CN208174658U - A kind of MEMS capacitive accelerometer interface circuit - Google Patents

Abstract

The utility model relates to a MEMS capacitive accelerometer interface circuit, which includes a sensitive unit and a readout device; the readout device includes: a switch, a preamplifier, a positive reference voltage and a common-mode voltage generation circuit; a positive reference voltage and a common-mode voltage generation circuit The circuit includes a boost charge pump and a first low-noise linear regulator and a second low-noise linear regulator; wherein, the first low-noise linear regulator and the boost charge pump constitute a positive reference voltage generation circuit, and the second low-noise linear regulator A noise linear regulator and a boost charge pump constitute a common-mode voltage generating circuit; among them, a positive reference voltage generating circuit is used to generate a high voltage twice or higher relative to the low input power supply voltage, and convert it into a voltage equivalent to the low input power supply Positive reference voltage twice the voltage; the common-mode voltage generation circuit is used to generate a high voltage twice or higher than the low input power supply voltage, and convert it into a common-mode voltage equivalent to half the low input power supply voltage.

Description

A MEMS capacitive accelerometer interface circuit

technical field

The utility model relates to a capacitive inertial sensor, in particular to a MEMS (Micro ElectroMechanical System) capacitive accelerometer interface circuit.

Background technique

Capacitive inertial sensors generally include inertial sensors such as acceleration sensors and gyroscopes. These inertial sensors measure the acceleration of the carrier relative to the ground and other parameters in real time to determine the position of the carrier and the parameters of the earth's gravity field, and the measured changes translates into a change in capacitance.

The following is an example of a MEMS (Micro Electro Mechanical System) capacitive inertial sensor.

With the increasing maturity of MEMS (Micro Electro Mechanical System) technology, MEMS capacitive inertial sensors are widely used due to their small size, high sensitivity, stable DC characteristics, small drift, low power consumption, and small temperature coefficient. However, MEMS The capacitive inertial sensor has a small capacitance change, so the servo circuit of the MEMS capacitive inertial sensor is required to have the characteristics of high precision, good linearity, and large dynamic range.

The existing MEMS capacitive inertial sensor servo circuit is divided into closed-loop structure and open-loop structure from the structure, and is divided into analog signal output and digital signal output from the output signal. The capacitive inertial sensor servo circuit with an open-loop structure is constrained in linearity, measurement range, and dynamic range; the closed-loop implementation scheme is divided into two types, one is a negative feedback scheme based on analog closed-loop, and the other is based on digital closed-loop. Negative feedback scheme, the negative feedback scheme based on digital closed loop has better dynamic measurement accuracy and temperature stability, and can also realize digital output. Whether it is a closed-loop circuit or an open-loop circuit, an interface circuit must be included.

The input power supply of the existing MEMS capacitive inertial sensor servo circuit is usually a dual power supply or a high-voltage single power supply, which is convenient for realizing positive and negative reference voltages and high output sensitivity of the MEMS sensitive unit. The performance of high-voltage devices used in high-voltage circuits is often inferior to low-voltage devices, limiting the performance of the entire system. At the same time, high input power means high power consumption. It is not suitable for long-term operation in applications such as geophysical exploration and inertial navigation that require battery power. Low input power usually also reduces the positive and negative reference voltage values of MEMS sensitive cells, which cannot provide enough feedback force in closed-loop applications.

Utility model content

The purpose of the utility model is to solve the above-mentioned technical problems, and provide a low-power consumption open-loop structure interface circuit of a MEMS capacitive accelerometer with a single power supply, and has excellent noise suppression ability.

In order to achieve the above object, a MEMS capacitive accelerometer interface circuit provided by the utility model includes a sensitive unit and a readout device; the readout device includes: a switch, a preamplifier, a positive reference voltage and a common-mode voltage generating circuit; a positive reference The voltage and common-mode voltage generation circuit includes a boost charge pump, a first low-noise linear regulator LDO1, and a second low-noise linear regulator LDO2; wherein, the first low-noise linear regulator LDO1 and the boost charge pump constitute The positive reference voltage generation circuit, the second low-noise linear regulator LDO2 and the boost charge pump constitute a common-mode voltage generation circuit; wherein, the positive reference voltage generation circuit is used to generate a voltage twice or higher than the low input power supply voltage high voltage, and convert the high voltage twice or higher relative to the low input power supply voltage into a positive reference voltage equivalent to twice the low input power supply voltage; the common-mode voltage generation circuit is used to generate a Or higher high voltage, and convert the high voltage twice or higher relative to the low input supply voltage to a common-mode voltage equivalent to half the low input supply voltage.

Further, the output of the positive reference voltage generating circuit and the ground are respectively used as positive and negative reference voltages of the MEMS sensitive unit, and the output of the common-mode voltage generating circuit is used as the common-mode voltage of the MEMS sensitive unit and the preamplifier.

Furthermore, the preamplifier is powered by a low input power supply, and is designed with a high-performance low-voltage MOS tube.

Further, the interface circuit is applied to a low-power open-loop or closed-loop accelerometer interface circuit.

Further, the MEMS capacitive accelerometer interface circuit also includes a MEMS sensitive unit, and the output signal of the MEMS sensitive unit is a capacitance change signal.

The beneficial effect of the utility model is that it realizes the MEMS capacitive accelerometer interface circuit with low voltage single power input, which is different from the current common dual power supply or high voltage single power supply interface circuit. The preamplifier works at low voltage and can be designed with high-performance low-voltage MOS transistors, which is beneficial to achieve lower noise and higher bandwidth. A boost charge pump is used to achieve a high reference voltage for MEMS sensitive cells at low input supply conditions. It can be applied to low-power open-loop or closed-loop accelerometer servo circuits according to requirements.

Description of drawings

Fig. 1 is the schematic structural diagram of the open-loop servo readout circuit of the existing general-purpose capacitive inertial sensor;

Fig. 2 is the schematic diagram of two phases of PH1 and PH2 in the circuit of Fig. 1;

Fig. 3 is the generation circuit of the positive and negative reference voltages of the open-loop servo readout circuit of the existing dual power supply capacitive inertial sensor;

Fig. 4 is a schematic structural diagram of a MEMS capacitive accelerometer interface circuit provided by the utility model and a schematic structural diagram of a positive reference voltage and a common-mode voltage generating circuit.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present utility model clearer, the present utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are part of the embodiments of the present utility model, not all of them. the embodiment. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not intended to limit the utility model. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present utility model.

In order to make the public have a better understanding of the utility model, some specific details are described in detail in the detailed description of the utility model below. Those skilled in the art can fully understand the present invention without the description of these detailed parts.

Figure 1 is an embodiment of the interface circuit of the MEMS accelerometer, including a MEMS sensitive chip and a readout device. The usual acceleration sensitive chip is equivalent to a second-order system model, which can be embedded in an accelerometer open-loop or closed-loop system.

The general-purpose capacitive inertial sensor interface circuit in Figure 1 includes: a preamplifier OTA; three electrodes connected to the three plates of the inertial sensor: top, ctr and bot, where top is connected to the upper plate of the sensor, and ctr is connected to the sensor The middle plate of the bot is connected to the lower plate of the sensor; the three voltages connected to the plate are: Vp, Vn and Vcom, where Vp is the positive reference voltage, Vn is the negative reference voltage, and Vcom is the common-mode voltage; the sensor, reference The voltage and the preamplifier are connected through 6 switches; the capacitor Cf is the feedback capacitor, which controls the gain of the amplifier OTA; the clock control signals ph1 and ph2 are non-overlapping clocks, which control the on and off of the switch.

Fig. 2 is the equivalent circuit diagram of two phases of PH1 and PH2 in the general capacitive inertial sensor interface circuit.

Fig. 3 is the positive and negative reference voltage generating circuit in the existing dual power supply interface circuit, comprising: bandgap reference source BandGap, used to generate reference voltage Vbg; Buffer Buffer, used to generate positive reference voltage; Inverter, used To generate a negative reference voltage Vn. Where Vp and Vn are reference voltages with equal absolute values and symmetrical with respect to Gnd, and Gnd is the common-mode voltage of the preamplifier.

FIG. 4 is a schematic structural diagram of an interface circuit of a MEMS capacitive accelerometer provided by the present invention. As shown in Figure 4, the MEMS capacitive accelerometer interface circuit includes a sensitive unit and a readout device; the readout device includes: a switch, a preamplifier, a positive reference voltage and a common-mode voltage generation circuit; a positive reference voltage and a common-mode voltage generation circuit The circuit includes a boost charge pump, a first low-noise linear regulator and a second low-noise linear regulator; wherein, the first low-noise linear regulator LDO1 and the boost charge pump constitute a positive reference voltage generating circuit, and the second The low-noise linear regulator LDO2 and the boost charge pump constitute a common-mode voltage generation circuit; among them, the positive reference voltage generation circuit is used to generate a high voltage that is twice or higher than the low input power supply voltage, and will be compared to the low input A high voltage that is twice or higher than the power supply voltage is converted into a positive reference voltage that is twice the low input power supply voltage; the common-mode voltage generation circuit is used to generate a high voltage that is twice or higher than the low input power supply voltage, and the relative High voltage twice or more than the low input supply voltage translates to a common-mode voltage equal to half the low input supply voltage.

The interface circuit structure of a MEMS capacitive accelerometer shown in Figure 4 is consistent with that of a general-purpose capacitive inertial sensor interface circuit. The difference is that a low power supply is used, and the positive and negative reference voltage values and common-mode voltage values are adjusted. The low-input power supply generates a high voltage that is twice or higher than the power supply through a boost charge pump, and then passes through two low-noise LDOs to generate a positive reference voltage Vp that is twice the power supply voltage and a common voltage that is half the power supply voltage. Mode voltage Vcom, equivalent negative reference voltage Vn is Gnd.

Since this embodiment is consistent with the general capacitive inertial sensor interface circuit structure, referring to accompanying drawing 2, in the PH1 stage, the top plate top of the sensor is connected to Vp, the bottom plate bot is connected to Vn, and the left plate of the feedback capacitor Cf is connected to OTA The inverting input terminal, the right plate is connected to the common mode voltage. The charges on the three capacitors are:

Qt(PH1)=(Vp-Vcom)Ct

Qb(PH1)=(-Vcom)Cb

Qf(PH1)=0

When PH2 is at a high level, the upper plate top of the sensor is connected to Vn, the lower plate bot is connected to Vp, and the charges on Ct and Cb are transferred to the feedback capacitor Cf. The charges on the three capacitors are:

Qt(PH2)=(-Vcom)Ct

Qb(PH2)=(Vp-Vcom)Cb

Qf(PH2)=(Vx-Vcom)Cf

According to the law of conservation of charge: Vx=(Ct-Cb)Vp/Cf+Vcom

It can be seen that the output of the interface circuit Vx has nothing to do with the absolute value and symmetry of Vp and Vn.

This embodiment implements a low power consumption capacitive inertial sensor interface circuit. The preamplifier is designed with a high-performance low-voltage MOS tube, which can achieve lower noise and higher bandwidth; the boost charge pump ensures the reference voltage value of the MEMS sensitive unit, and can provide appropriate feedback force in closed-loop applications.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the utility model in detail, so it should be understood that the above description is only one of the specific implementation modes of the utility model, and is not intended to limit Within the protection scope of the present utility model, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present utility model shall be included in the protection scope of the present utility model.

Claims (5)

1. An MEMS capacitive accelerometer interface circuit comprises a sensitive unit and a reading device; characterized in that said reading device comprises: a switch, a preamplifier and a positive reference voltage and common mode voltage generating circuit; the positive reference voltage and common mode voltage generating circuit comprises a boost charge pump and a first low noise linear regulator (LDO) 1 and a second LDO 2; the first low noise linear regulator LDO1 and the boost charge pump form a positive reference voltage generating circuit, and the second low noise linear regulator LDO2 and the boost charge pump form a common mode voltage generating circuit; wherein,

the positive reference voltage generating circuit is used for generating a high voltage which is two times or higher than the low input power supply voltage and converting the high voltage which is two times or higher than the low input power supply voltage into a positive reference voltage which is two times of the low input power supply voltage;

the common mode voltage generating circuit is used for generating a high voltage which is two times or more higher than the low input power supply voltage and converting the high voltage which is two times or more higher than the low input power supply voltage into a common mode voltage which is half of the low input power supply voltage.

2. The interface circuit of claim 1, wherein the output of said positive reference voltage generating circuit and ground are used as positive and negative reference voltages for the MEMS sensitive unit, respectively, and the output of said common mode voltage generating circuit is used as a common mode voltage for the MEMS sensitive unit and the preamplifier.

3. The interface circuit of claim 1, wherein the preamplifier is powered by a low input power supply, using a high performance low voltage MOS transistor design.

4. The interface circuit of claim 1, wherein the interface circuit is applied to a low power consumption open loop or closed loop accelerometer interface circuit.

5. The interface circuit of claim 1, further comprising a MEMS-sensitive unit, wherein the MEMS-sensitive unit outputs a signal that is a change in capacitance.