CN114509579A - MEMS capacitive accelerometer interface circuit using voltage-controlled proportional readout technology - Google Patents

Abstract

The invention discloses a MEMS capacitive accelerometer interface circuit using a voltage control proportional readout technology, comprising a dynamic excitation source, a differential charge-voltage converter, a common-mode charge-voltage converter, and an analog-digital converter, wherein, Dynamic excitation source for generating excitation signals to excite external sensing units to generate charge signals; common-mode charge-voltage converters for reading out and converting the common-mode components in the charge signals into common-mode voltages; differential charge-voltage The converter is used to read out and convert the differential component in the charge signal to a differential voltage; the analog-to-digital converter is used to convert the differential voltage according to the common-mode voltage to achieve voltage-controlled proportional readout. The architecture proposed by the present invention supports dynamic excitation, so that the excitation source is no longer limited to the use of bandgap references and buffers, thereby improving the overall energy efficiency of the interface circuit, and only one MEMS sensing unit is required to form a fully differential structure, thereby reducing the cost of manufacturing cost.

Description

MEMS capacitive accelerometer interface circuit using voltage-controlled proportional readout technology

technical field

The invention belongs to the technical field of portable electronic applications, and in particular relates to a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology.

Background technique

Micro Electro-Mechanical System (MEMS) accelerometer is one of the important sensors in the micro-inertial navigation system. It has the characteristics of small size, low cost, light weight and low power consumption. Therefore, in our production It plays a huge role in life and is currently mainly used in motion perception, motion recognition, attitude control, vibration detection, security alarm, etc. Based on the acceleration sensor, more detection functions can be realized and more extensive applications can be achieved.

MEMS accelerometers can be divided into open-loop accelerometers and closed-loop accelerometers according to their working principles. The open-loop accelerometer measures acceleration by measuring the capacitance change caused by the displacement change of the mass block, which has low accuracy and poor linearity. The closed-loop accelerometer is also called a force-balanced accelerometer. Its working principle is: when the inertial force acts on the mass block, the closed-loop system detects the displacement of the mass block, and generates an electrostatic force equal to and opposite to the inertial force to offset the inertial force. , so that the mass is always in the equilibrium position. Due to its working principle, closed-loop accelerometers have high linearity and low noise, and are very suitable for high-precision measurements such as earthquake monitoring and inclination measurement. The commonly used closed-loop accelerometer interface circuits include: full-analog PID closed-loop control and digital-analog hybrid Delta-sigma closed-loop control. Compared with the closed-loop architecture, the MEMS capacitive accelerometer with the open-loop architecture obtains the advantages of low cost and low power consumption because it does not need to use high-gain design and loop compensation design in the signal chain. of Things, referred to as IoT) is the mainstream choice for applications. One of the main problems faced by the open-loop architecture is the nonlinear error caused by the inverse-proportional transfer function characteristics of the sensing unit. The nonlinear error increases with the increase of the input acceleration signal, thus greatly limiting the open-loop architecture. Dynamic Range. At present, MEMS capacitive accelerometers with common open-loop architecture are implemented by a charge-controlled interface circuit with a proportional transfer function. Two MEMS sensing units are required to realize a fully differential architecture. The interface circuit with a proportional transfer function can well cancel the transmission. The inverse proportional function characteristic of the sensor unit.

However, the traditional charge-controlled interface circuit with a proportional transfer function uses a bandgap reference and a buffer as excitation sources, which limits the overall energy efficiency of the interface circuit, and requires two MEMS sensing units to implement a fully differential architecture, resulting in manufacturing costs. high.

SUMMARY OF THE INVENTION

In order to solve the above problems existing in the prior art, the present invention provides a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology.

An embodiment of the present invention provides a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology, including:

Including dynamic excitation source, differential charge-voltage converter, common-mode charge-voltage converter, analog-digital converter, among which,

The dynamic excitation source is used to generate an excitation signal to excite an externally connected sensing unit to generate a charge signal;

the common-mode charge-voltage converter, connected to the sensing unit, for reading out and converting the common-mode component in the charge signal into a common-mode voltage;

the differential charge-voltage converter, connected to the sensing unit, for reading out and converting the differential component in the charge signal into a differential voltage;

The analog-to-digital converter is connected to the common-mode charge-voltage converter and the differential charge-voltage converter, and is used for converting the differential voltage according to the common-mode voltage, so as to realize voltage-controlled proportional readout.

In an embodiment of the present invention, the dynamic excitation source is implemented by an open-loop charge pump.

In an embodiment of the present invention, the external sensing unit includes an input common electrode R, a capacitor C _S1 , a capacitor C _S2 , a first output differential electrode INA, and a second output differential electrode INB, wherein,

The input common electrode R is respectively connected to one end of the capacitor C _S1 and one end of the capacitor C _S2 , the other end of the capacitor C _S1 is connected to the first output differential electrode INA, and the other end of the capacitor C _S2 is connected to the first output differential electrode INA. The second output differential electrode INB is connected.

In one embodiment of the present invention, the common-mode charge-voltage converter includes a common-mode charge amplifier constructed by a capacitor C _CM and a common-mode amplifier A1.

In an embodiment of the present invention, the common-mode charge-voltage converter further includes a capacitor C _H1 and a capacitor C _CAL1 , which are composed of the capacitor C _CM , the capacitor C _H1 , the capacitor C _CAL1 , and the common Mode amplifier A1 constructs a common mode charge amplifier.

In one embodiment of the present invention, the differential charge-to-voltage converter includes a differential charge amplifier constructed from a capacitor _CD and a fully differential amplifier A2.

In one embodiment of the present invention, the differential charge-voltage converter further includes a capacitor C _H2 and a capacitor C _CAL2 , which are composed of the capacitor C _D , the capacitor C _H2 , the capacitor C _CAL2 , and the fully differential Amplifier A2 constructs a differential charge amplifier.

In an embodiment of the present invention, the analog-to-digital converter uses the common-mode voltage as a reference voltage to convert differential voltages to realize voltage-controlled proportional readout, wherein the converted differential voltages are expressed as:

Among them, D _OUT represents the output of the analog-to-digital converter, V _OC represents the output of the common-mode charge-voltage converter, V _OD represents the output of the differential charge-voltage converter, and C _S1 represents the capacitances C _S1 and C in the sensing unit. _S2 represents the capacitance C _S2 in the sensing unit, C _CM represents the capacitance C _CM in the common mode charge-voltage converter, and CD represents the capacitance C _D in the differential charge-voltage converter _.

Compared with the prior art, the beneficial effects of the present invention:

The MEMS capacitive accelerometer interface circuit using the voltage control proportional readout technology provided by the present invention supports dynamic excitation, so that the excitation source is no longer limited to the way of using bandgap reference and buffer, thereby improving the interface circuit Overall energy efficiency, and only one MEMS sensing unit is required to form a fully differential structure, thereby reducing manufacturing costs.

The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

Description of drawings

1 is a schematic structural diagram of a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention;

2 is a schematic structural diagram of a typical structure of a sensing unit in a MEMS capacitive accelerometer provided by an embodiment of the present invention;

3 is a schematic structural diagram of an interface circuit traditionally using a charge-controlled proportional readout technology provided by an embodiment of the present invention;

4 is a schematic diagram of a circuit structure of a dynamic excitation source in a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention;

5 is a schematic structural diagram of another MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention;

6 is a schematic diagram of the circuit structure of CMCV, DCV, and sensing units in a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention.

Description of reference numbers:

101-detection mass; 102-spring; 103-fixed plate; 104-moving plate; 201-first sensing unit; 202-second sensing unit; 203-integrator; 204-adder; 205- Bandgap Reference; 206-Output Buffer; 301-Common Mode Charge-Voltage Converter; 302-Differential Charge-Voltage Converter; 303-Analog-Digital Converter; 304-Dynamic Excitation Source; 305-Sensing Unit;306 - Clock waveform output circuit.

Detailed ways

The present invention will be described in further detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

Example 1

Please refer to FIG. 1. FIG. 1 is a schematic structural diagram of a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention. This embodiment proposes a MEMS capacitive accelerometer interface circuit using the voltage-controlled proportional readout technology. The MEMS capacitive accelerometer interface circuit using the voltage-controlled proportional readout technology includes:

Dynamic excitation source, differential charge-voltage converter, common-mode charge-voltage converter, and analog-digital converter, wherein the dynamic excitation source is used to generate an excitation signal to excite an externally connected sensing unit to generate a charge signal; The mode charge-voltage converter is connected to the sensing unit and is used to read out and convert the common mode component in the charge signal into a common mode voltage; the differential charge-voltage converter is connected to the sensing unit and used to convert the common mode component in the charge signal into a common mode voltage; The differential components are read out and converted into differential voltages; the analog-to-digital converter is connected to the common-mode charge-voltage converter and the differential charge-voltage converter for converting the differential voltage according to the common-mode voltage to realize voltage-controlled proportional readout.

Specifically, due to the influence of the mechanical comb-tooth capacitance structure, the transfer function of the sensing unit of the MEMS capacitive accelerometer is an inverse proportional function, which brings about a nonlinearity that increases with the increase of the signal amplitude. Please refer to FIG. 2. FIG. 2 is a schematic diagram of a typical structure of a sensing unit in a MEMS capacitive accelerometer provided by an embodiment of the present invention, which is a typical structure of a sensing unit of a MEMS capacitive accelerometer. The proof mass 101 is suspended by a spring 102 and is electrically connected to the common electrode R. The fixed electrode plate 103 and the movable electrode plate 104 form a differential sensing capacitor C _S1 and a capacitor C _S2 . The fixed electrode plates 103 of the differential sensing capacitors C _S1 and C _S2 are electrically connected to the differential electrodes INA and INB of the sensing unit, respectively. The moving electrode plate 104 is the electrode plate that moves with the proof mass 101 , and is also electrically connected to the common electrode R. When the external acceleration signal a comes, the detection mass 101 is displaced, which drives the moving plate 104 to be displaced, so that the capacitance value of the sensing capacitor changes. After completing the conversion of acceleration signal-capacitance signal, the expression of sensing capacitance is expressed as:

Among them, C ₀ represents the static capacitance value of the sensing capacitor, Δd represents the displacement value of the moving pole plate of the sensing capacitor under the excitation of the acceleration signal a, which has a linear relationship with the acceleration signal a, and d ₀ represents the static moving pole plate and fixed pole plate pitch, x is the modulation depth, and k is the linear coefficient. The capacitance change value produced by the sensing capacitor. It can be seen from formula (1) that the transfer function from the acceleration a to the sensing capacitor C _S is an inverse proportional function, which has nonlinearity, and the nonlinearity increases significantly with the increase of the acceleration signal a, which greatly limits the dynamics of the accelerometer. scope. To avoid inversely proportional non-linearity of the transfer function, one of the most efficient ways is to design a proportional transfer function:

Equation (2) shows that the proportional transfer function can avoid inverse proportional nonlinearity, thereby effectively expanding the dynamic range of the accelerometer.

Please refer to FIG. 3 . FIG. 3 is a schematic structural diagram of an interface circuit using a traditional charge-controlled proportional readout technology provided by an embodiment of the present invention. FIG. 3 is a traditional MEMS accelerometer interface circuit using the charge-controlled proportional readout technology, also known as "Self-balancing bridge". The circuit of this architecture includes: a first sensing unit 201, a second sensing unit 202, an integrator 203 and an adder 204 to complete the proportional transfer function, the excitation voltage source is composed of a bandgap reference 205 and an output buffer 206, wherein, The capacitance C _S1 and the capacitance C _S2 are both differential capacitances of the first sensing unit 201 , the capacitance C _S3 and the capacitance C _S4 are two differential capacitances of the second sensing unit 202 , and _VR is a reference for the DAC The voltage source, for example, may be the excitation voltage V _EXE . The first sensing unit 201 and the second sensing unit 202 need to be matched in design, so that C _S1 =C _S4 and C _S2 =C _S3 , the first sensing unit 201 and the second sensing unit 202 pass through differential electrodes ( INA1, INB1, INA2 and INB2) for feedback excitation, the charge difference generated by the capacitor C _S1 and the capacitor C _S2 is output to the integrator 203 through the common electrode R1, and the charge difference generated by the capacitor C _S3 and the capacitor C _S4 is passed through The common electrode R2 is output to the integrator 203 . After the first sensing unit 201 and the second sensing unit 202 are balanced, the integrator 203 is stable, and the common electrode R1 and the common electrode R2 no longer generate a charge difference, that is, the charge on the capacitor C _S1 and the charge on the capacitor C _S1 are equal, and the charge on capacitor C _S3 is equal to the charge on capacitor C _S4 , so we have:

Since the capacitance C _S1 and the capacitance C _S4 are the same, and the capacitance C _S2 and the capacitance C _S3 are the same, the solution of the expression obtained by the formula (3) is:

Equation (4) shows that the self-balancing bridge can realize proportional readout, and the proportional readout is related to the excitation source V _EXE . The excitation source is limited to the way of using the bandgap reference and buffer, which limits the overall energy efficiency of the interface circuit, and requires two Each MEMS sensing unit forms a fully differential structure, which increases the manufacturing cost.

In order to solve the above problems, please refer to FIG. 1 again. This embodiment proposes a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology. The dynamic excitation source 304 generates an excitation signal to excite an externally connected sensing unit. 305 , thereby outputting a charge signal at the output end of the sensing unit 305 , and a common-mode charge-voltage converter (Common-mode Capacitance to Voltage Converter, referred to as CMCV) 301 converts the common-mode component of the charge signal transmitted from the sensing unit 305 The differential charge-voltage converter (Differential Capacitance to Voltage Converter, DCV) 302 absorbs and converts the differential component of the charge signal transmitted from the sensing unit 305 into a corresponding differential voltage , and the analog-to-digital converter 303 of the subsequent stage converts the differential voltage output by the DCV circuit according to the common mode voltage output by the CMCV circuit. The architecture proposed in this embodiment supports dynamic excitation, so that the excitation source is no longer limited to the use of bandgap references and buffers, thereby improving the overall energy efficiency of the interface circuit, and only one MEMS sensing unit is required to form a fully differential structure, thereby Reduced manufacturing costs.

Further, the dynamic excitation source 304 in this embodiment is implemented by an open-loop charge pump.

和放大器等效输入电压噪声

这两类噪声等效到传感电容中的噪声分别表示为：Specifically, the dynamic excitation source is a voltage source whose amplitude does not need to be fixed, and is implemented by an open-loop charge pump, which improves the energy efficiency of the interface circuit because it does not require high-power bandgap references and buffers that use closed-loop control. In addition, the excitation source using the charge pump can output excitation higher than the power supply voltage. The higher the excitation source voltage amplitude, the stronger the excitation signal, and the lower the equivalent input noise obtained by the interface circuit. Please refer to FIG. 4. FIG. 4 is a schematic diagram of a circuit structure of a dynamic excitation source in a MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention, and FIG. 4 is a dynamic excitation source used in the interface circuit. The excitation source is implemented by a specific circuit, but the circuit implementation is not limited. The specific circuit of the dynamic excitation source 304 in this embodiment adopts a conventional open-loop cross-coupled charge pump as shown in FIG. 4 , and the charge pump outputs a voltage three times the power supply voltage VDD through three-stage boosting. In a 1.8V CMOS process, the charge pump can be designed using a 5V thick gate oxide device. The reason for using a charge pump drive is that the charge pump can provide a higher excitation voltage amplitude, thereby reducing noise. Specifically: the common-mode capacitance of the sensing unit is much larger than the differential capacitance (10-100 times), so the output noise of the DCV circuit dominates in the result of the final voltage control ratio readout, not the output noise of the CMCV circuit dominate. The noise of the DCV circuit mainly comes from the charge noise of the parasitic capacitance

and amplifier equivalent input voltage noise

These two types of noise equivalent to the noise in the sensing capacitor are expressed as:

It can be seen from formula (5) that increasing the amplitude of the excitation source voltage V _EXE can effectively reduce the noise, and can improve the signal-to-noise ratio SNR under the condition that the signal strength remains unchanged. The charge pump shown in Figure 4 is designed as an open-loop charge pump for low power consumption. Since it is an open-loop charge pump, the output voltage will vary significantly with the port parasitic capacitance:

Among them, V _ZL represents the ideal voltage of the open-loop charge pump output when there is no load capacitor. For a VDD of 1.8V, the value of V _ZL is 5.4V, C _CP represents the power transmission capacitor in the open-loop charge pump, and C _L represents The load capacitance value mainly depends on the sum of the differential sensing capacitance and parasitic capacitance in the sensing unit 305 .

Further, a sensing unit 305 externally connected in this embodiment includes an input common electrode, a capacitor C _S1 , a capacitor C _S2 , a first output differential electrode, and a second output differential electrode.

Specifically, please refer to FIG. 5 . FIG. 5 is a schematic structural diagram of another MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology provided by an embodiment of the present invention. In this embodiment, the sensing unit 305 has an input common The electrodes R are respectively connected to one end of the capacitor C _S1 and one end of the capacitor C _S2 , the other end of the capacitor C _S1 is connected to the first output differential electrode INA, and the other end of the capacitor C _S2 is connected to the second output differential electrode INB. Compared with the circuit architecture shown in FIG. 3 , this embodiment only needs one sensing unit 305 to implement a fully differential architecture, and the sensing unit 305 includes two differential sensing capacitors, a capacitance C _S1 and a capacitance C _S2 . The architecture is excited through the common electrode R of the sensing unit 305 and then read out through the first differential electrode INA and the second differential electrode INB of the sensing unit 305 .

Further, referring to FIG. 5 again, the common-mode charge-voltage converter 301 in this embodiment includes a common-mode charge amplifier constructed by a capacitor C _CM and a common-mode amplifier A ₁ , specifically: the output end of the common-mode amplifier A ₁ is connected to the A capacitor C _CM is connected across the first inverting input terminals, the _first inverting input terminal of the common mode amplifier A1 is also connected to the _first differential electrode INA, and the output terminal of the common mode amplifier A1 is connected to the second inverting input terminal A capacitor C _CM is connected across the terminals, the second inverting input terminal of the common _- mode amplifier A1 is also connected with the second differential electrode INB, and the _first non-inverting input terminal and the second non-inverting input terminal of the common-mode amplifier A1 Both are connected to the bias voltage VA _. In the CMCV circuit, the common mode amplifier A ₁ detects the change of the common mode signal on the first differential electrode INA and the second differential electrode INB of the sensing unit 305, and absorbs the feedback from the sensing unit 305 through the common mode feedback capacitor C _CM . The common-mode charge signal (C _S1 +C _S2 )V _EXE , forming an output voltage V _OC proportional to the common-mode charge signal, forming the common-mode charge-voltage converter 301 The common-mode output voltage of the converter 301 is expressed as:

Further, referring to FIG. 5 again, the differential charge-voltage converter in this embodiment includes 302 a differential charge amplifier constructed by a capacitor C _D and a fully differential amplifier A ₂ , specifically: the inverting output terminal of the fully differential amplifier A ₂ and the The capacitor CD is connected across the non- _inverting input terminals, the non _- inverting input terminal of the fully differential amplifier A2 is also connected to the first differential electrode INA, and the non _- inverting output terminal of the fully differential amplifier A2 is connected to the inverting terminal. The capacitor CD is connected across the phase input terminals, and the _inverting input terminal of the fully differential amplifier A2 is also connected to the _second differential electrode INB. In the DCV circuit, after the differential amplifier A2 detects the change of the differential signal on the first differential electrode INA and the _second differential electrode _INB of the sensing unit 305, it feedbacks and absorbs the differential charge from the sensing unit 305 through the differential feedback capacitor CD The signal (C _S1 - C _S2 ) V _EXE , which forms a differential output voltage V _OD proportional to the differential charge signal, forms the differential output voltage of the differential charge-to-voltage converter 302 expressed as:

Further, please refer to FIG. 6. FIG. 6 is a schematic diagram of the circuit structure of CMCV, DCV, and sensing units in a MEMS capacitive accelerometer interface circuit using voltage control ratio readout technology provided by an embodiment of the present invention. The common-mode charge-voltage converter 301 further includes a capacitor C _H1 , a capacitor C _CAL1 , and a common-mode charge amplifier is constructed by the capacitor C _CM , the capacitor C _H1 , the capacitor C _CAL1 , and the common-mode amplifier A ₁ , specifically: the common-mode amplifier The capacitor C _CM is connected across the output end of A1 and the _first differential electrode INA, and the capacitor is connected across the output end _of the common mode amplifier A1 and the second differential electrode INB C _CM , the output terminal of the common _- mode amplifier A1 is also connected to a bias voltage _VB , and the capacitor C _H1 is connected across the output terminal of the common-mode amplifier A1 and the _first inverting input terminal , the capacitor C _H1 is connected across the output terminal of the common _- mode amplifier A1 and the second inverting input terminal, and the _first inverting input terminal of the common-mode amplifier A1 is connected to the first differential electrode The capacitor C CAL1 is connected between the _INAs , the capacitor C _CAL1 is connected between the second inverting input terminal of the common-mode amplifier A ₁ and the second differential electrode INB, and the common-mode amplifier A ₁ Both the first non-inverting input terminal and the second non _- inverting input terminal of , are connected to the bias voltage VA. The common-mode charge-voltage converter 301 has the output voltage V _OC of the above formula (7), and the capacitor C _CAL1 and the capacitor C _H1 connected to the common-mode amplifier A ₁ form a switched capacitor network, in order to correct the common-mode amplifier A ₁ . Gain error, cancel Offset, and reduce 1/f noise.

Further, referring to FIG. 6 again, the differential charge-voltage converter 302 in this embodiment further includes a capacitor C _H2 and a capacitor C _CAL2 , and the differential charge is constructed by the capacitor C _D , the capacitor C _H2 , the capacitor C _CAL2 and the fully differential amplifier A ₂ . Amplifier, specifically _: the capacitor C _D is connected across the inverting output terminal of the fully differential amplifier A2 and the first differential electrode INA, and the non _- inverting output terminal of the fully differential amplifier A2 is connected to the first differential electrode INA. The capacitor C _D is connected across the second differential electrode INB, the capacitor C _H2 is connected across the inverting output terminal and the non-inverting input terminal of the fully differential amplifier A2, and the fully differential amplifier A2 is connected across the capacitor C _H2 . The capacitor _CH2 is connected across the non-inverting output terminal of A2 and the inverting input terminal, and the capacitor is connected between the non _{- inverting} input terminal of the fully differential amplifier A2 and the first differential electrode INA C _CAL2 , the capacitor C _CAL2 is connected between the inverting input terminal of the fully differential amplifier A ₂ and the second differential electrode INB. Similarly, in addition to the output voltage V _OC of the above formula (8), the differential charge-voltage converter 302 forms a switched capacitor network with the capacitor C _CAL2 and the capacitor C _H2 connected to the differential amplifier A ₂ , in order to correct the differential amplifier A ₂ gain error, offset Offset, and reduce 1/f noise.

It should be noted that, in this embodiment, 306 shown in FIG. 6 is an external clock waveform output circuit. The switching sequence of switch Φ1, switch Φ2, and switch Φ1n shown in FIG. 6 is realized by the clock waveform output circuit 306. The specific clock waveform output sequence It is designed according to the actual scene needs.

Further, in the analog-to-digital converter 303 of this embodiment, the common-mode voltage is used as the reference voltage to convert the differential voltage, so as to realize the voltage-controlled proportional readout.

Specifically, referring to FIG. 3 again, the analog-to-digital conversion 303 in this embodiment includes an analog-to-digital converter (Analog-to-Digital Converter, ADC for short) and a digital-to-analog converter (Digital-to-Analog Converter, DAC for short) , where the ADC is an ADC of a switched capacitor circuit, which can be a Sigma-Delta architecture or a SAR architecture. In this embodiment, the ADC and the DAC together constitute a signal divider, the numerator is the differential voltage V _OD output by the DCV circuit, and the denominator is the common mode voltage V _OC output by the CMCV circuit. In this embodiment, the DCV circuit and the _CMCV circuit perform the readout operation at the same time, and absorb the differential charge part and the common mode charge part of the sensing unit 305 respectively. to convert the differential voltage V _OD , the resulting analog-to-digital converter 303 final digital output is expressed as:

Among them, D _OUT represents the output of the analog-to-digital converter 303 , V _OC represents the output of the common-mode charge-voltage converter 301 , V _OD represents the output of the differential charge-voltage converter 302 , and C _S1 represents the capacitance in the sensing unit 305 C _S1 and C _S2 represent the capacitances C _S2 in the sensing unit 305 , C _CM represent the capacitances C _CM in the common-mode charge-voltage converter 301 , and C _D represent the capacitances C _D in the differential charge-voltage converter 302 . It can be seen from formula (9) that the architecture proposed in FIG. 3 realizes the voltage-controlled proportional readout, and the readout gain can be adjusted by the ratio of the capacitor _{C CM} and the capacitor CD. Although the excitation voltage V _EXE of the open-loop charge pump is not fixed, it can be seen from formula (9) that in the interface circuit of the voltage control proportional readout in this embodiment, the digital output has nothing to do with the excitation voltage V _EXE , and the excitation voltage V _EXE does not affect the gain accuracy of the entire circuit.

To sum up, in the MEMS capacitive accelerometer interface circuit using the voltage-controlled proportional readout technology proposed in this embodiment, the dynamic excitation source 304 forms a pulse voltage signal with a certain duty cycle, and the dynamic excitation source 304 forms a pulse voltage signal with a certain duty cycle. The two capacitors C _S1 and C _S2 are excited at the same time, so that the first output differential electrode INA and the second output differential electrode INB of the sensing unit 305 output charge signals. The CMCV circuit absorbs the common mode component in the charge signal transmitted by the first output differential electrode INA and the second output differential electrode INB, and converts it into a corresponding common mode voltage. The DCV circuit absorbs the differential components in the charge signals transmitted from the first output differential electrode INA and the second output differential electrode INB, and converts them into corresponding differential voltages. The analog-to-digital converter of the subsequent stage uses the common-mode voltage output by the CMCV circuit as a reference voltage to convert the differential voltage output by the DCV circuit. Since the ADC+DAC structure in the analog-to-digital converter 303 functions as a divider, the ADC is at the output end. A proportional transfer function is formed to counteract the nonlinearity of the inverse proportional transfer function of conventional sensing elements, thereby improving dynamic range. In addition, in the interface circuit of the voltage control proportional readout technology in this embodiment, the gain of the transfer function is independent of the amplitude of the excitation voltage V _EXE , so that the excitation voltage V _EXE can use a low-precision high-voltage voltage source with uncontrolled amplitude (using The open-loop charge pump implementation) replaces the high-precision low-voltage voltage source (bandgap reference plus buffer combination) to improve the overall energy efficiency of the interface circuit and reduce noise, and only one MEMS sensing unit 305 is required to form a fully differential structure, thereby reducing manufacturing costs. cost.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (8)

1. a MEMS capacitive accelerometer interface circuit that adopts voltage control ratio readout technology, is characterized in that, comprises dynamic excitation source, differential charge-voltage converter, common mode charge-voltage converter, analog-digital converter, in, The dynamic excitation source is used to generate an excitation signal to excite an externally connected sensing unit to generate a charge signal; the common-mode charge-voltage converter, connected to the sensing unit, for reading out and converting the common-mode component in the charge signal into a common-mode voltage; the differential charge-voltage converter, connected to the sensing unit, for reading out and converting the differential component in the charge signal into a differential voltage; The analog-to-digital converter is connected to the common-mode charge-voltage converter and the differential charge-voltage converter, and is used for converting the differential voltage according to the common-mode voltage, so as to realize voltage-controlled proportional readout. 2 . The MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology according to claim 1 , wherein the dynamic excitation source is realized by an open-loop charge pump. 3 . 3. The MEMS capacitive accelerometer interface circuit using voltage control proportional readout technology according to claim 1, wherein the external sensing unit comprises an input common electrode R, a capacitance C _S1 , a capacitance C _S2 , a first An output differential electrode INA, a second output differential electrode INB, wherein, The input common electrode R is respectively connected to one end of the capacitor C _S1 and one end of the capacitor C _S2 , the other end of the capacitor C _S1 is connected to the first output differential electrode INA, and the other end of the capacitor C _S2 is connected to the first output differential electrode INA. The second output differential electrode INB is connected. 4. The MEMS capacitive accelerometer interface circuit using voltage control proportional readout technology according to claim 3, wherein the common mode charge-voltage converter comprises a capacitor C _CM and a common mode amplifier A ₁ constructed by common-mode charge amplifier. 5. The MEMS capacitive accelerometer interface circuit using voltage control proportional readout technology according to claim 4, wherein the common-mode charge-voltage converter further comprises a capacitor C _H1 and a capacitor C _CAL1 , which are formed by the The capacitor C _CM , the capacitor C _H1 , the capacitor C _CAL1 , and the common-mode amplifier A ₁ form a common-mode charge amplifier. 6. The MEMS capacitive accelerometer interface circuit using voltage-controlled proportional readout technology according to claim 3, wherein the differential charge-voltage converter comprises a capacitor C _D , a fully differential amplifier A ₂ constructed Differential charge amplifier. 7. The MEMS capacitive accelerometer interface circuit using voltage control proportional readout technology according to claim 6, wherein the differential charge-voltage converter further comprises a capacitor C _H2 and a capacitor C _CAL2 , which are composed of the The capacitor C _D , the capacitor _CH2 , the capacitor C _CAL2 , and the fully differential amplifier A ₂ form a differential charge amplifier. 8 . The MEMS capacitive accelerometer interface circuit using a voltage-controlled proportional readout technology according to claim 6 , wherein the analog-to-digital converter uses the common mode voltage as a reference voltage to convert differential voltages 8 . , to achieve a voltage-controlled proportional readout, where the converted differential voltage is expressed as:

Among them, D _OUT represents the output of the analog-to-digital converter, V _OC represents the output of the common-mode charge-voltage converter, V _OD represents the output of the differential charge-voltage converter, and C _S1 represents the capacitances C _S1 and C in the sensing unit. _S2 represents the capacitance C _S2 in the sensing unit, C _CM represents the capacitance C _CM in the common mode charge-voltage converter, and CD represents the capacitance C _D in the differential charge-voltage converter _.

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