CN106921383B - Low-power consumption low-noise MEMS accelerometer interface circuit - Google Patents
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Abstract
The invention discloses a low-power consumption low-noise MEMS accelerometer interface circuit, which comprises: the MEMS accelerometer comprises a charge converter circuit, a PI controller circuit, a differential driving circuit, a MEMS accelerometer detection positive electrode SP and a MEMS accelerometer detection negative electrode SN, wherein pulse voltages with opposite phases are respectively input into the MEMS accelerometer detection positive electrode SP and the MEMS accelerometer detection negative electrode SN, the MEMS accelerometer driving positive electrode and the MEMS accelerometer driving negative electrode are respectively connected with two output ends of the differential driving circuit, and an MEMS accelerometer middle electrode MASS is connected with an input end of the charge converter circuit; the output end of the charge converter circuit is connected with the input end of the PI controller circuit; the input of the PI controller circuit is single-ended input, the output is differential output, the output of the PC controller circuit is connected with the input end of the differential drive circuit, monolithic integration of all control systems is realized, external discrete devices are not needed, the structure is simpler, and the power consumption and noise are lower.
Description
Technical Field
The invention relates to the field of MEMS accelerometers, in particular to a low-power-consumption low-noise MEMS accelerometer interface circuit.
Background
The MEMS accelerometer is mainly used for measuring the acceleration of a moving object relative to an inertial space, and has the characteristics of small volume, low power consumption, easy integration, mass production and the like, so that the MEMS accelerometer plays an increasingly important role in occasions such as automobile engineering, vibration detection, aviation navigation, military application and the like.
MEMS accelerometers can be classified into open-loop accelerometers and closed-loop accelerometers according to their principle of operation. The open-loop accelerometer measures acceleration through measuring capacitance change caused by displacement change of the mass block, and has low precision and poor linearity. The closed-loop accelerometer is also called a force balance accelerometer, and the working principle is as follows: when inertial force acts on the mass block, the closed loop system detects the displacement of the mass block and generates electrostatic force with the same magnitude and opposite direction to the inertial force to counteract the inertial force, so that the mass block is always in the balance position. Due to the working principle of the closed-loop accelerometer, the closed-loop accelerometer has high linearity and low noise, and is very suitable for high-precision measurement such as seismic monitoring and dip angle measurement.
The relatively common closed loop accelerometer interface circuit at present comprises: a full-simulation PID closed-loop control mode and a digital-analog mixed Delta-sigma closed-loop control mode; compared with a Delta-sigma closed-loop control mode, the PID closed-loop control method has the advantages of simple structure, low power consumption and mature and reliable technology; because the high-precision closed-loop MEMS accelerometer has a very low resonant frequency, typically around one or two kilohertz, the capacitance required in the integrating or differentiating circuit is very large in the conventional PID closed-loop accelerometer, and cannot be integrated in an ASIC, and usually a discrete device is required, which is not beneficial to miniaturization and system integration.
Disclosure of Invention
The invention provides a low-power-consumption low-noise MEMS accelerometer interface circuit, which solves the technical problems that the traditional PID closed-loop accelerometer cannot be integrated in an ASIC (application specific integrated circuit), is unfavorable for miniaturization and system integration, realizes the monolithic integration of all control systems, does not need external discrete devices, and has the technical effects of simpler structure and lower power consumption and noise.
In order to solve the technical problem, the application provides a low-power consumption low-noise MEMS accelerometer interface circuit, and the whole system comprises: a MEMS accelerometer 1, a charge converter circuit 2, a PI controller circuit 3 and a differential drive circuit 4.
The detection positive electrode SP and the detection negative electrode SN of the MEMS accelerometer 1 are respectively input with pulse voltages with opposite phases, the driving positive electrode and the driving negative electrode of the MEMS accelerometer 1 are respectively connected with two output ends of the differential driving operational amplifier 4, and the MEMS acceleration middle electrode MASS is connected with the input end of the charge converter circuit 2; the output end of the charge converter circuit 2 is connected with the input end of the PI controller circuit 3; the input of the PI controller circuit 3 is single-ended, the output is differential, and the output of the PC controller circuit 3 is connected with the input end of the differential driving circuit 4.
The charge converter circuit 2 is one of the core circuits of the present invention. The input end VI_CSA of the charge converter circuit 2 is connected with the positive end of the resistor R1 and the positive end of the capacitor C1; the negative end of the resistor R1 is connected with the analog reference voltage REF1; the negative end of the capacitor C1 is connected with the grid electrode of the NMOS tube MN1 and the positive end of the capacitor C2; the source electrode of MN1 is connected to analog ground, and the drain electrode is connected to current source I s1 A negative terminal; current source I s1 The positive end is connected with a power supply; current source I s1 The negative terminal and the negative terminal of C2, the drain of MN1 are connected together to the output VO_CSA of the circuit converter.
The PI controller circuit 3 is one of the core circuits of the present invention. The input end VI_PI of the PI controller circuit is connected to the positive end of the capacitor C3; the negative end of C3 is connected with the input ends of switches PH1, PH2 and PH3 respectively; the output end of the switch PH1 is connected with the positive end of the resistor R2 and the negative input end of the operational amplifier OP 1; the output end of the switch PH2 is connected with the positive end of the resistor R3 and the negative input end of the operational amplifier OP 2; the output end of the switch PH3 and the positive input ends of the operational amplifiers OP1 and OP2 are connected to a common mode ground together; the positive end of R2 is connected with the positive end of the capacitor C4; the negative end of C4 is connected with the output end of the operational amplifier OP1 and is connected to the output positive electrode of the PI controller circuit 3; the positive end of R3 is connected with the positive end of the capacitor C5; the negative terminal of C5 is connected with the output terminal of the operational amplifier OP1 and is connected to the output negative electrode of the PI controller circuit 3.
One or more technical schemes provided by the application have at least the following technical effects or advantages:
the invention provides a novel PI closed-loop control accelerometer interface circuit, which realizes monolithic integration of all control systems without external discrete devices, adopts advanced switched capacitor technology to realize PI controllers, reduces the integral capacitance to an integrable range, adopts novel low-noise charge converters with simple structures, and has lower power consumption and better performance of closed-loop systems.
Drawings
The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention;
FIG. 1 is a schematic diagram of the structure of a MEMS accelerometer interface circuit of the present application;
FIG. 2 is a schematic diagram of a charge converter circuit of the present application;
FIG. 3 is a schematic diagram of a PI controller circuit in this application;
FIG. 4 is a schematic diagram of an example of the operation of the charge converter circuit of the present application;
FIG. 5 is a timing diagram of the PI controller of the present application;
fig. 6 is a schematic diagram of the transient response of the closed loop system of the present application.
Detailed Description
The invention provides a low-power-consumption low-noise MEMS accelerometer interface circuit, which solves the technical problems that the traditional PID closed-loop accelerometer cannot be integrated in an ASIC (application specific integrated circuit), is unfavorable for miniaturization and system integration, realizes the monolithic integration of all control systems, does not need external discrete devices, and has the technical effects of simpler structure and lower power consumption and noise.
In order that the above-recited objects, features and advantages of the present invention will be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description. In addition, the embodiments of the present application and the features in the embodiments may be combined with each other without conflicting with each other.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced in other ways than within the scope of the description, and the scope of the invention is therefore not limited to the specific embodiments disclosed below.
Referring to fig. 1-6, the system provided in the present application includes: a 5-electrode MEMS accelerometer 1, a charge converter circuit 2, a PI controller circuit 3 and a differential drive circuit 4.
The detection positive electrode SP and the detection negative electrode SN of the MEMS accelerometer 1 are respectively input with pulse voltages with opposite phases, the driving positive electrode and the driving negative electrode of the MEMS accelerometer 1 are respectively connected with two output ends of the differential driving operational amplifier 4, and the MEMS acceleration middle electrode MASS is connected with the input end of the charge converter circuit 2; the output end of the charge converter circuit 2 is connected with the input end of the PI controller circuit 3; the input of the PI controller circuit 3 is single-ended, the output is differential, and the output of the PC controller circuit 3 is connected with the input end of the differential driving circuit 4.
Fig. 2 shows a circuit diagram of the charge converter circuit 2. The input end VI_CSA of the charge converter circuit 2 is connected with the positive end of the resistor R1 and the positive end of the capacitor C1; the negative end of the resistor R1 is connected with the analog reference voltage REF1; the negative end of the capacitor C1 is connected with the grid electrode of the NMOS tube MN1 and the positive end of the capacitor C2; the source electrode of MN1 is connected to analog ground, and the drain electrode is connected to current source I s1 A negative terminal; current source I s1 The positive end is connected with a power supply; current source I s1 The negative terminal and the negative terminal of C2, the drain of MN1 are connected together to the output VO_CSA of the circuit converter.
The charge converter is connected to the actual accelerometer and an example of operation is shown in figure 4. Current source I s1 And NMOS tube MN1 constitute a simple unipolar amplifier. Compared with the traditional operational amplifier, the monopole amplifier has simple structure and extremely low power consumption, and simultaneously, the noise is reduced due to the reduction of the number of devices. In this structure, the main device noise is the thermal noise of MN 1. By appropriately increasing I s1 The current and the aspect ratio of MN1 can effectively reduce noise, and even so, can ensure smaller power consumption than conventional op-amp.
A capacitor C1 separates the MEMS accelerometer intermediate electrode from the MN1 gate. The reason that the MEMS accelerometer middle electrode is not directly connected to the MN1 gate is that the gate voltage of MN1 will drift greatly with temperature change. The benefits of separating the MEMS accelerometer middle electrode and the MN1 gate with C1 are also: the MEMS accelerometer intermediate electrode may be provided with a stable clean bias voltage REF1 by a large resistor R1, preferably the bias voltage REF1 is grounded to analog ground.
The two detection electrodes of the MEMS accelerometer respectively input pulse voltages V with opposite phases s+ And V s- . C1 can couple the AC pulse signal with the detection electrode coupled to the middle electrode plate to the gate of MN1I.e. coupled to MN1 and I s1 And the input end of the monopole amplifier is formed. Therefore, the output voltage of the charge converter circuit is equal to V s+ And V s- Proportional pulse signals.
Suppose MN1 and I s1 The gain of the composed unipolar amplifier is infinite, and the output of the charge converter circuit can be deduced as:
wherein C is s+ And C s- The positive and negative electrode detection capacitors are respectively provided, and VO_CSA is the output voltage of the charge converter.
Let DeltaC s ＝C s+ -C s- Because of V s+ ＝-V s- Formula 1.1 may be changed to:
to enhance the sensitivity and signal-to-noise ratio of the charge converter circuit, the actual circuit design is designed such that C1 > C s+ Simplifying formula 1.2 to:
as shown in fig. 3, a circuit diagram of the PI controller circuit 3 is shown. The input end VI_PI of the PI controller circuit is connected to the positive end of the capacitor C3; the negative end of C3 is connected with the input ends of switches PH1, PH2 and PH3 respectively; the output end of the switch PH1 is connected with the positive end of the resistor R2 and the negative input end of the operational amplifier OP 1; the output end of the switch PH2 is connected with the positive end of the resistor R3 and the negative input end of the operational amplifier OP 2; the output end of the switch PH3 and the positive input ends of the operational amplifiers OP1 and OP2 are connected to a common mode ground together; the positive end of R2 is connected with the positive end of the capacitor C4; the negative end of C4 is connected with the output end of the operational amplifier OP1 and is connected to the output positive electrode of the PI controller circuit 3; the positive end of R3 is connected with the positive end of the capacitor C5; the negative terminal of C5 is connected with the output terminal of the operational amplifier OP1 and is connected to the output negative electrode of the PI controller circuit 3.
In the PI control circuit, the capacitor C3 and the switches PH1, PH2, PH3 form a switched capacitor circuit, and charge is continuously transferred to the integrating capacitors C4 and C5.
As shown in fig. 5, a timing diagram of the circuit operation is shown. PH1, PH2 and PH3 do not overlap each other. When pulse signal V s+ And V s Electrically smooth timing, switch PH3 is opened, bringing the C3 negative terminal voltage to zero. After PH3 is closed, switch PH1 or PH2 is opened, and the negative terminal of C3 and the negative input terminal of OP1 or OP2 are connected. Then V s+ And V s- The level is inverted, the output voltage of the charge converter is also inverted, and the charge is transferred to the integrating capacitor C4 or C5 through C3, and the transferred charge quantity Q is as follows:
where VO_CSA represents the amplitude of the pulse signal output by the charge converter, V s Represents V s+ And V s- Is a function of the amplitude of (a).
Equivalent resistance R of switch capacitor circuit formed by C3 and switch EQ The method comprises the following steps:
wherein f s Is the switching frequency.
Let c4=c5=ci, r2=r3=rp, transfer function H of PI controller PI (s) is:
because the high-precision MEMS accelerometer has a very low resonant frequency, typically around one or two kilohertz, the integrator unity gain bandwidth is required to be very low to meet stability requirements. Conventional PI circuits typically reduce the integrator unity gain bandwidth by increasing the integration capacitance. But this has the problem that the integration capacitance is too large to achieve on-chip integration.
In the PI controller circuit shown in the invention, R can be easily set EQ To the 10M ohm level, for example, when c3=0.8 pf, switching frequency 200KHz, R EQ I.e. up to about 10M ohms. The integrator unity gain bandwidth can be reduced without requiring a very large integration capacitance, so that integration capacitances C4 and C5 can be integrated on-chip.
By way of example, the interface circuit of the present invention implements a closed loop system with a MEMS accelerometer having a resonant frequency of 1.5 KHz. The PI controller circuit parameters are as follows: c3 =0.8pf, c4=c5=250pf, r2=r3=50kΩ, can be fully integrated in-chip. As shown in fig. 6, is a closed loop system transient response. At an acceleration of 2g, the differential output voltage is about 1.6V and the transient response settling time is about 2.5mS.
The technical scheme in the embodiment of the application at least has the following technical effects or advantages:
the invention provides a novel PI closed-loop control accelerometer interface circuit, which realizes monolithic integration of all control systems without external discrete devices, adopts advanced switched capacitor technology to realize PI controllers, reduces the integral capacitance to an integrable range, adopts novel low-noise charge converters with simple structures, and has lower power consumption and better performance of closed-loop systems.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (1)
1. A fully integrated low power consumption low noise MEMS accelerometer interface circuit, the interface circuit comprising:
the MEMS accelerometer comprises a charge converter circuit, a PI controller circuit, a differential driving circuit, a MEMS accelerometer detection positive electrode SP and a MEMS accelerometer detection negative electrode SN, wherein pulse voltages with opposite phases are respectively input into the MEMS accelerometer detection positive electrode SP and the MEMS accelerometer detection negative electrode SN, the MEMS accelerometer driving positive electrode and the MEMS accelerometer driving negative electrode are respectively connected with two output ends of the differential driving circuit, and an MEMS accelerometer middle electrode MASS is connected with an input end of the charge converter circuit; the output end of the charge converter circuit is connected with the input end of the PI controller circuit; the input of the PI controller circuit is single-ended input, the output is differential output, and the output of the PC controller circuit is connected with the input end of the differential drive circuit;
the charge converter circuit includes: the resistor R1, the capacitors C1 and C2, the NMOS tube MN1 and the bias current source Is, and the input end VI_CSA of the charge converter circuit Is connected with the positive end of the resistor R1 and the positive end of the capacitor C1; the negative end of the resistor R1 is connected with the analog reference voltage REF1; the negative end of the capacitor C1 is connected with the grid electrode of the NMOS tube MN1 and the positive end of the capacitor C2; the source electrode of MN1 is connected to analog ground, and the drain electrode is connected to current source I s1 A negative terminal; current source I s1 The positive end is connected with a power supply; current source I s1 The negative terminal is connected with the negative terminal of the C2 and the drain electrode of the MN1 together to the output end VO_CSA of the circuit converter;
the PI controller circuit includes: capacitors C3, C4 and C5, resistors R2 and R3, switches PH1, PH2 and PH3 and single-ended operational amplifiers OP1 and OP2, and an input end VI_PI of a PI controller circuit is connected to the positive end of the capacitor C3; the negative end of C3 is connected with the input ends of switches PH1, PH2 and PH3 respectively; the output end of the switch PH1 is connected with the positive end of the resistor R2 and the negative input end of the operational amplifier OP 1; the output end of the switch PH2 is connected with the positive end of the resistor R3 and the negative input end of the operational amplifier OP 2; the output end of the switch PH3 and the positive input ends of the operational amplifiers OP1 and OP2 are connected to a common mode ground together; the positive end of R2 is connected with the positive end of the capacitor C4; the negative end of the C4 is connected with the output end of the operational amplifier OP1 and is connected to the output positive electrode of the PI controller circuit (3); the positive end of R3 is connected with the positive end of the capacitor C5; the negative end of C5 is connected with the output end of the operational amplifier OP1 and is connected to the output negative electrode of the PI controller circuit (3).
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| CN107290566B (en) * | 2017-07-17 | 2023-06-23 | 四川知微传感技术有限公司 | Basic capacitance compensation circuit for digital accelerometer |
| CN107192851B (en) * | 2017-07-17 | 2023-05-26 | 四川知微传感技术有限公司 | Capacitance detection system of charge modulator accelerometer |
| CN110350905B (en) * | 2018-04-03 | 2024-04-19 | 中国科学院声学研究所 | MEMS capacitive accelerometer interface circuit |
| CN111551761B (en) * | 2020-04-03 | 2021-11-30 | 四川知微传感技术有限公司 | Low-noise MEMS accelerometer |
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