CN107508601B - Noise reduction method based on combined MEMS accelerometer sensor chopping and electronic circuit - Google Patents
Noise reduction method based on combined MEMS accelerometer sensor chopping and electronic circuit Download PDFInfo
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- 238000006243 chemical reaction Methods 0.000 claims abstract description 34
- 230000008859 change Effects 0.000 claims abstract description 32
- 239000011159 matrix material Substances 0.000 claims description 41
- 230000001133 acceleration Effects 0.000 claims description 21
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- 238000006073 displacement reaction Methods 0.000 description 3
- 230000002596 correlated effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
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- 230000005483 Hooke's law Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M3/00—Conversion of analogue values to or from differential modulation
- H03M3/04—Differential modulation with several bits, e.g. differential pulse code modulation [DPCM]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
- B81B7/0032—Packages or encapsulation
- B81B7/0035—Packages or encapsulation for maintaining a controlled atmosphere inside of the chamber containing the MEMS
- B81B7/0038—Packages or encapsulation for maintaining a controlled atmosphere inside of the chamber containing the MEMS using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
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- G—PHYSICS
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups
- G01P21/02—Testing or calibrating of apparatus or devices covered by the preceding groups of speedometers
- G01P21/025—Testing or calibrating of apparatus or devices covered by the preceding groups of speedometers for measuring speed of fluids; for measuring speed of bodies relative to fluids
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M3/00—Conversion of analogue values to or from differential modulation
- H03M3/30—Delta-sigma modulation
- H03M3/322—Continuously compensating for, or preventing, undesired influence of physical parameters
- H03M3/324—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by means or methods for compensating or preventing more than one type of error at a time, e.g. by synchronisation or using a ratiometric arrangement
- H03M3/344—Continuously compensating for, or preventing, undesired influence of physical parameters characterised by means or methods for compensating or preventing more than one type of error at a time, e.g. by synchronisation or using a ratiometric arrangement by filtering other than the noise-shaping inherent to delta-sigma modulators, e.g. anti-aliasing
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Abstract
The invention discloses a noise reduction method based on chopping of a merging type MEMS accelerometer sensor and an electronic circuit. Wherein the electronic circuit comprises a capacitance-to-voltage conversion circuit configured to be electrically connected to a microelectromechanical system (MEMS) sensor circuit. The capacitance-voltage conversion circuit includes: a differential chopper circuit path configured to receive a differential MEMS sensor output signal and to reverse a polarity of the differential chopper circuit path; and differential sigma-delta analog-to-digital converter (ADC) circuitry configured to sample the differential MEMS sensor output signal and provide a digital signal representative of a change in capacitance in the MEMS sensor.
Description
The application is filed in 2013, 04, 08 and is filed as 201310120172.8, and is named as a divisional application of a noise reduction method and an electronic circuit based on combined MEMS accelerometer sensor chopping.
Technical Field
The present invention relates generally to electronic circuits, and more particularly to MEMS sensor circuits.
Background
Microelectromechanical Systems (MEMS) include small mechanical devices that perform both electrical and mechanical functions, and are fabricated using lithographic techniques similar to those used to fabricate integrated circuits. Some MEMS devices are sensors that detect motion (e.g., accelerometers), or that detect angular velocity (e.g., gyroscopes). An accelerometer is a device that undergoes a measurable change in response to acceleration acting upon it. MEMS accelerometers include piezoelectric accelerometers, piezoresistive accelerometers, and capacitive accelerometers. MEMS sensors are included in electronic devices (e.g., video game controllers and smart phones) due to their small size.
In response to acceleration, the capacitance of the capacitive accelerometer changes. The sensing circuit is used for sensing capacitance change in the MEMS sensor. The design of these sensing circuits presents challenges to noise reduction and size minimization.
Disclosure of Invention
The present disclosure discusses, among other things, systems and methods for reducing noise in a MEMS sensor. An example of an apparatus is an electronic circuit that includes a capacitance-to-voltage conversion circuit configured to be electrically connected to a MEMS sensor circuit. The capacitance-to-voltage conversion circuit comprises a differential chopper circuit path configured to receive a differential MEMS sensor output signal and to reverse a polarity of the differential chopper circuit path and a differential Sigma-delta analog-to-digital converter (ADC) circuit; the differential Sigma-delta analog-to-digital converter (ADC) circuit is configured to sample a differential MEMS sensor output signal and provide a digital signal representative of a change in capacitance of the MEMS sensor.
The present invention also provides another electronic circuit comprising: a capacitance-to-voltage conversion circuit configured to be electrically connected to the MEMS sensor circuit. The capacitance-voltage conversion circuit includes: a differential circuit path configured to receive a differential MEMS sensor output signal; a differential sigma-delta ADC circuit configured to sample the differential MEMS sensor output signal and provide a digital signal representative of a change in capacitance in the MEMS sensor circuit, wherein the differential sigma-delta ADC circuit comprises a comparator circuit; and a pseudo random noise generation circuit electrically connected to the comparator circuit and configured to add dither noise to an input of the comparator circuit.
The invention also provides a method for reducing signal noise, which comprises the following steps: sensing an output of a micro-electro-mechanical system (MEMS) sensor to generate a differential sensor output signal; applying the output of the MEMS sensor to a differential chopper circuit path, wherein the polarity of the differential chopper circuit path is reversed at time intervals; and sampling the chopped MEMS sensor output signal using a differential sigma-delta analog-to-digital converter (ADC) circuit to produce a digital signal representative of a change in capacitance in the MEMS sensor.
This section is intended to summarize the subject matter of the present patent application and is not intended to be an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.
Drawings
In the drawings, which are not necessarily drawn to scale, like reference numerals may describe similar components in different views. Like reference numerals having different letter suffixes may represent different instances of like components. The drawings generally illustrate, by way of example and not by way of limitation, various examples discussed herein.
FIG. 1 is a schematic diagram of an example portion of a MEMS sensor and sensing circuitry for monitoring changes in the output of the MEMS sensor;
FIG. 2 shows an example of a chopped switch matrix circuit;
FIG. 3 shows another example of a capacitance-to-voltage conversion circuit having differential chopper circuit paths;
FIG. 4 is a flow chart of a method for reducing noise in a MEMS accelerometer sensing circuit.
Detailed Description
FIG. 1 is a schematic diagram of an example portion of a MEMS sensor circuit 105 and a sensing circuit 110, wherein the sensing circuit 110 is electrically connected to the MEMS sensor circuit 105 to monitor changes in the output of the MEMS sensor. The MEMS sensor circuitry 105 may be a capacitive accelerometer in which the sensing circuitry 110 monitors changes in capacitance of a sensor responsive to acceleration acting on the sensor.
A typical MEMS capacitive accelerometer includes a movable proof mass (proof mass) with capacitive elements connected in a reference structure by a mechanical suspension. As shown in FIG. 1, the two capacitive elements of the MEMS sensor are circuit capacitors, labeled C1mem and C2 mem. The actual capacitive element may be made up of a plurality of plates electrically connected (e.g., in parallel) to produce a total capacitance value represented by capacitors C1mem and C2mem in the figure. The capacitors form a bridge from the two outputs of the MEMS sensor circuit 105 to a common circuit node 145, which common circuit node 145 may represent a circuit connection to the movable proof mass. One plate or group of plates of each capacitor can be connected to a movable proof mass while the other plate or group of plates is stationary.
The acceleration signal is induced by the detection of the charge imbalance across the differential capacitive bridge formed by the capacitors C1mem, C1ofs, C2mem and C2 ofs. Capacitors C1mem and C1ofs form one leg of the differential capacitance bridge, and capacitors C2mem and C2ofs form the second leg of the differential capacitance bridge. The two input ends of the differential bridge are: 1) a circuit node 145, which is a MEMS proof mass connection driven by the drive circuit 140; and 2) a circuit node 150 driven in anti-phase with node 145. The outputs of the differential bridge are circuit nodes 155 and 160. Thus, nodes 155 and 160 form the sensor inputs of sensing circuit 110. Any differential imbalance of the capacitors in the capacitive bridge circuit will manifest at nodes 155 and 160 as a differential charge that will be measured by sensing circuit 110.
Acceleration on the MEMS accelerometer causes movement of the proof mass. The displacement of the proof mass changes the spacing between capacitor plates. The displacement is approximately proportional to the difference in capacitance values induced between the two capacitive elements. The proof mass and mechanical suspension act as elastic elements, which allow acceleration to be determined from displacement according to Hooke's Law.
In general, the change in capacitance of a capacitor pair is related to linear acceleration in one direction. Another capacitor pair perpendicular to the first capacitor pair may enable acceleration in a second direction to be determined. This can provide a two-axis accelerometer. Three capacitor pairs may implement a three-axis or three-dimensional (3D) accelerometer.
The sensing circuit 110 senses the capacitance change of the MEMS sensor and converts the capacitive change into a voltage. Thus, the sensing circuit 110 functions as a capacitance-to-voltage conversion circuit or capacitance-to-voltage (C2V) sensor. The capacitance-to-voltage conversion circuit receives the MEMS sensor output signal from the MEMS sensor circuit 105. The capacitance-to-voltage conversion circuit includes a differential sigma-delta analog-to-digital converter (ADC) circuit that samples the differential MEMS sensor output signal and provides a digital signal representative of a change in capacitance in the MEMS sensor circuit 105. As can be seen, the capacitors in the MEMS sensor circuit 105 are used together with the biasing capacitors C1ofs and C2ofs as the sensing capacitors of the sigma-delta ADC; effectively integrating capacitance-voltage sensing with sigma-delta ADC circuits.
In the example shown in fig. 1, the sigma-delta ADC circuit includes an integrating circuit and a comparator circuit 120. The integration circuit in the example is a first order integration circuit and includes an operational amplifier (opamp) circuit 125. In some examples, the integration circuit comprises a higher order (e.g., second order) integration circuit. The comparator circuit provides a digital output signal and is followed by a low pass filter to reduce switching noise generated by sampling the MEMS sensor output.
The capacitance-voltage conversion circuit further comprises a differential chopper circuit path, and the differential chopper circuit path receives the output signal of the differential MEMS sensor and reverses the polarity of the differential chopper circuit path. Other methods of sensing the MEMS sensor output include correlated double sampling of the MEMS sensor output signal. In an analog front end sensing circuit of the MEMS accelerometer, the chopping method improves the noise reduction of 1/f noise. The chopping method also employs fewer capacitors than the correlated double sampling method. The reduction in the number of capacitors reduces thermal noise (KT/C) and reduces the area used by the capacitance-to-voltage conversion circuit on an integrated circuit, such as an application specific integrated circuit or ASIC. The reduction in the number of capacitors also enables a reduction in settling time of an amplifier (e.g., an op amp used in an integrating circuit). The reduction of the settling time can reduce power consumption. Based on the noise reduction method described herein, a first order sigma-delta ADC circuit is capable of providing a dynamic range of greater than 100 decibels.
The differential chopper circuit path is implemented by chopping a switch matrix circuit (115A, 115B, 115C). Fig. 2 shows an example of a chopper switch matrix circuit 215. The circuit operates according to chopping clock signals CK _ a and CK _ B supplied from the chopping clock circuit 230. When the chopping switch matrix circuit is clocked by the chopping clock phase CK _ A, the differential signal at the circuit input is passed. When the chopping switch matrix circuit is clocked by the chopping clock phase CK _ B, the differential signal at the input end of the circuit is inverted. CK _ B is off when CK _ a is active or "on" and vice versa.
In the example of FIG. 1, the differential chopper circuit paths include a first chopping switch matrix circuit 115A that inverts the polarity of the differential chopper circuit paths at the input of the opamp circuit 125 and a second chopping switch matrix circuit 115B that inverts the polarity of the differential chopper circuit paths at the output of the opamp circuit 125. In some examples, the differential chopping circuit path includes a third chopping switch matrix circuit 115C that converts the polarity of the differential feedback circuit path in the differential sigma-delta ADC circuit. In the example shown, a differential feedback circuit path extends from the output of the second chopping switch matrix circuit 115B to the input of the third chopping switch matrix circuit 115C.
Fig. 3 shows another example of a capacitance-to-voltage conversion circuit having a differential chopper circuit path. This example includes only two chopping switch matrix circuits 315A and 315B in the differential chopper circuit path. The differential chopping circuit path also includes a differential feedback circuit path that extends from the output of the second chopping switch matrix circuit 315B to the input of the first chopping switch matrix circuit 315A.
Returning to FIG. 1, the drive circuit 140 may be electrically connected to the MEMS sensor circuit 105 to apply a square wave excitation signal to the drive input of the MEMS sensor. The drive input may be electrically connected to a circuit node 145 representing a proof mass in the ME MS sensor circuit 105. The sensing circuitry 110 may include phase clock circuitry (not shown) that generates a first operational clock phase (Ph1) and a second operational clock phase (Ph 2). The operational clock phases Ph1 and Ph2 are non-overlapping and have opposite polarities. During Ph1, the first chopping switch-matrix circuit 115A electrically isolates the MEMS sensor circuit 105 from the differential sigma-delta ADC circuit. Second chopping switch matrix circuit 115B and third chopping switch matrix circuit 115C hold the original values of the sensor output signals.
During Ph2, the first, second, and third chopping switch matrix circuits 115A, 115B, and 115C invert the polarity of the differential chopper circuit paths. The capacitance value of the MEMS sensor circuit 105 may be sampled with respect to the excitation signal. The first and second operational clock phases Ph1, Ph2 may have the same frequency and duty cycle as the square wave excitation signal. The second and third chopping switch matrix circuits 115B, 115C may be switched together by a chopping clock. The first chopping switch matrix circuit 115A may be switched by a signal that logically AND (AND) the chopping clock AND the Ph2 clock.
sigma-delta ADC circuits are susceptible to dead-bands or dead-zones. When a signal is sampled, the output contains a repeating pattern of 1's and 0's, sometimes referred to as idle tones. The sigma-delta circuit may output continuously in a repetitive pattern for small amplitude input signals. The small amplitude input signal may not be encoded by a sigma-delta ADC that results in a dead-band range of the input signal. However, it is preferable to encode a small amplitude signal to take advantage of the full dynamic range of the differential sigma-delta ADC circuit shown in fig. 1 and 3.
The capacitance-to-voltage conversion circuit may include a chopping clock circuit that provides a periodic or regular chopping clock signal to the differential chopping circuit path. To prevent or minimize dead bands in the differential sigma-delta ADC circuit, the capacitance-to-voltage conversion circuit may include a chopper clock circuit that provides a pseudo-random clock signal to the differential chopper circuit path. The pseudo-random clock signal includes a high-to-low random transition while ensuring that only CK _ a is on when CK _ B is off and vice versa. The pseudo-random clock reduces the limit cycles of the integrator circuit that can lead to dead bands.
Another way to prevent or minimize dead bands in the differential sigma-delta ADC circuit is to add dither noise in the comparator circuit 120. The capacitance-to-voltage conversion circuit may include a pseudo random noise generation circuit 135, the pseudo random noise generation circuit 135 being electrically connected to the comparator circuit to add dither noise to an input of the comparator circuit. If the output of the comparator evaluates at the end of the second operational clock phase Ph2, a pseudo-random dither noise signal can be added to the comparator during Ph2 to remove dead band idle tones. Dither noise forces the output of the sigma-delta ADC circuit out of the dead band.
As explained above, the MEMS sensor circuit may be a two-axis accelerometer. In this case, the MEMS sensor circuit may change the first capacitance value in response to linear acceleration in a first direction and may change the second capacitance value in response to linear acceleration in a second direction (e.g., a direction orthogonal to the first direction). The sensing circuit may include a first capacitance-to-voltage conversion circuit that generates a first digital signal indicative of a change in the first capacitance and a second capacitance-to-voltage conversion circuit that generates a second digital signal indicative of a change in the second capacitance. The output of the three-axis accelerometer may be sensed by a third capacitance-to-voltage conversion circuit.
FIG. 4 is a flow chart of a method 400 of reducing noise in a MEMS accelerometer sensing circuit. At block 405, the output of the MEMS sensor is sensed to produce a differential sensor output signal. At block 410, the output of the MEMS sensor is applied to a differential chopper circuit path to reduce noise in the circuit. To achieve chopping, the polarity of the differential chopper circuit paths is reversed at intervals. In some instances, the polarity of the circuit paths is reversed at certain intervals, and in some instances, the polarity is reversed or chopped at pseudo-random intervals. The chopped MEMS sensor output signal is sampled by a differential sigma-delta ADC circuit to produce a digital signal representative of a change in capacitance in the MEMS sensor, block 415.
Chopping the output sampled from the MEMS sensor reduces 1/f noise and thermal noise, so that the first-order sigma-delta ADC circuit has a dynamic range greater than 100 dB. To fully exploit the dynamic range, signal chopping may be performed at pseudo-random time intervals to minimize the occurrence of dead bands in the output of the sigma-delta ADC circuit, and dither noise may be applied to the differential sigma-delta ADC circuit to remove idle tones.
Supplementary notes and examples
Example 1 can include or use a subject (e.g., an apparatus) comprising a capacitance-to-voltage conversion circuit configured to be electrically connected to a MEMS sensor circuit. The capacitance-to-voltage conversion circuit may include a differential chopper circuit path and a differential sigma-delta analog-to-digital converter (ADC) circuit, wherein the differential chopper circuit path is configured to receive a differential MEMS sensor output signal and reverse a polarity of the differential chopper circuit path; the differential sigma-delta analog-to-digital converter (ADC) circuit is configured to sample the differential MEMS sensor output signal and provide a digital signal representative of a change in capacitance in the MEMS sensor.
In example 2, the subject matter of example 1 optionally includes: a differential sigma-delta ADC circuit including a comparator circuit and a pseudo-random noise generation circuit electrically connected to the comparator circuit and configured to add dither noise to an input of the comparator circuit.
In example 3, the subject matter of one or any combination of examples 1 and 2 optionally includes a chopping clock circuit configured to provide a pseudo-random clock signal to the differential chopper circuit path.
In example 4, the subject matter of one or any combination of examples 1-3 optionally includes: the differential sigma-delta ADC circuit comprises an opamp circuit, a first chopping switch matrix circuit and a second chopping switch matrix circuit, wherein the first chopping switch matrix circuit is configured to reverse the polarity of the differential chopping circuit path at the input end of the opamp circuit, and the second chopping switch matrix circuit is configured to reverse the polarity of the differential chopping circuit path at the output end of the opamp circuit.
In example 5, the subject matter of example 4 can optionally include a third chopping switch matrix circuit configured to convert a polarity of a differential feedback circuit path in the differential sigma-delta ADC circuit. The differential feedback circuit path optionally extends from an output of the second chopping switch matrix circuit to an input of the third chopping switch matrix circuit.
In example 6, the subject matter of example 4 can optionally include a differential feedback circuit path extending from an output of the second chopping switch matrix circuit to an input of the first chopping switch matrix circuit.
In example 7, the subject matter of one or any combination of examples 1-6 can optionally include a phase clock circuit configured to generate the first operational clock phase and the second operational clock phase. During the first operational clock phase, the first chopping switch matrix circuit is optionally configured to electrically isolate the MEMS sensor circuit from a differential sigma-delta ADC circuit; during the second operational clock phase, the first and second chopping switch matrix circuits are optionally configured to invert the polarity of the differential chopping circuit paths.
In example 8, the subject matter of one or any combination of examples 1-7 can optionally include a drive circuit electrically connected to the MEMS sensor. The drive circuit is optionally configured to apply a square wave excitation signal to the drive input of the MEMS sensor, and the first and second operational clock phases have the same frequency and duty cycle as the square wave excitation signal.
In example 9, the subject matter of one or any combination of examples 1-8 optionally includes MEMS sensor circuitry. The MEMS sensor circuit is optionally configured to change capacitance in response to linear acceleration in a first direction.
Example 10 may include the following subject matter (e.g., an apparatus) or optionally in combination with the subject matter of one or any combination of examples 1-9 to include the following subject matter: the method comprises the following steps: a capacitance-to-voltage conversion circuit configured to be electrically connected to the MEMS sensor circuit. The capacitance-to-voltage conversion circuit may include a differential circuit path configured to receive a differential MEMS sensor output signal and a differential sigma-delta ADC circuit configured to sample the differential MEMS sensor output signal and provide a digital signal representative of a change in capacitance in the MEMS sensor. The differential sigma-delta ADC circuit may include a comparator circuit and the capacitance-to-voltage conversion circuit may include a pseudo-random noise generation circuit, wherein the pseudo-random noise generation circuit is electrically connected to the comparator circuit and configured to add dither noise to an input of the comparator circuit.
In example 11, the subject matter of example 10 can optionally include MEMS sensor circuitry. The MEMS sensor circuit is optionally configured to change capacitance in response to linear acceleration in a first direction.
In example 12, the subject matter of example 11 can optionally include: a switching circuit electrically connected to the MEMS sensor, a driving circuit electrically connected to the MEMS sensor and configured to apply a square wave excitation signal to a drive input of the MEMS sensor, and a phase clock circuit electrically connected to the switching circuit and configured to generate a first operational clock phase and a second operational clock phase. The first and second operational clock phases optionally have the same frequency and duty cycle as the square wave excitation signal. During the first operational clock phase, the switching circuit is optionally configured to electrically isolate the MEMS sensor circuit from the differential sigma-delta ADC circuit, and the MEMS sensor circuit is configured to sample linear acceleration.
In example 13, the subject matter of one or any combination of examples 11 and 12 optionally includes: a MEMS sensor circuit, a first capacitance-to-voltage conversion circuit, and a second capacitance-to-voltage conversion circuit, wherein the MEMS sensor circuit is configured to change a first capacitance in response to linear acceleration in a first direction and to change a second capacitance in response to linear acceleration in a second direction; said first capacitance-to-voltage conversion circuit generating a first digital signal representative of a change in said first capacitance; the second capacitance-to-voltage conversion circuit generates a second digital signal representative of a change in the second capacitance.
Example 14 can include the following subject matter (e.g., a method, means, or machine-readable medium comprising instructions, which when executed by a machine, cause the machine to perform the acts) or, optionally, in combination with the subject matter of one or any combination of examples 1-13, to include the following subject matter: the method comprises the following steps: sensing an output of the MEMS sensor to produce a differential sensor output signal; applying the output of the MEMS sensor to a differential chopper circuit path, wherein the polarity of the differential chopper circuit path is reversed at time intervals; and sampling the chopped MEMS sensor output signal to produce a digital signal representative of a change in capacitance in the MEMS sensor. These subject matter may include a method of sensing an output of a MEMS sensor to generate a differential sensor output signal, an illustrative example of which may include a charge-to-voltage conversion circuit. These subjects may include a method of applying the output of the MEMS sensor to a differential chopper circuit path, illustrative examples of which may include a charge-to-voltage conversion circuit. These subjects may include a method of sampling a chopped MEMS sensor output signal to produce a digital signal representative of a change in capacitance in the MEMS sensor, illustrative examples of which may include a differential ADC circuit and a sigma-delta ADC circuit.
In example 15, the subject matter of example 14 can optionally include: the chopped MEMS sensor output signal is sampled using a differential sigma-delta AD C circuit and dither noise is added to the differential sigma-delta ADC circuit.
In example 16, the subject matter of one or any combination of examples 14 and 15 optionally includes: a random clock signal is provided to the differential chopper circuit path.
In example 17, the subject matter of one or any combination of examples 14-16 optionally includes: sampling the chopped MEMS sensor output signal by using a differential sigma-delta ADC circuit, reversing the polarity of a differential chopper circuit channel at the input end of an opamp circuit of the differential sigma-delta ADC circuit, and reversing the polarity of the differential chopper circuit channel at the output end of the opamp circuit.
In example 18, the subject matter of one or any combination of examples 14-17 can optionally include: and feeding back the differential output of the opamp circuit to the differential input of the opamp circuit, and reversing the polarity of the differential feedback circuit path at time intervals.
In example 19, the subject matter of one or any combination of examples 14-18 optionally includes: electrically isolating the MEMS sensor circuit from the differential sigma-delta ADC circuit during a first operational clock phase; and inverting a polarity of the differential chopper circuit path during a second operational clock phase.
In example 20, the subject matter of one or any combination of examples 14-18 can optionally include: applying a square wave excitation signal to a drive input of the MEMS sensor such that the first operational clock phase and the second operational clock phase have the same frequency and duty cycle as the square wave excitation signal; and sampling the linear acceleration using the MEMS sensor during the first operational clock phase.
In example 21, the subject matter of one or any combination of examples 14-20 can optionally include sensing a change in capacitance of the MEMS sensor in response to linear acceleration in a first direction.
In example 22, the subject matter of one or any combination of examples 14-21 can optionally include: sensing a first output of the MEMS sensor to sense a change in capacitance of the MEMS sensor in response to linear acceleration in a first direction; and sensing a second output of the MEMS sensor to sense a change in capacitance of the MEMS sensor in response to linear acceleration in a second direction.
Example 23 can include the following subject matter or can be optionally combined with any portion or combination of any portion of any one or more of examples 1-22 to include the following subject matter: may include a means for performing any one or more of the functions of examples 1-22, or a machine-readable medium containing instructions which, when executed by a machine, cause the machine to perform any one or more of the functions of examples 1-22.
Each non-limiting example can exist independently or can be combined with one or more other examples in various permutations or combinations.
The foregoing detailed description includes references to the accompanying drawings, which form a part hereof. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as "examples". All publications, patents and patent documents referred to in this application are incorporated by reference herein in their entirety, as though individually incorporated by reference. If there is a usage difference between the present application and the reference, the usage of the reference should be considered supplementary to the usage of the present application; if there is an irreconcilable difference between the two, the use of the present application shall control.
In this application, the terms "a" or "an" as used generally in patent documents are intended to include one or more than two, other examples or uses of the term "at least one" or "one or more. In this application, unless otherwise indicated, the use of the term "or" means nonexclusive or "a or B" includes: "A but not B", "B but not A", and "A and B". In the appended claims, the terms "including" and "in which" are used in an inclusive sense as opposed to the plain-english meaning of the respective terms "comprising" and "wherein". Furthermore, in the following claims, the terms "comprising" and "including" are open-ended, i.e., a system, apparatus, article, or step that includes elements in addition to those elements listed after such term in a claim is still considered to be within the scope of that claim. Furthermore, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not required to be quantitative for their objects.
The above embodiments are intended to be illustrative and not limiting. In other embodiments, the examples of the above embodiments (or one or more aspects thereof) may be used in combination with each other. For example, one of ordinary skill in the art, upon reviewing the above description, may use other embodiments. The abstract is provided to comply with 37c.f.r. § 1.72(b), to enable the reader to quickly ascertain the type of technical invention. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Moreover, in the foregoing detailed description, various features may be combined to simplify the present disclosure. This should not be construed as an admission that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
Claims (7)
1. An electronic circuit, comprising: a capacitance-to-voltage conversion circuit configured to be electrically connected to a microelectromechanical system (MEMS) sensor circuit, the capacitance-to-voltage conversion circuit comprising: a differential chopper circuit path configured to receive a differential MEMS sensor output signal and to reverse a polarity of the differential chopper circuit path; and differential sigma-delta analog-to-digital converter (ADC) circuitry configured to sample the differential MEMS sensor output signal and provide a digital signal representative of a change in capacitance in the MEMS sensor circuitry;
the electronic circuitry further includes the MEMS sensor circuitry being a two-axis accelerometer, wherein the MEMS sensor circuitry is configured to change a first capacitance value in response to linear acceleration in a first direction and a second capacitance value in response to linear acceleration in a second direction;
wherein the electronic circuit comprises a first capacitance-to-voltage conversion circuit that generates first digital information indicative of the first capacitance change and a second capacitance-to-voltage conversion circuit that generates second digital information indicative of the second capacitance change;
the electronic circuit further includes a chopping clock circuit configured to provide a pseudo-random clock signal to the differential chopper circuit path;
the circuit works according to chopping clock signals CK _ A and CK _ B provided by a chopping clock circuit, when a chopping switch matrix circuit is clocked by a chopping clock phase CK _ A, a differential signal at the input end of the circuit is transmitted, and when the chopping switch matrix circuit is clocked by a chopping clock phase CK _ B, the differential signal at the input end of the circuit is inverted;
the pseudo-random clock signal includes a low-to-high random transition, with only CK _ a being on when CK _ B is off.
2. The electronic circuit of claim 1, wherein the differential sigma-delta ADC circuit comprises a comparator circuit; and the electronic circuit further comprises a pseudo random noise generating circuit electrically connected to the comparator circuit and configured to add dither noise to an input of the comparator circuit.
3. The electronic circuit of claim 1, wherein the differential sigma-delta ADC circuit comprises an operational amplifier (opamp) circuit; and the electronic circuit further comprises:
a first chopper switch matrix circuit configured to reverse a polarity of the differential chopper circuit path at an input of the opamp circuit; and a second chopping switch matrix circuit configured to reverse the polarity of the differential chopping circuit path at the output of the opamp circuit.
4. The electronic circuit of claim 3, further comprising: a third chopping switch matrix circuit configured to convert a polarity of a differential feedback circuit path in the differential sigma-delta ADC circuit, and wherein the differential feedback circuit path extends from an output of the second chopping switch matrix circuit to an input of the third chopping switch matrix circuit.
5. The electronic circuit of claim 3, further comprising a differential feedback circuit path extending from an output of the second chopping switch-matrix circuit to an input of the first chopping switch-matrix circuit.
6. The electronic circuit of claim 3, further comprising: a phase clock circuit configured to generate a first operational clock phase and a second operational clock phase, wherein during the first operational clock phase, the first chopped switch matrix circuit is configured to electrically isolate the MEMS sensor circuit from the differential sigma-delta ADC circuit; and wherein during the second operational clock phase, the first and second chopping switch matrix circuits are configured to invert a polarity of the differential chopping circuit path.
7. The electronic circuit of claim 6, further comprising: a drive circuit electrically connected to the MEMS sensor circuit, wherein the drive circuit is configured to apply a square wave excitation signal to a drive input of the MEMS sensor circuit; and wherein the first operational clock phase and the second operational clock phase have the same frequency and duty cycle as the square wave excitation signal.
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| Application Number | Priority Date | Filing Date | Title |
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| US201261620019P | 2012-04-04 | 2012-04-04 | |
| US61/620,019 | 2012-04-04 | ||
| CN201310120172.8A CN103368577B (en) | 2012-04-04 | 2013-04-08 | Based on the noise-reduction method and electronic circuit to combination type MEMS accelerometer sensor copped wave |
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| CN201310120172.8A Division CN103368577B (en) | 2012-04-04 | 2013-04-08 | Based on the noise-reduction method and electronic circuit to combination type MEMS accelerometer sensor copped wave |
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| CN107508601A CN107508601A (en) | 2017-12-22 |
| CN107508601B true CN107508601B (en) | 2021-12-28 |
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| CN2013201717578U Expired - Lifetime CN203261317U (en) | 2012-04-04 | 2013-04-08 | Electronic circuit based on chopping for merged MEMS accelerometer sensor |
| CN201310120172.8A Active CN103368577B (en) | 2012-04-04 | 2013-04-08 | Based on the noise-reduction method and electronic circuit to combination type MEMS accelerometer sensor copped wave |
| CN201710561498.2A Active CN107508601B (en) | 2012-04-04 | 2013-04-08 | Noise reduction method based on combined MEMS accelerometer sensor chopping and electronic circuit |
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| CN2013201717578U Expired - Lifetime CN203261317U (en) | 2012-04-04 | 2013-04-08 | Electronic circuit based on chopping for merged MEMS accelerometer sensor |
| CN201310120172.8A Active CN103368577B (en) | 2012-04-04 | 2013-04-08 | Based on the noise-reduction method and electronic circuit to combination type MEMS accelerometer sensor copped wave |
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| KR (1) | KR102045784B1 (en) |
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| KR102045784B1 (en) | 2019-11-18 |
| CN103368577B (en) | 2017-08-08 |
| CN107508601A (en) | 2017-12-22 |
| CN103368577A (en) | 2013-10-23 |
| CN203261317U (en) | 2013-10-30 |
| KR20130112792A (en) | 2013-10-14 |
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