CN215066770U

CN215066770U - Low-noise capacitive MEMS acceleration sensor

Info

Publication number: CN215066770U
Application number: CN202120889453.XU
Authority: CN
Inventors: 彭朝勇; 杨建思; 陈安富; 郑钰; 徐志强; 谷红岩; 赵明远; 姜旭东
Original assignee: Beijing Yijin Technology Co ltd; INSTITUTE OF GEOPHYSICS CHINA EARTHQUAKE ADMINISTRATION
Current assignee: Beijing Yijin Technology Co ltd; INSTITUTE OF GEOPHYSICS CHINA EARTHQUAKE ADMINISTRATION
Priority date: 2021-04-27
Filing date: 2021-04-27
Publication date: 2021-12-07
Anticipated expiration: 2031-04-27

Abstract

The utility model relates to a low noise capacitanc MEMS acceleration sensor, including the trisection signal conditioning unit and the sensor group of being parallelly connected to form by a plurality of sensor unit, the trisection signal output part of sensor group connects correspondingly the trisection signal conditioning unit. The technical scheme of the utility model reach the MEMS acceleration sensor that the user required from a certain extent and fall the level of making an uproar, the product price reduces by a wide margin for directly selecting for use the MEMS acceleration sensor that the noise level is equivalent.

Description

Low-noise capacitive MEMS acceleration sensor

Technical Field

The utility model relates to a sensor field among the micro-electro-mechanical systems (MEMS) technical field especially relates to a low noise capacitanc MEMS acceleration sensor.

Background

With the development of MEMS technology, the inertial sensor device has become one of the most successful and widely used MEMS devices in the last years, and a microaccelerometer (microaccelerometer) is an outstanding representative of the inertial sensor device. The theoretical basis of a micro-accelerometer is that, according to newton's second law, within a system, velocity is not measurable, but acceleration is measurable. If the initial velocity is known, the linear velocity, and hence the linear displacement, can be calculated by integration. As the most mature inertial sensor, the MEMS accelerometers of today have a very high integration level, i.e. the sensing system and the interface circuit are integrated on one chip.

The existing MEMS acceleration sensor mostly adopts a structure based on capacitance transduction, and charge feedback realizes closed-loop feedback control and measurement of acceleration. Capacitive MEMS accelerometers have excellent zero frequency response. At very low frequencies, there is high sensitivity and excellent temperature stability, but there is a large difference in product noise level. From the noise level, the MEMS accelerometers can be classified into commodity and consumer grade MEMS accelerometers and special industrial grade MEMS accelerometers according to the manufacturing process thereof. Since MEMS sensor systems are susceptible to switching noise, brownian motion thermodynamic noise, etc., the noise level of commodity and consumer grade MEMS accelerometers is much higher than that of dedicated industrial grade MEMS accelerometers. The noise levels of both commodity and consumer MEMS accelerometers are typically 20 to 150 pg/v Hz, and the noise levels of dedicated industrial grade MEMS accelerometers are typically 0.5 to 10 pg/v Hz.

In the application fields of seismic exploration, seismic early warning, structural health monitoring, debris flow landslide monitoring and the like, a high-precision low-noise MEMS acceleration sensor is needed, and an MEMS acceleration sensor with a noise level lower than 10 mu g/V Hz is preferably selected, but the noise level of the current civil and consumer grade is generally more than 20 mu g/V Hz, the noise level of only part of special MEMS acceleration sensors can reach 1 mu g/V Hz, the noise level requirements of the fields can be met, but most of the special MEMS acceleration sensors are output in a single direction, and each piece of the special MEMS acceleration sensors is very expensive and difficult to use in batch in practical application. Therefore, how to reduce the noise index of the MEMS acceleration sensor in a cost controllable range on the basis of the existing consumer and consumer grade MEMS accelerometers becomes an urgent problem to be solved in order to meet the actual requirements of the application field.

SUMMERY OF THE UTILITY MODEL

To above technical problem, the technical scheme of the utility model a low noise capacitanc MEMS acceleration sensor is proposed, including the trisection signal conditioning unit and the sensor group of being connected in parallel by a plurality of sensor unit and forming, the trisection signal output part of sensor group connects correspondingly the trisection signal conditioning unit.

As an improvement, each sensor unit comprises a capacitive MEMS acceleration sensor, a power supply filtering circuit and a bandwidth conditioning circuit.

As a further improvement, the power supply filter circuit comprises an inductor connected with a power supply end, and the other end of the inductor is connected with a voltage input end of the acceleration sensor; the power supply filter circuit further comprises a capacitor connected with the inductor in series, and the other end of the capacitor is grounded and connected with the acceleration sensor in parallel.

As a further improvement, the bandwidth conditioning circuit comprises a three-way buffer and a frequency-selecting capacitor bank.

As a further improvement, the three-way signal output end of each acceleration sensor is respectively connected with one end of one frequency-selecting capacitor and correspondingly connected in series with the input end of the three-way buffer; the tail end signals of all the frequency-selecting capacitors are grounded; and the output ends of all the three-way buffers are correspondingly connected with the three-way signal output ends of the array sensor.

As a further improvement, the three-way signal conditioning unit comprises a three-way operational amplifier, and the three-way signal output ends of the sensor array are respectively and correspondingly connected with the input ends of the three-way operational amplifier.

As a further improvement, a group of parallel capacitors is arranged at the voltage input end of the sensor group.

The utility model discloses on the basis of current analog output civilian grade MEMS acceleration sensor (belong to first type capacitanc MEMS acceleration sensor), through cascading array noise reduction technique with multi-disc MEMS acceleration sensor and forming MEMS acceleration sensor array, can reach when reducing MEMS acceleration sensor noise level √ N doubly, the effect that the cost increases N doubly about.

The technical scheme of the utility model reach the MEMS acceleration sensor that the user required from a certain extent and fall the level of making an uproar, the product price reduces by a wide margin for directly selecting for use the MEMS acceleration sensor that the noise level is equivalent.

Drawings

FIG. 1 is a schematic structural diagram of a low-noise capacitive MEMS acceleration sensor;

FIG. 2, a supply filter circuit diagram;

FIG. 3 is a circuit diagram of a low noise capacitive MEMS acceleration sensor;

FIG. 4 is a noise detection diagram of a parallel array of 8 MEMS acceleration sensors;

fig. 5 and a noise detection diagram of a parallel array of 16 pieces of MEMS acceleration sensors.

Detailed Description

The technical solution of the present invention is explained in detail below with reference to the accompanying drawings and embodiments. It is obvious that the drawings in the following description are only some of the embodiments described in the present application, and that other drawings can be derived from these drawings by a person skilled in the art without inventive effort.

Some embodiments include a low-noise capacitive MEMS acceleration sensor, which is structured as shown in fig. 1, and includes a three-way (X, Y, Z) signal conditioning unit (BX, BY, BZ) and a plurality of sensor units (a)₁₁…A_ij…A_mn) The sensor group is formed by connecting in parallel, and the three-way signal output ends (Xo, Yo and Zo) of the sensor group are correspondingly connected with the three-way signal conditioning unit.

Wherein a plurality of sensor units (A)₁₁…A_ij…A_mn) Are typically arranged in an array including a rectangular array, a circular array, etc., and also in a multi-layer array combination.

The capacitive MEMS acceleration sensor is a polar distance changing type capacitive sensor based on a capacitance principle, and includes a fixed electrode and a movable electrode (mass m). The movable electrode is displaced by an external force to change the capacitance.

The small displacement of the mass m caused by the acceleration can be converted into the change of the differential capacitance, and the difference value of the two capacitances is in direct proportion to the displacement. The relationship between the input acceleration a and the change of the differential capacitance C can be obtained as follows:

the main source of self-noise of the MEMS acceleration sensor is Brownian thermal noise of the MEMS sensor, and the equivalent formula of Brownian motion thermodynamic noise of the MEMS acceleration sensor is

Wherein g is noise, m is capacitance equivalent mass, and Q is accelerometer quality factorNumber, omega₀K is the boltzmann constant for the accelerometer natural frequency.

The sensitivity from acceleration change to sensitive capacitance change is

Where Δ C is the capacitance of the accelerometer change, d₀The total capacitance variation is C for the differential capacitance gap in the static state₀。

When N MEMS acceleration sensors are arranged in parallel to form an array, the capacitance is equivalent to C₀And deltac are both increased by N times, so the sensitivity from acceleration change to sensitive capacitance change is unchanged. However, since the capacitance piece equivalent mass m increases by N times, the noise level decreases by √ N times.

Some embodiments include that each sensor unit comprises one capacitive MEMS acceleration sensor, one supply filtering circuit and one bandwidth conditioning circuit.

The capacitive MEMS acceleration sensor mainly comprises a civil-grade MEMS acceleration sensor with lower price.

In some more specific embodiments, the power supply filter circuit is shown in fig. 2, and includes an inductor (FB is preferably a magnetic bead) connected to the power supply terminal, and the other end of the inductor is connected to the voltage input terminal of the acceleration sensor; the power supply filter circuit further comprises a capacitor C connected with the inductor FB in series, and the other end of the capacitor C is grounded and connected with the MEMS acceleration sensor in parallel.

And power supply VCC and GND of a system are filtered by a magnetic bead FB and a capacitor C and then are connected to power supply terminals VCC and GND of each capacitive MEMS acceleration sensor so as to reduce power supply crosstalk among units in the sensor array.

In some more specific embodiments, the bandwidth conditioning circuit includes a tri-directional buffer and a frequency selective capacitor bank.

In some more specific embodiments, the circuit is shown in fig. 3, and the three-way signal output terminal (Xo) of each acceleration sensor_ij、Yo_ij、Zo_ij) Are respectively provided withConnecting one of said frequency-selective Capacitors (CX)_ij、 CY_ij、CZ_ij) One end of (A) is correspondingly connected in series with a three-way buffer (AX)_ij、AY_ij、AZ_ij) An input end; the tail end signals of all the frequency-selecting capacitors are grounded; the output ends of all the three-way buffers are correspondingly connected with three-way signal output ends (Xo, Yo and Zo) of the sensor group.

In some embodiments, the three-way signal conditioning unit includes a three-way operational amplifier, and the three-way signal output ends of the sensor group are respectively and correspondingly connected with the input ends of the three-way operational amplifier.

In some embodiments, the voltage input end of the sensor group is provided with a group of parallel capacitors, and the voltage is subjected to noise reduction and filtering by the parallel capacitors before being loaded to the sensor array.

In some more specific embodiments, the objective of reducing the noise level by 2 times is achieved by connecting 4 civil-grade MEMS sensors (LIS344ALH, mouse Electronics, Inc.) in parallel to form a sensor group (array), and the cost is increased by about 4 times, and compared with the existing MEMS sensors directly selecting noise level which is 2 times lower, the cost for achieving the same noise level through an array technology noise reduction mode is only one fifth.

The aim of reducing the noise level by 4 times is achieved by connecting 16 civil-grade MEMS sensors (LIS344ALH, mouse Electronics, Inc.) in parallel to form a sensor group (array), the cost is increased by about 16 times, and compared with the existing MEMS sensors which directly select and use the sensors with the noise level being 4 times lower, the cost for achieving the same noise level is only one twentieth through an array technology noise reduction mode.

In order to further verify the noise reduction effect of the MEMS acceleration sensor array, 8 pieces of MEMS acceleration sensors (LIS344ALH, mouse Electronics, Inc.) are respectively connected in parallel to form an array, the array is accessed to the same data collector for recording, and the noise spectral densities of the MEMS acceleration sensor group (8 pieces of MEMS acceleration sensors and 16 pieces of MEMS acceleration sensors) in three directions are respectively plotted, and the dynamic range pairs are as shown in table 1:

TABLE 1 MEMS sensor array dynamic Range vs. array number relationship

Detect 8 pieces of MEMS acceleration sensor array and 16 pieces of MEMS acceleration sensor group (array) noise respectively, the testing result has reflected the utility model discloses technical scheme's noise reduction effect: wherein, the noise level of the 8-piece MEMS acceleration sensor array is shown in FIG. 4; the noise level of the 16-piece MEMS acceleration sensor array is shown in fig. 5. From the effect, the 16-piece MEMS acceleration sensor array has the noise level reduced by 2 times and the dynamic range improved by 3dB compared with the 8-piece MEMS acceleration sensor array, and basically accords with the theoretical calculation.

Particular embodiments of the subject matter have been described. Other implementations are within the scope of the following claims. For example, the activities recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results.

Claims

1. A low-noise capacitive MEMS acceleration sensor is characterized by comprising a three-way signal conditioning unit and a sensor group formed by connecting a plurality of sensor units in parallel, wherein three-way signal output ends of the sensor group are correspondingly connected with the three-way signal conditioning unit.

2. The sensor of claim 1, wherein each of said sensor cells comprises a capacitive MEMS acceleration sensor, a supply filtering circuit and a bandwidth conditioning circuit.

3. The sensor of claim 2, wherein the power supply filter circuit comprises an inductor connected to a power supply terminal, and the other end of the inductor is connected to a voltage input terminal of the acceleration sensor; the power supply filter circuit further comprises a capacitor connected with the inductor in series, and the other end of the capacitor is grounded and connected with the acceleration sensor in parallel.

4. The sensor of claim 3, wherein the bandwidth conditioning circuit comprises a three-way buffer and a frequency-selective capacitor bank.

5. The sensor according to claim 4, wherein the three-way signal output end of each acceleration sensor is respectively connected with one end of one frequency-selecting capacitor and correspondingly connected with the input end of the three-way buffer in series; the tail end signals of all the frequency-selecting capacitors are grounded; and the output ends of all the three-way buffers are correspondingly connected with the three-way signal output ends of the sensor group.

6. The sensor of claim 4, wherein the three-way signal conditioning unit comprises three-way operational amplifiers, and the three-way signal output ends of the sensor group are respectively and correspondingly connected with the input ends of the three-way operational amplifiers.

7. The sensor of claim 6, wherein the voltage input of the set of sensors is provided with a set of parallel capacitors.