CN112526169B - MEMS capacitive accelerometer signal readout circuit - Google Patents

MEMS capacitive accelerometer signal readout circuit Download PDF

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CN112526169B
CN112526169B CN201910885020.4A CN201910885020A CN112526169B CN 112526169 B CN112526169 B CN 112526169B CN 201910885020 A CN201910885020 A CN 201910885020A CN 112526169 B CN112526169 B CN 112526169B
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CN112526169A (en
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段王楠
张兴成
孟真
刘谋
田易
钟燕清
李继秀
阎跃鹏
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Institute of Microelectronics of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P1/00—Details of instruments
    • G01P1/12—Recording devices
    • G01P1/127—Recording devices for acceleration values
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H11/00—Networks using active elements
    • H03H11/46—One-port networks

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Abstract

The invention provides a signal reading circuit of an MEMS capacitive accelerometer, which comprises: the differential modulation unit is connected with the MEMS capacitive accelerometer gauge head and is used for converting a low-frequency acceleration signal detected by the MEMS capacitive accelerometer gauge head into a high-frequency voltage signal, wherein the low-frequency acceleration signal is represented by the capacitance variation of the gauge head; the demodulation unit is used for demodulating the high-frequency voltage signal output by the differential modulation unit into a low-frequency voltage signal; the filtering unit is used for filtering low-frequency noise in the low-frequency voltage signal output by the demodulation unit; and the amplifying circuit unit is used for amplifying the output signal of the filtering unit. The signal reading circuit of the invention has stable work and achieves the effects of reducing noise and improving detection performance.

Description

MEMS capacitive accelerometer signal readout circuit
Technical Field
The invention relates to the technical field of MEMS micro-inertial instruments, in particular to a signal reading circuit of an MEMS capacitive accelerometer.
Background
MEMS (Micro Electro Mechanical Systems) is a Micro Electro Mechanical system, which means a system integrating a Micro sensor, a controller, an actuator and a circuit by using Micro machining technology. A MEMS accelerometer is an accelerometer fabricated using MEMS technology. The MEMS capacitive accelerometer which adopts electrostatic force drive and differential capacitance change to detect displacement (or rotation angle) has the advantages of simple structure, high resolution, low temperature drift, fast dynamic response and the like.
The capacitance variation of the differential capacitance micro-accelerometer is very small, and is generally 10 -15 F, and is seriously affected by parasitic capacitance and various noises, so that the output signal is very weak, and therefore, in order to realize high-precision detection of the micro-accelerometer, a signal reading circuit with better performance needs to be designed.
Disclosure of Invention
The signal reading circuit of the MEMS capacitive accelerometer provided by the invention has stable work and achieves the effects of reducing noise and improving detection performance.
The invention provides a signal reading circuit of an MEMS capacitive accelerometer, which comprises:
the differential modulation unit is connected with the MEMS capacitive accelerometer gauge head and is used for converting a low-frequency acceleration signal detected by the MEMS capacitive accelerometer gauge head into a high-frequency voltage signal, wherein the low-frequency acceleration signal is represented by the capacitance variation of the gauge head;
the demodulation unit is connected with the differential modulation unit and is used for demodulating the high-frequency voltage signal output by the differential modulation unit into a low-frequency voltage signal;
the filtering unit is connected with the demodulating unit and is used for filtering low-frequency noise in the low-frequency voltage signal output by the demodulating unit;
and the amplifying circuit unit is connected with the filtering unit and is used for amplifying the output signal of the filtering unit.
Optionally, the filtering unit employs a sixth-order bandpass filtering circuit.
Optionally, the sixth-order band-pass filter circuit is formed by connecting three-level second-order band-pass filter circuits in series.
Optionally, the sixth-order bandpass filter circuit has a center frequency of 12.5kHz and a gain of 0dB.
Optionally, the amplifying circuit unit employs a proportional amplifier.
Optionally, the differential modulation unit modulates the low-frequency acceleration signal into a high-frequency carrier in a single-path carrier-two-path feedback modulation manner.
Optionally, the frequency of the high-frequency carrier used by the differential modulation unit is 80kHz.
Optionally, the demodulation unit includes a demodulation chip TS5a23159.
The invention provides a signal reading circuit of an MEMS capacitive accelerometer, which comprises a differential modulation unit, a demodulation unit, a filtering unit and an amplifying circuit unit, wherein the differential modulation unit is used for converting a low-frequency acceleration signal detected by a meter head of the MEMS capacitive accelerometer into a high-frequency voltage signal, the demodulation unit is used for demodulating the high-frequency voltage signal output by the differential modulation unit into a low-frequency voltage signal, the filtering unit is used for filtering low-frequency noise in the low-frequency voltage signal output by the demodulation unit, the amplifying circuit unit is used for amplifying an output signal of the filtering unit, the filtering unit and the amplifying circuit unit are mutually independent, the gain of the amplifying circuit is not influenced by the central frequency of the filtering unit, and the gain of the amplifying circuit is adjusted to meet the index requirement of a subsequent signal processing circuit.
Drawings
FIG. 1 is a block diagram of a MEMS capacitive accelerometer signal readout circuit according to an embodiment of the invention;
FIG. 2 is a simplified schematic diagram of an accelerometer header;
fig. 3 is a schematic circuit diagram of a differential modulation unit according to an embodiment of the present invention;
fig. 4 is a schematic circuit diagram of a filtering unit according to an embodiment of the present invention;
fig. 5 is a schematic circuit diagram of an amplifying circuit unit according to an embodiment of the present invention;
FIG. 6 is a simulation diagram of the AC characteristic of the six-order bandpass filter circuit;
FIG. 7 is a graph showing transient simulation when Δ C is 2/3 pF;
FIG. 8 is a graph showing a transient simulation at Δ C of 5/6pF.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An embodiment of the present invention provides a signal readout circuit for a MEMS capacitive accelerometer, as shown in fig. 1, including:
the differential modulation unit 101 is connected with the MEMS capacitive accelerometer gauge head 100, and is configured to convert a low-frequency acceleration signal detected by the MEMS capacitive accelerometer gauge head 100 into a high-frequency voltage signal, where the low-frequency acceleration signal is represented by a capacitance variation of the gauge head;
a demodulating unit 102, wherein the demodulating unit 102 is connected to the differential modulating unit 101, and is configured to demodulate the high-frequency voltage signal output by the differential modulating unit 101 into a low-frequency voltage signal;
a filtering unit 103, where the filtering unit 103 is connected to the demodulating unit 102, and is configured to filter low-frequency noise in the low-frequency voltage signal output by the demodulating unit 102;
and the amplifying circuit unit 104 is connected with the filtering unit 103, and is used for amplifying the output signal of the filtering unit 103.
The MEMS capacitive accelerometer signal reading circuit provided by the embodiment of the invention has the advantages of stable work and high detection precision, and achieves the effects of reducing noise and improving detection performance. And the single amplifying circuit unit can freely set the gain value according to the requirements of the subsequent signal processing circuit and is not influenced by the change of the central frequency of the filtering unit.
Optionally, since a parasitic capacitance exists between the accelerometer head 100 and the ground and a large parasitic capacitance also exists in the peripheral readout circuit, in order to suppress the influence of such a parasitic capacitance, the differential modulation unit 101 modulates the low-frequency acceleration signal into a high-frequency carrier in a single-channel carrier-dual-channel feedback modulation manner, that is, the carrier signal is loaded to the movable plate of the head, and the feedback signal is loaded to the fixed plate of the head.
FIG. 2 is a simplified diagram of a header of an accelerometer including an upper fixed plate, a lower fixed plate, and a movable plate forming an upper and a lower differential capacitance assuming a base capacitance value of C 0 When no acceleration is input, the capacitance between the fixed polar plate and the movable polar plate at both sides is C 0 (ii) a When acceleration is input, the capacitance difference change value is Delta C; with C 0 +. DELTA C and C 0 -. DELTA.C represents two capacitances.
Fig. 3 is a schematic diagram of a specific circuit structure of the differential modulation unit 101 according to an embodiment of the present invention, which employs a single carrier T-type differential modulation circuit, where Vz is a high-frequency modulated carrier, the frequency is 80kHz, the modulated carrier employs a sine wave, and the amplitude is 5V; s 1 、S 2 For a completely consistent operational amplifier, a carrier signal Vz connected to a movable polar plate of a meter head of an accelerometer modulates a sensitive detection capacitance signal to high frequency to realize frequency domain separation of a detection signal and a driving coupling signal, and a double-channel operational amplifier is adopted to output a double-sideband amplitude-modulated voltage signal V with a carrier 1 And V 2 ；C f1 、C f2 、C f3 、C f4 For feedback capacitance, R f1 、R f2 、R f3 、R f4 As a feedback resistance, C x1 、C x2 Is a ground resistor.
According to the kirchhoff current equation and the principles of virtual short and virtual break of operational amplifier, the method can obtain the following results:
Figure BDA0002206358610000051
Figure BDA0002206358610000052
so that the output voltage V can be obtained 1 、V 2 ：
Figure BDA0002206358610000053
Let C f ＝C f1 ＝C f2 ＝C f3 ＝C f4 ，R f ＝R f1 ＝R f2 ＝R f3 ＝R f4 ，C x ＝C x1 ＝C x2 Then, the output voltage after single carrier differential modulation:
Figure BDA0002206358610000054
Figure BDA0002206358610000055
in the above equation, the parameters may be set as: c f ＝C f1 ＝C f2 ＝C f3 ＝C f4 ＝100pF，C x ＝C x1 ＝C x2 ＝1nF，R f ＝R f1 ＝R f2 ＝R f3 ＝R f4 ＝100Ω。
Further, the demodulation unit 102 includes a demodulation chip TS5a23159 for demodulating the signal from the high frequency band to the low frequency band, and the input is a double-sideband amplitude-modulated voltage signal V with carrier 1 、V 2 The output is a demodulated voltage signal V J . The output voltage demodulated by the demodulation unit 102 is:
Figure BDA0002206358610000061
further, the demodulated signal enters the filtering unit 103, fig. 4 is a schematic circuit structure diagram of the filtering unit 103 according to an embodiment of the present invention, the filtering unit 103 employs a six-order band-pass filtering circuit to extract the input signal, so as to not only filter out low-frequency noise, but also suppress the entry of high-frequency signals, and the filtering unit 103 is formed by connecting three-level second-order band-pass filtering circuits in series.
Through circuit simulation verification, the noise suppression capability of the six-order band-pass filter circuit is far better than that of a low-pass filter circuit. In addition, the filtering unit 103 may also adopt a fourth-order band-pass filtering circuit or an eighth-order band-pass filtering circuit, and although the function of reading out signals can be realized by adopting the fourth-order band-pass filtering circuit, the accuracy rate only reaches about 90%; the accuracy of signal detection by adopting the eight-order band-pass filter circuit is high, but compared with a six-order band-pass filter circuit which needs to be connected with a second-order band-pass filter circuit in a multi-cascade mode, the required number of devices is increased, and more circuit noise can be introduced into the increased circuit. The six-order band-pass filter circuit is adopted, so that the problem of low accuracy of four-order detection can be solved, and unnecessary device waste and unnecessary circuit noise caused by the use of the eight-order band-pass filter circuit are avoided.
For the filtering unit 103 shown in fig. 4, its central angular frequency is:
Figure BDA0002206358610000062
the circuit gain is:
Figure BDA0002206358610000063
the quality factor is:
Figure BDA0002206358610000064
the specific parameters of the sixth-order bandpass filter circuit can be set as follows: the center angular frequency was set to 12.5kHz and the circuit gain was 0dB.
The output voltage after passing through the six-order band-pass filter circuit is as follows:
Figure BDA0002206358610000071
further, a first-stage independent amplifying circuit unit 104 is further disposed on the output side of the bandpass filtering unit 103, and is used for amplifying a signal for a subsequent signal processing circuit. As shown in fig. 5, the amplification circuit unit 104 employs a proportional amplifier circuit, and the amplification gain is:
Figure BDA0002206358610000072
the amplification gain can be freely adjusted using the independent amplification circuit unit.
The output voltage after passing through the amplifying circuit unit 104 is:
Figure BDA0002206358610000073
wherein R can be adjusted 10 、R 11 The value of (2) sets the circuit gain to meet the index requirements of the subsequent signal processing circuit.
According to the embodiment of the invention, a six-order band-pass filter circuit and an independent amplifying circuit are introduced into the MEMS accelerometer signal processing technology to process signals, so that more accurate capacitance-voltage conversion is realized.
In order to further verify the characteristics of the MEMS capacitive accelerometer signal reading circuit, circuit simulation is carried out.
Based on a Multisim simulation platform, a designed signal reading circuit is subjected to simulation verification, the change of an output signal is observed, and the delta C is 2/3pF and 5/6pF respectively. FIG. 6 is a simulation curve of the AC characteristic of the six-order bandpass filter circuit, FIG. 7 is the output voltage signal when Δ C is 2/3pF, and FIG. 8 is the output voltage signal when Δ C is 5/6pF. As can be seen from fig. 6, the sixth-order bandpass filter circuit can suppress both high-frequency signals and low-frequency noise; as can be seen from FIG. 7, when the input capacitance signal Δ C takes 2/3pF, the output voltage signal V is obtained OUT About 1.55V; as can be seen from fig. 8, when the input capacitance signal Δ C is 5/6pF, the output voltage signal VOUT is about 1.7V, which is close to the actual calculation result, verifying that the signal readout circuit has high detection accuracy and stronger noise suppression capability.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (7)

1. A MEMS capacitive accelerometer signal readout circuit, comprising:
the differential modulation unit is connected with the MEMS capacitive accelerometer gauge head and is used for modulating a low-frequency acceleration signal detected by the MEMS capacitive accelerometer gauge head into a high-frequency carrier by adopting a single-path carrier-double-path feedback modulation mode and outputting a double-sideband amplitude modulation voltage signal with a carrier, wherein the low-frequency acceleration signal is reflected by the capacitance variation of the gauge head, the single-path carrier signal is loaded to a movable polar plate of the gauge head, and the double-path feedback signal is loaded to two fixed polar plates of the gauge head;
the demodulation unit is connected with the differential modulation unit and is used for demodulating the double-sideband amplitude modulation voltage signal with the carrier output by the differential modulation unit into a low-frequency voltage signal;
the filtering unit is connected with the demodulating unit and is used for filtering low-frequency noise in the low-frequency voltage signal output by the demodulating unit;
and the amplifying circuit unit is connected with the filtering unit and is used for amplifying the output signal of the filtering unit.
2. The MEMS capacitive accelerometer signal readout circuit of claim 1, wherein the filter unit employs a six-order bandpass filter circuit.
3. The MEMS capacitive accelerometer signal readout circuit of claim 2, wherein the sixth order bandpass filter circuit is formed by a series connection of three-level second order bandpass filter circuits.
4. The MEMS capacitive accelerometer signal readout circuit of claim 3, wherein the sixth order bandpass filter circuit has a center frequency of 12.5kHz and a gain of 0dB.
5. The MEMS capacitive accelerometer signal readout circuit of claim 1, wherein the amplification circuit unit employs a proportional amplifier.
6. The MEMS capacitive accelerometer signal readout circuit of claim 1, wherein the frequency of the high frequency carrier used by the differential modulation unit is 80kHz.
7. The MEMS capacitive accelerometer signal readout circuit of claim 1, wherein the demodulation unit comprises a demodulation chip TS5a23159.
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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102072737A (en) * 2009-11-25 2011-05-25 中国科学院电子学研究所 High accuracy capacitive readout circuit with temperature compensation
CN103105508A (en) * 2013-01-11 2013-05-15 江苏物联网研究发展中心 Micro-electro-mechanical system (MEMS) micro accelerometer closed loop drive circuit using chopping technique
CN104406612A (en) * 2014-11-07 2015-03-11 无锡纳讯微电子有限公司 Capacitive sensor interface circuit
CN104678126A (en) * 2015-02-04 2015-06-03 浙江大学 Phase-shift temperature compensation method based on parasitic resistance for micro-mechanical capacitive accelerometer
CN108759645A (en) * 2018-05-30 2018-11-06 华中科技大学 A kind of capacitive displacement sensing device transmitted at a distance based on transformer secondary output

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2428774B1 (en) * 2010-09-14 2013-05-29 Stichting IMEC Nederland Readout system for MEMs-based capacitive accelerometers and strain sensors, and method for reading
JP6373786B2 (en) * 2015-03-30 2018-08-15 日立オートモティブシステムズ株式会社 Capacitance detection type sensor signal detection method, capacitance detection type sensor, and system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102072737A (en) * 2009-11-25 2011-05-25 中国科学院电子学研究所 High accuracy capacitive readout circuit with temperature compensation
CN103105508A (en) * 2013-01-11 2013-05-15 江苏物联网研究发展中心 Micro-electro-mechanical system (MEMS) micro accelerometer closed loop drive circuit using chopping technique
CN104406612A (en) * 2014-11-07 2015-03-11 无锡纳讯微电子有限公司 Capacitive sensor interface circuit
CN104678126A (en) * 2015-02-04 2015-06-03 浙江大学 Phase-shift temperature compensation method based on parasitic resistance for micro-mechanical capacitive accelerometer
CN108759645A (en) * 2018-05-30 2018-11-06 华中科技大学 A kind of capacitive displacement sensing device transmitted at a distance based on transformer secondary output

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