CN114509579B - MEMS capacitive accelerometer interface circuit adopting voltage control proportion reading technology - Google Patents
MEMS capacitive accelerometer interface circuit adopting voltage control proportion reading technology Download PDFInfo
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- 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
Abstract
The invention discloses an MEMS capacitive accelerometer interface circuit adopting a voltage control proportion reading technology, which comprises a dynamic excitation source, a differential charge-voltage converter, a common-mode charge-voltage converter and an analog-digital converter, wherein the dynamic excitation source is used for generating an excitation signal to excite an external sensing unit to generate a charge signal; the common-mode charge-voltage converter is used for reading out the common-mode component in the charge signal and converting the common-mode component into a common-mode voltage; a differential charge-voltage converter for reading out and converting a differential component in the charge signal into a differential voltage; and the analog-digital converter is used for converting the differential voltage according to the common-mode voltage so as to realize voltage control proportional reading. The framework provided by the invention supports dynamic excitation, so that an excitation source is not limited to a mode of using a band gap reference and a buffer any more, the overall energy efficiency of an interface circuit is improved, only one MEMS sensing unit is needed to form a fully differential structure, and the manufacturing cost is reduced.
Description
Technical Field
The invention belongs to the technical field of portable electronic application, and particularly relates to an MEMS capacitive accelerometer interface circuit adopting a voltage control ratio reading technology.
Background
An accelerometer of a Micro Electro-Mechanical System (MEMS for short) is one of important sensors in a Micro inertial navigation System, and has the characteristics of small volume, low cost, light weight, low power consumption and the like, so that the accelerometer plays a great role in production and life, is mainly applied to aspects of motion sensing, motion recognition, attitude control, vibration detection, security alarm and the like at present, can realize more detection functions based on the accelerometer, and is widely applied.
MEMS accelerometers can be classified into open-loop accelerometers and closed-loop accelerometers according to their operating principle. The open-loop accelerometer measures acceleration by measuring capacitance change caused by mass block displacement change, and has low precision and poor linearity. The closed-loop accelerometer is also called a force balance accelerometer, and the working principle of the closed-loop accelerometer is as follows: when the inertial force acts on the mass block, the closed-loop system detects the displacement of the mass block, generates an electrostatic force which is equal to the inertial force in magnitude and opposite to the inertial force in direction, counteracts the inertial force and enables the mass block to be always in a balance position. The closed-loop accelerometer has high linearity and low noise due to the working principle, and is very suitable for high-precision measurement such as earthquake monitoring, dip angle measurement and the like. The current common closed-loop accelerometer interface circuit includes: and a fully-analog PID closed-loop control mode and a digital-analog mixed Delta-sigma closed-loop control mode. Compared with a closed-loop architecture, the MEMS capacitive accelerometer with the open-loop architecture has the advantages of low cost and low power consumption because a high-gain design, a loop compensation design and the like are not needed in a signal link, and thus becomes a mainstream choice for Internet of Things (Internet of Things, ioT for short). One of the main problems faced by the open-loop architecture is the non-linear error caused by the inverse proportional transfer function characteristic of the sensing unit, which increases with the increase of the input acceleration signal, thus greatly limiting the dynamic range of the open-loop architecture. At present, a common open-loop structured MEMS capacitive accelerometer is realized by adopting a charge-controlled interface circuit with a proportional transfer function, two MEMS sensing units are required for realizing a fully-differential structure, and the interface circuit with the proportional transfer function can well offset the anti-proportional function characteristic of the sensing units.
However, the conventional interface circuit with a proportional transfer function of such charge control uses a bandgap reference and a buffer as an excitation source, which limits the overall energy efficiency of the interface circuit, and two MEMS sensing units are required to realize a fully differential architecture, resulting in high manufacturing cost.
Disclosure of Invention
In order to solve the above problems in the prior art, the present invention provides an interface circuit of an MEMS capacitive accelerometer using a voltage control proportional sensing technique.
One embodiment of the present invention provides an interface circuit of a MEMS capacitive accelerometer using a voltage-controlled proportional sensing technique, including:
comprises a dynamic excitation source, a differential charge-voltage converter, a common-mode charge-voltage converter, and an analog-digital converter, wherein,
the dynamic excitation source is used for generating an excitation signal to excite an externally connected sensing unit to generate a charge signal;
the common-mode charge-voltage converter is connected with the sensing unit and used for reading out a common-mode component in the charge signal and converting the common-mode component into a common-mode voltage;
the differential charge-voltage converter is connected with the sensing unit and used for reading out the differential component in the charge signal and converting the differential component into a differential voltage;
the analog-digital converter is connected with 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 control proportional readout.
In one embodiment of the invention, the dynamic excitation source is implemented using an open-loop charge pump.
In one embodiment of the invention, the external sensing unit comprises an input common electrode R, a capacitor C S1 Capacitor C S2 A first output differential electrode INA, a second output differential electrode INB,
the input common electrode R is respectively connected with the capacitor C S1 One terminal of (1), a capacitor C S2 One terminal of said capacitor C S1 Is connected to the first output differential electrode INA, the capacitor C S2 And the other end thereof is connected to the second output differential electrode INB.
In one embodiment of the invention, the common mode charge-voltage converter comprises a capacitor C CM And a common mode charge amplifier constructed by the common mode amplifier A1.
In one embodiment of the invention, the common mode charge-voltage converter further comprises a capacitor C H1 Capacitor C CAL1 From said capacitor C CM The capacitor C H1 The capacitor C CAL1 The common mode amplifier A1 constructs a common mode charge amplifier.
In one embodiment of the invention, the differential charge-voltage converter comprises a capacitor C D And a differential charge amplifier constructed by a fully differential amplifier A2.
In one embodiment of the invention, the differential charge-electricityThe voltage converter also comprises a capacitor C H2 Capacitor C CAL2 From said capacitor C D The capacitor C H2 The capacitor C CAL2 The fully differential amplifier A2 constitutes a differential charge amplifier.
In one embodiment of the present invention, the analog-to-digital converter converts a differential voltage by using the common mode voltage as a reference voltage to realize voltage control proportional sensing, wherein the converted differential voltage is expressed as:
wherein D is OUT Representing the output of an analog-to-digital converter, V OC Representing the output of a common-mode charge-voltage converter, V OD Representing the output of a differential charge-voltage converter, C S1 Representing the capacitance C in the sensing unit S1 ，C S2 Representing the capacitance C in the sensing unit S2 ，C CM Representing the capacitance C in a common-mode charge-voltage converter CM ，C D Representing the capacitance C in a differential charge-voltage converter D 。
Compared with the prior art, the invention has the beneficial effects that:
the MEMS capacitive accelerometer interface circuit adopting the voltage control proportion reading technology provided by the invention supports dynamic excitation, so that an excitation source is not limited in a mode of using a band gap reference and a buffer any more, the overall energy efficiency of the interface circuit is improved, only one MEMS sensing unit is needed to form a fully differential structure, and the manufacturing cost is reduced.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
Fig. 1 is a schematic structural diagram of an interface circuit of a MEMS capacitive accelerometer using a voltage-controlled proportional sensing technique according to an embodiment of the present invention;
fig. 2 is a schematic diagram of an exemplary structure of a sensing unit in a MEMS capacitive accelerometer according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an interface circuit according to a conventional charge-controlled proportional sensing technique according to an embodiment of the present invention;
fig. 4 is a schematic circuit structure diagram of a dynamic excitation source in an interface circuit of an MEMS capacitive accelerometer using a voltage control proportional sensing technique according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of another MEMS capacitive accelerometer interface circuit using voltage-controlled proportional sensing technology according to an embodiment of the present invention;
fig. 6 is a schematic circuit structure diagram of a CMCV, a DCV, and a sensing unit in an MEMS capacitive accelerometer interface circuit using a voltage control proportional sensing technique according to an embodiment of the present invention.
Description of reference numerals:
101-a proof mass; 102-a spring; 103-fixing the polar plate; 104-moving pole plate; 201-a first sensing unit; 202-a second sensing unit; 203-an integrator; 204-an adder; 205-bandgap reference; 206-an output buffer; 301-common mode charge-voltage converter; 302-differential charge-voltage converter; 303-analog-to-digital converter; 304-a dynamic excitation source; 305-a sensing unit; 306-clock waveform output circuit.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.
Example one
Referring to fig. 1, fig. 1 is a schematic structural diagram of an interface circuit of a MEMS capacitive accelerometer using a voltage-controlled proportional sensing technique according to an embodiment of the present invention. The embodiment provides an interface circuit of an MEMS capacitive accelerometer using a voltage control ratio reading technique, where the interface circuit of the MEMS capacitive accelerometer using the voltage control ratio reading technique includes:
the device comprises a dynamic excitation source, a differential charge-voltage converter, a common-mode charge-voltage converter and an analog-digital converter, wherein the dynamic excitation source is used for generating an excitation signal to excite an externally connected sensing unit to generate a charge signal; the common-mode charge-voltage converter is connected with the sensing unit and used for reading out the common-mode component in the charge signal and converting the common-mode component into a common-mode voltage; the differential charge-voltage converter is connected with the sensing unit and used for reading out the differential component in the charge signal and converting the differential component into differential voltage; and the analog-digital converter is connected with the common-mode charge-voltage converter and the differential charge-voltage converter and is used for converting differential voltage according to the common-mode voltage so as to realize voltage control proportional reading.
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, and the inverse proportional transfer function brings nonlinearity which increases with the increase of the signal amplitude. Referring to fig. 2, fig. 2 is a schematic diagram of a typical structure of a sensing unit in a MEMS capacitive accelerometer according to an embodiment of the present invention, which is a typical sensing unit structure of a MEMS capacitive accelerometer. The proof mass 101 is suspended by springs 102 and is electrically connected to the common electrode R. The fixed plate 103 and the movable plate 104 form a differential sensing capacitor C S1 And a capacitor C S2 . Differential sensing capacitor C S1 And a capacitor C S2 The stationary plate 103 is electrically connected to the differential electrodes INA, INB of the sensing unit, respectively. The movable plate 104 is a plate that moves with the proof mass 101, and is also electrically connected to the common electrode R. When an external acceleration signal a comes, the detection mass block 101 displaces, and the movable electrode plate 104 is driven to displace, so that the capacitance value of the sensing capacitor changes. And completing the conversion of the acceleration signal to the capacitance signal, wherein the expression of the sensing capacitance is as follows:
wherein, C 0 Representing static capacitance value of sensing capacitor, delta d representing displacement value of movable polar plate of sensing capacitor under the excitation of acceleration signal a, which is linear relation with acceleration signal a, d 0 The distance between the static time-motion polar plate and the fixed polar plate is shown, x represents the modulation depth, and k represents the linear coefficient. The capacitance change value generated by the sensing capacitance. Is prepared from formula (1)It can be seen that the acceleration a goes to the sensing capacitance C S The transfer function of (a) is an inversely proportional function, has nonlinearity, and the nonlinearity is remarkably increased along with the increase of the acceleration signal a, so that the dynamic range of the accelerometer is greatly limited. To avoid the inverse proportional non-linearity of the transfer function, one of the most efficient methods is to design a proportional transfer function:
formula (2) shows that the proportional transfer function can avoid inverse proportional nonlinearity, thereby effectively expanding the dynamic range of the accelerometer.
Referring to fig. 3, fig. 3 is a schematic structural diagram of a conventional interface circuit using a charge control ratio readout technology according to an embodiment of the present invention, and fig. 3 is a conventional MEMS accelerometer interface circuit using a charge control ratio readout technology, which is also referred to as a "self-balancing bridge". The circuit of the architecture comprises: the first sensing unit 201, the second sensing unit 202, the integrator 203 and the adder 204 are used for completing a proportional transfer function, the excitation voltage source is formed by a band gap reference 205 and an output buffer 206, wherein a capacitor C S1 And a capacitor C S2 Two differential capacitances, capacitance C, both of the first sensing cell 201 S3 And a capacitor C S4 Two differential capacitances, V, each of the second sensing unit 202 R Is a reference voltage source for the DAC, e.g. the excitation voltage V EXE . The first sensing unit 201 and the second sensing unit 202 need to be designed to keep matching, so that C S1 ＝C S4 And C S2 ＝C S3 The first sensing unit 201 and the second sensing unit 202 are respectively excited by feedback through differential electrodes (INA 1, INB1, INA2 and INB 2), and a capacitor C S1 And a capacitor C S2 The generated charge difference value is output to the integrator 203 through the common electrode R1, and the capacitor C S3 And a capacitor C S4 The generated charge difference value is output to the integrator 203 through the common electrode R2. After the first and second sensing units 201 and 202 are balanced, the integrator 203 is stabilized, and the common electrodes R1 and R2 are not producedGenerating a difference in charge, i.e. capacitance C S1 Charge on and capacitance C S1 Are equal in charge and a capacitance C S3 Charge on and capacitance C S4 Are equal, so that there is:
due to the capacitance C S1 And a capacitor C S4 Same, capacitance C S2 And a capacitor C S3 Similarly, the expression obtained by equation (3) is solved as:
formula (4) shows that the self-balancing bridge can realize proportional reading, and the proportional reading and the excitation source V EXE In this regard, the excitation source is limited to the use of a bandgap reference and a buffer, which limits the overall energy efficiency of the interface circuit, and two MEMS sensing units are required to form a fully differential structure, which increases the manufacturing cost.
In order to solve the above problem, referring to fig. 1 again, this embodiment provides an MEMS capacitive accelerometer interface circuit using Voltage-controlled proportional sensing technology, a dynamic excitation source 304 generates an excitation signal to excite an externally connected sensing unit 305, so as to output a charge signal at an output end of the sensing unit 305, a Common-mode charge-Voltage Converter (CMCV) 301 absorbs a Common-mode component in the charge signal transmitted by the sensing unit 305 and converts the Common-mode component into a corresponding Common-mode Voltage, a Differential charge-Voltage Converter (DCV) 302 absorbs a Differential component in the charge signal transmitted by the sensing unit 305 and converts the Differential component into a corresponding Differential Voltage, and a subsequent analog-to-digital Converter 303 converts a Differential Voltage output by a DCV circuit according to the Common-mode Voltage output by the CMCV circuit. The framework provided by the embodiment supports dynamic excitation, so that an excitation source is not limited to a mode of using a band-gap reference and a buffer any more, the overall energy efficiency of an interface circuit is improved, only one MEMS sensing unit is needed to form a fully differential structure, and the manufacturing cost is reduced.
Further, the dynamic excitation source 304 of the present embodiment is implemented by an open-loop charge pump.
Specifically, the dynamic excitation source is a voltage source with the amplitude not needing to be fixed, the dynamic excitation source is realized by adopting an open-loop charge pump, and because a high-power-consumption band-gap reference and a buffer which are controlled in a closed-loop mode are not needed, the energy efficiency of the interface circuit is improved. In addition, the excitation source adopting the charge pump can output excitation higher than power supply voltage, and the higher the amplitude of the voltage of the excitation source is, the stronger the excited signal is, and the lower the equivalent input noise obtained by the interface circuit is. Referring to fig. 4, fig. 4 is a schematic circuit structure diagram of a dynamic excitation source in an interface circuit of an MEMS capacitive accelerometer using a voltage control proportional sensing technology according to an embodiment of the present invention, and fig. 4 is a specific circuit implementation of the dynamic excitation source used in the interface circuit, but is not limited to the circuit implementation. The dynamic excitation source 304 of the embodiment adopts a conventional open-loop cross-coupled charge pump as shown in fig. 4, and the charge pump outputs a voltage 3 times the power supply voltage VDD through three-stage boosting. In a 1.8V CMOS process, the charge pump may use a 5V thick gate oxide device design. 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 method comprises the following steps: the common-mode capacitance of the sensing unit is far larger than the differential capacitance (10-100 times), so the output noise of the DCV circuit is dominant in the final voltage control ratio reading result, but not the output noise of the CMCV circuit. While 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 capacitance are respectively expressed as:
as can be seen from equation (5), the boost driver voltage V EXE The amplitude of the signal can effectively reduce noise, and the signal-to-noise ratio (SNR) can be improved under the condition that the signal intensity is unchanged. The charge pump shown in fig. 4 is designed as an open-loop charge pump to achieve low power consumption. Due to the open-loop charge pump, the output voltage can vary significantly with the variation of the port parasitic capacitance:
wherein, V ZL Representing the ideal voltage when the open-loop charge pump output has no load capacitance, V for VDD of 1.8V ZL The value of (A) is 5.4V CP Capacitance representing power transfer in an open-loop charge pump, C L Representing a load capacitance value that depends primarily on the sum of the differential sense capacitance and the parasitic capacitance in the sense cell 305.
Further, the sensing unit 305 externally connected in the present embodiment includes an input common electrode, a capacitor C S1 Capacitor C S2 The first output differential electrode and the second output differential electrode.
Specifically, referring to fig. 5, fig. 5 is a schematic structural diagram of another MEMS capacitive accelerometer interface circuit adopting a voltage control proportional sensing technology according to an embodiment of the present invention, in which an input common electrode R and a capacitor C in a sensing unit 305 of the embodiment are respectively connected to each other S1 One terminal of (1), a capacitor C S2 One terminal of (C), a capacitor C S1 Is connected to the first output differential electrode INA, a capacitor C S2 And the other end thereof is connected to the second output differential electrode INB. Compared with the circuit architecture shown in fig. 3, the present embodiment only needs one sensing unit 305 to implement the fully differential architecture, and the sensing unit 305 includes a capacitor C S1 And a capacitor C S2 Two differential sensing capacitances. This architecture is excited by the common electrode R of the sensing cell 305 and then read by the first and second differential electrodes INA, INB of the sensing cell 305And (6) discharging.
Further, referring to fig. 5, the common mode charge-voltage converter 301 of the present embodiment includes a capacitor C CM Common mode amplifier A 1 The constructed common-mode charge amplifier specifically comprises the following components: common mode amplifier A 1 A capacitor C is connected between the output end and the first inverting input end in a bridging way CM Common mode amplifier A 1 Is further connected to a first differential electrode INA, a common mode amplifier A 1 A capacitor C is connected between the output end and the second inverting input end in a bridging way CM Common mode amplifier A 1 Is also connected to a second differential electrode INB, a common mode amplifier a 1 The first positive phase input end and the second positive phase input end are connected with a bias voltage V A And (4) connecting. In the CMCV circuit, a common mode amplifier A 1 The common mode signal variation on the first and second differential electrodes INA and INB of the sensing unit 305 is detected and passes through the common mode feedback capacitor C CM The feedback absorbs the common mode charge signal (C) from the sensing cell 305 S1 +C S2 )V EXE Forming an output voltage V proportional to the common-mode charge signal OC The common-mode output voltage forming the common-mode charge-voltage converter 301 is represented as:
further, referring to fig. 5 again, the differential charge-voltage converter of the present embodiment includes a capacitor C302 D Fully differential amplifier A 2 The constructed differential charge amplifier specifically comprises the following components: fully differential amplifier A 2 The capacitor C is connected between the inverting output end and the non-inverting input end in a bridging way D The fully differential amplifier A 2 Is further connected to the first differential electrode INA, a fully differential amplifier A 2 The capacitor C is connected between the positive phase output end and the negative phase input end in a bridging way D The fully differential amplifier A 2 Is also connected to the second differential electrode INB. In a DCV circuit, a differential amplifier A 2 Detect the second of the sensing unit 305After the differential signals on the first differential electrode INA and the second differential electrode INB are changed, the differential signals pass through the differential feedback capacitor C D The feedback absorbs the differential charge signal (C) from the sensing cell 305 S1 -C S2 )V EXE Forming a differential output voltage V proportional to the differential charge signal OD The differential output voltage forming the differential charge-voltage converter 302 is represented as:
further, referring to fig. 6, fig. 6 is a schematic circuit structure diagram of a CMCV, a DCV and a sensing unit in an interface circuit of an MEMS capacitive accelerometer adopting a voltage control proportional sensing technology according to an embodiment of the present invention, in which the common mode charge-voltage converter 301 further includes a capacitor C H1 Capacitor C CAL1 From a capacitor C CM Capacitor C H1 Capacitor C CAL1 Common mode amplifier A 1 Constructing a common-mode charge amplifier, specifically: the common mode amplifier A 1 And the first differential electrode INA is connected across the capacitor C CM The common mode amplifier A 1 And the second differential electrode INB is connected across the capacitor C CM The common mode amplifier A 1 And the output end is also connected with a bias voltage V B Connected, the common mode amplifier A 1 The output end and the first inverting input end of the capacitor C are connected in a bridging way H1 The common mode amplifier A 1 The output end and the second inverting input end of the capacitor C are connected in a bridging way H1 The common mode amplifier A 1 Is connected with the capacitor C between the first inverting input terminal and the first differential electrode INA CAL1 The common mode amplifier A 1 Is connected with the capacitor C between the second inverting input terminal and the second differential electrode INB CAL1 The common mode amplifier A 1 The first positive phase input end and the second positive phase input end are connected with a bias voltage V A And (4) connecting. The common mode charge-voltage converter 301 has an output voltage V of the above formula (7) OC External, common mode amplifier A 1 Connected capacitor C CAL1 And a capacitor C H1 Forming switched capacitor network for rectifying common mode amplifier A 1 Offset, and 1/f noise reduction.
Further, referring to fig. 6, the differential charge-voltage converter 302 of the present embodiment further includes a capacitor C H2 Capacitor C CAL2 From a capacitor C D Capacitor C H2 Capacitor C CAL2 Fully differential amplifier A 2 Constructing a differential charge amplifier, in particular: the fully differential amplifier A 2 Across said capacitor C between said inverting output terminal and said first differential electrode INA D The fully differential amplifier A 2 The positive phase output end of the first differential electrode INB is connected with the second differential electrode INB in a cross-connection way through the capacitor C D The fully differential amplifier A 2 The capacitor C is connected between the inverting output end and the non-inverting input end in a bridging way H2 The fully differential amplifier A 2 The positive phase output end and the negative phase input end are connected with the capacitor C in a bridging way H2 The fully differential amplifier A 2 The positive phase input end of the first differential electrode INA is connected with the capacitor C CAL2 The fully differential amplifier A 2 Is connected with the capacitor C between the inverting input terminal and the second differential electrode INB CAL2 . Also, the differential charge-voltage converter 302 divides the output voltage V having the above formula (8) OC External AND differential amplifier A 2 Connected capacitor C CAL2 And a capacitor C H2 Forming a switched capacitor network to rectify the differential amplifier A 2 Offset, and 1/f noise reduction.
It should be noted that, in this embodiment, 306 is an external clock waveform output circuit, the switching order of the switch Φ 1, the switch Φ 2, and the switch Φ 1n shown in fig. 6 is implemented by the clock waveform output circuit 306, and the specific timing sequence of the clock waveform output is designed according to the actual scene needs.
Further, the analog-to-digital converter 303 converts the differential voltage using the common mode voltage as a reference voltage to realize the voltage control ratio sensing.
Specifically, referring to fig. 3, the Analog-to-Digital Converter 303 of the present embodiment includes an Analog-to-Digital Converter (ADC) and a Digital-to-Analog Converter (DAC), where the ADC is an ADC of a switched capacitor circuit, and may be a Sigma-Delta architecture or an SAR architecture. In the embodiment, the ADC and the DAC jointly form a signal divider, and the numerator is the differential voltage V output by the DCV circuit OD The denominator is the common-mode voltage V output by the CMCV circuit OC . In this embodiment, the DCV circuit and the CMCV circuit perform readout operations simultaneously, absorb the differential charge portion and the common-mode charge portion of the sensing unit 305, respectively, and the analog-to-digital converter 303 at the subsequent stage uses the common-mode voltage V OC As a reference voltage to convert the differential voltage V OD The resulting final digital output of the analog-to-digital converter 303 is represented as:
wherein D is OUT Representing the output, V, of the analog-to-digital converter 303 OC Representing the output, V, of a common-mode charge-voltage converter 301 OD Representing the output, C, of the differential charge-to-voltage converter 302 S1 Representing the capacitance C in the sensing cell 305 S1 ，C S2 Representing the capacitance C in the sensing cell 305 S2 ，C CM Representing the capacitance C in the common-mode charge-voltage converter 301 CM ，C D Representing the capacitance C in the differential charge-to-voltage converter 302 D . As can be seen from equation (9), the architecture proposed in fig. 3 realizes voltage-controlled proportional sensing, and the sensing gain can be obtained through capacitor C CM And a capacitor C D Is adjusted. Although the excitation voltage V of the open-loop charge pump EXE It is not fixed, but it can be seen from the formula (9) that in the interface circuit of voltage control proportional reading, the digital output and the excitation voltage V are in the present embodiment EXE Independently of the excitation voltage V EXE The gain precision of the whole circuit is not influenced.
To sum upIn the MEMS capacitive accelerometer interface circuit adopting the voltage-controlled proportional sensing technique proposed in this embodiment, the dynamic excitation source 304 forms a pulse voltage signal with a certain duty ratio, and excites two capacitors C at the same time at the common electrode R of the sensing unit 305 S1 Capacitor C S2 Thereby outputting charge signals at the first and second output differential electrodes INA and INB of the sensing unit 305. The CMCV circuit absorbs a common mode component in the charge signal transmitted from the first output differential electrode INA and the second output differential electrode INB, and converts the common mode component into a corresponding common mode voltage. The DCV circuit absorbs the differential component in the charge signals transmitted from the first output differential electrode INA and the second output differential electrode INB, and converts the differential component into a corresponding differential voltage. The analog-digital converter of the later stage converts the differential voltage output by the DCV circuit by taking the common mode voltage output by the CMCV circuit as a reference voltage, and because the ADC + DAC structure in the analog-digital converter 303 has a divider function, the ADC forms a proportional transfer function at the output end, thereby canceling the nonlinearity of the inverse proportional transfer function of the traditional sensing unit and further improving the dynamic range. In addition, in the interface circuit of the voltage control proportional sensing technology, the gain of the transfer function and the excitation voltage V are EXE Amplitude independent, excitation voltage V EXE Therefore, a high-voltage source (realized by using an open-loop charge pump) with uncontrolled amplitude and low precision can be used for replacing a low-voltage source (a band-gap reference and buffer combination) with high precision 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, so that the manufacturing cost is reduced.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.
Claims (3)
1. An MEMS capacitive accelerometer interface circuit using voltage control ratio readout technology is characterized by comprising a dynamic excitation source, a differential charge-voltage converter, a common mode charge-voltage converter and an analog-digital converter, wherein,
the dynamic excitation source is used for generating an excitation signal to excite an externally connected sensing unit to generate a charge signal;
the common-mode charge-voltage converter is connected with the sensing unit and used for reading out a common-mode component in the charge signal and converting the common-mode component into a common-mode voltage;
the differential charge-voltage converter is connected with the sensing unit and used for reading out a differential component in the charge signal and converting the differential component into a differential voltage;
the analog-digital converter is connected with 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 control proportional reading;
the dynamic excitation source is realized by adopting an open-loop charge pump; the common mode charge-voltage converter comprises a capacitor C CM Capacitor C H1 Capacitor C CAL1 Common mode amplifier A 1 From said capacitor C CM The capacitor C H1 The capacitor C CAL1 The common mode amplifier A 1 Constructing a common-mode charge amplifier; the differential charge-voltage converter comprises a capacitor C D Capacitor C H2 Capacitor C CAL2 Fully differential amplifier A 2 From said capacitance C D The capacitor C H2 The capacitor C CAL2 The fully differential amplifier A 2 Constructing a differential charge amplifier; the analog-digital converter comprises an analog-digital converter (ADC) and a digital-analog converter (DAC), the ADC and the DAC form a signal divider, and the numerator is a differential voltage V output by a differential charge-voltage converter (DCV) circuit OD And the denominator is the common-mode voltage V output by the CMCV circuit of the common-mode charge-voltage converter OC 。
2. The MEMS capacitive accelerometer interface of claim 1 employing voltage controlled proportional sensingA circuit, wherein the sensing unit comprises an input common electrode R, a capacitor C S1 Capacitor C S2 A first output differential electrode INA, a second output differential electrode INB,
the input common electrode R is respectively connected with the capacitor C S1 One terminal of (1), a capacitor C S2 One terminal of said capacitor C S1 Is connected to the first output differential electrode INA, the capacitor C S2 And the other end thereof is connected to the second output differential electrode INB.
3. The MEMS capacitive accelerometer interface circuit with vcpdr sensing of claim 1, wherein the analog-to-digital converter converts the differential voltage using the common mode voltage as a reference voltage to realize vcpdr sensing, wherein the converted differential voltage is represented by:
wherein D is OUT Representing the output of an analog-to-digital converter, V OC Representing the output of a common-mode charge-voltage converter, V OD Representing the output of a differential charge-voltage converter, C S1 Representing the capacitance C in the sensing unit S1 ，C S2 Representing the capacitance C in the sensing unit S2 ，C CM Representing the capacitance C in a common-mode charge-voltage converter CM ，C D Representing the capacitance C in a differential charge-voltage converter D 。
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN202110351837.0A CN114509579B (en) | 2021-03-31 | 2021-03-31 | MEMS capacitive accelerometer interface circuit adopting voltage control proportion reading technology |
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| US5661240A (en) * | 1995-09-25 | 1997-08-26 | Ford Motor Company | Sampled-data interface circuit for capacitive sensors |
| CN103872991A (en) * | 2012-12-18 | 2014-06-18 | 马克西姆综合产品公司 | Input common-mode control using special comparator for sensor interface |
| JP2018087829A (en) * | 2018-03-01 | 2018-06-07 | 株式会社日立製作所 | Acceleration sensor |
| CN211927125U (en) * | 2020-08-25 | 2020-11-13 | 深圳市汇顶科技股份有限公司 | Temperature measurement circuit, temperature measurement and light measurement circuit, chip, module and electronic equipment |
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| DE102013218973B4 (en) * | 2013-09-20 | 2015-11-19 | Albert-Ludwigs-Universität Freiburg | Method and circuit for time-continuous detection of the position of the sensor mass with simultaneous feedback for capacitive sensors |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5661240A (en) * | 1995-09-25 | 1997-08-26 | Ford Motor Company | Sampled-data interface circuit for capacitive sensors |
| CN103872991A (en) * | 2012-12-18 | 2014-06-18 | 马克西姆综合产品公司 | Input common-mode control using special comparator for sensor interface |
| JP2018087829A (en) * | 2018-03-01 | 2018-06-07 | 株式会社日立製作所 | Acceleration sensor |
| CN211927125U (en) * | 2020-08-25 | 2020-11-13 | 深圳市汇顶科技股份有限公司 | Temperature measurement circuit, temperature measurement and light measurement circuit, chip, module and electronic equipment |
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