so the output signal Vd corresponds to the acceleration of the capacitance Cs in the physical quantity detection capacitor 21. Shows the amount of change. Then, the voltage adjustment circuit 5 amplifies the output signal Vd output from the operational amplifier 31 and outputs the amplified signal to the reference capacitor 22 as a DC feedback voltage Vr.

  When the feedback voltage Vr is applied to the reference capacitor 22, the distance between the electrodes is reduced by the electrostatic attractive force generated between the electrodes 209 and 210 and the electrodes 211 and 212, and the capacitance Cref is increased. Then, due to the feedback loop composed of the operational amplifier 31, the voltage adjustment circuit 5, and the reference capacitor 22, the electrostatic capacitance Cref increases and becomes equal to the electrostatic capacitance Cs, and the potential of the inverting input terminal in the operational amplifier 31 is increased. The feedback voltage Vr is increased until it becomes equal to the reference potential of the non-inverting input terminal.

  As a result, the feedback voltage Vr rises so as to cancel out the difference between the capacitance Cs and the capacitance Cref caused by the acceleration applied to the physical quantity detection capacitor 21. As a result, the feedback voltage Vr becomes the physical quantity detection. This indicates the change in the capacitance Cs in the capacitor 21, that is, the detected physical quantity, and is output to the outside as the detection signal Vout by the voltage adjustment circuit 5.

  Thereby, the physical quantity detection capacitor 21 and the reference capacitor 22 are formed on the same MEMS substrate 2 by the same semiconductor process, and the capacitance Cs of the physical quantity detection capacitor 21 and the reference capacitor 22 are as described above. Since the influence of the manufacturing variation on the difference with the capacitance Cref is reduced, the variation in the detection signal Vout obtained per unit acceleration between the plurality of sensor devices 1, that is, the variation in the detection sensitivity of the physical quantity is reduced. Can do.

  As in the sensor device 1a shown in FIG. 3, instead of the detection unit 3 shown in FIG. 1, a fully differential operational amplifier 33 (fully differential operational amplifier), feedback capacitors 34 and 35, and differential The detection unit 3a configured to include the amplifier 36 may be used. In the sensor device 1 a shown in FIG. 3, the DC voltage Vdc is output from the DC voltage source 4 through the physical quantity detection capacitor 21 to one signal input terminal of the fully differential operational amplifier 33. The differential output signal is amplified by the differential amplifier 36 and fed back to the other signal input terminal of the fully differential operational amplifier 33 through the voltage adjustment circuit 5 and the reference capacitor 22.

  Further, like the sensor device 1b shown in FIG. 4, an operational amplifier 37 (first operational amplifier), an operational amplifier 38 (second operational amplifier), and an operational amplifier 37 are used instead of the detection unit 3 shown in FIG. Alternatively, the detection unit 3b configured to include the feedback impedance 39, the feedback impedance 40 of the operational amplifier 38, and the subtraction circuit 41 (difference output unit) may be used.

  In the sensor device 1 b shown in FIG. 4, the DC voltage Vdc is output from the DC voltage source 4 to the inverting input terminal of the operational amplifier 37 via the physical quantity detection capacitor 21, inverted and amplified by the operational amplifier 37, and supplied to the subtracting circuit 41. The difference between the output signal of the operational amplifier 37 and the output signal of the operational amplifier 38 is output as a feedback signal to the inverting input terminal of the operational amplifier 38 via the voltage adjustment circuit 5 and the reference capacitor 22 by the subtracting circuit 41. Yes.

(Second Embodiment)
Next, a sensor device according to a second embodiment of the present invention will be described. FIG. 5 is a block diagram showing an example of the configuration of the sensor device 1c according to the second embodiment of the present invention. The sensor device 1c shown in FIG. 5 differs from the sensor device 1 shown in FIG. 1 in the following points. That is, the sensor device 1c shown in FIG. 5 includes an AC voltage source 42 that outputs an AC voltage Vac1 instead of the DC voltage source 4 in the sensor device 1. Further, an AC voltage source 43 that outputs an AC voltage Vac2 and an adder 6 are further provided.

  Further, as shown in FIG. 6, the AC voltage Vac2 output from the AC voltage source 43 is 180 degrees out of phase with the AC voltage Vac1 output from the AC voltage source 42. Further, the frequencies of the AC voltages Vac1 and Vac2 are sufficiently separated from the mechanical resonance frequency of the movable member 202 in the physical quantity detection capacitor 21 and the reference capacitor 22, and are used for physical quantity detection by the AC voltages Vac1 and Vac2. The movable member 202 of the capacitor 21 and the reference capacitor 22 is vibrated, and the capacitances Cs and Cref are prevented from changing.

  The adder 6 is provided between the voltage adjustment circuit 5 and the reference capacitor 22, and adds the feedback voltage Vr output from the voltage adjustment circuit 5 and the AC voltage Vac 2 output from the AC voltage source 43 for reference. Supply to the capacitor 22.

  Instead of the detection unit 3, the detection units 3a and 3b may be used similarly to the sensor devices 1a and 1b. Since the other configuration is the same as that of the sensor device 1 shown in FIG. 1, the description thereof will be omitted, and the characteristic operation of the present embodiment will be described below. In the sensor device 1c shown in FIG. 5, since the AC voltage Vac1 is applied to the physical quantity detection capacitor 21 by the AC voltage source 42, the sensor devices 1, 1a, 1b to which the DC voltage Vdc is applied to the physical quantity detection capacitor 21 In comparison, the impedance of the physical quantity detection capacitor 21 is reduced, and the current flowing from the AC voltage source 42 to the detection unit 3 through the physical quantity detection capacitor 21, that is, the capacitance Cs of the physical quantity detection capacitor 21 is reflected. The signal component increases.

  In the sensor device 1c, the AC voltage Vac2 output from the AC voltage source 43 is added to the feedback voltage Vr output from the voltage adjustment circuit 5 and applied to the reference capacitor 22. Compared with the sensor devices 1, 1 a, 1 b to which the DC feedback voltage Vr is applied, the impedance of the reference capacitor 22 with respect to the AC voltage Vac 2 is lowered, and accordingly, the adder 6 passes the reference capacitor 22 to the detection unit 3. The signal component reflecting the flowing current, that is, the electrostatic capacitance Cref of the reference capacitor 22 increases.

  Thus, in the sensor device 1c, the signal component input from the physical quantity detection capacitor 21 and the reference capacitor 22 to the detection unit 3 is increased as compared with the sensor devices 1, 1a, and 1b, and the S / N ratio (signal pair) is increased. Noise ratio) is improved, so that the influence of noise on the output signal Vd output from the detection unit 3 is reduced. As a result, the influence of noise on the detection signal Vout output from the voltage adjustment circuit 5 can be reduced.

(Third embodiment)
Next, a sensor device according to a third embodiment of the present invention will be described. FIG. 7 is a block diagram showing an example of a configuration of a sensor device 1d according to the third embodiment of the present invention. The sensor device 1d shown in FIG. 7 is different from the sensor device 1c shown in FIG. 5 in the following points. That is, the sensor device 1 d shown in FIG. 7 is different in that a voltage adjustment circuit 5 a is provided instead of the voltage adjustment circuit 5. Instead of the detection unit 3, the detection units 3a and 3b may be used similarly to the sensor devices 1a and 1b.

  The voltage adjustment circuit 5a includes a comparison circuit 51 (comparison unit) that compares the feedback voltage Vr output from the detection unit 3 with a preset threshold voltage Vref, and an oscillator that generates a periodic signal CLK having a preset frequency. 52 (periodic signal generation unit) and the number of periods of the periodic signal CLK output from the oscillator 52 according to the comparison result by the comparison circuit 51 are counted, and the count value CT is detected by representing the detected value of acceleration as a digital value. For example, a 10-bit counter 53 (counter) that outputs the value Dout to the outside and outputs signals b0 to b9 representing each bit of the count value CT to one end of the resistors R0 to R9 connected in parallel is connected in parallel. The operational amplifier 54 having the other ends of the resistors R0 to R9 connected to the inverting input terminal and the non-inverting input terminal connected to the ground, and the inverting input terminal of the operational amplifier 54 And a resistor 55 for feedback that connects the power terminals.

  The operational amplifier 54 and the resistor 55 constitute a feedback amplifier that converts a current supplied from the counter 53 via a parallel circuit of resistors R0 to R9 into a feedback voltage Vr. The resistance values of the resistors R0 to R9 are set so that the resistance value decreases from the resistor R0 to the resistor R9, and the parallel circuit of the resistors R0 to R9 is turned on as the upper bit of the count value CT is turned on. Is greatly increased. Therefore, the count value CT of the counter 53 is converted into the current Ict by the parallel circuit of the resistors R0 to R9, converted into the feedback voltage Vr by the operational amplifier 54 and the resistor 55, and output to the adder 6. In other words, the parallel circuit of the resistors R0 to R9, the operational amplifier 54, and the resistor 55 constitute a DA converter 56 that converts the count value CT of the counter 53 into the feedback voltage Vr.

  Since the other configuration is the same as that of the sensor device 1c shown in FIG. FIG. 8 is a signal waveform diagram for explaining the operation of the sensor device 1d shown in FIG. First, when acceleration is applied to the MEMS substrate 2, the capacitance Cs of the physical quantity detection capacitor 21 is increased, and a difference is generated from the capacitance Cref of the reference capacitor 22. Then, the signal level of the output signal Vd output from the detection unit 3 to the comparison circuit 51 increases in accordance with the difference in capacitance.

  The comparison circuit 51 compares the output signal Vd output from the detection unit 3 with the threshold voltage Vref so as to detect the timing at which the electrostatic capacitance Cs and the electrostatic capacitance Cref become substantially equal. In the example of the sensor device 1d, the comparison circuit 51 outputs the control signal CC to the counter 53 at a low level to stop the counting operation of the counter 53 when the voltage of the output signal Vd is substantially zero, and the output signal Vd When the voltage is not substantially zero, the control signal CC is output to the counter 53 at a high level so that the counting operation by the counter 53 is performed. For this reason, the threshold voltage Vref is set to a minute voltage value for determining whether or not the output signal Vd is substantially zero. Now, since the output signal Vd is not substantially zero but exceeds the threshold voltage Vref, as shown in FIG. 8C, the control signal CC is output from the comparison circuit 51 to the counter 53 at a high level.

  Next, when the control signal CC is at a high level, the counter 53 counts, for example, rising edges of the periodic signal CLK output from the oscillator 52, thereby counting the number of periods of the periodic signal CLK. As shown in d), the count value CT of the counter 53 increases and the count value CT is output to the DA converter 56. Then, the count value CT is converted into the feedback voltage Vr by the DA converter 56, and the voltage value of the feedback voltage Vr output from the DA converter 56 to the adder 6 increases as shown in FIG. 8 (e).

  Then, when the voltage value of the feedback voltage Vr increases, the feedback composed of the adder 6, the reference capacitor 22, the detection unit 3, and the voltage adjustment circuit 5a is subsequently performed as in the case of the sensor device 1c shown in FIG. 8B, the capacitance Cref of the reference capacitor 22 gradually increases as shown in FIG. 8A, and the difference from the capacitance Cs of the physical quantity detection capacitor 21 decreases as shown in FIG. 8B. As shown, the voltage level of the output signal Vd output from the detection unit 3 to the comparison circuit 51 gradually decreases.

  Then, as shown in FIG. 8C, the control signal CC is output from the comparison circuit 51 to the counter 53 at a high level until the voltage level of the output signal Vd reaches substantially zero, as shown in FIG. Thus, the count value CT of the counter 53 increases.

  Further, when the electrostatic capacitance Cref becomes substantially equal to the electrostatic capacitance Cs, the voltage level of the output signal Vd output from the detection unit 3 becomes substantially zero and becomes equal to or lower than the threshold voltage Vref in the comparison circuit 51. The control signal CC is output to the counter 53 at a low level, and the counting operation of the counter 53 is stopped.

  Then, as the difference between the capacitance Cs caused by acceleration and the capacitance Cref is larger, the capacitance Cref becomes substantially equal to the capacitance Cs by the feedback loop described above, and the voltage level of the output signal Vd is substantially zero. Thus, since the time until the control signal CC becomes low level and the counting operation of the counter 53 is stopped is long, the count value CT of the counter 53 when the control signal CC becomes low level is generated by acceleration. The difference between the capacitance Cs and the capacitance Cref, that is, the acceleration detected by the MEMS substrate 2 is shown. Then, the counter 53 outputs the count value CT when the control signal CC becomes low level to the outside as a detection value Dout that represents the acceleration detection value as a digital value.

  As a result, the detected acceleration value can be represented as a detected value Dout as a digital value, and therefore, for example, a process such as correcting the acceleration detected by the sensor device 1d using a digital circuit such as a microcomputer can be performed. It becomes easy.

  Note that the number of bits of the counter 53 is equivalent to the difference between the capacitance Cs and the capacitance Cref, that is, the resolution of acceleration detected by the MEMS substrate 2, and about 10 bits is practical as described above. The acceleration may be increased or decreased according to the acceleration detection accuracy required for the sensor device 1d.

It is a block diagram which shows an example of a structure of the sensor apparatus which concerns on the 1st Embodiment of this invention. It is a front view which shows an example of the structure of the MEMS board | substrate shown in FIG. It is a block diagram which shows the modification of the sensor apparatus shown in FIG. It is a block diagram which shows the modification of the sensor apparatus shown in FIG. It is a block diagram which shows an example of a structure of the sensor apparatus which concerns on the 2nd Embodiment of this invention. It is a signal waveform diagram which shows the waveform of the alternating voltage output from the alternating voltage source shown in FIG. It is a block diagram which shows an example of a structure of the sensor apparatus which concerns on the 3rd Embodiment of this invention. It is a signal waveform diagram for demonstrating operation | movement of the sensor apparatus shown in FIG. It is a block diagram which shows the structure of the sensor apparatus which concerns on background art.

Explanation of symbols

1, 1a, 1b, 1c, 1d Sensor device 2 MEMS substrate 3, 3a, 3b Detection unit 4 DC voltage source 5, 5a Voltage adjustment circuit 6 Adder 21 Physical quantity detection capacitor 22 Reference capacitor 31 Operational amplifier 32 Feedback impedance 33 Fully differential operational amplifier 37, 38 Operational amplifier 41 Subtraction circuit 42, 43 AC voltage source 51 Comparison circuit 52 Oscillator 53 Counter 56 DA converter 201 Main substrate CLK Periodic signal Cref, Cs Capacitance CT Count value Dout Detection value

Claims (6)

A physical quantity detection capacitor that has a semiconductor micromechanical structure and whose capacitance changes according to a physical quantity applied from the outside;
A reference capacitor in which a change in capacitance with respect to the physical quantity is smaller than the physical quantity detection capacitor;
A detection unit that detects the physical quantity based on a difference between a capacitance of the physical quantity detection capacitor and a capacitance of the reference capacitor;
The sensor device according to claim 1, wherein the reference capacitor is formed on the same substrate as the physical quantity detection capacitor with the semiconductor micromechanical structure. The detector is
An operational amplifier;
A voltage source that outputs a voltage to one signal input terminal of the operational amplifier through the physical quantity detection capacitor;
The sensor device according to claim 1, wherein the operational amplifier feeds back an output signal of the operational amplifier as a feedback signal to the one signal input terminal via the reference capacitor. The detector is
A fully differential operational amplifier;
A voltage source that outputs a voltage to one signal input terminal of the fully differential operational amplifier through the physical quantity detection capacitor;
The fully differential operational amplifier feeds back an output signal of the fully differential operational amplifier as a feedback signal to the other signal input terminal of the fully differential operational amplifier via the reference capacitor. The sensor device according to claim 1. The detector is
First and second operational amplifiers;
A voltage source that outputs a voltage to one signal input terminal of the first operational amplifier via the physical quantity detection capacitor;
The difference output which feeds back the difference between the output signal of the first operational amplifier and the output signal of the second operational amplifier as a feedback signal to one signal input terminal of the second operational amplifier via the reference capacitor. The sensor device according to claim 1, further comprising: a unit.   The sensor device according to claim 2, wherein the voltage source is an AC voltage source. A comparator for comparing the feedback signal with a preset threshold;
A periodic signal generator for generating a periodic signal having a preset frequency;
A counting unit that counts the number of periods of the periodic signal generated by the periodic signal generation unit according to a comparison result by the comparison unit, and outputs the count value as a detection value of the physical quantity. The sensor device according to claim 2.

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