WO2015098893A1

WO2015098893A1 - Capacitance trimming circuit

Info

Publication number: WO2015098893A1
Application number: PCT/JP2014/084002
Authority: WO
Inventors: 信昭 ▲辻▼
Original assignee: 株式会社村田製作所
Priority date: 2013-12-27
Filing date: 2014-12-22
Publication date: 2015-07-02
Also published as: JP2015125088A

Abstract

　A capacitance trimming circuit (7) is provided with: a capacitance trimming unit (5); and a capacitance voltage division generating unit (6) which, when the electrostatic capacitance is to be adjusted by the capacitance trimming unit (5), applies a reference voltage (Vc) to one end of a first feedback capacitor (Cf1) to produce a voltage (V1) voltage-divided by a first capacitor (8), and applies a reference voltage (Vc) to one end of a second feedback capacitor (Cf2) to produce a voltage (V2) voltage-divided by a second capacitor (9).

Description

Capacitor trimming circuit

The present invention relates to a capacitance trimming circuit in a CV conversion circuit for detecting a signal output from a capacitance type sensor or the like.

Conventionally, as various sensors such as an acceleration sensor mounted on an automobile or a portable terminal device, a capacitive sensor in which a movable electrode is arranged between two fixed electrodes by a MEMS (Micro Electro Mechanical Systems) structure is known. Yes. In general, this type of capacitance type sensor includes a CV conversion circuit for detecting a change in capacitance caused by displacement of the movable electrode in accordance with acceleration acting on the sensor (for example, Patent Documents). 1). Since the CV conversion circuit detects a change in capacitance based on the amount of charge transferred from the movable electrode or the fixed electrode as a minute voltage change of, for example, about 0.1 to 1.0 μV, charge transfer is caused by disturbance noise. When this occurs, it becomes impossible to accurately detect the amount of change in capacitance.

For this reason, in recent years, a circuit configuration has been adopted in which signal detection is performed using a fully differential amplifier in a CV conversion circuit to cancel disturbance noise and detect a minute change in capacitance. For example, when a capacitive sensor is connected to one of the two input terminals of the fully differential amplifier and a dummy capacitor having substantially the same capacitance as that of the capacitive sensor is connected to the other, Even if disturbance noise acts on both the signal line connected to the capacitive sensor and the signal line connected to the dummy capacitor, the disturbance noise can be canceled by the difference between the two output signals of the fully differential amplifier. The influence of noise can be reduced.

Japanese Laid-Open Patent Publication No. 5-340958

However, when elements having different structures are connected to the two input terminals of the fully-differential amplifier as described above, it is difficult to form their capacitances in substantially the same state in advance. In addition, the parasitic capacitance parasitic to the capacitive sensor does not necessarily match the parasitic capacitance parasitic to the dummy capacitor. If the capacitance connected to each of the two input terminals of the fully-differential amplifier is not substantially the same, if disturbance noise acts, charge transfer of different amounts of charge occurs in each of the two signal lines. Will not be able to cancel well.

Therefore, when a CV conversion circuit is configured using a fully differential amplifier, a large number of trimming capacitors are arranged, and a capacitor selected from the large number of trimming capacitors is connected to two input terminals of the fully differential amplifier. By connecting to or disconnecting from at least one of these, the unbalance of the capacitance connected to the two input terminals of the fully differential amplifier is eliminated in advance. In other words, the two output signals of the fully differential amplifier are amplified by a post-stage circuit, and the trimming capacitors are connected and disconnected individually while determining the actual noise amount increase / decrease based on the AD conversion of the amplified signals. As a result, the capacitances connected to the two input terminals of the fully differential amplifier are adjusted to substantially the same state.

However, when adjusting the capacitance, adopting a method of determining the actual noise amount increase / decrease with the value obtained by AD conversion of the amplified signal obtained by amplifying the output signal of the fully differential amplifier, the difference in capacitance is small. In some cases, it is difficult to accurately determine the amount of increase or decrease in noise. Therefore, there is a problem that it takes time to trim the capacitance, and it is difficult to perform trimming setting with high accuracy of about several fF (femtofarad).

The present invention has been made for the purpose of solving the above-described problems. In a CV conversion circuit using a fully differential amplifier, a capacitance can be easily and accurately detected without detecting an actual amount of noise. Therefore, a capacitor trimming circuit capable of performing the above trimming is provided.

According to one embodiment of the present invention, the first feedback capacitor is connected between the inverting input terminal and the non-inverting output terminal of the fully differential amplifier, and the non-inverting input terminal is provided. In the CV conversion circuit in which the first feedback capacitor and the second feedback capacitor having substantially the same capacitance are connected between the inverting output terminal and the first feedback capacitor, the first feedback capacitor includes at least one first capacitor connected to the inverting input terminal. A capacitance trimming circuit for trimming a capacitance difference between a capacitance and a second capacitance caused by at least one second capacitor connected to the non-inverting input terminal is connected to the inverting input terminal or the non-inverting input terminal. Multiple trimming capacitors that can be individually connected to or disconnected from each other, and multiple trimming capacitors are individually inverting input terminals or non-inverting inputs A capacitance trimming unit that adjusts the first capacitance and the second capacitance to substantially the same state by being connected to or disconnected from the child, and when capacitance adjustment is performed by the capacitance trimming unit. By applying a reference voltage to one end of the first feedback capacitor, a voltage corresponding to the capacitance division between the first feedback capacitor and the first capacitor is generated at the inverting input terminal, and a reference is applied to one end of the second feedback capacitor. By applying a voltage, a voltage corresponding to the capacitance division between the second feedback capacitor and the second capacitor is generated at the non-inverting input terminal, and the voltage generated at the inverting input terminal is compared with the voltage generated at the non-inverting input terminal. A capacity partial pressure generation unit for outputting the result.

FIG. 1 is a diagram illustrating a configuration example of a sensor device including a capacitor trimming circuit. FIG. 2 is a diagram illustrating an equivalent circuit of the sensor unit. FIG. 3 is a diagram illustrating a first operation state in the adjustment mode. FIG. 4 is a diagram illustrating a second operation state in the adjustment mode.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each embodiment demonstrated below, the same code | symbol is attached | subjected to the member which is mutually common, and the overlapping description about them is abbreviate | omitted.

FIG. 1 is a diagram showing a configuration example of a sensor device including a capacitor trimming circuit 7 according to the present invention. This sensor device includes a sensor unit 1 having a capacitance type sensor 3 constituted by MEMS, a CV conversion circuit 2 connected to the sensor unit 1 and detecting the capacitance of the capacitance type sensor 3, The capacitor trimming circuit 7 incorporated in the CV conversion circuit 2 is provided, and is configured as a sensor for detecting acceleration acting on the sensor unit 1.

The capacitance type sensor 3 provided in the sensor unit 1 includes a weight 13 that is supported by a spring structure and can be displaced in a predetermined direction, and the two capacitors 11 having variable capacitance with the weight 13 interposed therebetween. , 12 are connected in series. These

capacitors

11 and 12 are configured by a movable electrode that is displaced in conjunction with the weight 13 and a fixed electrode that faces the movable electrode. When the weight 13 is in the intermediate position, the

capacitors

11 and 12 have the same capacitance C1. When acceleration acts on the sensor unit 1 and the weight 13 is displaced from the intermediate position in a predetermined direction, the capacitances of the

capacitors

11 and 12 change according to the amount of displacement. For example, when the capacitance of one capacitor 11 increases to (C1 + ΔC), the capacitance of the other capacitor 12 decreases to (C1−ΔC). When the capacitance of one capacitor 11 decreases to (C1−ΔC), the capacitance of the other capacitor 12 increases to (C1 + ΔC). The movable electrodes of the

capacitors

11 and 12 have the same potential as the weight 13 and are connected to the output terminal mb to the CV conversion circuit 2 via the weight 13. The fixed electrode of the capacitor 11 is connected to the input terminal X1, and the fixed electrode of the capacitor 12 is connected to the input terminal X2. These input terminals X1 and X2 receive high-frequency signals of about several hundred kHz, for example, and rectangular wave signals φ1 and φ2 whose polarities are inverted from each other, and are applied to the fixed electrodes of the

capacitors

11 and 12, respectively. Therefore, the electrostatic capacity type sensor 3 outputs a charge signal corresponding to the electrostatic capacity of each of the

capacitors

11 and 12 and modulated by the rectangular wave signals φ 1 and φ 2 to the CV conversion circuit 2.

In addition, the sensor unit 1 has a dummy capacitor 4 having a capacitance C2 that is substantially the same as the capacitance of the capacitance type sensor 3 (the combined capacitance of the capacitors 11 and 12) viewed from the CV conversion circuit 2. The dummy capacitor 4 is composed of a pair of fixed electrodes facing each other, and the capacitance C2 is fixed. The dummy capacitor 4 has one end connected to the output terminal mbv to the CV conversion circuit 2 and the other end grounded.

The CV conversion circuit 2 mainly includes a fully differential amplifier 21, a first feedback capacitor Cf1, a second feedback capacitor Cf2, and

switches

22 and 23 for resetting accumulated charges of the first and second feedback capacitors Cf1 and Cf2. It is configured with. The first feedback capacitor Cf1 is connected between the inverting input terminal and the non-inverting output terminal of the fully differential amplifier 21, and the second feedback capacitor Cf2 is connected to the non-inverting input terminal and the inverting output terminal of the fully differential amplifier 21. Connected between. The switch 22 is connected between the inverting input terminal and the non-inverting output terminal of the fully differential amplifier 21 in parallel with the first feedback capacitor Cf1. The switch 23 is connected between the non-inverting input terminal and the inverting output terminal of the fully differential amplifier 21 in parallel with the second feedback capacitor Cf2. The inverting input terminal of the fully differential amplifier 21 is connected to the weight 13 of the capacitive sensor 3 via the signal line L1 connected to the terminal mb of the sensor unit 1, and the non-inverting input terminal is a terminal of the sensor unit 1. It is connected to one end of the dummy capacitor 4 via a signal line L2 connected to mbv. With this configuration, the fully differential amplifier 21 operates as an integrating amplifier.

Then, the CV conversion circuit 2 temporarily turns on the

switches

22 and 23 at a predetermined timing to reset the accumulated charges of the first and second feedback capacitors Cf1 and Cf2, and then the capacitance type sensor 3 and the dummy capacitor 4 The charge signal output from each of the first and second feedback capacitors Cf1 and Cf2 is accumulated in each of them to perform CV conversion. That is, the CV conversion circuit 2 stores the charge signal output from the capacitive sensor 3 in the first feedback capacitor Cf1 by applying the rectangular wave signals φ1 and φ2 to both ends of the

capacitors

11 and 12, and An output signal Vop corresponding to the capacitance of each of the

capacitors

11 and 12 and having a predetermined reference voltage Vref as a center voltage is output from the non-inverting output terminal of the differential amplifier 21. On the other hand, if the voltage applied to the dummy capacitor 4 is constant, charge transfer does not occur between the dummy capacitor 4 and the second feedback capacitor Cf2, so that the fully differential amplifier 21 has a predetermined reference voltage from the inverting output terminal. An output signal Von corresponding to Vref is output.

In the above configuration, for example, when disturbance noise acts on the signal lines L1 and L2, the voltages Vin and Vip of the inverting input terminal and the non-inverting input terminal of the fully-differential amplifier 21 vary due to the influence of the disturbance noise. At this time, if the amount of charge transferred from the signal line L1 to the first feedback capacitor Cf1 due to the influence of disturbance noise and the amount of charge transferred from the signal line L2 to the second feedback capacitor Cf2 are equal to each other, Disturbance noise can be canceled by the difference signal Vout (= Vop−Von) between the two output signals Vop and Von output from the differential amplifier 21. However, in practice, as shown in FIG. 1, the parasitic capacitance Cp <b> 1 parasitic on the capacitive sensor 3 provided in the sensor unit 1 and the parasitic capacitance Cp <b> 2 parasitic on the dummy capacitor 4 do not match. Therefore, even if the capacitance C2 of the dummy capacitor 4 is substantially the same as the capacitance of the capacitance type sensor 3 (the combined capacitance of the capacitors 11 and 12), the non-inversion and the inverting input terminal of the fully differential amplifier 21 The capacitances of the sensor units 1 connected to the input terminals are not substantially the same.

FIG. 2 is a diagram showing an equivalent circuit of the sensor unit 1 when the sensor unit 1 is viewed from the CV conversion circuit 2. As shown in FIG. 2, when viewed from the CV conversion circuit 2, the sensor unit 1 includes a first capacitor Cs connected to a terminal mb and a first capacitor Cs, and a second capacitor connected to the terminal mbv. This is equivalent to the connection of the second electrostatic capacitance Cv of 9. Here, the first capacitance Cs is a capacitance obtained by combining the

capacitors

11 and 12 and the parasitic capacitance Cp1. The second capacitance Cv is a capacitance obtained by combining the dummy capacitor 4 and the parasitic capacitance Cp2. Since the parasitic capacitances Cp1 and Cp2 are different from each other, the first electrostatic capacitance Cs and the second electrostatic capacitance Cv are not substantially in the same state. In such a situation, when disturbance noise acts on the signal lines L1 and L2, the amount of charge absorbed from the signal lines L1 and L2 to the sensor unit 1 side is not equal, and the disturbance noise causes the first feedback capacitor Cf1. The amount of stored charge does not match the amount of stored charge in the second feedback capacitor Cf2. Therefore, disturbance noise cannot be canceled satisfactorily even if the difference between the two output signals Vop and Von output from the fully differential amplifier 21 is calculated. That is, the unbalance between the first electrostatic capacitance Cs and the second electrostatic capacitance Cv becomes a factor that the disturbance noise cannot be canceled satisfactorily.

Therefore, the CV conversion circuit 2 according to the present embodiment includes the capacitor trimming circuit 7, and the first electrostatic capacitance of the sensor unit 1 connected to each of the inverting input terminal and the non-inverting input terminal of the fully differential amplifier 21. The imbalance between the capacitance Cs and the second electrostatic capacitance Cv can be eliminated in advance. The capacitor trimming circuit 7 includes a capacitor trimming unit 5 provided in the signal line L2, the first feedback capacitor Cf1 in the CV conversion circuit 2 and the non-inverting output terminal of the fully differential amplifier 21, and the second feedback capacitor. The capacitor voltage generating unit 6 is provided between the Cf2 and the inverting output terminal of the fully differential amplifier 21.

The capacitor trimming unit 5 includes a plurality of trimming capacitors 51, and the plurality of trimming capacitors 51 are individually connected to or disconnected from the signal line L2 connected to the non-inverting input terminal of the fully differential amplifier 21. Can do. That is, the capacitor trimming unit 5 includes a plurality of trimming elements 53 having a configuration in which a trimming capacitor 51 and a switch 52 are connected in series between the signal line L2 and the ground point. By turning on the switch 52 of the selected element, an arbitrary capacitance is applied to the signal line L2 connected to the non-inverting input terminal of the fully differential amplifier 21. Then, by trimming the electrostatic capacity applied to the signal line L2, the electrostatic capacity connected to each of the inverting input terminal and the non-inverting input terminal of the fully differential amplifier 21 is set in advance to be approximately the same state. The plurality of trimming capacitors 51 may have the same capacitance, or may have different capacitances.

For example, each switch 52 provided in the capacity trimming unit 5 is turned on / off based on information written in a memory (not shown) from the outside. Therefore, after the sensor device is manufactured, the capacitance is adjusted before shipment, and the capacitance of each switch 52 in which the capacitance connected to each of the inverting input terminal and the non-inverting input terminal of the fully-differential amplifier 21 is substantially the same. If the on / off state is written in the memory in advance, it is not necessary to adjust the capacitance after shipment of the sensor device.

When the capacitance trimming unit 5 performs capacitance adjustment by the capacitance trimming unit 5, the capacitances connected to the inverting input terminal and the non-inverting input terminal of the fully differential amplifier 21 are substantially the same. This is a circuit that makes it possible to determine whether or not there is high accuracy. The capacitance partial pressure generating unit 6 includes a plurality of switches 61 to 66 that operate when the capacitance is adjusted by the capacitance trimming unit 5. The switches 61 to 63 are provided between the non-inverting output terminal of the fully differential amplifier 21 and the first feedback capacitor Cf1. The switch 61 is a switch that connects one end of the first feedback capacitor Cf1 to the non-inverting output terminal of the fully-differential amplifier 21 or opens it from the non-inverting output terminal. The switch 62 is a switch that connects one end of the first feedback capacitor Cf1 to the ground point or opens from the ground point. The switch 63 is a switch for connecting one end of the first feedback capacitor Cf1 to the reference voltage Vc or releasing from the reference voltage Vc. The switches 64 to 66 are provided between the inverting output terminal of the fully differential amplifier 21 and the second feedback capacitor Cf2. The switch 64 is a switch for connecting one end of the second feedback capacitor Cf2 to the inverting output terminal of the fully-differential amplifier 21 or opening it from the inverting output terminal. The switch 65 is a switch that connects one end of the second feedback capacitor Cf2 to the ground point or opens it from the ground point. The switch 66 is a switch for connecting one end of the second feedback capacitor Cf2 to the reference voltage Vc or releasing from the reference voltage Vc.

The

switches

61 and 64 are normally in an on state in which one ends of the first and second feedback capacitors Cf1 and Cf2 are connected to the non-inverting output terminal and the inverting output terminal of the fully differential amplifier 21, and are input from the outside. By the control signal, one end of the first and second feedback capacitors Cf1 and Cf2 is turned off from the non-inverting output terminal and the inverting output terminal of the fully differential amplifier 21. The

switches

62 and 65 are normally in an off state in which one ends of the first and second feedback capacitors Cf1 and Cf2 are opened from the ground point, and the first and second feedback capacitors Cf1 and Cf1 are controlled by a control signal input from the outside. One end of Cf2 is turned on to connect to the ground point. Further, the

switches

63 and 66 are normally in an off state in which one ends of the first and second feedback capacitors Cf1 and Cf2 are released from the reference voltage Vc, and the first and second feedback capacitors Cf1 are controlled by a control signal input from the outside. , Cf2 is connected to one end of the reference voltage Vc. Hereinafter, the operation of the capacitive partial pressure generator 6 will be described in detail.

When an adjustment mode in which capacitance adjustment by the capacitance trimming unit 5 is performed is designated, the capacitance partial pressure generating unit 6

first switches

61 and 63 as shown in FIG. 3 based on a control signal input from the outside. 64, 66 are turned off, and switches 62, 65 are turned on. At this time, the

switches

22 and 23 provided in the CV conversion circuit 2 are turned on. In this adjustment mode, acceleration does not act on the sensor unit 1, and the state where the weight 13 is in the intermediate position is maintained. In the adjustment mode, the input terminals X1 and X2 of the sensor unit 1 are grounded.

In the state shown in FIG. 3, the fully differential amplifier 21 operates as a buffer amplifier. Here, assuming that the offset voltage of the fully differential amplifier 21 is Voff and that the offset voltage Voff is included only in the output signal Vop, the output signal Vop of the fully differential amplifier 21 is Vop = Vref + Voff, and the output signal Von becomes Von = Vref. At this time, the voltage (Vref + Voff) is applied to the first feedback capacitor Cf1 and the first capacitor 8, and the voltage Vref is applied to the second feedback capacitor Cf2 and the second capacitor 9. That is, in the state shown in FIG. 3, initial charges are accumulated in the

capacitors

8, 9, Cf 1, and Cf 2 including the offset voltage Voff of the fully differential amplifier 21.

When the initial charge is accumulated as described above, the capacitive voltage dividing unit 6 next turns off the

switches

61, 62, 64, 65 as shown in FIG. 63 and 66 are turned on. At this time, the

switches

22 and 23 provided in the CV conversion circuit 2 are turned off. That is, the capacitive voltage dividing unit 6 disconnects one end of the first feedback capacitor Cf1 from the non-inverting output terminal of the fully-differential amplifier 21, and applies the reference voltage Vc to the one end, thereby the first feedback capacitor Cf1 and the first feedback capacitor Cf1. A voltage V 1 corresponding to the capacity division with one capacitor 8 is generated at the inverting input terminal of the fully differential amplifier 21. As a result, the voltage V1 based on the capacitive voltage division generated at the inverting input terminal of the fully differential amplifier 21 is V1 = Cf1 / (Cf1 + Cs) * Vc. Similarly, the capacitive voltage dividing unit 6 disconnects one end of the second feedback capacitor Cf2 from the inverting output terminal of the fully-differential amplifier 21, and applies the reference voltage Vc to one end of the second feedback capacitor Cf2. A voltage V <b> 2 corresponding to the capacity division with the second capacitor 9 is generated at the non-inverting input terminal of the fully differential amplifier 21. As a result, the voltage V2 based on the capacitance division generated at the non-inverting input terminal of the fully differential amplifier 21 is V2 = Cf2 / (Cf2 + Cv) * Vc.

Further, in the state shown in FIG. 4, since the feedback path of the fully differential amplifier 21 is opened, the fully differential amplifier 21 operates as a comparator. Therefore, the fully differential amplifier 21 outputs the result of comparing the voltage V1 input to the inverting input terminal and the voltage V2 input to the non-inverting input terminal as output signals Vop and Von.

For example, when the reference voltage Vc is 1.3 V, the capacitance Cf1 of the first feedback capacitor Cf1 is 200 fF, and the capacitance Cs of the first capacitor 8 is 2000 fF, the input to the inverting input terminal of the fully differential amplifier 21 The voltage V1 to be used is V1 = 200 / (200 + 2000) * 1.3 = 0.118182V. Similarly, when the reference voltage is 1.3 V, the capacitance Cf2 of the second feedback capacitor Cf2 is 200 fF, and the capacitance Cv of the second capacitor 9 is 1998 fF, the non-inverting input terminal of the fully differential amplifier 21 The voltage V2 input to the voltage V2 = 200 / (200 + 1998) * 1.3 = 0.118289V. At this time, the difference (V2−V1) between the voltages V1 and V2 input to the fully differential amplifier 21 operating as a comparator is (V2−V1) = 0.107 mV, so that the DC gain of the fully differential amplifier 21 is Assuming 100 dB, the output signals Vop and Von of the fully differential amplifier 21 are Vop−Von = 10.7V. Therefore, the fully-differential amplifier 21 functions sufficiently as a comparator, the output signal Vop that is a comparator output is “High”, and the output signal Von is “Low”.

Further, under the same conditions as described above, for example, when the capacitance Cv of the second capacitor 9 is set to 2002 fF, the voltage V2 input to the non-inverting input terminal of the fully differential amplifier 21 is V2 = 200 / (200 + 2002). * 1.3 = 0.118074V. At this time, the difference (V2−V1) between the voltages V1 and V2 input to the fully differential amplifier 21 operating as a comparator is (V2−V1) = − 0.108 mV. Is 100 dB, the output signals Vop and Von of the fully-differential amplifier 21 are Vop−Von = −10.8V. Therefore, the fully differential amplifier 21 functions sufficiently as a comparator in the same manner as described above, the output signal Vop as the comparator output becomes “Low”, and the output signal Von becomes “High”.

In this way, the capacitive voltage divider 6 applies the reference voltage Vc to one end of the first feedback capacitor Cf1 to generate the voltage V1 corresponding to the capacitive voltage division between the first feedback capacitor Cf1 and the first capacitor 8. At the same time, a reference voltage Vc is applied to one end of the second feedback capacitor Cf2 to generate a voltage V2 corresponding to the capacitance division between the second feedback capacitor Cf2 and the second capacitor 9, and the fully differential amplifier 21 is used as a comparator. The operation is performed and the comparison result of the voltages V1 and V2 is output. Thereby, even if the difference between the capacitance Cs of the first capacitor 8 and the capacitance Cv of the second capacitor 9 is a slight difference of about 2 fF as described above, it can be detected well. . Therefore, when the capacitance trimming is performed by the capacitance trimming unit 5, one of the output signals Vop and Von, which are comparator outputs of the fully differential amplifier 21, changes from “High” to “Low” or “Low”. By performing fine trimming at the point where the switching from “High” to “High” is performed, the difference between the capacitance Cs of the first capacitor 8 and the capacitance Cv of the second capacitor 9 can be suppressed to a range of about 2 fF or less. It is possible to perform highly accurate trimming.

In particular, the capacitive voltage divider 6 generates a voltage V1, V2 obtained by capacitively dividing the reference voltage Vc before the offset voltage Voff of the fully differential amplifier 21 is applied to each of the

capacitors

8, 9, Cf1, Cf2. Is stored, and thereafter, voltages V1 and V2 obtained by capacitively dividing the reference voltage Vc are generated. Therefore, when the difference between the capacitance Cs of the first capacitor 8 and the capacitance Cv of the second capacitor 9 is detected, a charge corresponding to the offset voltage Voff of the fully differential amplifier 21 is accumulated. Can be detected. Thereby, since the difference in capacitance can be detected in the same state as the state in which the fully differential amplifier 21 is operated as an integrating amplifier, even when the adjustment mode is switched to the normal operation mode after the trimming is completed, A balanced state in which the capacitance connected to the inverting input terminal of the fully-differential amplifier 21 and the capacitance connected to the non-inverting input terminal are adjusted to be substantially the same is maintained. The capacitance trimming unit 5 adjusts the capacitance based on the comparator output (High or Low) of the fully-differential amplifier 21, and then the capacitance connected to the inverting input terminal and the non-inverting input terminal. When reconfirming the balance state with the connected capacitance, each time the initial charge taking into account the offset voltage Voff of the fully-differential amplifier 21 is accumulated, the voltages V1, V2 obtained by dividing the reference voltage Vc by capacitance are stored. Is preferably generated.

When the trimming is completed and the adjustment mode is terminated and the operation mode is switched to the normal operation mode, the capacitive partial pressure generating unit 6 turns on the

switches

61 and 64 and switches the

switches

62, 63, 65, and 66 as shown in FIG. Turn off. Further, the capacitance trimming unit 5 always fixes the capacitance adjusted in the adjustment mode to a state where the capacitance is applied to the signal line L2. Therefore, when detecting the displacement of the weight 13 according to the acceleration in the normal operation mode, the capacitances connected to the inverting input terminal and the non-inverting input terminal of the fully-differential amplifier 21 are substantially the same. is there. Therefore, when disturbance noise acts on the signal lines L1 and L2, the amount of charge transferred from the signal line L1 to the first feedback capacitor Cf1 due to the influence of the disturbance noise, and transfer from the signal line L2 to the second feedback capacitor Cf2 Therefore, the disturbance noise can be satisfactorily canceled by the difference signal Vout (= Vop−Von) between the two output signals Vop and Von output from the fully differential amplifier 21. Will be able to.

Further, in order to be able to output the comparison results of the voltages V1 and V2 at high speed from the fully differential amplifier 21 operating as a comparator in the adjustment mode described above, a phase compensation capacitor (not shown) connected to the fully differential amplifier 21 is provided. Is preferably operated as a comparator in a state of being separated from the fully differential amplifier 21. In this case, when the adjustment mode ends and the operation mode is switched to the normal operation mode, the phase compensation capacitor is connected to the fully differential amplifier 21 again to prevent oscillation.

As described above, the capacitor trimming circuit 7 of the present embodiment has the first capacitance Cs connected to the inverting input terminal of the fully differential amplifier 21 and the first capacitor Cs connected to the non-inverting input terminal of the fully differential amplifier 21. Capacitance trimming unit 5 that adjusts so that the capacitance Cv of 2 is substantially the same, and when capacitance adjustment is performed by the capacitance trimming unit 5, the first and second feedback capacitors Cf1, By applying the reference voltage Vc to each of Cf2, voltages V1 and V2 corresponding to the capacitance division are generated at the inverting input terminal and the non-inverting input terminal, respectively, and the comparison result of the voltages V1 and V2 is output. And a pressure generator 6. According to such a configuration, it is not necessary to detect the actual amount of noise when the capacitance is adjusted by the capacitance trimming unit 5, so that it does not take time to adjust the capacitance. Further, since it is possible to determine the unbalance of the capacitance by comparing the magnitudes of the voltages V1 and V2 generated by the capacitance division, it is possible to easily adjust the capacitance with high accuracy.

In addition, as described above, the capacitive voltage dividing unit 6 disconnects one end of the first feedback capacitor Cf1 from the non-inverting output terminal of the fully-differential amplifier 21 and connects it to the reference voltage Vc at one end thereof. By disconnecting one end of Cf2 from the inverting output terminal of the fully differential amplifier 21 and connecting it to the reference voltage Vc at one end thereof, the fully differential amplifier 21 operates as a comparator, and the voltage V1 generated at the inverting input terminal and the non-inverting input The comparison result with the voltage V2 generated at the terminal is output from each of the inverting output terminal and the non-inverting output terminal. Therefore, it is not necessary to provide another comparator different from the fully differential amplifier 21 in order to compare the voltages V1 and V2, and there is an advantage that the circuit scale of the sensor device can be reduced.

Further, as described above, when the capacitance trimming unit 5 adjusts the capacitance, the capacitance voltage dividing unit 6 applies the reference voltage Vc to one end of each of the first and second feedback capacitors Cf1 and Cf2. Prior to this, an initial charge corresponding to the offset voltage Voff of the fully-differential amplifier 21 is accumulated in each of the first and second feedback capacitors Cf1 and Cf2. As a result, the capacitance can be adjusted in a state in which the offset voltage Voff of the fully differential amplifier 21 is reflected, so that the capacitance is adjusted to be substantially the same in the normal operation mode after the adjustment mode is finished. The disturbance state can be maintained and disturbance noise can be canceled satisfactorily.

As mentioned above, although one Embodiment regarding this invention was described, this invention is not limited to the content mentioned above, It is possible to apply a various modification.

For example, in the above embodiment, the case where the capacitor trimming unit 5 is provided on the signal line L2 connected to the non-inverting input terminal of the fully-differential amplifier 21 is exemplified. However, the present invention is not limited to this, and the capacitor trimming unit 5 may be provided on the signal line L1 connected to the inverting input terminal of the fully differential amplifier 21. The capacitor trimming unit 5 may be provided in each of the signal lines L1 and L2 connected to the non-inverting input terminal and the inverting input terminal of the fully differential amplifier 21, respectively. If the capacitance trimming unit 5 is provided for each of the signal lines L1 and L2, the capacitance can be finely adjusted, so that more accurate adjustment is possible.

In the above embodiment, the case where the sensor unit 1 is provided with the uniaxial capacitive sensor 3 has been exemplified. However, the present invention is not limited to this, and for example, the sensor unit 1 may be provided with three capacitive sensors 3 for detecting accelerations in three axial directions orthogonal to each other. In this case, since the weights 13 of the three capacitance sensors 3 are connected to the terminal mb, the capacitance C2 of the dummy capacitor 4 is equal to the capacitance obtained by synthesizing the three capacitance sensors 3. They are formed to be substantially the same.

In the above embodiment, the case where the fully differential amplifier 21 is operated as a comparator in the adjustment mode is illustrated, but the present invention is not limited to this, and a comparator used in the adjustment mode is provided separately from the fully differential amplifier 21. It doesn't matter. However, in this case, the circuit scale of the sensor device increases. Therefore, when it is desired to reduce the size of the sensor device, as described above, the fully differential amplifier 21 may be used as a comparator rather than providing the comparator separately from the fully differential amplifier 21.

In the above embodiment, the output terminal of the capacitive sensor 3 is connected to the inverting input terminal of the fully differential amplifier 21, and the dummy capacitor substantially the same as the capacitance of the capacitive sensor 3 is connected to the non-inverting input terminal. The state where 4 was connected was illustrated. However, the present invention is not limited to this, and the capacitance type sensor 3 may be connected to the non-inverting input terminal of the fully-differential amplifier 21 and the dummy capacitor 4 may be connected to the inverting input terminal.

Furthermore, without providing the dummy capacitor 4, the fixed electrode of the capacitor 11 of the capacitive sensor 3 may be connected to the terminal mb, and the fixed electrode of the capacitor 12 may be connected to the terminal mbv. In this case, a high-frequency rectangular wave signal is applied to the weight 13, and charge signals corresponding to the capacitances of the

capacitors

11 and 12 are output from the two fixed electrodes of the capacitance type sensor 3 to the CV conversion circuit 2. Is done. Even in such a configuration, if the parasitic capacitances Cp1 and Cp2 have variations, the capacitance trimming circuit 7 can adjust the variations of the parasitic capacitances Cp1 and Cp2 with high accuracy.

In the above embodiment, the case where the capacitive sensor 3 is a sensor that detects acceleration is illustrated as an example. However, the present invention is not limited to this, and the sensor is configured as a sensor that detects a physical quantity (for example, angular velocity) other than acceleration. It does not matter if it is

In the above configuration, the capacitive voltage dividing unit disconnects one end of the first feedback capacitor from the inverting output terminal and connects it to the reference voltage, and disconnects one end of the second Fordback capacitor from the non-inverting output terminal and connects to the reference voltage. Thus, the fully differential amplifier may be operated as a comparator, and the comparison result between the voltage generated at the inverting input terminal and the voltage generated at the non-inverting input terminal may be output from each of the inverting output terminal and the non-inverting output terminal.

In the above configuration, the capacitive voltage dividing unit responds to the offset voltage of the fully differential amplifier to each of the first and second feedback capacitors before applying the reference voltage to one end of each of the first and second feedback capacitors. The initial charge may be accumulated.

In the above configuration, either one of the inverting input terminal and the non-inverting input terminal is connected to the output terminal of the capacitance type sensor, and the other is a dummy capacitor substantially the same as the capacitance of the capacitance type sensor. May be connected.

This application is based on a Japanese patent application filed on December 27, 2013 (Japanese Patent Application No. 2013-270851), the contents of which are incorporated herein by reference.

According to the present invention, it is possible to generate a capacitance division when capacitance adjustment is performed by the capacitance trimming unit, and to compare the capacitance based on the voltage generated by the capacitance division. Therefore, it is possible to perform capacitance trimming easily and with high accuracy.

2. CV conversion circuit, 3. Capacitance type sensor, 4. Dummy capacitor, 5. Capacitor trimming unit, 6. Capacitance voltage dividing generator, 7. Capacitance voltage dividing circuit, 8. First capacitor, 9. Second capacitor, 21. Fully differential amplifier. , Cf1 first feedback capacitor, Cf2 second feedback capacitor, 51 trimming capacitor.

Claims

A first feedback capacitor connected between an inverting input terminal and a non-inverting output terminal of the fully differential amplifier, and a first feedback capacitor connected between the non-inverting input terminal and the inverting output terminal; In a CV conversion circuit to which a feedback capacitor and a second feedback capacitor having substantially the same capacitance are connected, a first capacitance by at least one first capacitor connected to the inverting input terminal; A capacitance trimming circuit for trimming a capacitance difference from a second capacitance due to at least one second capacitor connected to an inverting input terminal,
A plurality of trimming capacitors that can be individually connected to or disconnected from the inverting input terminal or the non-inverting input terminal, and the plurality of trimming capacitors are individually connected to the inverting input terminal or the non-inverting input terminal. A capacitance trimming unit that adjusts the first capacitance and the second capacitance to substantially the same state by connecting or disconnecting; and
When the capacitance is adjusted by the capacitance trimming unit, a voltage corresponding to the capacitance division between the first feedback capacitor and the first capacitor is applied by applying a reference voltage to one end of the first feedback capacitor. Is generated at the inverting input terminal, and the reference voltage is applied to one end of the second feedback capacitor, so that a voltage corresponding to the capacitance divided by the second feedback capacitor and the second capacitor is non-inverted. A capacitive voltage divider that generates a voltage at the input terminal and outputs a comparison result between the voltage generated at the inverting input terminal and the voltage generated at the non-inverting input terminal;
A capacitor trimming circuit comprising:
The capacitive voltage dividing unit disconnects one end of the first feedback capacitor from the non-inverting output terminal and connects the reference voltage to the reference voltage, and disconnects one end of the second feedback capacitor from the inverting output terminal and connects the reference voltage. By connecting the full differential amplifier as a comparator, and comparing the voltage generated at the inverting input terminal with the voltage generated at the non-inverting input terminal for each of the inverting output terminal and the non-inverting output terminal. The capacitor trimming circuit according to claim 1, wherein the capacitor trimming circuit is output from the capacitor trimming circuit.
The capacitive voltage divider generates an offset voltage of the fully-differential amplifier before applying the reference voltage to one end of each of the first and second feedback capacitors. 3. The capacitor trimming circuit according to claim 1, wherein the initial charge corresponding thereto is accumulated.
One of the inverting input terminal and the non-inverting input terminal is connected to the output terminal of the capacitive sensor, and the other is a dummy capacitor that is substantially the same as the capacitance of the capacitive sensor. 4. The capacitor trimming circuit according to claim 1, which is connected.