CN115598377A - Zero drift self-detection self-calibration system based on digital sigma delta closed-loop accelerometer - Google Patents
Zero drift self-detection self-calibration system based on digital sigma delta closed-loop accelerometer Download PDFInfo
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Abstract
The invention discloses a zero drift self-detection and self-calibration system based on a digital sigma delta closed-loop accelerometer, belongs to the technical field of sensors, and aims to solve the problem of zero drift of an existing MEMS accelerometer. It includes: an excitation source of the zero self-detection self-calibration circuit generates a low-distortion single-frequency sinusoidal excitation signal; the closed loop servo interface circuit generates a high-voltage electrostatic power feedback signal which acts on the MEMS sensitive component to form a self-detection loop; the MEMS sensitive component is forced to vibrate under the action of a low-distortion single-frequency sine excitation signal, and the servo position shifts when the accelerometer drifts, so that capacitance variation is generated; the closed-loop servo interface circuit collects capacitance variation, self-detection even harmonic distortion components are generated in output, the zero self-detection self-calibration circuit carries out amplitude and phase extraction, compensation control signals are generated, and the compensation control signals are transmitted to the MEMS sensitive component to compensate capacitance mismatch. The invention is used for carrying out online self-detection and self-calibration on zero drift.
Description
Technical Field
The invention relates to a self-detection and self-calibration system for zero drift of an accelerometer, belonging to the technical field of sensors.
Background
An accelerometer is an inertial sensor that is capable of measuring acceleration forces of an object. MEMS accelerometers are increasingly used in various industries due to their advantages of small size, low power consumption, light weight, and low cost. The digital sigma delta closed-loop accelerometer adopting the electrostatic force servo has excellent performance advantages in the aspects of noise, linearity, bandwidth, integration level and the like, and becomes a preferred implementation scheme of a high-end MEMS accelerometer.
However, the MEMS accelerometer has a small size and is seriously influenced by processing errors and residual stress, so that the output characteristic of the whole machine has obvious long-term drift, and the application of the MEMS accelerometer in the high-end inertial navigation field is influenced. The drift of the MEMS accelerometer is divided into zero drift and scale factor drift, and for inertial navigation in high speed and long voyage, the micro zero drift causes serious positioning error after long-time quadratic integration, and the influence on the inertial navigation is more serious.
Therefore, how to solve the zero drift problem of the MEMS accelerometer is crucial to the development of inertial navigation.
Disclosure of Invention
The invention aims to solve the problem of zero drift of an MEMS accelerometer, and provides a zero drift self-detection and self-calibration system based on a digital sigma-delta closed-loop accelerometer.
The invention provides a zero drift self-detection and self-calibration system based on a digital sigma delta closed-loop accelerometer, which comprises: a closed loop servo interface circuit and a zero self-detection self-calibration circuit;
an excitation source in the zero self-detection self-calibration circuit generates a low-distortion single-frequency sinusoidal excitation signal;
the closed-loop servo interface circuit generates a high-voltage electrostatic power feedback signal, the high-voltage electrostatic power feedback signal acts on an MEMS sensitive component of the accelerometer to realize servo control on the MEMS sensitive component, and a self-detection loop of the digital sigma delta closed-loop accelerometer is formed;
the MEMS sensitive component is forced to vibrate under the action of a low-distortion single-frequency sinusoidal excitation signal, so that the MEMS sensitive component generates deviation in a servo position when the accelerometer drifts, and further generates capacitance variation;
the closed loop servo interface circuit generates a self-detection even harmonic distortion component related to the offset degree in the output of the MEMS sensitive component by acquiring the capacitance variation of the MEMS sensitive component;
the zero self-detection self-calibration circuit extracts the amplitude and the phase of a self-detection even harmonic distortion component output by the closed-loop servo interface circuit, generates a compensation control signal according to the extracted amplitude and phase, and transmits the compensation control signal to the MEMS sensitive component to compensate the capacitor mismatch.
Preferably, the MEMS sensitive component comprises an upper plate, a movable mass block and a lower plate, wherein the upper plate, the movable mass block and the lower plate are bonded through a silicon melting process;
the movable mass block and the upper pole plate form a first sensitive capacitor, and the movable mass block and the lower pole plate form a second sensitive capacitor;
the movable mass moves between the upper pole plate and the lower pole plate under the action of inertia force, and differential change is generated between the first sensitive capacitor and the second sensitive capacitor.
Preferably, the closed-loop servo interface circuit comprises a multiplexer, a front-end capacitance detection amplifier, a loop compensator, a 1Bit Σ Δ a/D conversion circuit, a dc bias circuit, and a high-voltage electrostatic force feedback circuit;
the three interfaces of the first input end of the multi-path selector are respectively connected with an upper polar plate, a movable mass block and a lower polar plate, the multi-path selector acquires differential variation between a first sensitive capacitor and a second sensitive capacitor, the selection output end of the multi-path selector is connected with the selection input end of a front-end capacitor detection amplifier, the front-end capacitor detection amplifier converts the differential variation between the first sensitive capacitor and the second sensitive capacitor into output voltage in direct proportion to the differential variation, the voltage output end of the front-end capacitor detection amplifier is connected with the voltage input end of a loop compensator, the loop compensator generates a leading phase compensation signal for stably controlling a loop, the leading phase compensation signal output end of the loop compensator is connected with the leading phase compensation signal input end of a 1Bit sigma delta A/D conversion circuit, the analog-to-digital conversion output end of the 1Bit sigma delta A/D conversion circuit is connected with the analog-to-digital conversion input end of a high-voltage feedback circuit, the high-voltage electrostatic force feedback circuit generates a high-voltage feedback signal, the high-voltage electrostatic force feedback output end of the high-voltage electrostatic force feedback circuit is connected with the second input end of the multi-path selector, the high-voltage electrostatic force feedback signal acts on the movable electrostatic force and one polar plate, and the one electrostatic force mass block is one of the upper or lower polar plate; the direct current bias output end of the direct current bias circuit is connected with the third input end of the multiplexer; the output signal of the selection output end of the multi-path selector is switched among the first input end, the second input end and the third input end in a rotating way under the control of a switch time sequence;
the output end of the 1Bit sigma delta A/D conversion circuit is the output end of the accelerometer.
Preferably, the zero self-detection self-calibration circuit comprises an excitation source, a self-detection even harmonic extraction circuit, an automatic compensation calibration circuit and a compensation trimming capacitor array;
the low-distortion single-frequency sinusoidal excitation signal is superposed with a voltage signal output by a front-end capacitance detection amplifier, and the superposed signal is input into a closed-loop servo interface circuit through a loop compensator;
under the action of a low-distortion single-frequency sine excitation signal, the movable mass block generates sine vibration at a servo position, when the accelerometer drifts, the servo position generates offset, and the output of the accelerometer generates a self-detection even harmonic distortion component related to the offset degree;
the self-detection response input end of the self-detection even harmonic extraction circuit is connected with the output end of the accelerometer, the self-detection even harmonic extraction circuit extracts the amplitude and the phase of a self-detection even harmonic distortion component, the amplitude phase extraction output end of the self-detection even harmonic extraction circuit is connected with the amplitude phase extraction input end of the automatic compensation calibration circuit, the automatic compensation calibration circuit generates a compensation control signal according to the extracted amplitude and phase, the compensation control signal output end of the automatic compensation calibration circuit is connected with the compensation control signal input end of the compensation trimming capacitor array, the three paths of compensation capacitor output ends of the compensation trimming capacitor array are respectively connected with the upper electrode plate, the movable mass block and the lower electrode plate, and mismatch of the first sensitive capacitor or the second sensitive capacitor is compensated.
Preferably, the self-detection even harmonic extraction circuit comprises a synchronous quadrature demodulation excitation source, a digital multiplier, a digital low-pass filter and a phase amplitude settlement unit;
the input end of a synchronous orthogonal demodulation excitation source is connected with the output end of an accelerometer, the synchronous orthogonal demodulation excitation source generates two synchronous orthogonal demodulation reference signals, the output ends of the two orthogonal demodulation reference signals of the synchronous orthogonal demodulation excitation source and the output end of the accelerometer are connected to three input ends of a digital multiplier, the digital multiplier demodulates even harmonic components from the output of the accelerometer, the even harmonic components are filtered by a digital low-pass filter, the digital low-pass filter outputs self-detection even harmonic distortion components, and a phase amplitude settlement unit obtains the resolved amplitude and the phase according to the self-detection even harmonic distortion components output by the digital low-pass filter.
Preferably, the frequency of the two synchronous orthogonal demodulation reference signals generated by the synchronous orthogonal demodulation excitation source is twice the frequency of the low-distortion single-frequency sinusoidal excitation signal, and the phase difference between the two synchronous orthogonal demodulation reference signals is 90 °.
Preferably, the automatic compensation calibration circuit obtains a compensation control signal for adjusting the compensation and trimming capacitor array bit by bit from high to low according to the amplitude and phase settled by the self-detection even harmonic extraction circuit, and the compensation control signal comprises a compensation magnitude and a compensation direction.
Preferably, the compensation trimming capacitor array comprises a binary-valued capacitor C 1 ～C k Switch S 10 ～S k0 And S 11 ～S k1 (ii) a Wherein k represents the number of bits of the compensation capacitor;
capacitor C 1 ～C k The lower pole plates are connected to a movable mass block and a capacitor C k Upper pole plate simultaneously connecting switch S k0 And S k1 One end of (1), switch S 10 ～S k0 While the other end of the same is connected to the lower plate of the MEMS sensitive member, S 11 ～S k1 The other end of the MEMS sensor is simultaneously connected with an upper polar plate of the MEMS sensitive component;
switch S 10 ～S k0 And S 11 ～S k1 Switch control signal n k Obtained according to the compensation control signal of the automatic compensation calibration circuit.
Preferably, according to switch S 10 ～S k0 And S 11 ～S k1 Switch control signal n k The specific process of compensating the mismatch of the first sensitive capacitor or the second sensitive capacitor by the compensation trimming capacitor array includes:
when n is k When =1, S 11 ～S k1 Closure, S 10 ～S k0 Disconnecting, connecting the kth compensation capacitor in parallel between the upper pole plate and the movable mass block, and compensating the first sensitive capacitor;
when n is k When = -1, S 11 ～S k1 Breaking, S 10 ～S k0 And when the voltage is closed, the kth compensation capacitor is connected between the lower polar plate and the movable mass block in parallel to compensate the second sensitive capacitor.
The invention provides a zero drift self-detection self-calibration system based on a digital sigma delta closed-loop accelerometer, and provides an on-chip on-line self-detection and self-calibration circuit. Has the following advantages:
1. the MEMS sensitive structure is excited by adopting electrostatic force, the reference of detection and calibration is even harmonic distortion component in self-detection response, and the absolute amplitude of the electrostatic force is not required to be used as the reference of detection and calibration, so that under the condition that the absolute magnitude of the electrostatic force is up and the electrostatic force is easy to drift, the harmonic purity of electrostatic excitation is ensured by using a 1Bit sigma delta modulation technology, and the high precision of self-detection is ensured;
2. the zero self-calibration process can automatically control the size and direction of trimming according to the amplitude and phase of harmonic distortion, thereby realizing automatic calibration;
3. the self-detection and self-calibration processes are not interfered by acceleration offset, and the effective detection and the effective calibration of the zero drift of the accelerometer can be realized in any placing state.
Drawings
FIG. 1 is a schematic structural diagram of a digital sigma-delta closed-loop accelerometer-based zero drift self-detection self-calibration system according to the present invention;
FIG. 2 is a schematic diagram of the self-detecting even harmonic extraction circuit according to the present invention;
FIG. 3 is a schematic diagram of a compensation trimming capacitor array according to the present invention;
FIG. 4 is a small signal flow diagram of the digital Σ Δ closed loop-based accelerometer zero drift self-detection self-calibration system of the present invention;
FIG. 5 is a block diagram of the logic flow for compensating the compensation control signal generated by the auto-compensation calibration circuit according to the present invention;
FIG. 6 is a schematic structural diagram of a MEMS sensitive component of the present invention, wherein A represents a center equilibrium position, B represents a closed loop servo position, and C represents an offset.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.
Example 1:
the present embodiment is described below with reference to fig. 1 to fig. 3, and the system for self-detecting and self-calibrating zero drift based on digital Σ Δ closed-loop accelerometer in the present embodiment includes: a closed loop servo interface circuit 200 and a zero self-detection self-calibration circuit 300;
an excitation source in the zero self-detection self-calibration circuit 300 generates a low-distortion single-frequency sinusoidal excitation signal;
the closed loop servo interface circuit 200 generates a high voltage electrostatic power feedback signal, and the high voltage electrostatic power feedback signal acts on the MEMS sensitive member 100 of the accelerometer to realize servo control on the MEMS sensitive member 100, so that a self-detection loop of the digital sigma delta closed loop accelerometer is formed;
the MEMS sensitive component 100 is forced to vibrate under the action of a low-distortion single-frequency sinusoidal excitation signal, so that the servo position of the MEMS sensitive component 100 is deviated when the accelerometer drifts, and further capacitance variation is generated;
the closed loop servo interface circuit 200 generates a self-detection even harmonic distortion component related to the offset degree in the output of the MEMS sensitive component 100 by collecting the capacitance variation thereof;
the zero self-detection self-calibration circuit 300 extracts the amplitude and phase of the self-detection even harmonic distortion component output by the closed-loop servo interface circuit 200, generates a compensation control signal according to the extracted amplitude and phase, and transmits the compensation control signal to the MEMS sensitive component 100 to compensate for the capacitor mismatch.
Further, the MEMS sensitive component 100 includes an upper plate 101, a movable mass 102 and a lower plate 103, and the upper plate 101, the movable mass 102 and the lower plate 103 are bonded by a silicon fusion process;
the movable mass block 102 and the upper pole plate 101 form a first sensitive capacitor, and the movable mass block 102 and the lower pole plate 103 form a second sensitive capacitor;
the movable mass 102 moves between the upper plate 101 and the lower plate 103 under the action of inertia force, so that a differential change is generated between the first sensitive capacitor and the second sensitive capacitor.
Still further, the closed-loop servo interface circuit 200 includes a multiplexer 201, a front-end capacitance detection amplifier 202, a loop compensator 203, a 1Bit Σ Δ a/D conversion circuit 204, a dc bias circuit 206, and a high-voltage electrostatic force feedback circuit 205;
the three interfaces of the first input end of the multiplexer 201 are respectively connected with the upper plate 101, the movable mass block 102 and the lower plate 103, the multiplexer 201 acquires differential variation between a first sensitive capacitor and a second sensitive capacitor, the selection output end of the multiplexer 201 is connected with the selection input end of the front-end capacitor detection amplifier 202, the front-end capacitor detection amplifier 202 converts the differential variation between the first sensitive capacitor and the second sensitive capacitor into an output voltage in direct proportion to the differential variation, the voltage output end of the front-end capacitor detection amplifier 202 is connected with the voltage input end of the loop compensator 203, the loop compensator 203 generates a leading phase compensation signal for stabilizing a control loop, the leading phase compensation signal output end of the loop compensator 203 is connected with the leading phase compensation signal input end of the 1Bit Σ Δ a/D conversion circuit 204, the analog-to-digital conversion output end of the 1Bit Σ Δ a/D conversion circuit 204 is connected with the analog-to-digital conversion input end of the high-voltage feedback circuit 205, the high-voltage electrostatic force feedback circuit 205 generates a high-voltage electrostatic force feedback signal, the high-voltage electrostatic force feedback output end of the high-voltage electrostatic force feedback circuit 205 is connected with the second input end of the multiplexer 201, the high-voltage electrostatic force feedback circuit 205 is used as one of the upper plate 101 or one of the lower plate 103, and one of the electrostatic force electrostatic plate 103; the dc bias output terminal of the dc bias circuit 206 is connected to the third input terminal of the multiplexer 201; the output signal of the selection output end of the multiplexer 201 is switched among the first input end, the second input end and the third input end in a rotating way under the control of the switch time sequence;
the output of the 1Bit Σ Δ a/D conversion circuit 204 is the output of the accelerometer.
Still further, the zero self-detection and self-calibration circuit 300 comprises an excitation source 301, a self-detection even harmonic extraction circuit 302, an automatic compensation and calibration circuit 303 and a compensation and trimming capacitor array 304;
the excitation source 301 generates a low-distortion single-frequency sinusoidal excitation signal for self-detection, the low-distortion single-frequency sinusoidal excitation signal is superposed with a voltage signal output by the front-end capacitance detection amplifier 202, and the superposed signal is input into the closed-loop servo interface circuit 200 through the loop compensator 203;
under the action of a low-distortion single-frequency sine excitation signal, the movable mass block 102 generates sine vibration at a servo position, when the accelerometer drifts, the servo position generates deviation, and the output of the accelerometer generates a self-detection even harmonic distortion component related to the deviation degree;
the self-detection response input end of the self-detection even harmonic extraction circuit 302 is connected with the output end of the accelerometer, the self-detection even harmonic extraction circuit 302 extracts the amplitude and the phase of the self-detection even harmonic distortion component, the amplitude phase extraction output end of the self-detection even harmonic extraction circuit 302 is connected with the amplitude phase extraction input end of the automatic compensation calibration circuit 303, the automatic compensation calibration circuit 303 generates a compensation control signal according to the extracted amplitude and phase, the compensation control signal output end of the automatic compensation calibration circuit 303 is connected with the compensation control signal input end of the compensation trimming capacitor array 304, the three paths of compensation capacitor output ends of the compensation trimming capacitor array 304 are respectively connected with the upper electrode plate 101, the movable mass block 102 and the lower electrode plate 103, and the mismatch of the first sensitive capacitor or the second sensitive capacitor is compensated.
Still further, the self-detection even harmonic extraction circuit 302 includes a synchronous quadrature demodulation excitation source 3021, a digital multiplier 3022, a digital low-pass filter 3023, and a phase amplitude settlement unit 3024;
the input end of a synchronous orthogonal demodulation excitation source 3021 is connected with the output end of the accelerometer, the synchronous orthogonal demodulation excitation source 3021 generates two synchronous orthogonal demodulation reference signals, the output ends of the two orthogonal demodulation reference signals of the synchronous orthogonal demodulation excitation source 3021 and the output end of the accelerometer are connected to three input ends of a digital multiplier 3022, the digital multiplier 3022 demodulates the even harmonic component from the output of the accelerometer, the even harmonic component is filtered by a digital low-pass filter 3023, the digital low-pass filter 3023 outputs a self-detected even harmonic distortion component, and a phase amplitude settlement unit 3024 solves the amplitude and the phase according to the self-detected even harmonic distortion component output by the digital low-pass filter 3023.
Still further, the frequency of the two synchronous orthogonal demodulation reference signals generated by the synchronous orthogonal demodulation excitation source 3021 is twice the frequency of the low-distortion single-frequency sinusoidal excitation signal, and the phase difference between the two synchronous orthogonal demodulation reference signals is 90 °.
Further, the automatic compensation calibration circuit 303 obtains a compensation control signal for adjusting the compensation trimming capacitor array 304 bit by bit from high to low according to the amplitude and phase settled by the self-detection even harmonic extraction circuit 302, where the compensation control signal includes a compensation magnitude and a compensation direction.
Still further, the compensation trimming capacitor array 304 includes a binary valued capacitor C 1 ～C k Switch S 10 ～S k0 And S 11 ～S k1 (ii) a Wherein k represents the number of bits of the compensation capacitor;
capacitor C 1 ～C k The lower plates of which are connected to the movable mass 102, a capacitor C k Upper pole plate simultaneously connecting switch S k0 And S k1 One end of (1), switch S 10 ～S k0 While the other end is simultaneously connected to the lower plate 103 of the MEMS sensitive member 100 11 ～S k1 The other end of the MEMS sensor is simultaneously connected with an upper plate 101 of the MEMS sensitive component 100;
switch S 10 ～S k0 And S 11 ～S k1 Switch control signal n k According to the compensation control signal of the auto-compensation calibration circuit 303.
Still further, according to switch S 10 ～S k0 And S 11 ～S k1 Switch control signal n k The specific process of compensating the mismatch of the first sensitive capacitor or the second sensitive capacitor by the compensation trimming capacitor array 304 includes:
when n is k When =1, S 11 ～S k1 Closure, S 10 ～S k0 When the voltage is disconnected, the kth compensation capacitor is connected in parallel between the upper polar plate 101 and the movable mass block 102 to compensate the first sensitive capacitor;
when n is k When =1, S 11 ～S k1 Breaking, S 10 ～S k0 And when the voltage is closed, the kth compensation capacitor is connected between the lower plate 103 and the movable mass block 102 in parallel to compensate the second sensitive capacitor.
In the invention, as shown in fig. 1, a digital sigma-delta closed-loop MEMS accelerometer system with zero drift self-detection and self-calibration functions is formed by using an MEMS sensitive component 100, a closed-loop servo interface circuit 200 and a zero self-detection and self-calibration circuit 300.
The closed-loop servo interface circuit 200 detects capacitance change of the MEMS sensitive member 100, and implements servo control of the MEMS movable mass by applying electrostatic force between the plates of the MEMS sensitive member 100, thereby forming a closed-loop MEMS accelerometer detection loop.
The zero self-detection self-calibration circuit 300 generates a single-frequency sinusoidal excitation signal V through the excitation source 301 T And injecting the signals into a closed-loop accelerometer detection loop. Self-detecting excitation V of MEMS sensitive component 100 T The forced vibration is carried out under the action. When the MEMS accelerometer drifts, the movable mass (102) deviates from the central balance position A, and at the moment, the digital output D of the closed-loop accelerometer out Will produce even harmonic distortion.
Self-detecting even harmonic extraction circuit 302 detects closed-loop accelerometer output D out The magnitude and phase of the even harmonic distortion component in (a).
The automatic compensation calibration circuit 303 automatically controls the compensation size and direction of the compensation trimming capacitor array 304 according to the extracted amplitude and phase information, and performs trimming compensation on the drift of the MEMS sensitive component 100 in real time.
The MEMS sensitive component 100 is formed by bonding an upper plate 101, a movable mass 102 and a lower plate 103 through a silicon melting process.
The movable mass 102 and the upper plate 101 form a first sensing capacitor CS 1 The movable mass 102 and the lower plate 103 form a second sensitive capacitor CS 2 。
The movable mass 102 can move between the upper plate 101 and the lower plate 103 under the action of inertia force and cause the sensitive capacitor CS 1 And CS 2 Producing a differential change: Δ CS = CS 1 -CS 2 。
On the other hand, when the voltage between the upper plate 101 or the lower plate 103 and the movable mass 102 is not equal, an electrostatic force action is generated on the movable mass 102, and a closed-loop servo system can be formed by using the electrostatic force action, so that the bandwidth, the linearity and the measuring range of the MEMS accelerometer are improved.
As shown in fig. 1, the closed-loop servo interface circuit 200 is composed of a multiplexer 201, a front-end capacitance detection amplifier 202, a loop compensator 203, a 1Bit Σ Δ a/D conversion circuit 204, a dc bias circuit 206, and a high-voltage electrostatic force feedback circuit 205.
The input of the multiplexer 201 is connected to three electrodes of the MEMS sensitive component 100, namely, the upper plate 101, the movable mass block 102, and the lower plate 103;
the output of the multiplexer 201 is switched cyclically among the front-end capacitance detection amplifier 202, the dc bias circuit 206 and the high-voltage electrostatic force feedback circuit 205, respectively, under the control of the switching timing.
The input end of the front-end capacitance detection amplifier 202 is connected to the first output end of the multiplexer 201, and is responsible for detecting the differential capacitance change Δ CS of the MEMS sensitive capacitance value in the detection phase by using the charge conservation principle, and converting the differential capacitance change Δ CS into an output voltage proportional to Δ CS.
The loop compensator 203 is responsible for providing a leading phase compensation, stable control loop having an input coupled to the output of the front-end capacitive sense amplifier 202 and an output coupled to the input of the 1-Bit Σ Δ a/D conversion circuit 204. The 1Bit Σ Δ a/D conversion circuit 204 is responsible for implementing analog signalsThe conversion of the signal to a digital signal, the input of which is connected to the output of the loop compensator 203, the output of which is the output D of the closed-loop accelerometer out 。
Input terminal of high-voltage electrostatic force feedback circuit 205 and output D of closed-loop accelerometer out The output end of the electrostatic feedback voltage feedback circuit is connected with three electrodes of the MEMS sensitive structure through a multiplexer 201 in the electrostatic feedback phase, and the electrostatic feedback voltage V is applied to one side of the movable mass block 102 and the upper polar plate 101 or the lower polar plate 103 f Applying a digital output D of the direction-dependent accelerometer out And (4) controlling.
The feedback electrostatic force F generated by the closed loop servo interface circuit 200 is normally elec The inertia force caused by the external acceleration is equal in magnitude and opposite in direction. Therefore, as shown in fig. 6, the movable mass 102 is at the central equilibrium position a between the upper and lower plates regardless of the external acceleration. When there is a stress drift, the MEMS sensing member 100 deforms, and the servo position of the movable mass 102 deviates from the center equilibrium position a. At the same time, the symmetry of the system will be disrupted creating electrostatic force non-linearities.
The zero self-detection self-calibration circuit 300 realizes the on-line self-detection and self-calibration of the drift of the MEMS sensitive component 100 by utilizing the internal relation between the servo position offset and the nonlinearity of the electrostatic force.
The zero self-detection self-calibration circuit 300 includes: the device comprises an excitation source 301, a self-detection even harmonic extraction circuit 302, an automatic compensation calibration circuit 303 and a compensation trimming capacitor array 304.
Wherein, the excitation source 301 is responsible for generating the low-distortion single-frequency sinusoidal excitation V required by self-detection T . Self-detecting excitation V T And the output V of the front-end capacitance detection amplifier 202 pre Added and injected into the closed loop servo interface circuit 200 before the loop compensator 203.
In the self-detection of excitation V T The movable mass 102 will make a small sinusoidal vibration around its servo position. When there is a servo position offset, the output of the closed-loop accelerometer will produce a self-detected even harmonic distortion component that is related to the degree of offset。
Input to self-detect even harmonic extraction circuit 302 and output V of closed-loop accelerometer out Connected to, and responsible for outputting V at the system out The amplitude and phase of the even harmonic distortion component are extracted.
The input of the automatic compensation calibration circuit 303 is connected to the output of the self-detection even harmonic extraction circuit 302, and is responsible for generating a compensation control signal according to the extracted amplitude and phase, and automatically adjusting the compensation magnitude and the compensation direction of the compensation trimming capacitor array 304.
The input of the compensation trimming capacitor array 304 is connected to the output of the auto-compensation calibration circuit 303, the output of the compensation trimming capacitor array 304 is connected to three electrodes of the MEMS sensitive component 100, and the effective compensation capacitor thereof will be connected to the sensitive capacitor C of the MEMS sensitive component 100 S1 And C S2 One in parallel, is responsible for compensating for mismatches between the MEMS sensitive capacitances.
When the MEMS sensitive structure drifts, as shown in fig. 6, causing the closed loop servo position B to deviate from the center equilibrium position a, the symmetry of the system is broken. At this point the injection self-test stimulus V T Then, V will be output in the system out Generating even harmonic distortion components. While ideally there is no drift, the closed loop servo position B will coincide with the central equilibrium position A, at which time the system V out Will have no even harmonic distortion components and only contain odd harmonic distortion components.
Next, the above characteristics are demonstrated. As shown in fig. 4:
wherein H ms The kinematic characteristics of the acceleration a to the displacement x of the MEMS sensitive member 100; c 0 The balance value of the sensitive capacitors at the two sides when the movable mass block 102 is at the central balance position a; v S The reference voltage applied to the sensitive capacitor when the charge detection amplifier detects the voltage. C f A feedback capacitor of the charge detection amplifier; h C (z) is the transfer function of the loop compensator; STF A/D (z) is the signal transfer function of the a/D converter; f elec (x,V out ) For digital output V out The resulting feedback electrostatic force; m is the mass of the movable mass 102.
When the movable mass 102 is at the central balance position a, the distances between the movable mass 102 and the upper and lower plates 101, 103 on both sides are equal and are denoted as d 0 . When there is an acceleration input a in At this time, the movable mass 102 will deviate from the equilibrium position, resulting in a in A proportional displacement x. The displacement x is suppressed by the negative feedback of the closed-loop accelerometer. When the loop gain is large enough, the displacement x can be considered as a small signal near zero. When the MEMS sensitive component 100 has drift deformation, the servo position of the movable mass 102 will deviate from the equilibrium position, and the deviation is denoted as x drift Where the MEMS sensitive member 100 displacement x' is the operating point offset x drift The result of the joint superposition with the small signal displacement x, i.e. x' = x + x drift 。
Because of the closed loop servo interface circuit 200, the loop gain is mainly provided by the integral element in the loop compensator. For self-detecting excitation V T At this frequency, the gain of the cascaded subsystem of the loop compensator 203 and the 1Bit Σ Δ a/D conversion circuit 204 can be considered infinite. Thus, the self-detection excitation V T To the system output response D out The transfer function between the front-end capacitance detection amplifier 202 and the MEMS sensitive component 100 will be determined.
Namely, the following relation holds:
wherein, F elec For feedback of electrostatic force, F is due to the displacement modulation effect, i.e. the electrostatic force between parallel plates is affected by the change of the plate spacing elec Is a function of the displacement of the movable mass. F elec (x,D out ) Can be expressed as:
wherein,
the following formula (1), formula (2) and formula (3) can be combined:
by mixing V out Can be represented as V T Polynomial form of the respective harmonics, namely:
in formula (4), the corresponding item coefficients are compared to obtain:
as can be seen from equation (6), when the MEMS sensitive member 100 is deformed by stress, there is a servo position shift x drift When not equal to 0, self-detecting and outputting response D out In the presence of a deviation x from the servo position drift The even harmonic term in direct proportion; ideally, the closed loop servo position B coincides with the center equilibrium position A, i.e., x drift When =0, self-detection output response D out All even harmonic term coefficients in the harmonic filter are 0, and only odd harmonic terms exist. Thus, by measuring the self-test output response D out The even harmonic component in the signal can determine the existence of drift amount, and the magnitude and direction of the drift amount, and perform calibration and compensation according to the drift amount.
In addition, the servo electrostatic force generated by the closed loop servo interface circuit 200 cancels out when an external acceleration bias is present. Thus, external acceleration cannot change the closed-loop servo position B of the movable mass 102 without causing a servo position offset x drift . The self-detection method provided by the inventionOffset x from servo position only drift Is concerned and is therefore not affected by external acceleration biases.
Compared with the calibration method depending on the absolute precision of the electrostatic force, the reference datum selected by the self-detection and self-calibration method based on harmonic distortion is an even harmonic component in the self-detection response. Therefore, only the harmonic purity of the excitation source needs to be ensured, and the harmonic purity of the excitation source can be obtained by the ideal linear characteristic of the 1Bit Σ Δ modulation technique. The problem that the absolute amplitude of the electrostatic force is unknown and the electrostatic force is influenced by environmental changes and is easy to drift is effectively solved.
The magnitude and direction of the drift amount can be output from the self-detection through the self-detection even harmonic extraction circuit 302 to the self-detection output D out And performing synchronous orthogonal demodulation to obtain.
The self-detecting even harmonic extraction circuit 302 has a structure as shown in fig. 2, and includes a synchronous quadrature demodulation excitation source 3021, a digital multiplier 3022, a digital low-pass filter 3023, and a phase amplitude settlement unit 3024. Synchronous orthogonal demodulation excitation source 3021 for generating synchronous orthogonal demodulation reference signal R I 、R Q . The synchronous orthogonal demodulation reference signal R I 、R Q Of the frequency of the self-detecting excitation signal V T Is twice the frequency of (c), and R I And R Q The phase difference of (2) by 90 deg. guarantees orthogonality. Input of digital multiplier 3022 is respectively responsive to self-test output D out Synchronous quadrature demodulation reference signal R I 、R Q Connected to output a response D from the self-test by multiplication out And even harmonic components are demodulated. Self-detecting output response D according to the modem principle out The even harmonic component of the medium frequency and the reference signal with the same frequency is demodulated to direct current, and other frequency components are all located at high frequency. As a result, the digital low-pass filter 3023 filters out other frequency components, and the output Y of the digital low-pass filter 3023 I 、Y Q Contains only self-detected even harmonic components. Further, the phase amplitude resolving unit resolves the phase amplitude according to the output Y of the digital low-pass filter I 、Y Q The amplitude and phase of the self-detected even harmonic component are calculated.
According to the amplitude and phase information extracted by the self-detection even harmonic extraction circuit 302, the automatic compensation calibration circuit (303) judges and adjusts the compensation size and the compensation direction of the compensation trimming capacitor array (304) from high position to low position bit by bit, and the automatic compensation and calibration of the drift error of the MEMS sensitive structure are realized.
FIG. 5 is a block diagram of a compensation logic flow of the compensation control signal generated by the auto-compensation calibration circuit 303, which determines the current most significant bit n k If n is k If the phase is reversed, judging whether k is equal to 0, if the phase is reversed, finishing calibration, not reversing the phase, continuously judging whether the amplitude is reduced, if the amplitude is reduced, judging whether k is equal to 0, and if the amplitude is 0, finishing calibration; if the amplitude is not reduced, so that n k And =1, judging whether k is equal to 0, and if k is equal to 0, completing calibration. If k is not equal to 0, subtracting 1 from k, and returning to n k ＝1。
The internal structure of the compensation trimming capacitor array 304 is shown in fig. 3. The compensation trimming capacitor array 304 includes binary-valued trimming capacitor arrays C8 to C1 (taking 8 bits as an example), and control switches S81,80 to S11,10 connected to the upper electrode plate of the capacitor. The lower plate of the trimming capacitors C8-C1 is connected to the movable mass 102 of the MEMS sensitive component 100. The upper pole plate of the trimming capacitors C8-C1 is connected with one of the upper pole plate 101 or the lower pole plate 103 through control switches S81, 80-S11, 10. The control signals n8 to n1 for controlling the switches S81,80 to S11,10 are automatically determined by the automatic compensation calibration circuit (303) according to the self-detection result. When n is k When =1, S k1 One side switch closed, S k0 One side is open and the kth compensating capacitor is connected in parallel between the upper plate 101 of the MEMS sensing member 100 and the movable mass 102. On the contrary, when n k When =1, S k1 One side switch off, S k0 One side is closed, and the kth compensation capacitor is connected in parallel between the lower plate 103 of the MEMS sensitive member 100 and the movable mass 102.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that various dependent claims and the features described herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.
Claims (9)
1. The zero drift self-detection self-calibration system based on the digital sigma delta closed-loop accelerometer is characterized by comprising the following components: the device comprises a closed-loop servo interface circuit (200) and a zero self-detection self-calibration circuit (300);
an excitation source in the zero self-detection self-calibration circuit (300) generates a low-distortion single-frequency sinusoidal excitation signal;
the closed-loop servo interface circuit (200) generates a high-voltage electrostatic power feedback signal, the high-voltage electrostatic power feedback signal acts on an MEMS sensitive component (100) of the accelerometer to realize servo control on the MEMS sensitive component (100), and a self-detection loop of the digital sigma delta closed-loop accelerometer is formed;
the MEMS sensitive component (100) is forced to vibrate under the action of a low-distortion single-frequency sine excitation signal, so that the servo position of the MEMS sensitive component (100) is shifted when the accelerometer drifts, and further capacitance variation is generated;
the closed-loop servo interface circuit (200) generates a self-detection even harmonic distortion component related to the offset degree in the output of the MEMS sensitive component (100) by acquiring the capacitance variation of the MEMS sensitive component;
the zero self-detection self-calibration circuit (300) extracts the amplitude and the phase of a self-detection even harmonic distortion component output by the closed-loop servo interface circuit (200), generates a compensation control signal according to the extracted amplitude and phase, and transmits the compensation control signal to the MEMS sensitive component (100) to compensate capacitor mismatch.
2. The digital sigma delta closed-loop accelerometer-based zero drift self-calibration system according to claim 1, wherein the MEMS sensitive member (100) comprises an upper plate (101), a movable mass (102) and a lower plate (103), and the upper plate (101), the movable mass (102) and the lower plate (103) are bonded by a silicon fusion process;
the movable mass block (102) and the upper pole plate (101) form a first sensitive capacitor, and the movable mass block (102) and the lower pole plate (103) form a second sensitive capacitor;
the movable mass (102) moves between the upper pole plate (101) and the lower pole plate (103) under the action of inertia force, and differential change is generated between the first sensitive capacitor and the second sensitive capacitor.
3. The digital Σ Δ closed-loop accelerometer-based zero drift self-calibration system according to claim 2, wherein the closed-loop servo interface circuit (200) comprises a multiplexer (201), a front-end capacitive sense amplifier (202), a loop compensator (203), a 1-Bit Σ Δ a/D conversion circuit (204), a dc bias circuit (206) and a high voltage electrostatic force feedback circuit (205);
three interfaces of a first input end of a multiplexer (201) are respectively connected with an upper electrode plate (101), a movable mass block (102) and a lower electrode plate (103), the multiplexer (201) acquires differential variation between a first sensitive capacitor and a second sensitive capacitor, a selection output end of the multiplexer (201) is connected with a selection input end of a front-end capacitor detection amplifier (202), the front-end capacitor detection amplifier (202) converts the differential variation between the first sensitive capacitor and the second sensitive capacitor into an output voltage in direct proportion to the differential variation, a voltage output end of the front-end capacitor detection amplifier (202) is connected with a voltage input end of a loop compensator (203), the loop compensator (203) generates a lead phase compensation signal for stabilizing a control loop, a lead phase compensation signal output end of the loop compensator (203) is connected with a lead phase compensation signal input end of a 1Bit sigma delta A/D conversion circuit (204), an analog-to-digital conversion output end of a 1Bit delta A/D conversion circuit (204) is connected with a high-voltage electrostatic force feedback circuit (205) input end, the high-voltage feedback circuit (205) generates a high-to an analog-to-digital feedback signal output end of the high-voltage electrostatic force feedback circuit (205), the high-voltage feedback electrostatic force feedback circuit (201) is connected with the high-voltage electrostatic force feedback circuit (205), the electrostatic force feedback circuit (201), and the electrostatic force feedback circuit (205), the electrostatic force output end of the electrostatic force feedback circuit (201) is connected with the electrostatic force feedback circuit (201), the one polar plate is one of an upper polar plate (101) or a lower polar plate (103); the direct current bias output end of the direct current bias circuit (206) is connected with the third input end of the multiplexer (201); the output signal of the selection output end of the multi-path selector (201) is switched among the first input end, the second input end and the third input end in a rotating way under the control of a switch time sequence;
the output of the 1Bit Σ Δ a/D conversion circuit (204) is the output of the accelerometer.
4. The digital sigma-delta closed-loop accelerometer-based zero drift self-calibration system according to claim 3, wherein the zero self-detection self-calibration circuit (300) comprises an excitation source (301), a self-detection even harmonic extraction circuit (302), an automatic compensation calibration circuit (303), and a compensation trimming capacitor array (304);
the method comprises the following steps that an excitation source (301) generates a low-distortion single-frequency sinusoidal excitation signal for self-detection, the low-distortion single-frequency sinusoidal excitation signal is superposed with a voltage signal output by a front-end capacitance detection amplifier (202), and the superposed signal is input into a closed-loop servo interface circuit (200) through a loop compensator (203);
under the action of a low-distortion single-frequency sine excitation signal, the movable mass block (102) generates sine vibration at a servo position, when the accelerometer drifts, the servo position generates deviation, and the output of the accelerometer generates a self-detection even harmonic distortion component related to the deviation degree;
the self-detection response input end of the self-detection even harmonic extraction circuit (302) is connected with the output end of the accelerometer, the amplitude and the phase of a self-detection even harmonic distortion component are extracted by the self-detection even harmonic extraction circuit (302), the amplitude and phase extraction output end of the self-detection even harmonic extraction circuit (302) is connected with the amplitude and phase extraction input end of the automatic compensation calibration circuit (303), the automatic compensation calibration circuit (303) generates a compensation control signal according to the extracted amplitude and phase, the compensation control signal output end of the automatic compensation calibration circuit (303) is connected with the compensation control signal input end of the compensation trimming capacitor array (304), and the three compensation capacitor output ends of the compensation trimming capacitor array (304) are respectively connected with the upper electrode plate (101), the movable mass block (102) and the lower electrode plate (103) to compensate the mismatch of the first sensitive capacitor or the second sensitive capacitor.
5. The digital Σ Δ closed-loop accelerometer-based zero drift self-calibration system according to claim 4, wherein the self-detection even harmonic extraction circuit (302) comprises a synchronous quadrature demodulation stimulus (3021), a digital multiplier (3022), a digital low-pass filter (3023), and a phase magnitude clearing unit (3024);
the input end of a synchronous quadrature demodulation excitation source (3021) is connected with the output end of the accelerometer, the synchronous quadrature demodulation excitation source (3021) generates two synchronous quadrature demodulation reference signals, the two quadrature demodulation reference signal output ends of the synchronous quadrature demodulation excitation source (3021) and the output end of the accelerometer are connected to three input ends of a digital multiplier (3022), the digital multiplier (3022) demodulates the even harmonic component from the output of the accelerometer, the even harmonic component is filtered by a digital low-pass filter (3023), the digital low-pass filter (3023) outputs a self-detection even harmonic distortion component, and a phase amplitude settlement unit (3024) obtains the amplitude and the phase by resolving according to the self-detection even harmonic distortion component output by the digital low-pass filter (3023).
6. The digital Σ Δ closed-loop accelerometer-based zero drift self-calibration system according to claim 5, wherein the synchronous quadrature demodulation excitation source (3021) generates two synchronous quadrature demodulation reference signals with a frequency twice the frequency of the low-distortion single-frequency sinusoidal excitation signal, the two synchronous quadrature demodulation reference signals being 90 ° out of phase with each other.
7. The digital sigma-delta closed-loop accelerometer-based zero drift self-calibration system according to claim 5, wherein the automatic compensation calibration circuit (303) obtains compensation control signals for adjusting the compensation trimming capacitor array (304) bit by bit from high to low according to the amplitude and phase settled by the self-detection even harmonic extraction circuit (302), and the compensation control signals comprise a compensation magnitude and a compensation direction.
8. The digital sigma delta closed-loop accelerometer-based zero drift self-calibration system of claim 7, wherein the compensation trimming capacitor array (304) comprises a binary valued capacitor C 1 ～C k Switch S 10 ～S k0 And S 11 ～S k1 (ii) a Wherein k represents the number of bits of the compensation capacitor;
capacitor C 1 ～C k The lower pole plates of the two capacitors are connected to a movable mass block (102) and a capacitor C k Upper pole plate simultaneously connecting switch S k0 And S k1 One end of (1), switch S 10 ～S k0 While the other end is simultaneously connected to the lower plate (103), S of the MEMS sensitive member (100) 11 ～S k1 The other end of the MEMS sensor is simultaneously connected with an upper electrode plate (101) of the MEMS sensitive component (100);
switch S 10 ～S k0 And S 11 ～S k1 Switch control signal n k Is obtained according to a compensation control signal of an automatic compensation calibration circuit (303).
9. The digital sigma delta closed-loop accelerometer-based zero drift self-calibration system of claim 8, wherein the system is self-calibrated by a switch S 10 ～S k0 And S 11 ～S k1 Switch control signal n k The specific process of compensating the mismatch of the first sensitive capacitor or the second sensitive capacitor by the compensation and trimming capacitor array (304) comprises the following steps:
when n is k When =1, S 11 ～S k1 Closure, S 10 ～S k0 When the circuit is disconnected, the kth compensation capacitor is connected in parallel between the upper polar plate (101) and the movable mass block (102) to compensate the first sensitive capacitor;
when n is k When =1, S 11 ～S k1 Breaking, S 10 ～S k0 Closed, the k-th compensation capacitor is connected in parallel between the lower plate (103) and the movable mass block (102),the second sensitive capacitance is compensated.
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| CN116380135B (en) * | 2023-06-06 | 2023-08-11 | 成都市晶蓉微电子有限公司 | Charge transfer balance type capacitor-to-voltage conversion circuit |
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