KR20130112792A - Noise reduction method with chopping for a merged mems accelerometer sensor - Google Patents

Abstract

PURPOSE: A noise reduction method with chopping for a merged micro-electro-mechanical systems (MEMS) accelerometer sensor is provided to improve the reduction of 1/f noise in an MEMS accelerometer analog front end sensing circuit. CONSTITUTION: The output of an MEMS accelerometer sensing circuit is sensed to generate a differential sensor output signal (405). The output of an MEMS sensor is applied to a differential chopping circuit path (410). The polarity of the differential chopping circuit path is inverted at timed intervals. The chopped MEMS sensor output signal is sampled with a differential sigma-delta analog to digital converter (ADC) circuit to generate a digital signal representing a change in the capacitance of the MEMS sensor (415). [Reference numerals] (405) Output of an MEMS sensor is sensed to generate a differential sensor output signal; (410) Output of an MEMS sensor is applied to a differential chopping circuit path; (415) Chopped MEMS sensor output signal is sampled with a differential sigma-delta ADC circuit to generate a digital signal representing a change in the capacitance of the MEMS sensor

Description

Noise reduction method using chopping for a merged microelectromechanical accelerometer sensor

The present invention is directed to a noise reduction method using chopping for an integrated microelectromechanical accelerometer sensor.

Micro-electromechanical systems (MEMS) include small mechanical devices that perform electrical and mechanical functions fabricated using photolithography techniques similar to those used to fabricate integrated circuits. An example of a MEMS device is a sensor that can detect movement such as an accelerometer or an angular rate such as a gyroscope. An accelerometer is a device that undergoes a measurable change in response to the acceleration acting on the device. Examples of MEMS accelerometers include piezoelectric accelerometers, capacitive accelerometers, and piezoresistive accelerometers. Because of their small size, MEMS sensors are being integrated into electronic devices such as video game controllers and smartphones.

Capacitive accelerometers experience a change in capacitance in response to acceleration. Sensing circuits are used to detect changes in capacitance of the MEMS sensor. The design of these sensing circuits has a problem of reducing noise and miniaturizing size.

The present invention discusses, among other things, systems and methods for reducing noise in MEMS sensors. One example apparatus includes a capacitance-voltage converter circuit configured to be electrically connected to a microelectromechanical system (MEMS) sensor circuit. The capacitance-to-voltage converter circuit receives the differential MEMS sensor output signal, samples the differential chopping circuit path and the differential MEMS sensor output signal configured to invert the polarity of the differential chopping circuit path, and the MEMS sensor And a differential sigma-delta analog-to-digital converter (ADC) configured to provide a digital signal indicative of a change in capacitance.

The solution part of the present invention is intended to provide an overview of the claimed subject matter of the present patent application and is not intended to provide an exclusive or exhaustive description of the invention. Further information on this patent application is included in the detailed description.

In the drawings, which need not necessarily be drawn to scale, the same reference numerals may represent like elements in different drawings. Reference numerals having different numbers in the preceding figures may represent different examples of similar components. These drawings are intended to serve as an example and not as a limitation of the various embodiments discussed throughout the specification.
1 shows a block diagram of a portion of an example of a sensing circuit for monitoring a change in MEMS sensor and MEMS sensor output.
2 shows an example of a chopping switch matrix circuit.
3 shows another example of a capacitance-voltage converter circuit with a differential chopping circuit path.
4 is a flowchart of a method of reducing noise in a MEMS accelerometer sensing circuit.

FIG. 1 shows a block diagram of a portion of an example of a sensing circuit 110 electrically connected to the MEMS sensor circuit 105 to monitor changes in the MEMS sensor circuit 105 and the MEMS sensor output. The MEMS sensor circuit 105 may be a capacitive accelerometer that monitors the change in capacitance of the sensor in response to the acceleration that the sensing circuit 110 exerts on the sensor.

Typical MEMS capacitive accelerometers include a movable proof mass in which capacitive elements are attached to a reference frame via a mechanical suspension. Two capacitive elements of the MEMS sensor are shown as circuit capacitors labeled "C1mem" and "C2mem" in FIG. The actual capacitive element may consist of a plurality of plates electrically connected (eg in parallel) to provide the overall capacitance shown in the figure, such as capacitor C1mem or C2mem. The capacitor forms a bridge from the two outputs of the MEMS sensor circuit 105 to the common circuit node 115, which may represent a circuit connection to the operational verifying mass. One plate or group of plates of each capacitor may be attached to the moving verify mass with the other plate or group of plates stationary.

The acceleration signal is detected by detecting the charge imbalance across the differential capacitive bridge formed by capacitors C1mem, C1ofs, C2mem and C2ofs. Capacitors C1mem and C1ofs form one leg of the differential capacitive bridge, while capacitors C2mem and C2ofs form the second leg of the differential capacitive bridge. The two inputs to this differential bridge are: 1) a circuit node 145, which is a MEMS verified mass connection driven from the driver circuit 140, and 2) a circuit node 150 driven out of phase with the node 145. )to be. The output of this differential bridge is circuit nodes 155 and 160. Thus, nodes 155 and 160 form a sensor input to sense circuit 110. Any differential imbalance in the capacitors of this circuit will appear as high at nodes 155 and 160 as the differential charge to be measured by sense circuit 110.

Acceleration applied to the MEMS accelerometer causes movement of the proof mass. The displacement of the proof mass changes the spacing between the plates of the capacitor. The displacement is approximately proportional to the difference in the resulting capacitance between the two capacitive elements. Modeling the proof mass and the mechanical suspension as a spring allows acceleration to be determined from displacement in accordance with Hooke's Law.

In general, the change in capacitance for a pair of capacitors is related to linear acceleration in one direction. Additional capacitor pairs arranged perpendicular to the first pair allow the acceleration in the second direction to be determined. This can provide a two-axis accelerometer. Three capacitor pairs enable three-axis or three-dimensional (3D) accelerometers.

The sensing circuit 110 detects a change in capacitance of the MEMS sensor and converts the capacitive change into a voltage. Therefore, the sense circuit 110 functions as a capacitance-voltage converter circuit or a C2V sensor. The capacitance-voltage converter circuit receives the differential MEMS sensor output signal from the MEMS sensor circuit 105. The capacitance-voltage converter circuit includes a differential sigma-delta analog-to-digital converter (ADC) circuit, which samples the differential MEMS sensor output signal and provides a digital signal indicative of the change in capacitance of the MEMS sensor circuit 105. do. In the figure, the capacitor of the MEMS sensor circuit 105 is used with offset capacitors C1ofs and C2ofs as sense capacitors for the sigma-delta ADC, effectively merging capacitance-voltage sensing with the sigma-delta ADC circuit. Able to know.

In the example shown in FIG. 1, the sigma-delta ADC circuit includes an integrator circuit and a comparator circuit 120. The integrator circuit in this example is a primary integrator circuit and includes a differential amplifier circuit 125. In a particular example, the integrator circuit includes a higher order (eg, secondary) integrator circuit. The comparator circuit provides a digital output signal, which may be followed by a low pass filter to reduce switching noise from sampling of the MEMS sensor output.

The capacitance-voltage converter circuit also includes a differential chopping circuit path that receives the differential MEMS sensor output signal and inverts the polarity of the differential chopping circuit path. Another method of sensing the MEMS sensor output includes correlated-double sampling of the MEMS sensor output signal. The chopping method improves noise reduction of 1 / f noise in a MEMS accelerometer analog front end sensing circuit. Chopping also uses fewer capacitors than the correlated-double sampling method. Reducing the number of capacitors further lowers the thermal noise (KT / C) and reduces the area used by the capacitance-voltage converter circuit on the integrated circuit (eg, custom semiconductor or ASIC). Reducing the number of capacitors can also reduce the settling time of amplifiers, such as operational amplifiers used in integrated circuits. Reduced settling time can reduce power consumption. As a result of the noise reduction method described here, the first-order sigma-delta ADC circuit can provide a dynamic range greater than 100 decibels.

The differential chopping circuit path is implemented using chopping switch matrix circuits 115A, 115B, 115C. 2 shows an example of the chopping switch matrix circuit 215. The chopping switch matrix circuit operates according to the chopping clock signals CK_A and CK_B provided by the chopping clock circuit 230. When the chopping switch matrix circuit is clocked into the chopping clock phase CK_A, a differential signal at the input to the circuit is passed through. When the chopping switch matrix circuit is clocked into the chopping clock phase CK_B, the differential signal at the input to the circuit is inverted. When CK_A is active or "on", CK_B is off. When CK_B is active or "on", CK_A is off.

In the example of FIG. 1, the differential chopping circuit path includes a first chopping switch matrix circuit 115A that inverts the polarity of the differential chopping circuit path at the input of the operational amplifier circuit 125 and at the output of the operational amplifier circuit 125. A second chopping switch matrix circuit 115B that reverses the polarity of the differential chopping circuit path. In some examples, the differential chopping circuit path includes a third chopping switch matrix circuit 115C that switches the polarity of the differential feedback circuit path of the differential sigma-delta ADC circuit. In the example shown, the differential feedback circuit path extends from the output end of the second chopping switch matrix circuit 115B to the input end of the third chopping switch matrix circuit 115C.

3 shows another example of a capacitance-voltage converter circuit with a differential chopping circuit path. This example includes only two chopping switch matrix circuits 315A, 315B in the differential chopping circuit path. The differential chopping circuit path also includes a differential feedback circuit path extending from the output end of the second chopping switch matrix circuit 315B to the input end of the first chopping switch matrix circuit 315A.

Referring again to FIG. 1, the driver circuit 140 may be electrically connected to the MEMS sensor circuit 105 to apply a square wave excitation signal to a drive input of the MEMS sensor. The drive input may be electrically connected to a circuit node 145 representing the proof mass of the MEMS sensor circuit 105. The sensing circuit 110 may include a phase clock circuit (not shown) for generating a first operation clock phase Ph1 and a second operation clock phase Phh2. The operational clock phases Ph1 and Ph2 do not overlap 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. The second chopping matrix circuit 115B and the third chopping switch matrix circuit 115C maintain previous values of the sensor output signal.

During Ph2, the first, second and third chopping switch matrix circuits 115A, 115B, 115C invert the polarity of the differential chopping circuit path. The capacitance of the MEMS sensor circuit 105 can be sampled with respect to the excitation signal. The first and second operational clock phases Ph1 and Ph2 may have the same frequency and duty cycle as the square wave excitation signal. The second and third chopping switch matrix circuits 115B and 115C may be switched together by a chopping clock. The first chopping switch matrix circuit 115A may be switched by a signal that is a logical sum AND of the chopping clock and the Ph2 clock.

Sigma-delta ADC circuits can be sensitive to dead-band or dead-zone. When the signal is sampled, the output may include a repeating pattern of zeros and ones, also referred to as idle tones. For input signals with small amplitudes, the output of the sigma-delta circuit can be continuous in a repeating pattern. Small amplitude input signals may not be encoded by the sigma-delta ADCs, resulting in a dead-band range of the input signal. However, it may be desirable to encode a small amplitude signal to take advantage of the full dynamic range of the differential sigma-delta ADC circuits shown in FIGS. 1 and 3.

The capacitance-voltage converter circuit may include a chopping clock circuit that clocks the differential chopping circuit with a periodic or regular chopping clock signal. To prevent or minimize deadband in the differential sigma-delta ADC circuit, the capacitance-voltage converter circuit may include a chopping clock circuit that clocks the differential chopping circuit path as a pseudo-random clock signal. have. The pseudo random clock signal includes a random transition from high to low, with CK_A turning on when CK_B is off and CK_B turning on when CK_A is off. This pseudo random clocking minimizes the limit cycles of the integrator circuit that can cause dead-band.

Another way to prevent or minimize dead-band in differential sigma-delta ADC circuits is to apply dither noise to comparator circuit 120. The capacitance-voltage converter circuit may include a pseudo random noise generator circuit 135 electrically connected to the comparator circuit for applying dither noise to the input of the comparator circuit. Once the output of the comparator is evaluated at the end of the second operational clock phase Ph2, a pseudo random dither noise signal may be injected into the comparator during Ph2 to remove dead-band idle tones. Dither noise shifts the output of the sigma-delta ADC circuit out of the deadband.

As described herein above, the MEMS sensor circuit may be a biaxial accelerometer. In this case, the MEMS sensor circuit changes the value of the first capacitance in response to the linear acceleration in the first direction and, for example, the value of the second capacitance in response to the linear acceleration in the second direction, such as in the orthogonal direction of the first direction. Can change. The sensing circuit includes a first capacitance-voltage converter circuit for generating a first digital signal representing a change in first capacitance, and a second capacitance-voltage converter circuit for generating a second digital signal representing a change in second capacitance. It may include. The output of the three-axis accelerometer can be sensed using a third capacitance-voltage converter circuit.

4 is a flowchart of a method 400 for reducing noise in a MEMS accelerometer sensing circuit. In step 405, the output of the MEMS sensor is sensed to produce a differential sensor output signal. In step 410, the output of the MEMS sensor is applied to the differential chopping circuit path to reduce noise in the circuit. To effect chopping, the polarity of the differential chopping circuit path is inverted at timed intervals. In some instances, the polarity of the circuit path is inverted at regular intervals, and in some instances, the polarity is inverted or chopped at pseudo random intervals. In step 415, the chopped MEMS sensor output signal is sampled with a differential sigma-delta ADC circuit to generate a digital signal indicative of a change in capacitance of the MEMS sensor.

Chopping the sampled output from the MEMS sensor reduces 1 / f noise and thermal noise, resulting in a primary sigma-delta ADC circuit with a dynamic range greater than 100 dB. To utilize the full dynamic range, signal chopping can be performed at pseudo-random intervals to minimize the occurrence of dead-bands at the output of the sigma-delta ADC circuit, and to the differential sigma-delta ADC circuit to remove idle tones. Dither noise may be applied.

Additional precautions and Example

Embodiment 1 may include or utilize the subject matter of the invention (such as an apparatus) that includes a capacitance-voltage converter circuit configured to be electrically connected to a MEMS sensor circuit. The capacitance-to-voltage converter circuit receives the differential MEMS sensor output signal, samples the differential chopping circuit path configured to invert the polarity of the differential chopping circuit path, the differential MEMS sensor output signal, and indicates a change in capacitance of the MEMS sensor. It may include a differential sigma-delta analog to digital converter (ADC) circuit configured to provide a digital signal.

In Example 2, the subject of the invention of Example 1, if necessary, is a pseudo sigma-delta ADC circuit including a comparator circuit, a pseudo-electrical connection to the comparator circuit, and configured to apply dither noise to the input of the comparator circuit. It may include a random noise generator circuit.

In Embodiment 3, the subject matter of one or any combination of Embodiments 1 and 2 may comprise a chopping clock circuit configured to clock the differential chopping circuit path with a pseudo random clock signal, if necessary. .

In Embodiment 4, the subject matter of one or any combination of Embodiments 1-3 is, if necessary, a differential sigma-delta ADC circuit comprising an operational amplifier circuit and a differential chopping circuit path at the input of the operational amplifier circuit. And a first chopping switch matrix circuit configured to reverse the polarity of the second chopping switch matrix circuit, and a second chopping switch matrix circuit configured to reverse the polarity of the differential chopping circuit path at the output of the operational amplifier circuit.

In Example 5, the subject matter of Example 4 may include a third chopping switch matrix circuit configured to switch the polarity of the differential feedback circuit path of the differential sigma-delta ADC circuit, if necessary. The differential feedback circuit path may extend from the output end of the second chopping switch matrix circuit to the input end of the third chopping switch matrix circuit, if desired.

In Embodiment 6, the subject matter of Embodiment 4 may include a differential feedback circuit path extending from the output end of the second chopping switch matrix circuit to the input end of the first chopping switch matrix circuit, if necessary.

In Embodiment 7, the subject matter of one or any combination of Embodiments 1 through 6 may include a phase clock circuit configured to generate a first operational clock phase and a second operational clock phase, if necessary. During the first operational clock phase, the first chopping switch matrix circuit can be configured to electrically separate the MEMS sensor circuitry from the differential sigma-delta ADC circuitry, if desired. During the second operational clock phase, the first and second chopping switch matrix circuits may be configured to reverse the polarity of the differential chopping circuit path if necessary.

In Embodiment 8, the subject matter of one or any combination of Embodiments 1-7 may comprise a driver circuit electrically connected to a MEMS sensor, if necessary. The driver circuit may be configured to, if necessary, apply a square wave excitation signal to a drive input of the MEMS sensor, wherein the first and second operational clock phases have the same frequency and duty cycle as the square wave excitation signal.

In Embodiment 9, the subject matter of one or any combination of Embodiments 1 through 8 may comprise a MEMS sensor circuit, if necessary. The MEMS sensor circuit can be configured to change the capacitance, if necessary, in response to the line acceleration in the first direction.

Embodiment 10 includes the subject matter of the invention (such as an apparatus) comprising a capacitance-voltage converter circuit configured to be electrically connected to a MEMS sensor circuit, or includes a capacitance-voltage converter circuit configured to be electrically connected to a MEMS sensor circuit. May be combined with one or any combination of the claimed subject matter of Examples 1-9. The capacitance-voltage converter circuit includes 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 indicative of a change in capacitance of the MEMS sensor. It may include. The differential sigma-delta ADC circuit may include a comparator circuit, and the capacitance-voltage converter circuit may include a pseudo random noise generator circuit electrically connected to the comparator circuit and configured to apply dither noise to an input terminal of the comparator circuit. .

In the eleventh embodiment, the subject matter of the tenth invention may include a MEMS sensor circuit, if necessary. The MEMS sensor circuit can be configured to change the capacitance, if necessary, in response to the line acceleration in the first direction.

In the twelfth embodiment, the subject matter of the eleventh embodiment is, if necessary, a switch circuit electrically connected to the MEMS sensor, and a driver circuit electrically connected to the MEMS sensor and configured to apply a square wave excitation signal to a drive input terminal of the MEMS sensor. And a phase clock circuit electrically connected to the switch circuit and configured to generate a first operational clock phase and a second operational clock phase. The first and second operational clock phases may have the same frequency and duty cycle as the square wave excitation signal, if necessary. During the first operational clock phase, the switch circuit can be configured to electrically separate the MEMS sensor circuit from the differential sigma-delta ADC circuit, if necessary, and the MEMS sensor circuit is configured to sample the line acceleration.

In Example 13, the subject matter of one or any combination of Embodiments 11 and 12, if necessary, changes the first capacitance in response to the linear acceleration in the first direction and linear acceleration in the second direction. A MEMS sensor circuit configured to change the second capacitance in response to the first capacitance; a first capacitance-voltage converter circuit for generating a first digital signal representing a change in the first capacitance; and a second digital representing a change in the second capacitance. And a second capacitance-voltage converter circuit for generating a signal.

Example 14 detects the output of a MEMS sensor to generate a differential sensor output signal, applies the output of the MEMS sensor to a differential chopping circuit path in which the polarity is reversed at timed intervals, and changes in capacitance of the MEMS sensor. Claimed subject matter (method, means for performing an operation, or performing the operation when the device is performed by the device, comprising sampling a chopped MEMS sensor output signal to generate a digital signal indicative of Such as a device readable medium containing instructions for detecting or outputting the MEMS sensor to generate a differential sensor output signal, and outputting the MEMS sensor output at a timed interval to reverse polarity. Chopping to generate a digital signal that is applied to the differential chopping circuit path and represents a change in capacitance of the MEMS sensor Claims of the invention of Examples 1 to 13, one or any combination of to include the subject matter of the invention, which comprises sampling the MEMS sensor output signal may be combined with target. The subject matter of this invention may include means for sensing the output of the MEMS sensor to generate a differential sensor output signal, an exemplary embodiment of which may include a charge-voltage converter circuit. This subject matter may include means for applying the output of the MEMS sensor to a differential chopping circuit path, an exemplary embodiment of which may include a charge-voltage converter circuit. The subject matter of this invention may include means for sampling the chopped MEMS sensor output signal to generate a digital signal indicative of a change in capacitance of the MEMS sensor, an exemplary embodiment of which is a differential ADC circuit and a sigma-delta ADC. It may include a circuit.

In Example 15, the subject matter of Example 14, if desired, samples a chopped MEMS sensor output signal using a differential sigma-delta ADC circuit and applies dither noise to the differential sigma-delta ADC circuit. It may include.

In Embodiment 16, the subject matter of one or any combination of Embodiments 14 and 15 may include clocking the differential chopping circuit path as a pseudo random clock signal, if necessary.

In Example 17, the subject matter of one or any combination of Examples 14-16, if required, samples the chopped MEMS sensor output signal using a differential sigma-delta ADC circuit, and differential sigma-delta. Inverting the polarity of the differential chopping circuit path at the input of the op amp circuit of the ADC circuit, and inverting the polarity of the differential chopping circuit path at the output of the op amp circuit.

In Embodiment 18, the subject matter of one or any combination of Embodiments 14-17, if necessary, reverses the differential output of the operational amplifier circuit to the differential input stage of the operational amplifier circuit to form a differential feedback circuit path. Supplying and inverting the polarity of the differential feedback circuit path at timed intervals.

In Example 19, the subject matter of one or any combination of Embodiments 14-18, if necessary, is to separate the MEMS sensor circuit from the differential sigma-delta ADC circuit during the first operational clock phase, Inverting the polarity of the chopping circuit path during the second operational clock phase.

In Example 20, the subject matter of one or any combination of Embodiments 14-18, if necessary, applies a square wave excitation signal such that the first and second operational clock phases have the same frequency and duty cycle as the square wave excitation signal. Applying to the drive input of the MEMS sensor and sampling the line 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 may include detecting a change in capacitance of the MEMS sensor in response to the line acceleration in the first direction, if necessary. .

In Embodiment 22, the subject matter of one or any combination of Embodiments 14-21 can, if necessary, detect a change in the capacitance of the MEMS sensor in response to pre-acceleration in the first direction. Sensing a first output and sensing a second output of the MEMS sensor to detect a change in capacitance of the MEMS sensor in response to a linear acceleration in a second direction perpendicular to the first direction.

In Embodiment 23, the subject matter of the invention, which may include means for performing one or more of the functions of Embodiments 1-22, or when executed by the device causes the device to perform one or more of the functions of Embodiments 1-22. Claimed subject matter of the invention, which may include a device readable medium comprising instructions to perform a task, or may comprise means for performing one or more of the functions of embodiments 1 to 22, or when executed by a device Any portion or combination of any portion of one or more of embodiments 1 to 22 to include a device readable medium containing instructions for causing the device to perform one or more of the functions of embodiments 1 to 22 May be

Each of these non-limiting embodiments may be used alone or in combination in the form of various substitutions or combinations with one or more of the other embodiments.

The above detailed description includes references to the drawings, which form a part of the detailed description. The drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. This embodiment is also referred to herein as an "example." All publications, patents, and patent documents mentioned in this specification are individually incorporated by reference, the entire contents of which are incorporated herein by reference. In the event of any inconsistency between this specification and the documents incorporated by reference, usage in the referenced references should be regarded as ancillary to the usage of this specification, for example in the case of incompatible inconsistencies, Usage in the specification takes precedence.

In this specification, the expression "work" or "one" is intended to encompass one or more than one, regardless of the usage of the phrase "at least one" Is used. In the present specification, the expression "or" means that the expression " A or B "includes" not A or B, " Used to refer to. In the appended claims, the words "including" and "in which" are used as "common" equivalents of "comprising" and "wherein". Also, in the claims that follow, the expressions "including" and "having" have open-ended meaning. That is, a system, apparatus, article, or process that includes elements other than those listed in the claims in the claims is still considered to be within the scope of the claims. Moreover, in the following claims, the expressions "first "," second ", and "third ", etc. are used merely as labels and are not intended to impose numerical requirements on such objects.

The foregoing description is for the purpose of illustration and is not to be construed as limiting the present invention. For example, the above-described embodiments (or one or more features of such embodiments) may be used in combination with each other. Other embodiments may be utilized by those skilled in the art having reviewed the above description. The abstract included herein is provided in accordance with 37 C.F.R §1.72 (b) to enable a reader of the specification to quickly understand the nature of the technical disclosure. This summary is provided to aid the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Further, in the detailed description of the present invention, the disclosure may be simplified by grouping various features together. This should not be construed to be intended as an essential feature of any claimed claim that is not claimed. Rather, the subject matter of the invention may be less than all features of a particular disclosed embodiment. Accordingly, the following claims are hereby incorporated into the Detailed Description, and each claim represents 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 (15)

A capacitance-voltage converter circuit configured to be electrically connected to micro-electromechanical systems (MEMS) sensor circuitry, the capacitance-voltage converter circuit comprising:
A differential chopping circuit path configured to receive the differential MEMS sensor output signal and to reverse the polarity of the differential chopping circuit path;
A differential sigma-delta analog-to-digital converter (ADC) circuit configured to sample the differential MEMS sensor output signal and provide a digital signal indicative of a change in capacitance of the MEMS sensor.
Device. The method of claim 1,
The differential sigma-delta ADC circuit comprises a comparator circuit,
The apparatus further comprises a pseudo-random noise generator circuit electrically connected to the comparator circuit and configured to apply dither noise to an input of the comparator circuit,
Device. The method of claim 1,
And a chopping clock circuit configured to clock the differential chopping circuit path with a pseudo random clock signal. The method of claim 1,
The differential sigma-delta ADC circuit comprises an operational amplifier circuit,
The apparatus comprises:
A first chopping switch matrix circuit configured to invert the polarity of the differential chopping circuit path at an input of the operational amplifier circuit;
Further comprising a second chopping switch matrix circuit configured to invert the polarity of the differential chopping circuit path at an output of the operational amplifier circuit;
Device. 5. The method of claim 4,
The apparatus further comprises a third chopping switch matrix circuit configured to switch a polarity of a differential feedback circuit path of the differential sigma-delta ADC circuit,
The differential feedback circuit path extends from an output end of the second chopping switch matrix circuit to an input end of the third chopping switch matrix circuit;
Device. 5. The method of claim 4,
And the apparatus further comprises a differential feedback circuit path extending from an output end of the second chopping switch matrix circuit to an input end of the first chopping switch matrix circuit. 5. The method of claim 4,
The apparatus further comprises a phase clock circuit configured to generate a first operational clock phase and a second operational clock phase,
During the first operational clock phase, the first chopping switch matrix circuit is configured to electrically isolate the MEMS sensor circuit from the differential sigma-delta ADC circuit,
During the second operational clock phase, the first chopping switch matrix circuit and the second chopping switch matrix circuit are configured to invert the polarity of the differential chopping circuit path.
Device. The method of claim 7, wherein
The apparatus further comprises a driver circuit electrically connected to the MEMS sensor,
The driver circuit is configured to apply a square wave excitation signal to a drive input of the MEMS sensor,
The first operational clock phase and the second operational clock phase have the same frequency and duty cycle as the square wave excitation signal,
Device. The method according to any one of claims 1 to 8,
The apparatus comprises the MEMS sensor circuit, the MEMS sensor circuit configured to change capacitance in response to linear acceleration in a first direction. A capacitance-to-voltage converter circuit configured to be electrically connected to the MEMS sensor circuit;
The capacitance-voltage converter circuit,
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 indicative of a change in capacitance of the MEMS sensor, the comparator circuit comprising: a comparator circuit;
A pseudo random noise generator circuit electrically connected to the comparator circuit and configured to apply dither noise to an input terminal of the comparator circuit,
Device. The method of claim 10,
The apparatus comprises the MEMS sensor circuit, the MEMS sensor circuit configured to change capacitance in response to line acceleration in a first direction. 12. The method of claim 11,
The apparatus comprises:
A switch circuit electrically connected to the MEMS sensor;
A driver 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 switch circuit, the phase clock circuit configured to generate a first operational clock phase and a second operational clock phase having the same frequency and duty cycle as the square wave excitation signal,
During the first operational clock phase, the switch circuit is configured to electrically isolate the MEMS sensor circuit from the differential sigma-delta ADC circuit, wherein the MEMS sensor circuit is configured to sample the line acceleration.
Device. 13. The method according to claim 11 or 12,
The MEMS sensor circuit is configured to change the first capacitance in response to the line acceleration in the first direction, and change the second capacitance in response to the line acceleration in the second direction,
The apparatus includes a first capacitance-voltage converter circuit for generating a first digital signal indicative of a change in the first capacitance, and a second capacitance-voltage for generating a second digital signal indicative of a change in the second capacitance. Further comprising a converter circuit,
Device. Sensing the output of a microelectromechanical system (MEMS) sensor to produce a differential sensor output signal;
Applying the output of the MEMS sensor to a differential chopping circuit path whose polarity is inverted at a timed interval; And
Sampling the chopped MEMS sensor output signal with a differential sigma-delta analogue digital converter (ADC) circuit to generate a digital signal indicative of a change in capacitance of the MEMS sensor.
Way. 15. The method of claim 14,
Applying dither noise to the differential sigma-delta ADC circuit, and clocking the differential chopping circuit path with a pseudo random clock signal.

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